Rev. Biol. Trop.,39 (2):203-206, 1991

Diet of tbe corallivorous pufferfisb Arothron meleagris (Pisces: Tetraodontidae) at Gorgona Island, Colombia.

Héctor M. Guzmán and Juan D. López

Smithsonian TropicalResearchInstitute, Apartado 2W2, Balboa, Panama .

(Rec.13-IX-1990,Acep. 2O-II-1991)

Abstrad: The density and diet of Arothro1'l meleagris and lhe abundance of corals are compared between Playa Blanca and La Azufradaree fs at Gorgona lsland,.Colombia.Corals, an important food resource for A. meleagris, are abundantafter lhe widespread coralmortality causedby lheEl Niño event in 1982-83. Bolhpuffee density and percent live coral cover were similar between reefs. The diet of A. meleagris showed strong preferences foc lhe abundant Pocilloporaspp. Arothro1'l may affect lhe recovety ofsome eastem Pacific reefs, where lhefish has been reportedfee­ ding on rare or less abundant corals.In contrast,lhe effect of A meleagris on Gorgona reefsmay be non significant; in fact, the fish may help lhe process of recovery,by fragmenting and dispersing colonies while feeding onpocilloporid coral!,but not feeding on raeecoral species.

Key words: Corallivory, Colombia,coral reef s,eastemPacifiCo

Arothron meleagris (Bloch & Schneider) is of me corallivores that consumed the greatest an Indo-Pacific pufferfish (Tetraodontidae)that amount of live coral, and fed mainly on poci­ is widely distributed throughout the eastern lloporids. Thisinference was basedon its abun­ Pacific Ocean. It lives on rocky shores,bom on dance and feeding habits, and not on stomach me mainland andoffshore islands (Thomson et contents. Prahl (1983) reported87% coral mor­ 'al. 1979). Almough its diet consists largely of tality at sorne reefs at Gorgona during the live corals (Glynn et al. '1972, Guzmán and 1982-83 El Niño warming event, when most of

Robertson 1989),"ü also feeds on tunicates the coral species,except Pocillopora eydouxi , (Hobson 1974), crus10se coralline algae, spon­ were affected. By December 1987, Uve coral ges, echinoids, and other invertebrates cover (only reported for La Azufradareef) was (Guzmán and Robertson 1989). Guzmán and 43% (prahl et al. 1988), wim pocilloporid co­ Robertson (1989) found that A. meleagris has rals (P. capitata?) comprising 69% and me ability 10switch its diet when changes on Psammocora 30.5%. That unprecedented and !he coral composition occur. They also found catastrophic disturbance.produced large chan­ mat ilS feeding preference on several eastem ges in community structure al me level of spe­ Pacific reefs is not related in a consistent way cies composition, abundance, and zonation. 10the abundance or availability of different co­ Therefore. changes in corallivoresdistributions ral species. and feeding habits might also beexpected. The coral reef community structure al We present data from November 1989 con­ Gorgona Island in Colombia, andme influence ceming the diet and abundance of A. me lea­ of corallivoreshave been examined byPrahl el gris that complements previous studies at ',al. (1979), Cantera (1983) and Glynn el aL Gorgona and elsewhere in meeastem Pacific (1982). The reef-building coraIs at Gorgona are (e.g., Glynn et.al. 1972, Guzmán and similar 10Panamanian reefs, where pocillopo­ Robertson 1989). The puffer's diet, and coral rid corals are me· dominant species. Glynn el cover composition of two fringing reefs were al. (l982) reported that A. meleagris was one compared. We also examined me relation bet- 204 REVISTA DE BIOLOGIA 1ROPICAL ween puffer distribution in different habitats on 1989 (Guzmán andRobertson 1989), thediffe­ a reef and habitat-related variation on its dieL rence was notsigniftcant (t= .91, P>0.05). Thispaper is theftrst of a series on the ecology As expected, the proportion of ca:als in tl;te of easternPaciftc coralreefs. ftsh's diet was similar10 the percent of coral cover found at each reef (Fig. 1). Pocillopora MATERIAL AND METHODS was moreconsumed thanPsammo cora ati>laya Blanca (t= 24.69, P< 0.01), where Gorgona Island (44 km2) is located 56 km Psammocora coverage was less than at La off the S.W. Colombian coast (2058'N, Azufrada (t= 2.55, P< 0.01). However. al La 78011'W). General descriptions of the flora, AzufradaA .. meleagrisconsumed (regardless of fauna and physical oceanography can be foqnd reef habitat) similar proportions oí both corals in Prahl et al. (1979), Glynn el m. (1982) and (t= L39, P> 0.05), in relation to their similar Rubio (1986). In the present study, coral distri­ availability (Fig. 2). Pocillopora and Pavona bution and coverage, and the pufferfish abun­ cover were similar between localities (t= .26. dance and diet were determined at Playa P> 0.05 and t= .69, P> 0.05, respectively). Blanca and La Azufrada reefs, bothlocated on Dead coralcover was notsigniftcant among re­ the eastern side of theisland, about 1 km apart ef SileS (t= L25, P> 0.05) but il was 17% grea­ from each other. The áreas of those two reefs terat Playa Blanca reef (Fig.·1). . are approximately 15 Ha and 8 Ha respectively (Glynn el al. 1982). Playa Blanca Reef

Diet composition was studied in 10 speared DIET FIELD fish at Playa Blanca reef, and 13 at La Azufrada reef. Stomach contents wereextrac­ ted within1h of collection and storedin ethanol (70%). AH contents were oven-dried (6510 80 oC) 10 a constant weight, then sorted under a dissecting microscope (sensu Guzmán and Robertson 1989). The percentage by weight of La Azufrada Reel dry material in each identiftable group was re­ corded. At La Azufradareefs, ftsh werecollec­ ted at two different coral zones (Pocillopora and Psammocora). At each reef, A. meleagris was censused along 5 belt transects (5-10 m wide depending on visibility) and the percent of substratum ca­ Fig. 1. ReJative abundance of live and dead c:ora1s intite vered by live corals was estimated from 5 line fieId. and diel compositiOll of Arothrtm meleagris al Playa transects. For both surveys, transects were ron Blanca and La Azufrada reefa. Colombia. "Others" cate-' perpendicular to the shore, about 25 m apart, gory in diel consista mainIy of un:bins and gaatropodl. and extended along the depthgradient (110 10 "Other" coral. were mainIy pavonids. Valuel are meana m). Line transects totalIy covered 730 m and (standard error). 766 m at Playa Blanca and La Azufrada reefs, respectively. Furthermore, variation in Arothron's diel AH datawere arcsine transformed for statis­ was related withthe availability oí coraIs wit­ tical anaIyses. hin differenl reeízones at La Azufrada, where Psammocora is abundanland formslarge den� RESULTS patches in the upperslope and al the base oíthe reeí.(Fig. 2). Fish captured within the In 1989, densities ofA. meleagris. which did Psammocora zone contained in their stomachs not differ between reefs (t= .11, P> 0.05), were 75% of that coral species. significaDtly more 2L9 ± 6.2 ind./Ha and 25.8 ± 4.9 ind./Ha at than Pocillopora (t= 3.56, P< 0.01). In the Playa Blanca and La Azufrada reefs, respecti­ Pocillopora zone. A. meleagrisconsumed more vely. Though densities at La Azufradá had de­ Pocillopora than Psammocora (t= 4.71, P< clined from 34 ind./Hain 1987 to 25 ind./Ha in 0.01). GUZMAN & LOPEZ: Diet of Arothron Colombia 205

A. meJeagris may affect therecovery of so­ rne eastem Pacific reefs, on one hand, by fee­ ding on rare corals (e.g., Psammocora at Caño Island, Costa Rica), but on ihe oiher band. the 100 puffer's apparentability te change the diet,may

80 favor the re-establishment of sorne coral spe� o� cies, as is the case for Pocillopora at Cafto o 60 Island (Guzmán and Robertson 1989). Rare co­ § 40 o ral species observed at Gorgona Island (e.g., "" 20 Pavona varians, P. clavus. Porites spp.) were not eatenby ihe puffer. This may be explained

H, 30 45 60 75 90. 105. 120 by the sOOentary nature of thefish, which con­ 3eaward DistS0ce (rn) centratesits feedingmovements to certainareas of the reef, where mere are large monospecific coral stands.Therefore, !he effect of A. me/ea­ Fig. 2. Otanges in me percentage cover of live and dead corals along a 120 m transect perpendicular 10 the shore, gris on Gorgona reefs may be remote; in fact, from the lagoon to me reefbase (layer graph); and puffer's the fish may help the process of recovery by diet at each reefzone within me reefprofile (pie diagrams), fragmenting and dispersing colonies while fee­ La Azufrada reef, Colombia. Diet values are means (stan­ ding upon Pocillopora and Psammocora. as dard error). observOO at !he lower reef slope and reef base. DISCUSSION Coral dispersion and fragmentation have been found 10 be an importantaspect of the recovery At GorgonaIsland the 1982-83 El Niño event of Panamanianand Costa Rican reefs (Guzmán caused a reduction in coral cover in excess of and Cortés 1989, Glynn 1990). 50% (Prahl 1983). Six years after coral morta­ lity, me Playa Blancaand La Azufrada reefs ha­ ACKNOWLEDGEMENTS ve about halfof their total areas covered with li­ ving corals. and pocilloporids are still abundant We mank me personnel al Parque Nacional andwidely distributedwithin eachreef. Natural Islas Gorgona y Gorgonilla, and INDE­ Both puffer density and percent Uve coral RENA,Colombia for facilitatingand supporting cover did nol differ between reefs, in spite of our study. Special manks to L. Fl6rez-González La Azufradareef being twiceme size. Guzmán and W. Henao for their help during the field and Robertson (1989) reportOO no relationship work, and to D.R. Robertson, andH. Sweatman between puffer and coraldensities, and·sugges ­ fortheir comments 10 the manuscrlpt too that puffer densíty on eastem Pacific reefs is not set by coral availabilíty. Similaror higher RESUMEN population densities are known from reefs in Panama, where me total area of Uve coral is Se comparan la abundancia de coral, y la less than 2% (Guzmán and Robertson 1989). densidad y la dieta del pez timboril_�!gthr()n­ The pattems of bothvariation in density of puf­ meleagris de los arrecifes de Playa Blanca y La ferfish and resource abundanee may suggest Azufrada, Isla Gorgona, Colombia. Ciertas es­ that populations are recruitment-limited ramer peciesde coral,recurso alimenticio principal de than resource-limited. A. meleagris, continuan siendo abundantes des­ A. meleagris feeding preferenees have been pués de 6 añosde la mortandad masiva ocurri� shown to be eomplex and variable. In sorne da a causa del fenómeno de El Niño 1982-83. plaees it behaves as apassive generalist, consu­ Ladensidad del pez y el porcentajede coral vi­ ming corals in relation te meir availability. In vo fue similar paraambos arrecifes estudiados. others it is an active generalist, broadening its A. meleagris demostró una marcadapreferencia diet by selecting the rarer corals (Guzmán and por el coral más abundante o disponible del Robertson 1989). At Gorgona Island. the fish arrecife (pocillopora). Arothron posiblemente showed strong preferences for what was availa­ irifluye en la recuperación de ciertos arrecifes ble, both within reef zones and me whole reef coralinos del Pacífico Oriental. debido a que area. puede consumir ciertas especies de coral raras RBVISTABIOLOGIA DB TR.OPICAL o poco abundantes. Por el contrario. en GIJ2lIÚn,H.M.1Ic. DA R.obeJtsOD. 1989. Popu1.adoaand fe­ Gotgoila el efecto posiblemente sea poco evi­ eding response. of the corallivoroul pufferfilh Arotllroa _'etJ,ris to coral mortality in the eutem dente. yaque el pez posiblemente ayude en el Pacific. Mar.BcoL Prog. � SS: 121-131. proceso de recuperación. debido a que. durante su alimentación. fragmenta y dispersa los cora­ Hiau. R.w. lIc. D.W. Strasbm¡. 1960. Ecologica1 relatioIII­ les. hips ofoltltefilh f� 0Il coral reer. ci' the Manba1l Islands.Ecol. Moaoar. 30:6S-1Z7; REFERENCES Hobaon, E.S. 1974. Feedingre1aticmhips ci'teleoItean fiI­ 0Il c:oral reefs Hawaii. BuD.. Cantera, J.R. 1983. DistributiOll des peupJements desclé­ hes in Kona, Fish. 72: 915- 1031. rac:tiiüaires sur unfrangeant récif de l'üe de Gorgona (cote pacifiqueCOlombia). de Téahys 11: 25-31. Prahl, H. VOll. 1983. Blanqueomasivo y muertede corales G1ynn, P.W.1990. Coralmortality diiturbance and s toc:oral en la Isla de Gorgona, Pacífico Colombiano. reef.in the tropk:al eutem Pacific, 1,.: P.W.Glym (ed.) Cespedesia12: 125-129. Global ecological CClIlse'luences of the 1982-83 El Niño-Southem Oscillation. Elsevier Oceanography Prahl, H. VOIl, F. Gublllc. M. GrOaL 1979. Gorgoaa. Futura, Series,New Yodc. Bog�,ColCllllbia. '1:19p.

Glynn, P.W., R.H. Stewart lIc.J.E. McCosker. 1972. Pacific Prahl, H. VOll, J.c. EscobarlIc. E.J. Peña.1988. Diversidad coral reefsof Panama: stnJcture, distributionand preda­ de especiesde un arrecife dec:oral dé la Isla Gorgona, torso GeoI.Rundschau 61: 483-519. Pacífico Colombiano. Memorias VI Seminario Nacional de pencias del Mar, Bogoti, Colombia., G1ynn, P.W., H. VOll Prahlllc. F. Gühl. 1982. Coral reefsof Comisión Colombianade Oceanografia,571-577. GorgonaIsland, Colombia, withspecial refe renceto ca­ rallivores and their influence in community structure Rubio, E. 1986. Nota, sobre la ictiofauna de la Isla and reef development. An. Inst. Inv. Mar. Punta Betin GorgOlla, Pacífico Colombiano. Boletín Ecotr6pica 13: 12: 185-214. 86-112.

Gumlán, H.M. lIc. J. Cortés. 1989. Coral reefstructure at ThomSOD,D.A., 1..T. FindleylIc. A.N. Kerstitch. 1979. Reef fishesof the Sea of Cortez. Wlley-Interscience,New Caño Island, PacificCosta Rica. P. S.z.Nl: Mar. Ecol. ' 10: 23-41. Yorlt.p. 302