Laamu Atoll Mariculture Project - Seaweed Mariculture Reichenbach and Holloway, 1997
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Transcript of Laamu Atoll Mariculture Project - Seaweed Mariculture Reichenbach and Holloway, 1997
Laamu Atoll Mariculture Project: Seaweed Mariculture
Norman Reichenbach and Steve Holloway
March, 1997
ii
Executive Summary
Kappaphycus alvarezii (commercially known as Eucheuma cottonii) and
Eucheuma denticulatum (commercially known as E. spinosum) were imported from the
Philippines in order to establish a pilot scale seaweed farm in Laamu atoll, Republic of
Maldives. Several attempts in using the traditional monoline culture method were
unsuccessful due to excessive fish herbivory. The bag culture method was then introduced
and proved to be effective in farming the seaweeds.
Site selection was then conducted in 9 areas around the islands between Fonadhoo
and Gan, Laamu atoll in order to select the best sites for pilot scale farm operations.
During the site screening, K. alvarezii was selected as the best species to work with since
this species grew at a much faster rate than E. denticulatum. The average growth rate for
E. denticulatum was -0.58%/day at all the sites while K. alvarezii had a growth rate
ranging from 0.45 to 5.27%/day depending upon the site. One site just south of the
Thundi village, Gan island (G site) and another site on the west side of Bodufinolhu (BF
site) were selected as the two best areas to start pilot scale farm operations.
At each site, a 25 m anchor line was placed. Growth rates were monitored starting
in July, 1996 for both the brown and green strains of K. alvarezii. Seaweeds at the G site
maintained a very high growth rate averaging 6.4%/day (11 day doubling time) for the SW
monsoon season and 5.7%/day (12 day doubling time) for the NE monsoon season. In
contrast, at the BF site, growth rates fluctuated from a high of about 7%/day to negative
growth during one month when excessive fish herbivory was noted. At the BF site growth
rates were generally between 2 to 4%/day. Other bag styles and culture methods were
examined at this site but it was not expanded beyond the one, 25 m anchor line.
The G site, with its consistently high growth rates, was expanded to six, 100 m
anchor lines with each line holding approximately 1000 bags. With the growth rates
recorded from the seaweeds at the G site, the six, 100 m lines could produce about 12,000
kg or more of fresh seaweed per month. Various farm design options at the G site were
evaluated for strength and cost of construction using various combinations of concrete
blocks, coconut tree logs, rerod and coral blocks.
Economics of farming seaweeds in the Maldives was also evaluated. Dried
seaweed sent to the Philippines for analysis indicated that our seaweed met the standards
iii
needed for international marketing. Costs were considered in three different ways
including 1) profit to a company that would pay salaries to the workers, 2) profit to the
farmer(s) if they owned the farm and sold the seaweed, and 3) cost to produce a ton of dry
seaweed under various labor rates, growth rates, and harvest intervals. Assuming direct
marketing to the buyer, fresh seaweed might sell for 1 rf per kg. This would be equivalent
to $683/MT of dry seaweed assuming 1 MT of dry seaweed can be produced from 8000
kg of raw seaweed (this price is reasonable when selling directly to a company using the
seaweed. If the farmers sell to a middle person they will likely get 50 laari per kg of raw
seaweed).
For a company owned farm the profits per ha per month would range between
$1,610 to $1,661 depending upon the farm design used. For a farmer owned farm the
return to the farmers per ha per month would range between $2,954 to $3,005 depending
upon the farm design used. This amount would be divided between the number of farmers
needed to service the one ha area which might be around 10 people. The costs to produce
a ton of dry seaweed were typically between $200 to $300 depending upon the growth
rate, harvest interval and labor rate.
In the recommendations, the exponential growth potential of seaweeds was
examined as to how it relates increasing production volume by increasing the starting
weight of seaweeds used and having a harvest interval of one month. The merits of a
larger bag were discussed in relation to increasing the starting weight of seaweeds and to
ensuring that the harvest interval would be one month. A farm was then designed which
would use larger bags.
Introduction
Eucheuma seaweed culture was started and developed in the Philippines in the late
1960's by Dr. Doty's group. Since this time, the Eucheuma seaweed industry has become
one of the Philippines top foreign exchange earners (Llana 1991). Due to the success of
farming seaweeds in the Philippines other countries such as the Pacific island countries,
Indonesia, Tanzania, and Malaysia have also started Eucheuma seaweed farming with
varying degrees of success.
Eucheuma seaweeds contain carrageenan which is commercially important due to
its excellent properties as a thickener, emulsifier, stabilizer, and gelling agent for a number
of products. Some of the products where carrageenan is used include ice cream, tooth
paste and desserts/sweets (Llana 1991).
Though Eucheuma is not an indigenous species to the Maldives, studies have
shown that introduction of Eucheuma to new areas has had minimal effect on the local
tropical reef environment (Neushul et al. 1989; Russell 1983). In addition, Eucheuma had
been imported to the Maldives before. In 1987-1988, private interests in the Maldives
brought in strains of Eucheuma for use in a pilot project on the island of Goiyadhoo in Baa
Atoll. The pilot project used typical monoline culture techniques which have been
successful in the Philippines. The Goiyadhoo project demonstrated that Eucheuma could
be grown in the Maldives (Holloway 1992).
The goal of this project was to establish a pilot scale Eucheuma seaweed farm in
Laamu atoll, Republic of Maldives. Details on establishing this pilot scale farm are
provided in this report which includes sections on: 1) seaweed importation and selection
of the best culture methodology, 2) selection of the best species, 3) selection of the best
site, 4) seaweed farm: growth rates, 5) seaweed farm: design considerations, 6) seaweed
farm: maintenance and harvesting/drying, 7) product quality, 8) economic analysis, 9)
environmental impact, 10) recommendations, 11) literature cited.
Section 1: Seaweed Importation and Selection of the best culture
methodology
Three trials were required to determine the most appropriate culture methodology
for areas in Laamu atoll. As is usually the case in introducing new technologies,
2
established culture techniques from other parts of the world must be refined and adapted
to the new environment (Adams and Foscarini 1990).
The details of these trials are given in the following three subsections.
Subsection 1a: Bodufinolhu - monoline trials
Bodufinolhu is an uninhabited island just north of island of Gan, in Laamu Atoll.
Initially, several test sites were identified in the lagoons around this island. Materials for
the monoline culture technique were prepared for these sites. This culture technique
consists of monofilament lines of 10 meters each, stretched between reinforcement rod
stakes, with one stake in the center. These stakes were driven into the sandy substrate of
the lagoon floor. Thirty to forty Eucheuma plants, each about 100 g, are then tied by
`plastic straw' to the monofilament line.
In late December 1994, 10 kg of Kappaphycus alvarezii (commercially known as
Eucheuma cottonii) and 10 kg Eucheuma denticulatum (commercially known as E.
spinosum), were imported from GENU Corporation in the Philippines. The monolines
were distributed around the Bodufinolhu area, to find favorable conditions. All of the E.
denticulatum were lost in the first month. The plants wasted away on the lines showing
symptoms of the stress-related condition called ice-ice. A significant portion of our K.
alvarezii seed stock was also lost because the monolines were too close to a reef where
there were a significant number of herbivores.
A site for the remaining K. alvarezii was found in late March 1995, between
Bodufinolhu and the next island north, Gasgandufinolhu, where the plants stabilized. This
site between the two islands is the exchange point between the extensive shallow lagoon
area between the atoll island chain and the barrier reef to the east, and the interior of the
atoll to the west. Current flow is primarily from the daily tidal surge going in and out of
the opening between the islands. A pen was built out of plastic netting (1/2" mesh size) to
protect the initial crop from herbivores. The pen was designed to contain 4 monolines.
Lines were then placed both inside and outside the pen. At this point measurements on
growth and environmental parameters were started. The data on growth indicated that the
seaweeds on the lines inside the pen demonstrated better specific growth rates (SGR) than
those outside (Table 1).
3
Table 1. Bodufinolhu monoline trials with Kappaphycus alvarezii (10 April - 3 May 1996)
Location Inside the Pen Outside the pen
Current (m/min) (24 hour averages)
Average 2.29 7.76
Range 0.91 - 4.52 5.43 - 11.16
Temperature (C)
High 33 32
Low 28 28
SGRa (%/day), average 2.46 (Line A)b
2.48 (Line B)
2.86 (Line F) 1.76 (Line G)
a: SGR = (ln(wt)-ln(wi))/t*100 where wt is final weight, wi is initial weight, t is time in days
b: Lines A and B are the original 'parent' plants from which cuttings were taken for lines F
(inside the pen) and G (outside the pen). Each monoline contained 25 plants.
In mid-May 1995, about 95% of the seaweeds were lost during the transition
period between the northeast (NE) and southwest (SW) monsoon seasons. There is a time
during this shift where winds and waves virtually cease. The sea becomes like a mirror and
the horizon can actually disappear. When the lines were checked just after this transition
period, there were only a few stumps of seaweed left attached to the lines, and a few
pieces scattered on the bottom of the pen, all with signs of severe ice-ice.
Evaluating the die-off during the first set of trials on both E. denticulatum and K.
alvarezii, it was apparent that several factors in the local lagoon area combined to over-
stress the plants. Grazing pressure was a major factor. A significant portion of our K.
alvarezii seed stock was lost because the monolines were initially too close to a reef
where there were a significant number of herbivores. The monolines with K. alvarezii
which were within the plastic pen had some protection from large herbivores, but not from
the juvenile siganids which lived in the lagoon area and could easily pass through the
mesh. Some lines were initially placed in waters too stagnant for the seaweeds, and were
moved to sites with better currents when the plants were observed to be stressed. There
was a difference between the current speeds inside the pen and outside the pen, and
though the plants inside had better growth rates, this was probably due to the protection
from grazing pressure. Temperatures in the lagoon were also at the high end of the
tolerance range for K. alvarezii and E. denticulatum. This would be particularly so during
the monsoon shift when it is very calm.
4
Subsection 1b: Kadhdhoo - monoline trials
The few remaining pieces of K. alvarezii left over from the initial Bodufinolhu die-
off were collected and moved to another site two islands to the south of Gan, near
Kadhdhoo, the atoll's airport island. Kadhdhoo, and several other islands near Gan, are
connected by a series of causeways across the lagoons. The longest causeway is between
Kadhdhoo and Fonadhoo to the south and it is a little less than 1/2 mile long. Here the
seaweed stubs began to recover but since they were not protected by a pen, they were
consumed by herbivores within a week of being out planted.
Kadhdhoo had been considered as an alternate site for monoline growth trials.
During a survey of this area conducted in 1992 a significant standing crop of seaweed and
marine plants was noted in the lagoon on the eastern side of the causeway between the
islands of Kadhdhoo and Fonadhoo. This seaweed population was characterized by
relatively large patches of Spiridia and Halymeda, with clumps of Hydroclathrus drifting
around on the lagoon floor, and a few areas of the marine angiosperm, Thalassia. This
was different from most of the reef flats of Laamu, which are characterized by extensive
Thalassia `meadows' and large areas of bare sand (Lewis et al. 1992).
In mid-September, 1995, a new site was prepared for seaweed growth trials near
Kadhdhoo. A new pen was constructed in the lagoon between the causeway and the atoll's
barrier reef to the east. This pen was larger than the one at Bodufinolhu, and could contain
11 monolines. New seaweeds were imported and trials at Kadhdhoo began.
K. alvarezii, at times, grew quite rapidly, with individual plants demonstrating
growth rates as high as 7.4% per day. The average growth rate was 5.5%/day (3.2 to
7.4%/day, minimum to maximum growth rates). The temperatures ranged from 26-31 C.
The overall good growth rates were surprising since the recorded current speeds were
extremely slow (24 hour average, 0.64 cm/sec, range during trials: 0.04 - 1.35 cm/sec)
compared to what is considered optimal for K. alvarezii (10-20 cm/sec).
5
E. denticulatum, in contrast, was especially stressed at this site.The average
growth rate was 0.6%/day (-3.1 to 3.0%/day; minimum to maximum growth rates). The
negative growth rate reflects, primarily, plant breakage due to ice-ice, with the plant
pieces falling and drifting to the floor of the pen. The pieces of E. denticulatum were
collected from the bottom of the pen and retied to the monolines, or if they were too
small, placed in net bags. In all probability, the slow current speeds contributed
significantly to their deterioration. In addition the light intensities may have been too high
for E. denticulatum (Ray Lewis, pers. communication).
In the Kadhdhoo trials, plants were divided when they grew beyond 300 g. The
cuttings were used to seed empty areas of the monolines in the pen in an effort to increase
biomass. All the plants in the pen were weighed because of the various genetic strains
present. Individual strains were tracked to look for ones that grew especially well in the
new environment. The trial started on 5 October with 19 kg, and on November 5, the
seaweed biomass had increased to 58 kg. By the next cutting, if the K. alvarezii growth
rates had continued, all available lines in the pen (eleven,10 m monolines, 30 plants on
each line) would have been occupied by seaweeds. The next step was to prepare
monolines outside the pen.
On 13 November 1995, project staff arrived at the pen to find all monolines
stripped, without even drift seaweed in the pen (usually there were drift pieces if the
seaweed had broken off from the lines). The monolines had only the empty plastic ties and
the individual plant identification tags attached. The only seaweed remaining, about 2 to 3
kg, was that in a net bag made up of pieces too small to tie to the monolines. The evidence
strongly pointed to the pen being stripped by herbivores. Vandalism, another option, was
ruled out because of the undisturbed empty ties on the monolines, lack of even small drift
seaweed pieces on the pen floor, and the untouched seaweeds in the net bags. The top of
the pen was about 22 cm under water at the highest tide. There were nocturnal tides (45
cm above the mean) during the full moon on the 7th and 8th of November which likely
allowed herbivores to enter the pen and consume the seaweeds.
Subsection 1c: Bodufinolhu - bag trials
In January 1996, Mr. Ruben Barraca Sr., an FAO seaweed consultant, visited our
project and demonstrated a new technique for seaweed farming. The culture technique
6
uses net bags which are anchored to lines staked out on the lagoon floor (Barraca, 1996).
This technique has several advantages over the traditional monoline method. The bag
netting gives the seaweed some protection from herbivores. This system is much less labor
intensive and it is easier to maintain, manage, and harvest the crop. The bags allow the
plants a much greater range of movement in the water, assisting them in nutrient uptake,
as well as giving increased resistance to algal blooms and diseases while protecting the
plants from photo-oxidation. The design of the bag culture system allows it to be more
resistant to adverse weather conditions.
This first trial (Table 2) was conducted near the site used for the first Bodufinolhu
monoline trials described above. The objectives of this initial trial were to evaluate the bag
culture technique in general, compare the growth rates at the western and eastern
extremities of the 125 m anchor line and compare the growth rates of the plants in the
bags relative to those on the monolines in our first trial. The seaweed remnants from the
Kadhdhoo monoline trials were initially used. Though there was some herbivorous grazing
on the seaweed tips that extended beyond the confines of the net bag, the seed stock
remained healthy throughout the trial, and displayed no symptoms of ice-ice. Growth rates
at both extremes of the anchor line were essentially the same for the two species, and so
they were combined. In addition the growth rates for plants in the bag were comparable to
those on the monolines in the first trial.
7
Table 2. Bodufinolhu bag culture trials with Kappaphycus alvarezii and Eucheuma
denticulatum.
current temperature SGRa
mean min-max min max old K. ab. new K. a.b E. d.b
date m/min m/min (C) (C) (%/day) (%/day) (%/day)
17/3-9/4/96 10.0 4.5-20.4 28 32 2.6 (1.5-3.6) -- 2.4 (1.8-3.9)
14/4-4/5/96 8.0 6.6-10.1 28 31 2.7 (1.4-3.7) 4.2 (3.0-5.1) 1.7 (0.9-2.7)
8/5-28/5/96 12.4 9.5-16.5 28 32 2.6 (1.1-3.7) 2.3 (0.5-3.5) 1.5 (0.4-2.7)
a: SGR = (ln(wt)-ln(wi))/t*100 where wt is final weight, wi is initial weight, t is time in days
b old K.a. is the K. alvarezii stock left over from Kadhdhoo, new K. a. is stock from a new
shipment of K. alvarezii and E.d. is E. denticulatum
Another shipment of both K. alvarezii and E. denticulatum was received from
GENU in late March 1996. The second trial (14/4 to 4/5/96; Table 2) was conducted to
quantify the observation that the newly acquired K. alvarezii from the Philippines was
growing more rapidly than the K. alvarezii seed stock left over from the Kadhdhoo pen.
The growth rate difference is much less pronounced in the third trial (8/5 to 28/5/96;
Table 2) which seems to confirm the idea that the high growth rates of the new seaweed
stock were a temporary phenomena.
This second trial spanned the period of monsoon change, which seemed to have
little effect on growth rates. This supports the hypothesis that seaweeds, protected from
the stress of herbivorous grazing, can survive and even thrive during this period.
In conclusion, both trials at two locations using the monoline culture method
demonstrated that the K. alvarezii can grow at a good rate. The trials also demonstrated
that the monoline method did not provide enough protection from grazers so that a stable
crop could be produced. The bag culture method seemed to provide an adequate
environment for the seaweeds protecting them from excessive herbivory and allowing the
seaweeds to transition through a monsoon season shift. The bag culture method was
therefore selected as the best culture method to pursue for our pilot scale farm.
Section 2: Selection of the best species
During all the initial trials to determine the best culture method, K. alvarezii grew
better than E. denticulatum (see Section 1). In the site screening study (Subsection 3a)
this was again confirmed at all of the sites evaluated. E. denticulatum lost weight and had
8
an average growth rate of -0.58%/day at all the sites while K. alvarezii had a growth rate
ranging from 0.45 to 5.27%/day depending upon the site. K. alvarezii was selected as the
species for use in the pilot scale seaweed farm.
Section 3: Selection of the best site
Many guidelines of site selection have been made, only to be broken by successful
farmers in other areas (Barraca, 1990). Since farming K. alvarezii was new to Laamu
atoll, our farm site selection was based upon measured seaweed growth rates at the
various sites rather than evaluating the physical environment for what would seem to be an
optimal environment for the seaweeds. Site selection was a two step process. The first was
to do a broad screening of different areas near Gan and Fonadhoo in order to identify 3
good sites using seaweed growth rates and other seaweed culture related information. The
second step was to see how homogenous these 3 best areas were and in the process to
locate two potential pilot scale farm sites as close as possible to the villagers who would
be doing the seaweed farm work.
Subsection 3a: Site screening
The purpose of this experiment was to evaluate 9 different sites which
characterized various environments in Laamu atoll to determine 3 'best' sites for further
evaluation.
The bag culture method was used and the duration of the experiment was one tidal
cycle or approximately 28 days during June and July, 1996. Eight bags of K. alvarezii (6
of the green strain and 2 of the brown strain) and 2 of E. denticulatum were placed at each
site with each bag containing approximately 1/2 kg seaweed (for E. denticulatum about
1/4 kg per bag). The number of bags and biomass per bag was dependent upon the
biomass available for each species and strain at the time of experiment initiation.
Measurements included initial and final weights of seaweed plus qualitative measures of
bag cleanliness, ease of conducting culture activities at the site (water depth, current
velocity, waves), and area available for farm construction. From the initial and final
weights a SGR was calculated. Doubling times were calculated using the SGR.
9
Site characteristics considered in site selection included water velocity, substrate,
exposure to air during extreme low tides, and general weather conditions of the area
during June and July, 1996 (Table 3 and Fig. 1).
Table 3: General characterization of sites selected for seaweed site screening experiment.
Site/description
Water velocity
(max)
Substrate
Exposure
(air)
Exposure
(weather)
1/island gap N of BF high rubble none rough
2/tip of BF high sand none rough
3/east of BF moderate sand yes calm
4/east of BF near Gan moderate Thalassia yes calm
5/east of Gan near reef moderate rubble/Thalassia yes moderate
6/west of BF near BF moderate sand none moderate
7/west of Gan moderate sand yes rough
8/Kadhdhoo west of causeway moderate sand/Thalassia yes moderate
9/Kadhdhoo east of causeway slow sand none calm
3
6
7
N
Bodufinolhu
Gan
1
2
4
5
8 9
Fonadhoo
Kadhdhoo
Figure 1. Site locations in Laamu atoll for seaweed site screening experiment.
The results for K. alvarezii are summarized in Table 4 and are discussed below on
a per site basis.
10
Table 4. Growth data and scores for various factors used to assess each site for its
potential for seaweed production.
Growth Rate Bag Area Ease of
Site SGR (%/d)a doubling (days)b scorec cleanlinessd Availablee Culturef Totalg
1 1.45+0.44ch 48 1 1 1 1 4
2 1.36+1.07cd 51 1 1 2 1 5
3 2.44+0.46b 28 2 1 2 2 7
4 1.36+0.54cd 51 1 1 2 2 6
5 0.45+0.24d 155 0 3 2 1 6
6 3.24+0.39b 21 2 2 2 2 8
7 5.27+0.41a 13 3 2 2 1 8
8 3.24+0.56b 21 2 1 2 2 7
9 -- -- -- 2 2 2 --
a SGR = (ln(wt)-ln(wi))/t*100 where wt is final weight and wi is initial weight and t is time in
days, the SGR is followed by + one standard deviation
b doubling time is ln(2)/(SGR/100)
c score based upon significant differences from ANOVA test using a 0 to 3 scale with 3 being the
highest growth rate and 0 the lowest.
d bag cleanliness scored on a 1-3 scale, 3 no cleaning needed, 2 some cleaning, 1 daily to every 2nd
day cleaning
e area available scored on a 1-2 scale, 2 several ha available, 1 one ha or less available
f ease of culture scored on a 1-2 scale, 2 easy access and currents/waves not to strong/large, 1
currents/waves strong/large at times
g total is simply a sum of the scores
h letters a, b, c, d reflect significant differences based on ANOVA test with Bonferroni multiple
comparison test (P<0.05)
Site 1 was the channel between Bodufinolhu and Gasgandufinolhu. The substrate
was coral rubble. The growth rate was low with a doubling time of 48 days (growth score
= 1). The bags needed frequent cleaning due to algae growing on the bags (bag cleanliness
score = 1). The current was also strong during tide changes and it was best to conduct
culture activities during low tide (ease of culture score = 1). The area available was about
1 ha (area score = 1). The total score was 4.
Site 2 was near the tip of Bodufinolhu on the east side. The substrate was coral
rubble. The growth rate was low with a doubling time of 51 days (growth score = 1). The
bags needed frequent cleaning due to algae growing on the bags (bag cleanliness score =
1). The current was also strong during tide changes and it was best to conduct culture
activities during low tide (ease of culture score = 1). The area available was several ha
(area score = 2). The total score was 5.
11
Site 3 was east of Bodufinolhu near the middle of the island. The substrate was
white sand. The growth rate was moderate with a doubling time of 28 days (growth score
= 2). The bags needed frequent cleaning due to algae growing on the bags (bag cleanliness
score = 1). The site was simple to access since the current was moderate and the water
depth was 1 to 2 meters (ease of culture score = 2). The area available was several ha
(area score = 2). The total score was 7.
Site 4 was just north of Gan over a bed of seagrass, Thalassia. The growth rate
was low with a doubling time of 51 days (growth score = 1). Damage to the seaweed due
to herbivory was noted multiple times. The bags needed frequent cleaning due to algae
growing on the bags (bag cleanliness score = 1). The site was simple to access since the
current was moderate and the water depth was 1 to 2 meters (ease of culture score = 2).
The area available was several ha (area score = 2). The total score was 6.
Site 5 was east of Gan about 20 meters from the barrier reef. The substrate was
seagrass and coral rubble. The growth rate was very low with a doubling time of 151 days
(growth score = 0). The seaweed at the end of the experiment were pale and did not look
healthy. The bags did not require any cleaning (bag cleanliness score = 3). While the site
was simple to access since the current was moderate and the water depth was less than 1
meter, the frequent twisting of the bags at the base due to the perpendicular nature of the
waves and the current added to the maintenance of the site (ease of culture score = 1).
The area available was several ha (area score = 2). The total score was 6.
Site 6 was west of the tip of Bodufinolhu about 20 meters from the shore. The
substrate was white sand. The growth rate was good with a doubling time of 21 days
(growth score = 2). The bags required a minimal amount of cleaning which in most cases
was no more than shaking the bag a little in order to remove deposited sediments.(bag
cleanliness score = 2). The site was simple to access since the waves were small and the
water depth was 1 to 2 meters (ease of culture score = 2). The area available was several
ha (area score = 2). The total score was 8.
Site 7 was west side of Gan about 1/2 km south of Thundi. The substrate was
white sand. The growth rate was the highest with a doubling time of 13 days (growth
score = 3). The bags required a minimal amount of cleaning which in most cases was no
more than shaking the bag a little in order to remove deposited sediments.(bag cleanliness
score = 2). The site was often difficult to access because of the large waves (ease of
12
culture score = 1). The area available was several ha (area score = 2). The total score was
8.
Site 8 was west of the causeway between Fonadhoo and Kadhdhoo. The substrate
was coral rubble and Thalassia. The growth rate was good with a doubling time of 21
days (growth score = 2). The bags needed frequent cleaning due to algae growing on the
bags (bag cleanliness score = 1). The site was simple to access since the waves were small
and the water depth was less than 1 meter (ease of culture score = 2). The area available
was several ha (area score = 2). The total score was 7.
Site 9 was east of the causeway between Fonadhoo and Kadhdhoo. The substrate
was sand. All the seaweed were gone within 4 days after placement. Presumably the
seaweed were eaten by fish. An additional bag placed at this site one week later was empty
several days after placement. The bags left in place were fairly clean throughout the
duration of the experiment. The area available was several ha but because of the herbivory,
this site was dropped as a potential farm site using the current version of the bag culture
methodology. No total score was assigned to this site.
The site total scores indicated that Sites 6 and 7 had the highest scores (total score
= 8). These sites are located on the west side of Bodufinolhu and Gan, respectively
(Figure 1). Sites 3 and 8 had the second highest scores (total score = 7). Site 3 was on the
east side of Bodufinolhu and Site 8 was on the west side of the causeway between
Fonadhoo and Kadhdhoo. Since the best sites, (Sites 6 and 7) were on the west side, Site
3 was selected as the third site since it was located on the east side. This provided a wide
range of environmental conditions especially with respect to the monsoon seasons.
Further trials were conducted in July/August, 1996 to determine how
homogeneous the growth rates are in areas around Sites 3, 6, and 7 (Fig. 2). Following
these trials, pilot scale seaweed farm operations were initiated.
13
N
Bodufinolhu
Gan
6b 6a
3a
3b6a6a6d 6c
7a
7b
Figure 2. Sites used to test for homogeneity of the growth rates within the areas
associated with potential farm sites 3, 6 and 7.
Subsection 3b: Site Homogeneity Experiment
The purpose of this experiment was to measure how homogeneous the growth
rates for K. alvarezii were in the 3 sites (Sites 3, 6 and 7) identified as the 'best' sites in the
site screening experiment (Fig. 1). Two sites were then selected to initiate pilot scale farm
operations.
Site 3a was the original Site 3 of the site screening study and Site 3b was placed in
an area similar to Site 3a but closer to Gan. Sites 6a through 6d were placed either near
the tip of Bodufinolhu or close to Gan, both close and far from the beach of Bodufinolhu.
Site 6b was close to the original Site 6 of the site screening study. Sites 7a and b were on
the west side of Gan. Site 7a was the original Site 7 of the site screening study and Site 7b
was simply a site closer to Gan (Fig. 2).
The bag culture method was used and the duration of the experiment was from 21
to 25 days depending upon the site. The experiment was conducted in July and August
1996. Ten bags of K. alvarezii (5 of the green strain and 5 of the brown strain) were
placed at each site with each bag containing approximately 1/2 kg seaweed. Measurements
included initial and final weights of seaweed. From the initial and final weights a SGR was
calculated. Doubling times were calculated using the SGR.
The growth data are summarized in Table 5 and are discussed on a per site basis.
14
Table 5. Growth data for site homogeneity study.
Site SGR (%/d)a Significanceb doubling (days)c
3a 0.47+1.11 a 147
3b 2.89+0.25 b 24
6a -4.31+2.88 c --
6b 5.72+1.12 a 12
6c 1.92+1.30 b 36
6d 5.02+0.51 a 14
7a 6.39+0.64 NS 11
7b 6.81+0.42 10
a SGR = (ln(wt)-ln(wi))/t*100 where wt is final weight and wi is initial weight
and t is time in days, average SGR value followed by one standard deviation
b NS indicates no significant difference between Sites a and b within a
numbered site, letters indicate sites within a numbered site which are
significantly different (P<0.05).
c doubling time is ln(2)/(SGR/100)
Site 3 had significant differences between the growth rates for Sites a and b (Table
5). This difference may have been due to the origin of the stock used in the experiment.
The stock used at Site 3a was from Site 3 in the site screening experiment. Essentially the
seaweeds were at this site for a 2 month period and the growth dropped from 2.44 to 0.47
during the second month at the site. The seaweeds during the second month became pale
and ice-ice was noted on several plants. The stock from Site 3b was from a high growth
site during the site screening experiment.
Sites 6a through d growth rates indicated that the sites near Bodufinolhu had low
growth rates. This was primarily due to herbivory. The seaweeds in some bags were
totally consumed. The sites further from Bodufinolhu had significantly higher growth rates
relative to the sites closer to the beach (Table 5). Site 6b had a growth pattern for the
brown strain similar to that seen at Sites 7a and b (see below).
Sites 7a and b had similar growth rates, both of which were high (Table 5). In
addition to the growth rates being high the growth pattern of the seaweeds at these sites
were dense clumps. These clumps could easily be dumped out of the bags. In contrast the
growth pattern at the other sites except Site 6b was such that seaweed removal was more
difficult. The seaweeds had to be carefully removed from the bags by hand.
15
The sites selected for pilot scale farm operations included Sites 7b and 6b. Site 7b
was selected because of the optimal growth rates (6.81%/day), the clumped growth
pattern and because of its proximity to Thundi. This site was frequently rough, with 1 m
high waves, which made the site difficult to maintain at times. Site 6b was selected
because of the high growth rates (5.72%/day), the clumped growth pattern seen in the
brown strain and because the waves were much smaller relative to Site 7b.
Section 4: Seaweed farm: growth rates
During June and July, 1996 pilot scale farms were initiated at sites 7b and 6b. Site
7b is called the Gan site (G site) and Site 6b is the Bodufinolhu site (BF site). At each site,
25 m anchor lines were initially constructed. Then 180 bags attached to the propagule
lines were placed at each site. Growth rates were monitored monthly at each site. The
usual measurement period was 2 weeks and generally 10 bags from each of the two strains
(brown and green) were weighed. If other bag types or culture methods were being tested
than weights were taken on a comparable number of units over a comparable period of
time. In all cases SGRs were calculated as well as doubling times.
For the BF site during the SW monsoon (Months 7 through 11), growth rates
declined over time due to fish herbivory (Fig. 3). The tips of the plants were frequently
missing due to herbivory. Plants were severely cropped by herbivores during December
(Month 12) at which time the lowest growth rates for the site were recorded. During the
NE monsoon period (Months 12 through 3) the growth rates were initially low and then
started to recover. Fish herbivory was not observed during the later months of this
monsoon period though the water temperatures would sometimes rise to 33 C. Due to the
low growth rates noted at this site, the number of lines was reduced and only the brown
strain was maintained at this site after Month 11. Other culture methods were tested at this
site including modifications to the original bags used, bags made of different netting
material, and propagule holder (PH) culture method (Ruben Baracca Sr., pers. comm.;
Fig. 4).
16
Figure 3. Growth rates (SGR, %/day) for seaweeds at the BF site.
float
propagule line
seaweed plant
rope loop
Figure 4. Illustration of the propagule holder (PH) where seaweeds are tied to the rope
loop.
Because of the fish herbivory noted in the SW monsoon period, the bags were
initially modified. First the bag normally used was simply doubled. That is one bag was
placed inside another bag. This style was tested over a 2 month period using only the
brown strain. In October, there was no significant difference in the growth rates for the
two styles of bag. In November the growth rates of seaweeds in the double bags was
better than those in the normal bags. For both months though the growth rates were low
with a best doubling time of 25 days (Table 6). An additional type of bag was then tested
17
which was larger and made with a heavier nylon material instead of the monofilament used
with the normal bags. In each of the large bags 2 kg of seaweed was placed initially as
opposed to the normal 0.5 kg which was placed in the normal bags. During December the
growth rates in the heavy bags were significantly better than for those in the normal bags
(Table 6). Seaweeds in the normal bags were heavily grazed during this month. During the
subsequent month (January) the normal bags resumed a more usual growth rate while
those in the heavy bags dropped to 0.5%/day (Table 6). This was most likely due to the
shift in the monsoon season where the water movement was much less at this site than
previously. The heavier and larger nature of the bag may have reduced water exchange
within the bag relative to the normal bag with the subsequent drop in growth rates in the
larger bags.
As noted above, fish herbivory declined during the NE monsoon period. Because
of this, the PH culture method was also tried at BF. Initially the growth rates were
somewhat slower than the seaweeds in the bags (Table 6) but during the second month the
growth rates were not significantly different from those in the bags (Table 6).
Table 6. Growth rates for the brown strain of seaweeds cultured in various modifications
to the net bags and PH method in relation the growth rates recorded for seaweeds in the
normal bags.
Time Period SGRa -normal bag SGRa-double bags t/df/Pb
Oct./1996 2.4+0.3 2.6+0.4 1.0/18/0.32
Nov./1996 2.2+0.5 2.8+0.5 2.8/18/0.01
SGRa-heavy bags
Dec./1996 -0.6+1.8 2.6+0.6 1.8/13/0.002
Jan./1997 2.0+0.5 0.5+0.4 5.8/13/<0.001
PH method
Feb./1997 3.4+0.8 2.7+0.3 2.4/18/0.03
March/1997 4.1+0.5 3.9+0.5 1.1/18/0.3
a SGR = (ln(wt)-ln(wi))/t*100 where wt is final weight and wi is initial weight and t is time in
days, average SGR value followed by one standard deviation
b t = t test value, df=degrees of freedom and P is the probability value
One final test was conducted at the BF site in March 1997 using plants attached to
PH units. One line of seaweeds from the G site was transferred to the BF site and growth
18
of these plants were compared to a line where the plants had been at the BF site since the
site was started. The plants from the G site grew significantly faster (SGR=6.7+0.6) than
those that had been at the BF site since the site was started (SGR 3.9+0.5) (t=11.2,
d.f.=18, P<0.001). The high growth rate of the plants transferred from the G site would
have to be tested over a longer period of time to see if they are able to maintain this high
rate of growth comparable to that noted at the G site.
The BF site was monitored for growth rates and testing various options until the
end of March 1997. Due to the low growth rates as compared to the G site, the BF site
was not expanded.
Site G maintained high growth rates from June 1996 to March 1997 and this site
was expanded from the original 25 m line to six, 100 m lines. The growth rates for the two
strains were not significantly different (F=2.6, d.f.=1, P=0.11) but there were significant
differences between the months of the study (F=10.9, d.f.=8, P<0.001) (Figs. 5, 6).
Instead of doing pairwise testing for differences between the months the data were divided
into two parts representing the two monsoon periods. This test indicated there were
significant differences between the growth rates of the seaweeds for the two monsoon
periods (t=4.4, d.f.=165, P<0.001). The NE monsoon period had a slightly lower growth
rate of 5.7+0.7%/day (12 day doubling time) relative to the SW monsoon period
(6.4+1.3%/day or 11 day doubling time). Both growth rates, though, are high and were
relatively consistent through time (Figs 5, 6).
Figure 5. Growth rates (SGR, %/day) for seaweeds at the G site.
19
Figure 6. Doubling times (days) for seaweeds at the G site.
A final set of experiments using the bags was conducted in March. This experiment
was to determine if the growth rates are consistent as the bags fill up with seaweeds.
Weights were taken 10 days after placing the bags in the ocean, 19 and then 28 days later.
One kg was placed in the bags at the beginning. The rates were good for the first 19 days
when the bags filled on average to 2650 or 2820 g (green and brown strain averages,
respectively) (Figs. 7, 8). The growth rates were not significantly different between the
first 10 days in the ocean and the time between days 10 and 19 (green strain t=1.9,
d.f.=18, P=0.07; brown strain t=0.7, d.f.=18, P=0.46). During the final 9 days of the trial
(days 19 to 28) the growth rate declined significantly compared to those from the previous
measurement period (green strain t=7.8, d.f.=18, P<0.001; brown strain t=10.6, d.f.=18,
P<0.001). The bags at the end of the trial were on average 3380 and 3730 g for the green
and brown strain, respectively. During this last 9 day measurement period another set of
bags with the brown strain were placed in the water. These bags had 1 kg per bag and the
growth rate was compared between these bags and the bags which were very full to see if
the rates were comparable. The bags with the 1 kg biomass had significantly higher
growth rates than those for the bags which were full (Fig. 9) (t=4.4, d.f.=18, P<0.001).
Figure 10 illustrates the amount of seaweed expected in the bags had the 5.44%/day rate
recorded during the first measurement period for the brown strain been maintained for the
full 28 days of the trial. The actual amount observed is similar to that expected during the
first 19 days of the trial but then, during the final 9 days of the trial, the observed amount
became less than the amount expected since the growth rates dropped. Based upon these
results, the current size of bag being used can fill rapidly to around 3 kg. Up to this weight
20
a high growth rate can be maintained. Beyond 3 kg the growth rates decline as the bags
become very full.
Figure 7. Growth rates (gsgr) and average weight per bag (g) (gwt) for the green strain.
Figure 8. Growth rates (bsgr)and average weight per bag (g) (bwt) for the brown strain.
21
Figure 9. Growth rate for the brown strain over time (bsgr) compared to another set of
bags started with 1 kg on day 19 and measured for 9 days (bnsgr).
Figure 10. Measured average weight per bag (g) (bwt) and the expected weight per bag
(g) (expwt) had the growth rates been maintained at the initial measured rate of 5.44%
day. Data are for the brown strain.
During the NE monsoon season the PH culture method was tested at the G site.
During this season the G site is calm and it was felt that the PH method might work. The
first set of lines were placed in mid December. We thought we were finished with the SW
monsoon period but we still had one more storm which made the site rough. The initial set
of plants were all stripped off of the PH units during this storm. Another set was placed in
January and the seaweeds were observed qualitatively for growth and herbivory damage.
Some herbivory was noted but the growth appeared to be very good. In mid January,
22
1997 growth studies were initiated on the PH units. Up to 10 plants could be tied to each
PH unit. We examined the effect of tying 1, 2, 3, 4, 6, 8, 10 plants to each unit. Each
treatment was replicated on 10 units or one propagule line. Each unit would contain 1 kg
of plants so for the 1 plant/unit a one kg plant was attached. For the 2 plants/unit each
plant weighed 500 g, etc. The data indicated that the growth rates were lower for the 1, 2,
3 and 4 plants/unit relative to the 6, 8, 10 plants per unit (Table 7). Breakage of plant
parts were noted more frequently in the lower number of plants per unit. For the higher
number of plants per unit (6 through 10 plants/unit) the growth rates were similar. At the
higher number of plants/unit the plants may have been too crowded to maintain a linearly
increasing growth rate. The final weights recorded for these higher number of plants/unit
were as high as 4.8 kg with growth rates being as high as 8.8%/day (Table 7). Based upon
these data we elected to tie on only 6 plants per PH loop since tying on more than 6 plants
did not produce more biomass. The additional time required to tie on the additional plants
was not warranted.
A comparison of 6 plants/unit to bags over the same time period indicated that
plants on the PH units grew significantly faster that those in the bags (PH 8.8%/day and
bags 6.6%/day in February/97, t=7.4, d.f.=18, p<0.001). While growth of the seaweeds on
the PH units was very good the seaweeds are vulnerable to herbivory. On several
occasions the plants on several propagation lines with PH units were eaten by fish
herbivores.
Table 7. Growth rates relative to the number of plants per PH unit.
Number of plants/PH unit SGR (%/d) significant difference
1 4.1+1.1 a
2 4.7+0.8 a,b
3 5.9+1.2 b,c
4 7.1+1.3 c,d
6 8.8+0.8 e
8 7.6+0.6 d,e
10 8.5+0.9 e
a letters a, b, c, d, e reflect significant differences based on ANOVA test
with Bonferroni multiple comparison test (P<0.05). Number of plants/unit
with the same letter are not significantly different.
With the growth rates recorded at the G site during both monsoon seasons, the
estimated production volume for the six, 100 m lines would be about 12,000 kg or more
(12 metric ton or more) of fresh seaweed per month. For a 1/2 ha farm in the Philippines
23
the production volume would be about 10,000 kg or 10 tons (Ruben Baracca Sr., pers.
comm.). The 6 line farm at the G sites would then exceed the production volume of a
typical 1/2 ha farm in the Philippines.
Section 5: Seaweed farm: maintenance and harvesting/drying
The general bag culture methodology is to put from 1/2 to 1 kg of seaweed in the
net bag and than harvest the contents after 14 to 28 days. The bags on a propagule line are
removed from the anchor line and taken to the beach where the seaweeds are easily
removed from the bags and dumped on tarps. Some of the seaweed is put into clean bags
and the rest of the seaweed is dried. The old bags are then buried in the sand for about 1
week. Drying of the seaweeds generally takes 2 to 3 days after which they are no longer
slimy and salt crystals have formed on the surface of the seaweeds.
Due to the extreme differences at the G site during the two monsoon seasons,
different culture strategies are recommended for each season. During the SW monsoon
season the site was rough with fairly steady wave action and periodic strong wave action
while during the NE monsoon the site was calm. During the SW monsoon the wave action
made work at the site somewhat difficult but the waves were advantageous in that they
helped keep the bags clean. Once a week cleaning was generally necessary and the bags
could be in the ocean for about one month before they needed to be buried in the sand for
one week to kill off the algae on the bags. One half kg of seaweed was placed in each bag
and with the growth rates measured during this season (average of 6.4%/day) the
seaweeds were harvested after 3 to 4 weeks(see recommendations for modifications on
the starting weight of seaweeds). At this time the bags contained about 3 kg. Propagule
lines were pulled to the beach and emptied. One half kg was put into clean bags and the
other 2 1/2 kg was dried. During the SW monsoon season the propagule lines at the G site
must be made of 4 mm rope. If fishing line is used it will get twisted due to the strong
waves and will eventually break causing a great deal of unnecessary labor to untangle the
lines. The loops on the propagule lines must also be much smaller than the 25 cm loop
recommended (Barraca, 1996). The larger the loop the more the bag twists due to the
wave action. Small loops, just large enough to loop the bag through should be used on the
propagule lines. The site must also be frequently checked to make sure the anchor lines are
strong and not wearing against coral. The farm site must also be cleaned of debris that
gets tangled on the lines during the storms of this monsoon season.
24
During the NE monsoon the G site is calm. The major difficulty encountered
during this time was algae growing on the bags. At times the algae fouling the bags
formed gassy mats that caused the whole bag to float near the surface. This would expose
the seaweed on one side of the bag excessively to sunlight causing parts of the seaweed to
turn white and die. This is essentially a type of ice-ice. Since the growth rates were still
good during the monsoon season one of two approaches can be taken to deal with the
algae: 1) continue to use bags but clean more often or 2) use PH units since the algae did
not attach itself to the plants. When bags were used 1 kg was placed initially in each bag
and bags were then harvested 2 to 4 weeks later (see recommendations on harvest interval
as related to starting weight of seaweeds). At this time there should be about 2 kg or more
in the bag depending upon how long the bags were left in the ocean. The bags should be
rigorously cleaned two to three times a week. During this season monoline can be used for
the propagule line instead of the 4 mm rope used during the SW monsoon since the G site
is calm during the NE monsoon.
The other approach during the NE monsoon is to use the PH units noted above in
the growth studies. During this monsoon season the G site is calm enough that an
excessive amount of seaweed is not lost due to plant breakage using this method. The
growth rates are also in general higher than those noted for seaweeds in the bags but the
plants on the PH units have a higher risk of being consumed by herbivores relative to
plants in the bags. Using the PH units, the seaweeds need only be cleaned once or twice a
week. The method of tying seaweeds onto the PHs is time consuming but the high growth
rates in addition to the less frequent cleaning needed may compensate for the time needed
to tie on the seaweeds. A minor modification to the PH units was tested to eliminate the
tying on of plants. A thin PVC (1/2" diameter high pressure PVC) ring was used instead of
a piece of rope for attaching the plants to the PH loop. The ring was about 5 mm in
thickness and was cut at one point. The ring was then tied to the PH loop, 6 to 10 rings
per loop. The ring could then be easy spread apart a little and the plant slid through the
gap so that it sits in the middle of the ring (Fig. 11). This modification significantly
reduced the amount of time it took to attach plants to the PH units.
25
float
propagule line
seaweed plant
rope loop
pvc
ring
Figure 11. Illustration of the propagule holder (PH) where seaweeds are clipped on the
loop using the PVC ring.
Therefore during the NE monsoon season, either method, bags or PHs, can be
used. When bags were used the starting biomass of seaweed was 1 kg and the bags were
well cleaned 2 to 3 times a week. Harvesting was done every 3 to 4 weeks depending
upon how full we allowed the bags to get. During the rougher SW monsoon only bags
were used at the G site. Seaweeds were stripped from the PH units during the SW
monsoon. The starting biomass was 1/2 kg during the SW monsoon and harvesting took
place 3 to 4 weeks later. Higher yields are obtained if a larger starting biomass is used (see
recommendations on starting weight and harvest interval of seaweeds). During the SW
monsoon bags needed to be cleaned only once per week.
Drying of the seaweeds is best done by emptying the bags and then placing the
seaweeds on drying tables similar to those constructed for drying fish. Local woods can be
used to support the platform made of petioles of the coconut tree. The platform is about 3
feet above the ground and 6 feet wide and any convenient length. The petioles could be
spaced about 1 inch apart if netting is not used and about 6 inches apart if netting is used.
It was found that about 1 square foot was needed to dry one kg of seaweed. At the G site
farm, 2,500 square feet of drying table were constructed to dry the estimated 12 tons of
seaweeds produced from the farm per month. Generally 1 1/2 to 3 days was needed to dry
to the seaweeds to a moisture level of about 1/8 of the original weight of the fresh
seaweed.
A harvest schedule might follow several different patterns. One could harvest daily
or one could do block harvests several times a week or month. In our 6, 100 m line farm
with 20 work days per month, 12 days could be used to change bags at a rate of 500 bags
26
per day. This would cycle through all the bags on the 6 lines in one month. The bags
would be emptied and part of the seaweed biomass dried while the other is returned to the
ocean in new bags. The other 8 days of the month would be used for activities such as
cleaning the bags, storing the dried seaweed, and farm maintenance. For the block harvest,
activities follow a different pattern. On one day 1000 bags would be completely emptied
and all the seaweed in the bags would be put on the drying tables. On the 2 subsequent
days, all the seaweed from 250 bags would be changed into 750 new bags and put in the
ocean. In this way 1500 bags could be processed in the 3 days. This type of processing
could be done each week so that all the bags on the 6 lines would be changed during one
month. The other two days of the week could then be used for the other activities noted
above.
Section 6: Product quality
Three kg of dry seaweed were sent to Mr. Ruben Barraca Sr. in December, 1996.
The following is the analysis report he submitted to OSM on the quality of our seaweeds
produced at the G site. He indicated that seaweed material was of marketable quality
(Ruben Baracca Sr., pers. comm.).
Table 8 Dried seaweed analysis report.
Parameter OSM Maldives Standarda
% moisture content 24.70 30.0
% clean anhydrous weed (CAW) 41.33 41.0
% Gum yield 26.33 29.0
% Gum yield from CAW 63.71 71.0
Gel strength, g 1094g 850 min./1100 target
Viscosity cps 65 25 min./50 target
pH 9.59
a standards provided by Ruben Baracca Sr.
Section 7: Seaweed farm: design considerations
Various designs for the seaweed farm were tested including different anchors at
the ends of the anchor lines and different intermediate supports to the anchor line. All
three styles were tested at Site G.
A general description of the farm used with the bag culture method follows that of
Baracca (1996) and includes anchor line construction and placement at the farm site. The
27
overall design for one anchor line was to have two 100 m ropes running parallel to each
other with a distance of 5 m between the lines. Between the pair of anchor lines are the
propagule lines to which the net bags are attached. Each propagule line was 5 m in length
and had 10 small loops to which the net bags were attached.
The ends of the anchor lines have to be firmly secured since a pair of 100 m lines
will hold at times in excess of 2,000 kg of seaweed. Along the length of the anchor lines
additional support can be given in order to secure the anchor line. While the anchor line
must be very secure, the propagule lines with the net bags should be easily detached from
the anchor line. We found it simplest to detach the propagule lines and do the loading and
unloading of the seaweeds in the beach area.
Each anchor line was constructed using one roll (220 m) of 10 mm rope. Knots
were initially placed along the rope at distances of 1 m. Looped through these knots were
4 mm pieces of rope to which the terminal loops on the propagules lines were attached
(see Fig. 12). In the figure the pvc pipe is an 8 cm (3 inch) piece cut from a 3/8" diameter
high pressure pipe. A hole is cut into the pipe through which the rope is thread and then a
knot is placed to secure the pvc piece to the rope. The rope length needed to construct
this loop is about 40 cm. Note that during the calm NE monsoon season the terminal loops
on the propagule lines could just be looped over the pvc pipe if desired. This would
eliminate the step of needing to loop the pvc pipe through the rope loop. Also note that
after knots are placed in the 10 mm rope the actual length of the anchor line is usually less
than 100 m. An alternative method is to not tie knots at one m intervals but rather to tie
thin rope (2 to 2.5 mm) through the 10 mm rope at two places about 1 inch apart and then
in between these two ropes to tie the loop with the pvc piece. This would preserve the
original length of the anchor line rope.
pvc pipe
rope loop through which
pvc pipe is inserted to hold
propagule linerope looped
through knot in
anchor line
Figure 12. Illustration of the loop with the pvc piece used to attach the propagule
line to the anchor line.
28
The final pair of anchor lines then has from 95 to 105, 4 mm rope loops plus pvc
pieces (the number of rope loops is dependent upon whether knots are placed at 1 m
intervals. If knots are place then the line will have about 95 rope loops). This would allow
from 95 to 105 propagule lines (950 to 1050 net-bags) to be attached to this pair of
anchor lines. The total cost of the materials for the anchor line was $45.65. Materials plus
labor was $64.85 (Table 9).
Two styles of anchors were used at the terminal ends of the anchor lines including
concrete blocks and coconut tree logs. The concrete blocks were in the shape of a disk.
They were from 10 to 15 cm thick and 1 meter in diameter. In the middle was placed one
to two holes using 2 cm (1 inch) pvc pipe. Two holes were placed in the large blocks since
these blocks could be used as the anchor for 2 anchor lines. Through the pvc pipe was
threaded thick rope (14 to 16 mm) and knots were placed on both ends. The anchor lines
could then be tied to these thick ropes. It was estimated that each large concrete block
weighed 250 kg. Two and a half bags of concrete along with aggregate, sand and pieces of
3 mm rerod were needed to make four concrete blocks. The total cost of the materials for
4 blocks was $33.28. Materials plus labor was $62.07 (Table 9).
The other style of anchor at the terminal ends of the anchor line was a coconut tree
log about 6 feet tall and sharpened into a point at one end. This log could be driven like a
stake into the substrate if coral, below the sandy surface, was not present. If this log could
be driven to a depth of about 70 to 100 cm, then the anchor was very secure. Generally 3
people were needed to move the log back and forth to drive it into the substrate.
Periodically one person can climb to the top of the log to provide extra weight to drive the
log into the substrate. The total cost for materials was $8.53. Materials plus labor was
$27.73 (Table 9).
Three styles of supports along the length of the anchor line were considered
including coral blocks, rerod and tree logs. The coral blocks were purchased from local
people who did this for a business. Blocks were generally at least 40 cm square. A piece of
8 mm rope about 3.5 m long with a loop on the end was looped around the coral rock.
This unit was then tied around the knots on the anchor lines at 2 m intervals. The block
was placed to the outside of the anchor lines at the maximum distance permitted by the
rope loop. Through time the coral blocks would become buried in the sand and the anchor
line was then secure. It was best to not attach the propagule lines with seaweeds until after
29
the coral blocks were buried. The total cost of the materials was $109.86. Materials plus
labor was $81.06 (Table 9).
The rerod supports were 2 cm (1 inch) in diameter and were 1 m (approximately 3
ft) long. These were driven into the substrate with an 18 lb hammer at a distance of 1 to 2
m from the anchor lines at intervals of 6 m. Rope (6 to 8 mm) was then attached between
the rerod and a knot on the anchor line. For extra support, where the rerod was attached
to the anchor lines, a 5 m piece of rope (6 to 8 mm) was placed between the pair of anchor
lines to essentially secure an 6 m long by 5 m wide section of the anchor line. In places
were coral was either exposed or subsurface, the rerod could be driven into the coral and
the length of the rerod could be shortened as appropriate. Total cost of materials was
$57.59. Materials plus labor was $86.39 (Table 9).
Tree log supports were either coconut tree logs or any other type of strong log
locally available that does not rot or become damaged rapidly in the ocean. These would
essentially be similar to that described above for the anchors. The logs would be driven
into the substrate at 8 m intervals at about a distance of 1 to 2 m from the anchor line.
Rope (6 to 8 mm) would then be attached between the log and the knot on the anchor
line. As with the rerod supports, if extra support was desired rope could be attached
between the anchor lines at the points were the tree log supports were placed. Total cost
of materials was $44.80. Materials plus labor was $83.19 (Table 9).
The structures noted above could be used in various configurations. The best
configurations would use combinations of concrete/log end anchors in conjunction with
rerod/log supports. The coral blocks are not recommended since the taking of the blocks
damages the local reefs in addition to being more costly and not as strong in comparison
to rerod or logs. In our G site we have several lines with both coconut tree logs plus rerod
supports. In areas where there is coral rock under the sand the logs could not be driven
into the sand. In these places rerod could be driven into the coral. In addition, depending
upon the size of the waves and strength of the current at the site, the intervals between
supports or the size of the end anchors could be modified. The site were we have the
above farm design configurations is very rough during several months of the SW
monsoon. The site is near the reef and while the current is not strong, during several
months each year the waves are sizable.
30
table of costs table 9
31
Section 8: Economic Analysis
Three analyses were performed in our evaluation of the economics of farming
seaweeds in the Maldives. The first portion of each of the following tables assumes the
farm is a business venture where farmers are hired at a set salary. The other portion of the
table ("no labor") is where the farm is owned by the individual(s) and labor costs are not
factored into the cost of making or maintaining the farm. In the third analysis, the cost to
produce one ton of dry seaweed is calculated.
Table 10 summarizes the values in Table 9 under Section 7: Design considerations,
except that here the cost of the bags are added in. The cost of the bags is the major
expense in establishing a farm averaging 66% of the cost for a farm where labor is costed
in. At this time this is a fixed cost since these bags are purchased from the Philippines. In
the future, the bags could be locally constructed and hence form another local industry for
the Maldives. Because the bags constitute such a large fraction of the overall cost of
making a farm, whether one chooses to use concrete blocks or logs changes the cost of
the farm only by a small fraction. The cost for making one line including labor and
materials ranges from $575 to $636. Materials alone would range from $498 to $559.
Note that each bag requires a float. In Laamu we put out a reward for children to
bring in discarded flip flop shoes and waste styrofoam found on the beaches. We combined
our need for material to make floats with a reward system for cleaning up the local
beaches. The response was tremendous and for about 400 rf ($34) we were able to
purchase enough material from the children for making 8,000 floats. The children were
happy with their monetary compensation, we received material to make floats for many
bags and the beaches were cleaned up.
32
Table 10. Cost of farm construction per 100 m anchor line. The upper half of the
table assumes farmers are paid a set salary of 1500 rf per month ($128)
while the lower half (no labor) assumes the farmers own the farm and no
labor costs are paid
anchor line bagsa farm design anchor supports total
($) ($) anchor/supports ($) ($) ($)
64.85 399.00 concrete/blocks 62.07 109.86 635.78
concrete/rerod 86.39 612.31
concrete/logs 83.19 609.11
logs/blocks 27.73 109.86 601.44
logs/rerod 86.39 577.97
logs/logs 83.19 574.77
no labor
45.65 399.00 concrete/blocks 33.28 81.06 558.99
concrete/rerod 57.59 535.52
concrete/logs 44.80 522.73
logs/blocks 8.53 81.06 534.24
logs/rerod 57.59 510.77
logs/logs 44.80 497.98
a cost of bags is $3.00 per 10 bag unit or one propagule line. Since bags have
to be buried in the sand each month more than 1000 bags are needed for a 100 m
line. In this costing it is assumed that 133, 10 bag units are needed per 100 m
line where 1000 bags could be in the ocean and 33, 10 bag units in rotation or
be available as replacement bags for damaged bags. If bag units are considered
only for burying in the sand (i.e. no replacement bags for damaged bags) than
only 125, 10 bag units would be needed if the bags are buried in the sand for
one week.
Using the cost of making a farm from Table 10 an overall evaluation of what the
business owner or farmer (no labor) might expect is provided in Table 11. Several
assumptions were made in constructing this economic analysis including:
1) materials used to make the farm would have to be replaced over a 2 year (24
month period) and so farm material costs are divided by 24,
2) labor charges were assumed to be 1500 rf per person per month,
3) price per kg of raw seaweed is 1 rf (this would be equivalent to $683/MT of dry
seaweed assuming 1 MT of dry seaweed can be produced from 8000 kg of raw
seaweed). This price is reasonable when selling directly to a company using the
seaweed. If the farmers sell to a middle person they will likely get 50 laari per kg
of raw seaweed and their profits would be less,
4) a line is 100 m long with 1000 bags,
5) production volume estimated using a doubling time of 2 weeks (SGR 5%/day),
6) each ha farm has 20, 100 m lines,
7) the farm starts with 1 kg of seaweed per bag and,
33
8) there are 10 people managing a one ha farm.
Profit per ha would range from $1610 to $1661 depending upon the farm design
desired. If the farm is owned by the farmer, then the profit to the farmers would range
from $2954 to $3005 (Table 11). Since it is assumed that 10 farmers are needed to
manage a one ha farm then this would mean that each individual would receive from $295
to $300 (3462 to 3522 rf) (Table 11).
Table 11. Costs, profits and income for a seaweed farm. The upper half of the table
assumes farmers are paid a set salary of 1500 rf per month ($128) while the lower half (no
labor) assumes the farmers own the farm and no labor costs are paid. Units are USD ($)
unless otherwise noted.
farm design material labor sales profit per month profit
anchor/support cost per moa per mob per moc per lined per hae rff
concrete/block 26.49 64.00 171.00 80.51 1610.20 18871
concrete/rerod 25.51 64.00 171.00 81.49 1629.80 19101
concrete/logs 25.38 64.00 171.00 81.62 1632.40 19131
logs/block 25.06 64.00 171.00 81.94 1638.80 19207
logs/rerod 24.08 64.00 171.00 82.92 1658.40 19436
logs/logs 23.95 64.00 171.00 83.05 1661.00 19467
no labor
concrete/block 23.29 0.00 171.00 147.71 2954.20 34623
concrete/rerod 22.31 0.00 171.00 148.69 2973.80 34853
concrete/logs 21.78 0.00 171.00 149.22 2984.40 34977
logs/block 22.26 0.00 171.00 148.74 2974.80 34865
logs/rerod 21.28 0.00 171.00 149.72 2994.35 35094
logs/logs 20.75 0.00 171.00 150.25 3005.00 35219
a cost is per 100 m line and assumes replacement of materials over a 2 year period
b assume 1/2 person month per 100m line @ 1500 rf/mo (11.72 rf per $1)(this is equivalent to 10
people per ha
c assume 2 kg per bag of seaweed produced for sale per month at 1 rf per kg raw seaweed. This is
equal to $683/MT of dry seaweed assuming 1 MT of dry seaweed can be produced from 8000 kg
of raw seaweed. This price is reasonable when selling directly to a company using the seaweed. If
the farmers sell to a middle person they will likely get 50 laari per kg of raw seaweed and the profit
would then be less than half that noted here.
d profit per line (100 m line) are sales minus labor and materials
e profit per ha are profit per line multiplied by 20
f profit in the local currency (rf) is on a per month and per ha basis. For the "no labor" option
where the farm is owned by the farmers, the per farmer income would be the profit divided by
however many farmers are needed to manage the 1 ha farm. Where the farmers are paid a salary,
10 farmers are assumed to be managing a 1 ha farm. Conversion to rf is 11.72 rf per $1.
34
Since growth rates change per month the farm owner or farmers might receive a
variable amount depending upon the month. Using the lowest cost farm design (log
anchors and log supports), profit per month per ha can be generated using the same
assumptions noted above except the production volume varies with the growth rate (Table
12). With growth rates as low as 3% the 10 farmers managing the farm would still exceed
the set salary of 1500 rf earned if they were hired labor for a farm (Table 12). As the
growth rates increase so do the profits so that during some months the farmers could net a
very respectable salary. An assumption made throughout this analysis is that the farmer is
willing to put in the extra hours of labor to harvest the larger biomass produced from
seaweeds growing at the higher rates.
Table 12. Profits in relationship to seaweed growth rates from a one ha log anchor/log
support farm design.
Growth Profit per month per ha ($)
(SGR) business pays farm labor farmers own farm (no labor)
3% 219 1563
4% 868 2212
5% 1661 3005
6% 2231 3575
7% 2688 4032
8% 3359 4703
9% 3681 5025
Another way to consider the economics of seaweed farming is to determine how
much it costs to produce a ton of dry seaweed. Using the lowest cost farm design (log
anchors and log supports), two growth rates corresponding to the average for the NE and
SW monsoon seasons, harvest intervals of 2, 3, or 4 weeks and 3 labor rates (1500, 1800,
and 2000 rf per month), the cost to make a ton of dry seaweed was calculated. The higher
the growth rate the lower the cost per ton (Table 13). The cost per ton also drops as the
harvest interval increases due to the exponential growth of seaweeds (see
recommendations on harvest interval). As the labor rate goes up so does the cost per ton.
Even at the highest labor rate, lowest growth rate and shortest harvest interval, the cost
per ton is below $400.
35
Table 13. Cost to produce one ton of dry seaweed depending upon the labor rate, seaweed
growth rates and harvest interval (for details on the effects of initial weight of seaweed
used, growth rates, and harvest intervals see recommendations).
Labor Rate per Month
Growth
Rate
(%/day)
Harvest Interval
(weeks)a
$128 (1500 rf)
$154 (1800 rf)
$171 (2000 rf)
Cost per ton ($)b
5.7c 2 285 326 353
3 246 282 306
4 176 202 219
6.4d 2 241 276 299
3 203 233 253
4 139 160 173
a harvest interval - the number of weeks between taking the excess seaweed out of the bags to dry. The
amount left in the bags would be 1 kg since this was the starting weight
b cost per ton of seaweed produced in Laamu. To ship to Male by dhoni is estimated to cost 25 rf per 80
kg bag or $27 per ton (based upon discussions with villages in Thundi)
c average growth rate during the NE monsoon period
d average growth rate during the SW monsoon period
Section 9: Environmental Impact
The areas where the seaweed farm was established had a substrate of bare white
sand. Therefore the actual substrate was not altered due to seaweed activities such as farm
construction or farm maintenance activities.
Seaweed pieces from the bags were rarely seen on the substrate. In contrast, in
areas where the PH units were used seaweed pieces were seen either near the site or
washed up on the beach. With either culture method, though, seaweeds were never seen to
establish themselves in or around the site. The pieces simply died or were eaten by fish or
other herbivores.
The physical seaweed farm structure (anchor lines, bags, etc.) provided structure
for small fish which would often be seen along the lines or around the bags. Whether the
seaweed farm actually promoted increases in the populations of these small fish or whether
they simply attracted the fish is not known.
36
Section 10: Recommendations
To provide a basis for several of the following recommendations a background in
growth rates of seaweeds is provided so that the relationship between starting weight of
the seaweed, harvest interval and amount of harvestable seaweed can be understood.
Seaweeds generally follow an exponential rate of growth, at least for a given time interval
(Fig. 13). For example if the weight is doubled in 2 weeks than in another 2 weeks it
would double again. Figure 13 illustrates the exponential rate of growth for several
different starting weights with a growth rate of 6.4%/day (equal to a doubling every 11
days which was the average doubling time recorded in the SW monsoon season). If you
start with 0.5 kg and have a growth rate of 6.4%/day then after 11 days you would have 1
kg and then in another 11 days, 2 kg and then at the end of the month or a 28 day period
about 3 kg or a little less than 3 doublings. If you start with 2 kg then you would have a
similar set of doublings and after 28 days you would have about 12 kg. So starting weight
will have a large impact on how much you will be able to harvest per bag. Figure 13 can
also be used to illustrate the basics for harvest interval. If you harvest every 2 weeks than
you slide back to the beginning of the curve to estimate how much you can harvest during
the second, 2 week interval. For example, if you placed 2 kg in the bag to begin with and
harvested after 2 weeks than you would get approximately 5 kg. You could take 3 kg to
dry and return the remaining seaweed to the bag for another grow out period. You would
get the same amount during the next 2 week interval or a total of 6 kg to dry. In contrast
if you left all of the seaweed in the bag another 2 weeks for a total of 4 weeks you would
be on the part of the curve at day 28 or about 12 kg. If you retain 2 kg in the bag you
could harvest 10 kg to dry or 4 more kg than if you harvested every 2 weeks. There would
also be a savings in labor in not having to process the bags so frequently. These points on
harvest frequency and starting weight are examined further below.
37
Figure 13. Amount of seaweed in the bag over time in relation to the starting
weight (0.5, 1, 1.5, 2 kg). Growth rate used was 6.4%/day (average growth rate
for the SW monsoon period).
As indicated above the starting weight of the seaweed placed in the bags is
important. Figure 14 illustrates the amount you can have in a bag after 28 days and the
amount you can harvest (final weight minus initial weight) relative to the starting weight
of seaweeds used (the growth rate used is 6.4 %/day which is the average rate recorded
for the SW monsoon period). The goal is to have a very full bag after one month or 28
days and then process the bags only once per month. For example, if you place 0.5 kg in
the bag initially you would have 3 kg in the bag after 28 days and could harvest 2.5 kg. If
you started with 1 kg you would have 6 kg in the bag and could harvest 5 kg. Because of
the size limitations of the bag currently being used, the maximum the bag can hold is
estimated to be about 3 to 4 kg (note the growth rates slowed between 3 to 4 kg in the
bag (see section of growth). Based upon Figure 14, 0.5 kg (1/2 kg) would be a good
starting weight during the SW monsoon season. With this starting weight about 3 kg of
seaweed would be in the bag after 28 days. Some seaweed is then taken out to dry (2.5
kg) and the rest (0.5 kg) is put in a new bag and returned to the ocean. It is likely that
putting a larger amount in the bags currently being used would not net a significantly great
yield since the growth rates drop as the bags fill beyond 3 kg (see section on growth
rates).
38
Figure 14. Final weight and harvestable amount relative to the starting weight of
seaweeds used. Assumed are a 28 day harvest cycle and 6.4%/day growth rate
(average growth rate during the SW monsoon period).
Figure 15 illustrates the same information as Figure 14 except the growth rate is
for the NE monsoon season. For the NE monsoon period where the growth is a little
slower than the SW monsoon, one could start with 0.6 kg per bag. Then at the end of the
month you would have 3 kg in the bag and could harvest 2.4 kg.
Figure 15. Final weight and harvestable amount relative to the starting weight of
seaweeds used. Assumed are a 28 day harvest cycle and 5.7%/day growth
rate.(average growth rate during the NE monsoon period).
39
As illustrated above if you could put 2 kg in a bag and wait 28 days to harvest you
could have about 12 kg in the bag. This would allow you to dry 10 kg and retain 2 kg in
the bag. The current bag size is too small for growing 12 kg of seaweed per bag per
month. Because of the potential benefits of using a larger bag size not only in harvesting
more seaweed biomass but also in processing a fewer number of bags (labor savings), the
following culture method modification is recommended for field testing.
Bags should be constructed which could hold maximally 4, 6, 8, 10, 12 kg.
Seaweed placed in these bags should be tested over a 28 day period for growth. The bag
which produces the greatest amount of harvestable seaweed should then be used in the
following farm design. In the following illustration of a modified farm design a bag which
can hold up to 12 kg is assumed.
A 10 mm rope could have our loop design (Fig. 12) placed every 0.5 m to which
the larger bag would be attached (Fig. 16). The opening of the bags could be at the
bottom since the bags would be opened and closed on the beach. An opening at the
bottom would also require only one knot to secure the bag and floats would not be lost
because the top of the bag has no opening. The bag could be 3 feet long and 2 feet wide.
There would be no propagule lines but rather a series of anchor lines placed 1 meter apart.
The anchor line would have coconut trees anchors at each end and then additional coconut
tree logs every 25 m to which the anchor line would be directly tied to. There would be
not additional supports attached to the anchor line. So for a 100 m anchor line you would
have four, 25 m units between logs to which 50 large bags would be attached per unit or a
total of 200 bags per 100 m anchor line (Fig. 16). From this anchor line you might be able
to harvest 10 kg per bag per month or a total of 2000 kg. Since the original design with
smaller bags has 5 m between sets of anchor lines you could have 6 lines for the larger
bags in a comparable area so that the total would be 1200 bags for the 6 lines (Fig. 17). At
2000 kg per line of harvestable seaweed you could harvest from 6 lines, 12000 kg from
the 1200 bags. In contrast, from the original design of 10 bags per propagule line and
1000 bags per set of anchor lines you would harvest a total of 2.5 kg per bag per month or
a total of 2500 kg (this assumes a starting weight of 0.5 kg and then harvesting at the end
of the month as illustrated in Figure 14).
40
each bag represents 10 bags
25m
distance between bags is 0.5m
Figure 16. Anchor line for a large bag seaweed farm.
5m
100m
Figure 17. Spacing of anchor lines for a large bag seaweed farm.
Whether one can effectively use a bag than can contain 12 kg of seaweed needs to
be determined. But any larger size bag which maintained a growth rate similar to that
noted for the bags currently being used would increase the amount of harvestable seaweed
biomass as well as reduce the number of bags needing to be processes for a comparable
amount of biomass.
Other recommendations would include:
1) construct anchor lines perpendicular to shore in the G site. The anchor lines are
currently placed parallel to the shore with one set near the beach and the other set further
out. With this configuration, to place the 20 lines for a one ha farm would require 1000 m
of linear shoreline. Placing the lines perpendicular to shore would allow more lines to be
placed for a given linear distance of shoreline. The logistics of placing the lines
perpendicular need to be worked out as coral is found further out and the water depth
increases as ones moves further from the shore.
41
2) large scale testing at the BF site. The BF site is a large area with several ha of lagoon
space available. It is also further from the reef and hence is not very rough during the SW
monsoon season. Fish herbivory might be overcome by increasing the amount of biomass
at the site. Bags and PH units should be tested on the scale of a least one, 100 m anchor
line. PH units could likely be used the entire year at this site if fish herbivory can be
overcome.
3) expand current farm operations and evaluate new sites in Laamu atoll plus other atolls.
Evaluate new sites first for a 12 month period and then develop the best sites.
4) develop a high quality drying, baling and packing facility in Laamu atoll.
5) develop strain of K. alvarezii best suited for the Maldivian environment
6) develop local industries which use carrageenan.
7) expand seaweed farming operations using other species of seaweed.
Section 11: Literature Cited
Adams, T. and R. Foscarini (eds). 1990. Proceedings of the regional workshop on
seaweed culture and marketing. South Pacific Aquaculture Development Project,
FAO GCP/RAS/116/JPN, FAO Field Document 1990/2.
Barraca, R. 1996. Feasibility study of farming, processing and exporting of Eucheuma
(seaweeds). Report for FAO TCP/MDV/4452.
Barraca, R. 1990. Agronomy protocol. Pages 34-36 In: Proceedings of the regional
workshop on seaweed culture and marketing, Adams, T. and R. Foscarini (eds),
South Pacific Aquaculture Development Project, FAO GCP/RAS/116/JPN, FAO
Field Document 1990/2.
Holloway, S. 1992. Harvesting the Bounty of the Reefs: An Evaluation of Mariculture
Candidates for the Republic of Maldives, Oceanographic Society of Maldives, Box
2075, Male, Republic of Maldives.
Llana, E. 1991. Production and utilization of seaweeds in the Philippines. Infofish
International 1/91:12-17.
42
Lewis, R. S. Holloway, and A. Shakeel. 1992. Preliminary survey of sea cucumber and
seaweed resources in Laamu atoll, Republic of Maldives. Oceanographic of
Maldives, Box 2075, Male, Republic of Maldives.
Neushul, M., C.D. Amsler, D.C. Reed, and R.J. Lewis. 1989. The Introduction of
Marine Plants for Aquacultural Purposes. Department of Biological Science,
University of California, Santa Barbara; Presented at Aquaculture '89, UCLA,
USA.
Russell, D. 1982. Introduction of Eucheuma to Fanning Atoll, Kiribati, for the purpose
of mariculture. Micronesia 18:3544.