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-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 connec$connec$veve $ssue (as is the case in Alcyonacea ) or byy cornealco rneal !ssue such as gor- gonians. Similarly, are referreded under the term "hard/s"hard/stonytony corals" species whose skeletogenesissk el etogenesis includes the foformrma$ona$ 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 stron$umstron$ um salts al tss).). Covering thishi s hard skeletonske le to n emergesem er ge s soso!! connec$veconn ec $v e $ssuesu e that houses bothbo th individualindivid ua l polypspo ly ps asa s differentdi ffe rent specialspe ci alizizeded ce- lls belonging to thet he colony.colon y. HardH ar d corals,co ra ls , as isi s wellwe ll known,no wn, con- sidering the size of theirthe ir polypspol yp s arear e popularlypo pu la rl y knownkn ow n as "small polyp corals " (SPS) anda nd "large polypp ol yp coralc or al " (LPS).( LP S) . host coral thet he organic compounds result of its processes of photosynthesis (mainly(mai nl y glucose). Addi!onally, some of these corals also provide certain essen$ales 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 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-de - red based almost exclusively on zooplankton organisms. TheT he 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, ro"fers 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 poten"al zooplanktonicon ic prey and would be responsiblrespons ib lee fforor the nutri"onal profilefil e of theset he se laer. However someso me sts tuudiesdi es ques"on this visionv is ion aboutab ou t phytoplanktonph yt op lankton as a secondarysec on da ry roler ol e for feeding coralsco ra ls ScleronephthyaScleronephth ya corymbosa ) respectre sp to concentraons of these same phyto- planktonpl ankton 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 distribu!onis tr ib u! on anda nd consump!onc on su mp !o n of phytopp hy to pllank-ank- the capture of it by so* corals already men"oned, 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 showss ho ws a herhe r orgaorganismsni sm belonging to different benthic taxa (bivalves, sponges, poly- significant reduc"on (betweenet we en 20 andan d 60%)60 %) of theth e mass of phy-ph y- chaetech ae te annelids). toplankton (in par"cular thehe subs ub -spectrumsp ec 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 inatedinat ed 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 men"oned above and dominant presence of her- FAFABRICIUS,BRICIUS, K. E., Y. BENBENAYAHU,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 concentra"on of phytoplankton. The authors aribute this fact to the intake of A. GENIN, AND Y. BENAYAHU. 11995b.99 Flow -dependent herbivory and growth in zooxanthellaezooxanthell ae -frfreeee so! ccorals.or al s. LLimnol.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. 191998.98 . PhytoplanktonPh yt op la nk to n distribu"ondi st and grazing near coral reefs Lmnol OcOceanogr.ea no gr . 43(4),43 (4), 1998,1 99 8, 555151 -565633 as species that feed on phytoplankton. SASATOHTO H N. ete t alal.. 2011.20 11 . UsingUs in g the AcroporaAc ro po ra digi"ferad ig genome to understand cocoralra l responsesre sp on se s to eenvironmentalnvironme 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 iinforma•onnf or ma •o n or contactc on ta ct the author: www.aqua•cnotewww.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 propor"on withh respect to the consump"on 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 poten"al consumersc on su me rs of pphytoplankton,hy toplan kt on , despitede sp it e theth e contribu"onco nt ri bu "o n of organico rg an ic carbonon that percperceiveei ve ffromro m ththeirei r sysymbio"cmbio"c algae.a lgae. Reef aquariums, haveve mmoreore cocontrollablent ro ll ab le condi"onsc on di "o ns ofo f expex peeri-ri- menta"on 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 phphytoplanktonytop la nk to n in the diet of many species of coral keptke pt in aquarium.aq ua ri um. The importance of phytoplankton for feeding corals 3 All rights reserved: ©José María Cid 2014 .