The importance of phytoplankton for feeding corals 1 All rights reserved: ©José María Cid 2014

The importance of phytoplankton for

feeding corals

Text & Photos : José María Cid Ruiz

The whole of tropical coral species usually marketed and kept

in aquarium (Phylum: Cnidaria Class: Anthozoa), are taxono-

mically concentrated in a small number of orders (Subclass

Hexacorallia, orders: Sclerac!nia, Ac!niaria, Zoantharia, An-

!phataria). Subclass Octocorallia, orders: Stolonifera, Alcyo-

nacea, Gorgonaria, Corallimorfaria) . Among aquarists, in po-

pular language, are called "so! corals” those species that sup-

port individual polyps colony by a flexibility connec$ve $ssue

(as is the case in Alcyonacea) or by corneal !ssue such as gor-

gonians. Similarly, are referred under the term "hard/stony

corals" species whose skeletogenesis includes the forma$on

of a hard structure (formed by aragonite at 90% and the re-

maining 10% by calcite and magnesium and stron$um salts).

Covering this hard skeleton emerges so! connec$ve $ssue

that houses both individual polyps as different specialized ce-

lls belonging to the colony. Hard corals, as is well known, con-

sidering the size of their polyps are popularly known as "small

polyp corals " (SPS) and "large polyp coral " (LPS).

Among so! corals and hard corals also, we can find species

that host in their $ssues the famous zooxanthellae algae.

These endosymbionts algae (belonging in most cases to the

genus Symbiodinium, a dinoflagellate algae) shares with its

host coral the organic compounds result of its processes of photosynthesis

(mainly glucose). Addi!onally, some of these corals also provide certain

essen$al amino acids to the algae that are living with (N Satoh, 2011). In

contrast, many other species of so! and hard corals completely lacking

zooxanthellae in their $ssues. These la*er depend solely on its ability to

capture planktonic organisms to survive.

lcyo-

rists, in po-

species that sup-

ility connec$ve $ssue

y corneal !ssue such as gor-

ed under the term "hard/stony

skskskeleleleleleletogenesis includes the forma$a$a$a$a$a$onononononon

e (formemememememed d d d d d bybybybybyby aragonite at 90% and d d d d d ththththththe e e e e rererererere--

by calcitititititite e e e e e anananananand d d d d d mamamamamamagngngngngngnesium and stron$umumumumumum s s s s s salalalaltstststststs).).).).).).

his hard skeleleleleletotototototon n n n n n ememememememerererererergegegegegeges s s s s s sososo! connecec$v$ve $s$s$s$s$s$ssusususususue e e e e e

both individuauauauauaual l popopopopopolylylylylylylypspspspspsps a a a a a as s s s s s didididididiffeffeffeffeffefferent specicializededed ce-

the colony.y. H H H H H Harararararard d d d d d cocococococorarararararals, asasasasasas is s wewewewewewell knonown, con-

of theirir polypypypypypyps s s s s s arararararare e e e e popopopopopopupupupupupularlrlrlrlrlrly y y y y y knowowowowowown n n n n n as "small

andnd "large p p p p p polypypypypypyp cororororororalalalalalal " (LPLPLPLPS)S)S)S)S)S)S)S)S).....

d corals alslslslslslso, w w w w w we can n finfinfinfinfinfind spspspspspspecies

famous z z z z z zooxaxaxaxaxaxanthellaeaeaeaeaeae algaeaeaeaeaeae.

elongingngngngngng in momomomomomost cases t t t t to the

llate alalalalalalgagae)e)e)e)e)e) shares with i

host coral the

(mainly

es

The importance of phytoplankton for feeding corals 2 All rights reserved: ©José María Cid 2014

In a classic and simplified scheme, we would say that for corals

kept in aquarium, there are three basic models of feeding: a)

species that feed solely through their symbio"c algae (I refuse

to use the term “photosynthe"c feeding” or “photosynthe"c

corals”, b) species with mixed feeding strategy: organic com-

pounds provided by the zooxanthellae algae supplemented

with planktonic organisms captured and c) species that feed

exclusively on pelagic organisms that capture.

Plankton capture by corals in categories “b” and “c” is conside-

red based almost exclusively on zooplankton organisms. The

various species of corals, depending mainly on the size of their

polyps, trap a wide range of prey (copepods, copepod nauplii,

ro"fers and even bacteria). In this vision about coral's diet,

phytoplankton have a secondary role, since it would not be a

direct source of food for coral , but it would serve to feed seve-

ral poten"al zooplanktonic prey and would be responsible for

the nutri"onal profile of these la#er. However some studies

ques"on this vision about phytoplankton as a secondary role

for feeding corals

A good example is the study of Yahel G. (G. Yahel et al., 1998)

with an extensive fieldwork conducted in the Gulf of Aqaba

(Red Sea) on the distribu!on and consump!on of phytoplank-

ton in various coral reefs. In general terms the study shows a

significant reduc"on (between 20 and 60%) of the mass of phy-

toplankton (in par"cular the sub-spectrum of species below 8

microns, "ultra-phytoplankton") in the waters that flow

through a narrow reef channel five meters in length dominated

by so* corals herbivores (Dendronephthya hemprichi and

Scleronephthya corymbosa) respect to concentra"ons of these same phyto-

plankton organisms in open water nearby (seven-point sampling to five me-

ters deep). The study's authors a#ribute the decrease of phytoplankton to

the capture of it by so* corals already men"oned, as well as preda"on by ot-

her organisms belonging to different benthic taxa (bivalves, sponges, poly-

chaete annelids).

The authors are not surprised of the fact that in the reef channel the domi-

nant alcyonacea (Dendronephthya and Scleronephthya) are feeding on the

surrounding phytoplankton, since they are corals without zooxanthellae and

usually feed on phytoplankton. However, they considered a surprising result,

de-

The

size of their

copepod nauplii,

about coral's diet,

ole, since it would not be a

, but it would serve to feed seve-

ononononononicic prey and would be responsibiblelelele f f f f f forororororor

file ofofofofofof t t t t t thehehehehehesesesesesese la#er. However somemememememe s s s s s stutututututudidididididieseseseseses

vision ababababababouououououout t t t t t phphphphphphytytytytytytopopopopopoplankton as a seconondadadadadadaryryryryryry rolololololole e e e e e

corals

le is the stududududududy y y y y y ofofofofofof Y Y Y Y Y Yahahahahahahelelelelelel G G G G G G. . . (G(G(G(G(G(G. YaYaYaYaYaYahel etet al., 1998)

e fieldwowork c c c c conononononondududududuductctctctctctedededededed in ththththththe GuGuGuGuGuGulflflflflflf o of f Aqaba

istribibu!u!on andndndndndnd c c c c c cononononononsusususususumpmpmpmpmpmp!o!o!o!on n n n n n ofofofofofof p phyhyhyhyhyhytotototototoplplplank-

eefsfs. In genererererereralal t t t t t termsmsmsmsmsms thehehehehehe s s stutudydydydydydy s s s shows a a a a a a

etetetweween 20 anananananand d d d d d 6060606060%)%)%)%)%)%) of ththththththe mass o o o o o of f f f f f phphphphphphy-y-

he subub-spspspspecececececectrtrtrtrtrumumumumumum of f f f spspspspspspecieieieieieies s below 8

ton") in thehehehehehe watatatatataters ththththththatatatatatat flowowowowowow

five memememememetersrsrsrsrsrs in lengthththththth d d d d d domomomomomominated

ronephphphphphphththththththyayayayaya hemprichi and

Scleronephthya corymbosa) resp

plankton organisms in open w

ters deep). The study's

the capture of it by

her organism

chaete

The importance of phytoplankton for feeding corals 3 All rights reserved: ©José María Cid 2014

the fact that in the reef slope with absence of the so! coral

species men"oned above and dominant presence of her-

matypic corals (reef-building stony corals), also was measu-

red in this area a significant decrease in the concentra"on of

phytoplankton. The authors a$ribute this fact to the intake of

phytoplankton due to these hematypic corals, despite being

species with zooxanthellae in their "ssues and are not known

as species that feed on phytoplankton.

Based on the reading of this study and other similar works

two conclusions seem to be able to extract:

Within the complex trophic network of the reef, several

species of corals could be consuming phytoplankton

in a propor"on with respect to the consump"on of

zooplankton significantly greater than it was thought.

The hermatypic corals could also be poten"al consumers

of phytoplankton, despite the contribu"on of organic

carbon that perceive from their symbio"c algae.

Reef aquariums, have more controllable condi"ons of experi-

menta"on than the natural environment and therefore offer

an ideal environment to experiment with the use of phyto-

plankton as part of the diet. These experiences can help to

assess more precisely the importance of phytoplankton in the

diet of many species of coral kept in aquarium.

works cited

FABRICIUS, K. E., Y. BENAYAHU, AND A. GENIN. 1995~. Herbivory in asymbio-

"c so! corals. Science 268: 90-92.

A. GENIN, AND Y. BENAYAHU. 1995b. Flow-dependent herbivory and growth

in zooxanthellae-free so! corals. Limnol. Oceanogr. 40: 1290-1301.

YAELl G. et al. 1998. Phytoplankton distribu"on and grazing near coral reefs

Lmnol Oceanogr. 43(4), 1998, 551-563

SATOH N. et al. 2011. Using the Acropora digi"fera genome to understand

coral responses to environmental change Nature 476: 320–23

For more informa�on or contact the author: www.aqua�cnotes.com

ar works

work of the reef, several

be consuming phytoplankton

h respect to the consump"on of

signgngngngnifiifiifiifiifiificacacacacacantly greater than it was t t t t t thohohohohohougugugugugughthththththt.

atypic c cororororororalalalalalals s s s s s cocococococoululululululd d d d also be poten"al cononononononsusususususumemememememersrsrsrsrsrs

phytoplanktonononononon, , , , , , dedededededespspspspspspitititititite e e ththththththe e cocontntriribubu"o"on ofofofofofof o o o o o orgrgrgrgrgrgananananicicicicicic

on that perceieieieieieiveveveveveve f f f f f frorororororom m m m m m ththththththeieieieieieir r r r r r sysysysysysymbio"c a algae.

ve m more contntntntntntrorollllllllllllababababablelelelelele c conononononondi"o"o"o"o"o"o"o"o"onsnsnsnsnsns of f exexexexexexpepepepepeperi-

tutural envirorororororonmnmnmnmnmnmenenenent anananananand d d d d ththththththerefeforororororore e e e e e offoffer

exexpeperimentntntntntnt w witititititith h h thththththe e e e e e use e e e e e ofofofofofof phyto-

et. These exexexexexexpeririririririences s s s s s cacacacacacan hehehehehehelp to

portancececececece of phphphphphphytoplalalalalalanknknknknknkton n n n n n in the

kept in aqaqaqaqaqaquaririririririum.

cited

FABRICIUS, K. E., Y. BENAYAH

"c so! corals. Science 268: 90

A. GENIN, AND Y. BENAYAHU. 199

in zooxanthellae-free so! c c c c c cororororororalalalalalals.s.s.s.s.s. L L L L L Limim

YAELl G. et al. 19989898989898. PhPhPhPhPhPhytytytytytytopopopopopoplalalalanknknknknknktotototon n n n n n didididididist

Lmnol Oceaeaeaeaeaeanonononononogrgrgrgrgrgr. . 434343434343(4), 1 1 1 1 1 19999999999998,8,8,8,8,8, 5 5 5 5 5 5515151515151-563

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