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Impacts on the primary production in Narragansett Bay, RI: Irradiance, grazing, and environmental conditions

Ashley Marranzino

Introduction

Marine phytoplankton play an important role in global carbon cycling. Through

photosynthesis, phytoplankton absorb atmospheric CO2 and produce O2. Large blooms of these

small photosynthetic organisms contribute greatly to oceanic CO2 absorption and have taken up

an estimated 50% of the global atmospheric CO2 which has been produced through

anthropogenic causes since the industrial revolution (Alkire et al., 2013). These blooms are also

largely important in the productivity of the marine environment, generating and recycling

nutrients via the biological pump.

Large winter-spring blooms have been noted as a major ecological event in the

Narragansett Bay, Rhode Island (Oviatt et al., 2002). The abundance and composition of the

phytoplankton assemblages in Narragansett Bay have been the subject of many studies (e.g.

Smayda, 1957; Martin, 1965; Keller, 1988; Smayda, 1998; Oviatt et al., 2002; Borkman and

Smayda, 2009) over the past several decades and studied through a long term monitoring

program at the Graduate School of Oceanography since the early 1950’s (Smayda, 1957).

Narragansett Bay is an estuarian system (approximately 100 square miles in size) along the

northeastern coast of the United States (Smayda, 1957). With multiple freshwater inputs,

prominently the Providence River in the northern bay, there is a salinity and nutrient gradient

(high nutrients and low salinity in the northern bay and lower nutrients and higher salinity in the

southern bay) throughout Narragansett Bay (Smayda, 2009).

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Several factors have been proposed to control the phytoplankton blooms in Narragansett

Bay. Irradiance has been contended as a major factor influencing the phytoplankton abundance

and productivity in Narragansett Bay. Estuary biomass has been shown to correspond to light

intensity (Keller, 1988). Diatoms, the major phytoplankton group found in Narragansett Bay,

also show increased productivity with higher light levels (Borkman and Smayda, 2009).

-esturary biomass associated with light (Keller, 1988). Changes in the water profiles

(temperature and nutrients available) have been cited as potential impacts on phytoplankton

communities in the bay (Borkman and Smayda, 2009; Nixon et al., 2009). Grazing has also been

proposed as a major control on the phytoplankton communities which impacts the timing and

sizes of phytoplankton blooms (Martin, 1965; Smayda, 1998). Despite the large number of

studies on the phytoplankton population of Narragansett Bay, there is still uncertainty

surrounding the factors impacting phytoplankton abundance. This study investigates the

phytoplankton abundance and productivity throughout Narragansett Bay in an effort to determine

if environmental parameters (i.e. temperature), irradiance, or zooplankton grazing is the major

influence on Narragansett Bay phytoplankton productivity.

Methods

Sampling was conducted September 13, 2013 at four stations in Narragansett Bay, Rhode

Island (Table 1; Fig. 1). Narragansett Bay is an estuarian system along the north eastern coast of

the  United  States  (Approximate  coordinates:  41°30’N,  71°20’W)  with  fairly  shallow  average  

depth (~9 m). The Providence River flows into the northern bay providing a nutrient-rich

freshwater input which creates a gradient as the lower saline water flows out of the southern bay

(Borkman and Smayda, 2009).

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Vertical Profile

A YSI temperature/salinity meter was deployed to measure salinity, water temperature, and

dissolved oxygen content throughout the water column. A light meter was deployed on the sunny

side of the boat to measure irradiance as well. YSI and light meter measurements were recorded

beginning at the surface and then in 0.5 m intervals until 2m depth, below which measurements

were taken at 1 m increments until the bottom was reached. Light data were analyzed using the

Beer-Lambert law (Iz=Ioe-kz) where Iz represents the irradiance at a depth in the water column

(z) based off of the surface irradiance (Io) and the depth of light extinction.

The extinction coefficient (k) was determined for each site and the above equation was used to

determine the fit of the irradiance through the water column to  Beer’s  Law  using  the irradiance

on the ship deck as Io.

Chlorophyll a

A single water sample was obtained from each station. From each sample, three

subsamples of 25 mL were collected in a syringe and concentrated down by running the sample

through a piece of filter paper. Filter paper was transferred to 90% acetone and stored overnight

in a freezer to allow for chlorophyll extraction. After 24 hours, fluorescence of chlorophyll

extraction was measured using a Turner AU10 fluorometer in conjunction with a standard

acetone blank. Fluorescence was measured for the entire chlorophyll extraction, which included

both chlorophyll a and all accessory pigments (Fb). Hydrochloric acid was then added to the

sample to separate out any chlorophyll a from the extraction. Fluorescence was measured again

for just the accessory pigments, phaeopigments, (Fa). From these two measurements, chlorophyll

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a fluorescence was calculated (Fa-Fb) and chlorophyll a and phaeopigment abundance was

determined using the equations below for each station replicate

Chlorophyll a = K(Fm/Fm-1)(Fb-Fa)(v/V)

Phaeopigment a = K(Fm/Fm-1)[Fm x (Fb-Fa)](v/V)

K is the sensitivity coefficient (equal to 1 on a 10-AU), Fm is the ratio of Fb to Fa for a pure

chlorophyll standard, v is the extracted volume (L), and V is the volume filtered (L).

Pigment abundance (in µg/L) was calculated for each of the three replicates from each

station. Standard deviation and coefficient of variation were calculated to show variation within

the water sample. Chlorophyll and phaeopigment abundance in the sample were used as a proxy

to estimate the phytoplankton abundance and production at the stations.

Phytoplankton abundance

Three phytoplankton samples were taken at each station. For each sample, 2 L of water

from Narragansett Bay was concentrated down to 20 ml with a 5µm mesh concentrator.

Concentrated samples were added to 2  ml  of  acid  Lugol’s  reagent  (10%  final  acid  Lugol  reagent  

concentration) and stored in a dark location. Abundance and diversity of phytoplankton were

estimated by counting 0.1 ml subsamples of each sample under compound light microscopy

(Table 2). Individual phytoplankton were identified to the highest level possible and totaled for

abundance. Species richness and evenness was determined for each station based on the total

number of individuals counted in all subsamples for each station. Diversity was calculated using

a Shannon index (H’=  -Σpi ln(pi); reported as eH’).

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Phytoplankton concentration was determined by counting the total number of cells in the

total volume subsampled for each replication. These replication concentrations were then

averaged together to calculate the average station phytoplankton concentration. Standard

deviation, standard error, and coefficient of variation were calculated for each station to estimate

counting error and variation between replications at a station. Because replicates were taken out

of two separate water samples, the error represents variation within Narragansett Bay

phytoplankton populations.

Zooplankton abundance

Zooplankton were sampled from the bay with a 202 µm mesh plankton net (opening of

0.25 m diameter). The plankton net was deployed off the side of the boat and remained in the

water column for approximately 5 min before being pulled back on board. Zooplankton were

rinsed to the cod-end of the net using a low pressure, seawater hose and collected in a 4 L sample

bottle. Specimens were preserved in 37% formaldehyde and sea water solution. Two net tows

were collected from each station. Abundance and diversity were estimated using dissecting

microscopes to count subsamples of each preserved sample, identifying each zooplankter in the

subsample to the highest taxonomic classification possible. The species richness and evenness

for each station was calculated using the Shannon index as mentioned above. Plankton

abundance was calculated by counting the total number of individuals per mL of subsample

counted.

Concentration for each sample was calculated by determining the volume towed through

the plankton net (V= area of cod end x distance towed) (Table 3). This was used to calculate the

concentration factor by dividing the volume of the cod end (0.001 m3) by the volume of water

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towed (m3). Zooplankton concentration was then calculated by multiplying abundance (#

individuals/L) by the concentration factor. Concentration is reported in number of

individuals/m3. Concentrations were calculated for each replicate of a particular station and

averaged to obtain an average station concentration. Standard deviation, standard error, and

coefficient of variation were calculated to estimate error between replications at each station

(Table 4). Because the replications represent two separate net tows, the error shows the variation

within the Narragansett Bay population.

The data for distance traveled during the trawl are absent for station 3 replication 2. For

this replication it was assumed that the distance traveled was the same as that traveled during the

first replication in order to calculate the concentration factor. There was no replication conducted

at station 4. Zooplankton concentrations are therefore not an average, but a single value and no

error was calculated.

Gelatinous Zooplankton

A coarse net (mesh size of 4mm2; 0.25 m diameter; 7 m long) was used to sample

gelatinous zooplankton. The net was deployed alongside the boat and pulled up through the

water column to capture specimens. Total volume was measured by recording the volume of all

ctenophores collected. A subsample of 20 ctenophores was separated out from the sample (when

sample size was large enough). Total volume of the subsample was measured along with

individual ctenophore lengths (mm). Only a single replication was conducted at each station.

Average ctenophore lengths were calculated along with standard deviation, standard

error, and coefficient of variation to determine error within the subsampled population.

Ctenophore abundance was calculated by measuring the number of individuals per volume of the

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subsample (# individuals/mL). A concentration factor for the ctenophore sampling was

calculated by dividing the volume of the cod end (0.001 m3) by the volume of the net (1.373 m3).

Ctenophore concentration was then calculated by multiplying the abundance (# individuals/L) by

the concentration factor and reported as number of individuals/m3.

Results

Water Profiles

The water profiles vary between the four sampling locations yet show some similar

trends with increasing depth (Fig. 2). Surface temperature increased by close to 1° C for each

station (station 1: 19.63° C; station 2: 20.6° C; station 3: 21.5° C; station 4: 22.6° C).

Temperature decreased with increasing depth across all four stations (Fig. 2a); however the

extent of change in temperature was not constant across stations. Station 4 showed the largest

change in temperature from surface to bottom recordings (1.43° C decrease), followed by station

3 (1.13° C decrease) and station 1 (0.55° C decrease) with station 2 showing the slightest

temperature change (0.4° C decrease).

Salinity was highest at sampling station 1 and water in Narragansett Bay becomes less

saline as stations progress towards the north (moving towards the Providence River). Across all

four stations, there was a slight increase in salinity with increasing depth (Fig. 2b). This increase

is most apparent at station 4 (0.46 ppt increase), followed by station 2 (0.26 ppt increase), station

3 (0.2 ppt increase) and finally by station 1 (0.16 ppt increase).

Dissolved oxygen content was highest at station 4 and decreased respectively with

decreasing station number. There was a decrease in dissolved oxygen content with increasing

depth; however the degree of difference between surface and bottom waters varies across

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stations (Fig. 2c). The slightest change in dissolved oxygen content between surface and bottom

waters was found at station 1 (3.9% decrease) and increased at each subsequent station (station 2:

15.8% decrease; station 3: 19.0% decrease; station 4: 19.3% decrease).

Irradiance profiles for all four stations showed an exponential decline with increasing

depth, yet the rate of declining irradiance through the water column was not constant across all

stations (Fig. 3). All four stations showed a  strong  fit  to  Beer’s  Law  with  r2 values above 0.97 for

all stations (Fig. 4). The depth of the light extinction was greatest for station 1 (8.57 m) while the

remaining three stations had relatively similar extinction depths (station 2: 6.94 m; station 3: 6.15

m; station 4: 6.84 m).

Phytoplankton Abundance

Chlorophyll a and phaeopigment concentrations varied between each station (Table 5;

Fig. 5). Chlorophyll a concentrations were highest at station 2 (5.68µg/L; standard deviation =

0.44; coefficient of variation = 7.78%) and lowest at station 4 (2.23µg/L; standard deviation =

1.95; coefficient of variation = 87.24%). Phaeopigment concentrations were highest at station 3

(4.80 µg/L; standard deviation = 0.80; coefficient of variation = 16.56%). The other three

stations showed phaeopigment concentrations of similar sizes (Station 1: 3.54 µg/L; standard

deviation = 0.17; coefficient of variation = 4.81%; Station 2: 3.76 µg/L; standard deviation =

0.02; coefficient of variation = 0.48%; Station 4: 3.38 µg/L; standard deviation = 2.28;

coefficient of variation = 67.54%).

Phytoplankton cell concentrations at each station appear to match trends in chlorophyll a

abundance (Table 6; Fig. 5). The highest cell concentration was found at station 2 (39,266,666

cells/m3; standard deviation = 33654469.7; standard error = 19430417.2; coefficient of variation

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= 85.70%), followed by station 3 (16,200,000 cells/m3 ; standard deviation = 9623062.6;

standard error = 5555877.76; coefficient of variation = 59.40%), station 4 (2,783,333 cells/m3;

standard deviation = 846069.3; standard error = 488478.36; coefficient of variation = 30.39%)

and finally by station 1 (2,466,666 cells/ m3; standard deviation = 1171893.1; standard error =

675592.77; coefficient of variation = 47.50%).

Diatoms were the major plankton group identified at each station (Table 7). Chaetoceros

cells were the most abundant in all samples except those from station 4 where Cerataulina was

the most abundant phytoplankton identified. Station 2 was by far the most specious with 25

different species identified in samples. Station 3 was the next most species rich with a total of 18

identified species. A total of 12 and 11 species were identified at station 4 and 1 respectively.

Trends in species richness do not indicate higher diversity (Table 6). Although species richness

was highest at station 2, diversity was greatest at station 3 (eH’= 9.307) and followed by station 1

(eH’ = 8.473) which had the lowest species richness. Diversity at station 2 is only slightly lower

(eH’= 7.299) than that of stations 3 and 1, but the diversity at station 4 is markedly lower than the

other 3 stations (eH’ = 2.836).

Zoplankton

Zooplankton abundance was much lower than phytoplankton abundance and composition

varied between each station (Table 8). Station 1 was the most speciose (11 identified

zooplankton types), followed by station 3 (10 identified zooplankton types), station 2 (9

identified zooplankton types), and finally by station 2 (5 identified zooplankton types).

Zooplankton concentration was similar across stations 1, 2 and 3 (Table 9; Fig. 6; Station 1:

462.52 individuals/m3; standard deviation = 390.27; standard error = 275.96; CV= 84.38%;

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Station 2: 468.03 individuals/m3; standard deviation = 261.55; standard error = 184.94; CV =

55.88%; Station 3: 462.52 individuals/m3; standard deviation = 30.74; standard error = 21.74;

CV = 53.82%) but lower at station 4 (256.08 individuals/m3). Although zooplankton

concentrations were similar across the first 3 stations, species diversity was variable between

stations with station 1 showing the highest level of diversity (eH’= 9.105). While having the exact

same zooplankton concentration as station 1, station 3 had a lower diversity (eH’ = 7.367). Station

2 had the lowest species diversity out of all four stations (eH’= 3.103), comparable to the

diversity found at station 4 (eH’ = 3.442) which had a much lower zooplankton concentration.

Gelatinous Zooplankton

Ctenophore abundance varied greatly between stations (Table 10). Concentrations were

highest at station 1 (145.56 individuals/m3), followed by a substantially lower concentration at

station 3 (46.09 individuals/m3), and very low concentrations at stations 2 and 4 (3.64 and 0.73

individuals/m3 respectively). Although concentrations were highest at station 2, the overall

ctenophore population sampled was made up of smaller individuals (average length of 26.9 mm;

standard deviation = 10.75; standard error = 2.404; CV = 39.96%) than were found at station 3

(average length = 48.68 mm; standard deviation = 15.96; standard error = 3.66; CV = 32.7%).

Both stations 2 and 4, which had very low ctenophore concentrations, also had comparably sized

but overall smaller individuals than found at stations 1 and 3 (station 2: average length = 5.25

mm; standard deviation = 0.979; standard error = 0.438; CV = 18.66 %; station 4: average length

= 5 mm).

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Discussion

Phytoplankton productivity (as determined based on pigment abundance and cell

concentrations) does not appear to be heavily dependent upon irradiance. Station 4 had the

highest surface irradiance yet hadthe lowest chlorophyll and phytoplankton concentrations,

indicating a low productivity at this site. Productivity is not solely dependent on surface

irradiance, however, and irradiance throughout the water column is important to consider. The

greatest light extinction depth was found at station 1, leading to the expectation that if irradiance

was the dominant factor influencing productivity, phytoplankton concentrations and chlorophyll

abundance would be greatest at this site. However, this was not the case. In fact, chlorophyll,

phaeopigment, and phytoplankton cell concentrations were all lowest at stations 4 and 1

respectively despite the higher irradiance levels at these two sites. Instead, phytoplankton

concentrations and pigment abundance were highest at station 2, which had the second lowest

surface irradiance and a light extinction depth very similar to that found for stations 3 and 4 (all

within 1 m of one another). This is contrary to previous studies which have found high

correlations between increased irradiance and higher primary productivity in Narragansett Bay

(Keller, 1988; Borkman and Smayda, 2009).

Former studies of the Narragansett Bay phytoplankton have attributed lower

phytoplankton productivity to increased zooplankton grazing rates (Oviatt, Keller, and Reed,

2002). Our data do not show this trend either. It would be expected that if grazing was the major

productivity constraint, the highest phytoplankton concentrations would be seen at the site with

lowest zooplankton concentrations. However, zooplankton concentrations were lowest (nearly

half that of the other stations) at station 4, which corresponded with the lowest phytoplankton

productivity. The highest productivity is conversely found at the station where zooplankton

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concentration was highest. Furthermore, stations 1, 2, and 3 had similar zooplankton

concentrations yet phytoplankton concentrations vary greatly between the three stations, showing

no solid correlation between the zooplankton and phytoplankton concentrations.

Ctenophores consume zooplankton and have been shown to decrease zooplankton

concentrations (Deason and Smayda, 1982), which should result in decreased grazing and

increased phytoplankton concentrations. There is no apparent correlation between increased

ctenophore concentrations and decreased zooplankton concentration. The phytoplankton,

zooplankton, and ctenophore concentrations across stations do not indicate grazing as a major

pressure controlling the phytoplankton productivity in Narragansett Bay.

Environmental factors may play a larger role in the phytoplankton productivity

throughout the bay. Highest productivity was found at a site intermediate for temperature,

salinity, and dissolved oxygen compared to the other stations. Station 4 has the lowest

concentration of phytoplankton, zooplankton and ctenophores and is also the station with the

lowest salinity and highest temperature. Although the temperature is still within reported annual

temperature ranges (Beaulieu et al., 2013), the low plankton abundance at this station may

indicate a preference for moderate environmental conditions. It is important to note that this

study did not measure nutrient availability at each station, which may heavily impact

productivity (Smayda, 1957).

This study shows no definitive factor which impacts and controls the phytoplankton

population in Narragansett Bay. Likely there is a complex of factors which all play into the

variations in phytoplankton throughout the bay (Keller, 1988). It is also important to keep in

mind the scope of the present study. Narragansett Bay phytoplankton has known variation in

composition, abundance and productivity on an annual and multidecadal scale (Oviat et al.,

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2002; Borkman and Smayda, 2009; Beaulieu et al., 2013). Data presented here represent the

trends for a single day and the conclusions drawn from the data are therefore limited. More

accurate pressures on phytoplankton productivity can be drawn from a larger examination of

phytoplankton over a more extensive spatial and temporal scale.

References Alkire, M. B., Perry, M. J., Asaro, E. D., & Lee, C. M. (2013). Using sensor-based , geochemical

measurements from autonomous platforms to estimate biological production and export of carbon during the 2008 North Atlantic Spring Bloom, 6(2), 1–20.

Beaulieu, W. T., Costello, J. H., Klein-Macphee, G., & Sullivan, B. K. (2013). Seasonality of the ctenophore Mnemiopsis leidyi in Narragansett Bay, Rhode Island. Journal of Plankton Research, 35(4), 785–791. doi:10.1093/plankt/fbt041

Borkman, D. G., & Smayda, T. (2009). Multidecadal (1959–1997) changes in Skeletonema abundance and seasonal bloom patterns in Narragansett Bay, Rhode Island, USA. Journal of Sea Research, 61(1-2), 84–94. doi:10.1016/j.seares.2008.10.004

Deason, E. F., & Smayda, T. (1982). Ctenophore-zooplankton-plankton interaction in Narragansett Bay, Rhode Island, USA, during 1972-1977. Journal of Plankton Research, 4(2), 203–217.

Keller, A. (1988). Estimating phytoplankton productivity from light availability and biomass in the MERL mesocosms and Narragansett Bay. Marine Ecology Progress Series, 45, 159–168. doi:10.3354/meps045159

Martin, J. H. (1965). PHYTOPLANKTON-ZOOPLANKTON RELATIONSHIPS IN Narragansett Bay. Limnology and Oceanography, 10(2), 185–191.

Nixon, S. W., Fulweiler, R. W., Buckley, B. a., Granger, S. L., Nowicki, B. L., & Henry, K. M. (2009). The impact of changing climate on phenology, productivity, and benthic–pelagic coupling in Narragansett Bay. Estuarine, Coastal and Shelf Science, 82(1), 1–18. doi:10.1016/j.ecss.2008.12.016

Oviatt, C., Keller, a., & Reed, L. (2002). Annual Primary Production in Narragansett Bay with no Bay-Wide Winter–Spring Phytoplankton Bloom. Estuarine, Coastal and Shelf Science, 54(6), 1013–1026. doi:10.1006/ecss.2001.0872

Smayda, T. (1998). Patterns of variability characterizing marine phytoplankton, with examples from Narragansett Bay. ICES Journal of Marine Science, 55(4), 562–573. doi:10.1006/jmsc.1998.0385

Smayda, T. J. (1957). Phytoplankton Studies in Lower Narragansett, 2(4), 342–359.

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Table 1: Information for each sampling station on the sampling day, including station location, time sampling began, and weather conditions during sampling

Station number Station name Latitude Longitude Start Time Weather Conditions

1 Dutch Island 41°29.36 N 71°24.31 W 8:56 Rainy, Calm

2 Fox Island 41°33.13 N 71°24.72 W 10:18 Overcast, but clearing, patchy sun

3 Hope Island 41°36.16 N 71°22.58 W 12:14 Sunny, partly cloudy

4 Warwick Neck 41°39.78 N

71°22.96 W 13:23 Cloudy

Table 2: Number of replicates and volumes of phytoplankton counted from each station

replicate. Volumes were used to calculate concentration of phytoplankton at each station.

Station Replicate Subsamples

Volume Sampled

Total Volume Sampled

Station 1 1 a 0.1 ml 0.3 ml

b 0.1 ml

2 a 0.1 ml Station 2 1 a 0.1 ml 0.3 ml

2 a 0.1 ml

3 a 0.1 ml Station 3 1 a 0.2 ml 0.5 ml

2 a 0.1 ml

3 a 0.1 ml

b 0.1 ml

Station 4 1 a 0.1 ml 0.3 ml

2 a 0.2 ml

3 a 0.1 ml

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Table 3: Distances and volumes of water towed through the cod end for the zooplankton net trawl. Volumes were used to calculate concentration factors. * for station 3 replicate 2 there was incomplete data on the total distance traveled during the zooplankton trawl. Distance was assumed to equal that of the first replicate at station 3 in order to calculate the concentration factor.

Station Station Replicate

Distance towed

Volume towed

station 1 1 69 m 3.385 m3

2 69 m 3.385 m3

station 2 1 23 m 1.128 m3

2 45 m 2.207 m3

station 3 1 240 m 11.775

m3

2 *240 m

11.775 m3

station 4 1 160 m 7.850 m3

2 150 m 7.359 m3

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Table 4: Number of replicates, subsamples of each replicate and volume sampled from each station for the zooplankton net trawl. Volumes were used to calculate zooplankton concentrations at each station.

Station Replicate Subsamples

Volume Sampled

Total Volume Sampled

Station 1 1 a 6 ml 29 ml

b 2 ml

c 2 ml

2 a 4 ml

b 8 ml

c 7 ml

Station 2 1 a 12 ml 27 ml

b 7 ml

2 a 2 ml

b 2 ml

c 4 ml Station 3 1 a 4 ml 38 ml

b 4 ml

c 4 ml

d 4 ml

e 4 ml

f 4 ml

2 a 2 ml

b 12 ml

Station 4 1 N/A N/A 29 ml

2 a 5 ml

b 24 ml

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Table 5: Average chlorophyll a (Chl) and phaeopigment (phaeo) concentrations for each station

Table 6: Phytoplankton diversity and concentration at each station

Station #

Shannon Index (eH')

# Cells Counted

Cell Concentration

(cells/m3) Standard Deviation

Standard Error CV (%)

1 8.473 74 2,466,666 1171893.1 676592.77 47.50 2 7.299 1178 39,266,666 33654469.7 19430417.2 85.70 3 9.307 614 16,200,000 9623062.6 5555877.76 59.40 4 2.836 167 2,783,333 846069.3 488478.36 30.39

Station 1 Station 2 Station 3 Station 4

Avg Chl ug/L) 2.53 5.68 3.62 2.23 Chl Stdev 0.10 0.44 1.58 1.95 CV (%) 3.90 7.78 43.67 87.24

Avg Phaeo 3.54 3.76 4.80 3.38 Phaeo Stdev 0.17 0.02 0.80 2.28

CV (%) 4.81 0.48 16.56 67.54

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Table 7: Phytoplankton species composition and number of species found at each station

Station 1

Station 2

Station 3

Station 4 Diatoms Diatoms Diatoms Diatoms

Chaetoceros didymus 3 Cerataulina pelagica 27 Cerataulina pelagica 10 Chaetoceros spp.** 2 Chaetoceros laciniosus 6 Chaetoceros didymus 40 Chaetoceros didymus 19 Pseudonitzchia spp. 2 Chaetoceros lorenzianus 3 Chaetoceros laciniosus 4 Chaetoceros spp.** 152 Skeletonema spp. 17 Chaetoceros spp.** 6 Chaetoceros socialis 81 Ditylum brightwellii 4 Thalassiosira spp. 1 Leptocylindrus danicus 7 Chaetoceros spp.** 540 Eucampia zodiacus 62 Cerataulina dentata 124 Pseudonitzchia spp. 14 Coscinodiscus spp. 1 Pseudonitzchia spp. 31 Cerataulina pelagica 11

Rhizosolenia spp. 1 Cylindrotheca closterium 2 Skeletonema spp. 85 Pseudonitzchia spp. 2

Chaetoceros Contorus 19 Eucampia zodiacus 10

Thalassionema nitzschiodes 7 Rhizosolenia spp. 1

Skeletonema spp. 6 Guinardia sp 7 Thalassiosira spp. 26 Dinoflagellates Thalassiosira spp. 7 Leptocylindrus danicus 9 Cerataulina Dentata 110 Akashiwo sanguinea 1 Dinoflagellates Leptocylindrus minimus 31 Chaetoceros subtilis 2 Cilliates Dinophysis acuminata 2 Pseudonitzchia spp. 37 Cerataulina spp 19 aloricate (uknown) 2

Total 74 Cerataulina dentata 99 Skeletonema spp. 59 Tintinnus 2

Corethron spp. 3 Thalassiosira spp. 22 Favella sp. 2

Skeletonema spp. 149

Unidentified centric diatom 1 Total 167

Thalassionema nitzschiodes 12 Dinoflagellates

Thalassiosira spp. 76 Dinophysis acuminata 2

Unidentified centric diatom 30 Protoperidinium spp. 1

Dinoflagellates Ciliates

Ceratium 1 Tintinnus 2

Dinophysis acuminata 1 Total 614

Prorocentrum gracile 1

Unknown 1

Other Flagellates

Unknown flagellates 1

Ciliates

Tintinnus 6

Favella sp. 9

Total 1178

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Table 8: Zooplankton species composition and abundance at each station as counted from zooplankton net trawls

Table 9: Zooplankton concentration and diversity at each station

Station Shannon

Index (eH')

Average Concentration

(# individuals/m3) Stddev.

Standard Error CV

1 9.105 462.52 390.27 275.96 84.38 2 3.103 468.03 261.55 184.94 55.88 3 7.367 462.52 30.74 21.74 53.82 4 3.442 256.08 N/A N/A N/A

Station 1

Station 2

Station 3

Station 4 Copepods Copepods Copepods Copepods

Calanoid copepod 2 Calanus sp. 11 Calanoid copepod 1

Calanoid copepod 34

Oithona sp. 1 Other crustaceans Copepod nauplii 2 Calanus sp. 2

Unidentified copepod 2 Amphipod 1

Unidentified copepod 6

Unidentified copepod 2

Other crustaceans Crab zoea 5

Other crustaceans

Other crustaceans

Amphipod 5 Crab larvae 1 Amphipod 1 Amphipod 3 Crab zoea 7 Mysid shrimp 1 Crab larvae 1 Crab zoea 1 Crab larvae 5 Total 19 Euphasid 1 Other

Isopod 1

Other invertebrates:

unknown fish egg 2

Other invertebrates:

Chaetognath 3

sea anemone larvae 2

Chaetognath 5

Polychaete 1 unidentified worm 2

Other

Other nauplius sp. 1 unidentified worm 3

unknown fish egg 6 Total 49

ctenophore 3

Unidentified nauplius 1

rathkea octopunctada 1

Total 23

Total 35

20

Table 10: Abundance, concentration and average length of ctenophores at each station

Station Volume all

Ctenophores Subsample

Size Volume

Subsample

Abundance (#

individuals/ L)

Concentration (#

individuals/m3)

Average Length

Std dev.

Standard Error CV

1 130 ml 20 100 ml 26 145.56 26.9 mm 10.75 2.404 39.96 2 15 ml 5 15 ml 5 3.64 5.25 mm 0.979 0.438 18.66 3 1000 ml 19 300 ml 63.3 46.09 48.68 mm 15.96 3.66 32.7 4 N/A N/A N/A 1 0.73 5 mm N/A N/A N/A

21

Figure 1: Map of Narragansett Bay, RI with approximate locations of four sampling sites. Station 2 is used as the sampling site for a long term phytoplankton monitoring study, indicated with black arrowhead. Map retrieved from: OCG 561 Plankton Cruise Laboratory.

22

Figure 2: Temperature (A), salinity (B) and dissolved oxygen (C) profiles with depth at each

station. Red line denotes station 1, green line denotes station 2, purple line denotes station 3, and blue line denotes station 4.

02468

101214

18 19 20 21 22 23

Dept

h (m

)

Temperature (°C) B

02468

101214

29 29.5 30 30.5 31 31.5

Dept

h (m

)

Salinity (ppt) C

0

2

4

6

8

10

12

70 80 90 100 110

Dept

h (m

)

Dissolved Oxygen (%)

A

23

Figure 3: Irradiance at depth through the water column at each station. Red line indicates station

1, green line indicates station 2, purple line indicates station 3, and blue line indicates station 4. All stations show an exponential decline in irradiance with increasing depth.

-1

1

3

5

7

9

11

13

15

17

0 500 1000 1500 2000

Dept

h (m

) Light Intensity (µmol photns m-2s-1)

24

Figure 4: Light profiles fist to Beers law for all stations. A- Station 1, B-Station 2, C-Station 3, D- Station 4. Left hand figures show the exponential decline of light observed at the station while the black line shows the calculated decline in irradiance  using  Beer’s  Law  calculations.  Right hand figures show the light intensities (blue dots) fitted  to  Beer’s  law  (black lines). Slope of black linee shows the extinction coefficient (k) for each station. R2 values show the degree the observed light intensities  fit  to  the  Beer’s  Law  expected  intensities.  

01234567

0 500 1000 1500 2000

Dept

h (m

)

0

2

4

6

8

10

0 500 1000 1500 2000

Dept

h (m

)

-2

0

2

4

6

8

10

0 100 200 300 400 500

Dept

h (m

)

02468

1012

0 50 100 150 200 250De

pth

(m)

Irradiance (µmol photons m-2s-1)

y = -0.5371x + 0.05 R² = 0.9967

-8

-6

-4

-2

0

2

0 5 10 15

Ln (I

z/I o)

(µm

ol

phot

ons/

m2 s

)

Depth (m)

y = -0.663x - 0.2221 R² = 0.9967

-6

-5

-4

-3

-2

-1

00 2 4 6 8 10

Ln (I

z/I o)

(µm

ol

phot

ons/

m2 s

)

y = -0.7494x + 0.1221 R² = 0.9992

-8

-6

-4

-2

00 2 4 6 8 10

Ln (I

z/I o)

(µm

ol

phot

ons/

m2 s

)

y = -0.6728x + 0.1582 R² = 0.9948

-5

-4

-3

-2

-1

00 2 4 6 8

Ln (I

z/I o)

(µm

ol

phot

ons/

m2 s

)

A

B

D

C

25

Figure 5: Primary production at each station shown by amount of chlorophyll a (light grey bars +/- 1 standard deviation), amount of phaeopigment (dark grey barsI; +/- 1 standard deviation) and phytoplankton cell concentration (red dashed line).

Figure 6 : Zooplankton and phytoplankton concentrations at each station. Zooplankton concentrations (zooplankton and gelatinous zooplankton) are shown on the left axis. Phytoplankton concentrations are shown on the right axis. Blue bars represent gelatinous zooplankton (Ctenophores), red bars represent zooplankton concentration (as calculated by zooplankton net trawl), and green bars represent phytoplankton concentrations.

0

5

10

15

20

25

30

35

40

45

0

1

2

3

4

5

6

7

1 2 3 4

Cel

l con

cetr

atio

n (m

illio

ns o

f cel

ls/m

3 )

Amou

nt o

f Pig

men

t (µg

/L)

Station

0

5

10

15

20

25

30

35

40

45

050

100150200250300350400450500

1 2 3 4 Phyt

opla

nkto

n co

ncen

trat

ion

(mill

ions

ce

lls/m

3 )

Zoop

lank

ton

conc

entr

atio

n (#

indi

vidu

als/

m3 )

Station