The Importance of Phytoplankton for Feeding Corals

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: Scleracnia, Acniaria, Zoantharia, An- phataria ). Subclass Octocorallia, orders: Stolonifera, Alcyo-lc yo - nacea, Gorgonaria, Corallimorfaria ) . Among aquarists,ri st s, in po- pular language, are called "so corals” those speciessp ecies thathatt sup- port individual polyps colony by a flexibilityil it y connecconnecveve ssue (as is the case in Alcyonacea ) or byy cornealco rneal ssue such as gor- gonians. Similarly, are referreded under the term "hard/s"hard/stonytony corals" species whose skeletogenesissk el etogenesis includes the foformrmaona on of a hard structuree (formed(f or me d by aragonite at 90% andan d theth e re-re - maining 10% byb y calcitecalc it e andan d magnesiumma gn esium and stronumstron um salts al tss).). Covering thishi s hard skeletonske le to n emergesem er ge s soso connecveconn ec v e s suesu e that houses bothbo th individualindivid ua l polypspo ly ps asa s differentdi ffe rent specialspe ci alizizeded ce- lls belonging to thet he colony.colon y. HardH ar d corals,co ra ls , as isi s wellwe ll known,no wn, con- sidering the size of theirthe ir polypspol yp s arear e popularlypo pu la rl y knownkn ow n as "small polyp corals " (SPS) anda nd "large polypp ol yp coralc or al " (LPS).( LP S) . host coral thet he organic compounds result of its processes of photosynthesis (mainly(mai nl y glucose). Addionally, some of these corals also provide certain essenales amino acids to the algae that are living with (N Satoh, 2011). In Among so corals and hardd corals also,a ls o, wew e canca n findfin d speciesp eciess contrast, many other species of so and hard corals completely lacking that host in their ssues the famousfa mous zooxanthellaez oo xa nthell ae alalggae.ae . zooxanthellae in their ssues. These laer depend solely on its ability to These endosymbionts algae (belongingel on gi ng in mostmo st cases tot o the capture planktonic organisms to survive. genus Symbiodinium, a dinoflagellatell at e algae)al ga e) shares withwi th itsi

The importance of phytoplankton for feeding corals 1 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 symbioc algae (I refuse to use the term “photosynthec feeding” or “photosynthec corals”, b) species with mixed feeding strategy: organic compounds 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-de - red based almost exclusively on zooplankton organisms. TThehe various species of corals, depending mainly on the sizs iz e of their polyps, trap a wide range of prey (copepods, copepodc op epod nauplii, rofers and even bacteria). In this vision abouta bo ut coral'coral'ss diet, phytoplankton have a secondary role,ol e, since it would not be a direct source of food for coral , butbu t it would serve to feed seve- ral potenal zooplanktonicon ic prey and would be responsiblrespons ib lee fforor the nutrional profilefil e of theset he se laer. However someso me sts tuudiesdi es queson this visionv is ion aboutab ou t phytoplanktonph yt op lankton as a secondarysec on da ry rroleol e for feeding coralsco ra ls ScleronephthScleronephthyaya corymbosa) rerespectsp to concentraons of these same phyto- plplanktonankton organisms in openop en waterw nearby (seven -point sampling to five me- A good examplele is the studyst ud y of YahelY ah el G.G . (G.(G . YahelYa hel et alal.,., 1998) ters deep). The studstudy'sy' s authors aribute the decrease of phytoplankton to with an extensivee fieldworkfield wo rk conductedc on du ct ed in theth e GulfGu lf ofo f Aqaba the capture of i t by (Red Sea) on the distribuonis tr ib u on anda nd consumponc on su mp o n of phytopp hy to pllank-ank- the capture of it by so corals already menoned, as well as predaon by ot- ton in various coral reefs.ee fs . In generalgen er al termst er ms thet he studs tu dyy sshowsho ws a heherr orgaorganismsni sm belonging to different benthic taxa (bivalves, sponges, poly- significant reducon (betweenet we en 20 andan d 60%)60 %) of theth e mass of phy-ph y- chchaeteae te annelids). toplankton (in parcular thehe subs ub -spspectrumec tr um ooff speciessp ec ie s below 8 The authors are not surprised of the fact that in the reef channel the domi- microns, "ultra -phytoplankton")to n" ) in thet he watersw at ers thatth at flowfl ow nant alcyonacea ( Dendronephthya and Scleronephthya ) are feeding on the through a narrow reef channel fivefiv e metersme te rs in lenglengthth domd om inatinateded surrounding phytoplankton, since they are corals without zooxanthellae and by so corals herbivores (Dendronephthyaro ne ph th ya hemprichi anda nd usually feed on phytoplankton . However, they considered a surprising result,

The importance of phytoplankton for feeding corals 2 All rights reserved: ©José María Cid 2014 the fact that in the reef slope with absence of the so coral works cicitedte d species menoned above and dominant presence of her- FAFABRICIUS,BRICIUS, K. E., Y. BENAYAHU,BEN AY AH AND A. GENIN. 1995~. Herbivory in asymbio- matypic corals (reef -building stony corals), also was measu- c so corals. Science 268: 90 -92. red in this area a signiﬁcant decrease in the concentraon of phytoplankton. The authors aribute this fact to the intake of A. GENIN, AND Y. BENAYAHU. 1995b.1 99 Flow -dependent herbivory and growth in zooxanthellaezooxanthell ae -freefr ee so ccorals.or al s. Limnol.L im Oceanogr. 40: 1290 -1301. phytoplankton due to these hematypic corals, despite being species with zooxanthellae in their ssues and are not known YAELl G. et al. 1998.19 98 . PhytoplanktonPh yt op la nk to n distribuondi st and grazing near coral reefs Lmnol OcOceanogr.ea no gr . 43(4),43 (4), 1998,1 99 8, 5515 51 -565633 as species that feed on phytoplankton. SASATOHTO H N. ete t al.al . 2011.20 11 . UsingUs in g the AcroporaAc ro po ra digiferad ig genome to understand cocoralra l responsesre sp on se s to environmentale nvironme nt al changec ha ng e NatureNa tu 476: 320–23

Based on the reading of this study and other similarar works two conclusions seem to be able to extract: FoForr more informaoni nf or ma o n or contactc on ta ct the author: www.aquacnotewww.a qu a s.com Within the complex trophic networkwo rk of the reef, sevseveraleral species of corals could be consumingc onsuming phytoplankton in a proporon withh respect to the consumpon of zooplankton signiﬁcantlysi gn iﬁ ca ntly greater than it was thought.t ho ug ht . The hermatypicat yp ic ccoralsor al s couldco ul d also be potenal consumersc on su me rs of phytoplankton,p hy toplan kt on , despitede sp it e theth e contribuonco nt ri bu o n of organico rg an ic carbonon that perceiveperc ei ve ffromro m ththeirei r sysymbiocmbioc algae.a lgae.

Reef aquariums, haveve mmoreore cocontrollablent ro ll ab le condionsc on di o ns ofo f expex peeri-ri- mentaon than the naturaltu ral environmentenvi ro nm en t andan d thereforeth er ef or e oﬀeoﬀ err an ideal environment to experimentex pe rime nt withw it h theth e useus e of pphyto-hyto- plankton as part of the diet.et . These experiencesex pe ri ence s canca n help to assess more precisely the importancepo rtan ce ooff phytoplanktonph ytop la nk to n in the diet of many species of coral keptke pt in aquarium.aq ua ri um.