Rev. Biol. Trop., 40(3): 309-324, 1992 Cocos Island (Pacificof Costa Rica) coral reefs after the 1982-83 El Niño disturbance Héctor M. Guzmán! y Jorge Cortés2 1 Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Panamá. 2 Centro de Investigación en Ciencias del Mar y Limnología and Escuela de Bic!ogía, Universidad de Costa Rica, San José, Costa Rica. (Rec. 27-X-1991. Acep. 8-VI-1992) Cocos Island coral reefs were adversely affected by tbe 1982-83 El Niño warming event. Surveys made in 1987Abstract: indicated dramatic coral mortality at aH depths (l-24m). Live coral cover on tbree studied coral reefs was 2.6, 2.9 and 3.5%. Population den sities of the coraHivores Acanthaster planci and Arothron meleagris were relatively high witb tbeir feeding activities concentrated on tbe few surviving colonies. Density of Diadema mexicanum was also high, being responsible for tbe erosion of large reef framework areas. It is predicted that recovery of the original reef-framework tbickness is in tbe order of centuries. Eastern Pacific, coral reef, El Niño, Cocos Island, recovery. Key words: Widespread death of reef-building corals after catastrophic predation by Acanthaster occurred in the eastem Pacific, associated with planci (Linnaeus) was faster than expected abnormally high sea surface temperatures that because the structural integrity of the reef persisted for long periods during the 1982-1983 framework was not destroy ed and cry ptic El Niño (Glynn et al. 1988, Glynn 1990). There colonies survived (Colgan 1987). There has were significant reductions in live coral (SO- been sorne recovery of the coral community 100 %) on reefs in the Galápagos, Colombia, after the 1982-1983 El Niño in sorne areas of Panamá and Costa Rica (review in GIy nn the tropical eastem Pacific, but in other areas 1990). The distribution and abundance of recovery has been impeded by intensification several reef-associated invertebrates such as of corallivore activity (Glynn 1985a, Guzmán Diadema mexicanum Agassiz, Jenneria Robertson 1989), red tides (Guzmán et al. & pustulata (Lightfoot), Trapezia spp., and 1990), low recruitment rates (G lynn et al. Alpheus lottini Guerin experienced major 1991), and an increase in the destruction of changes (Gly nn 1985a, b). the reef framework by echinoids (G ly nn Pearson (1981) has suggested that 1988). These disturbances may eventually recovery of coral reefs after major natural lead to a replacement of the coral s by fleshy disturbances can take several decades. and crustose algae and to changes in the reef Recovery occurs through one or a community structure. combination of three mechanisms: (l) The purpose of this paper is twofold: to regeneration of surviving colonies (Colgan describe the coral reef community structure at 1987), (2) fragmentation of surviving Cocos Island after the 1982-83 El Niño event, colonies (Highsmith 1982), and (3) larval and second, to speculate about possible settlement (Loya 1976). In Guam, recovery recovery times of the reefs. 310 REVISTA BIOLOGIA TROPICAL DE Caribbean Sea 0 10 --� Manuelita Pacific Cocos Is. Ocean F Isl. '-...... " E B � ®Chatham ay � @ O Go � ° ' Punta 5 33 _��_�_�� Wafer Bay Presidio Punta Pacheco J ... Cerro Iglesias I o =::.::::::i2 _3 .... Yglesias O __ © Kilometers oC Bay ' 87°03 Fig. l. Cocos Island Reef sites A through C, were visited in 1978; sites A through K in 1986; and sites A, B and G in 1987. MATERIAL AND METHODS National Park in 1978 (Boza 1978). 1984 the protected area was extended to includeIn the marine Study area: Cocos Island (Isla del Coco) is environment within 5 of the island and in located at 5°32'N and 87°04'W (Fig. 1), 1991 it was again expandedkm to within 25 approximately 500 southwest of Costa Rica Cocos Island is the only subaereallykm. and 630 northeastkm of the Galápagos Islands. exposed portion of the aseismic Cocos Ridge, Its perimeterkm is 23.3 and the area 46.6 and is of volcanic origin associated with the The highest point (575km m) is CerroIglesias onkm2• the Galápagos hot spot and superimposed by more west side (Castillo et al. 1988). The island was recent seamount volcanism (Castillo et al. claimed by Costa Rica in 1832 and declared a 1988). GUZMAN & CORTES: Cocos Island coral reefs after El Niño disturbance 311 Sampling: COCOS Island was first visited in Chatham (each 200 m) reefs, were run July 1978. Three reefs were surveyed at perpendicular to the shore from the shallow depths between 5 and 25 m (Fig. 1, sites A, B, part of the reef to its base. C). In December 1986, three years after the The sea urchins Eucidaris thouarsii event, eleven reefs were visited between and (Valenciennes) in Galápagos (Gly nn 1988, 1 30 m depth (Fig. 1, sites A to K). Colgan 1990) and D. mexicanum in Panamá Unfortunately, only general observations, and (Glynn 1988) and Caño Island, Costa Rica underwater photography of the coral species (Guzmán 1988) are eroding the reef composition and distribution could be made frameworks. To determine D. mexicanum during both expeditions. The information density at Cocos Island, lOxl m long transects conceming sites I and J was provided by J.K. were surveyed parallel to the shore, at 5 m Reed, who visited those reefs during the same intervals, at two stations in each of the three cruise. reefs. In December 1987, four years after the El Reef thickness was estimated measuring Niño event, quantitative surveys were with a metric tape the maximum height of performed (during a five days expedition) at exposed block s of framework or on larger three of the reefs visÍted previously (Fig. 1, colonies. sites A, B, G). Those reefs, namely Punta Temperature deviations relative to a 20 year Presidio (A), 10-30 m depth, Bahía Chatham average (1947-1967) were obtained from data (B), 3-20 m, and Punta Pacheco (G), 1.5-20 based on 4000 to 6000 ship observations per m, represent three of the four well month, with a precision of 0.2 oC a.'1d of 1 to 3 developed reefs around the island (the nautical miles in position (F. Miller, per. fourth is at site C). comm.) We ran 10m line transects (Loya 1978) at distance intervals of 5 m (reefs A and B) and 8 m (reef G), following depth contours, at three stations haphazardly selected at each of RES ULTS the three reefs. We did 72 transects at Punta Presidio, 80 at Bahía Chatham and 147 at A total of 29 coral species, of which 20 Punta Pacheco (total 2990 m of reefs). The are shallow-water dwellers, have been sections with dead coral framework were reported for the island (Table 1). The massive scrutinized to identify the species, and coral Pavona gigantea Verrill is reported reconstruct the structure (i.e. coral zonation, from Cocos Island for the first time. Several abundance, colony size and composition) of species have not been found after the El Niño the former reef. Colony size was measured evento along the maximum length of living tissue. Before the 1982/83 coral mortality, all Diversity was calculated using the Shannon­ the reefs had high live coral coverage (Fig. Weaver index (Margalef 1957) and compared 2a, pero obser. ), and large areas of agariciid using Hutchenson's formula (Hutchenson corals (Pavona spp. and Gardineroseris 1970). planulata (Dana») were commonly We estimated the density (ind./ha) of the observed. A. planci was abundant and it was corallivorous seastar A. planci and the never observed feeding upon poritid corals pufferfishA. meleagris (Bloch and Schneider) (Fig. 2c). Bakus (1975) reported that the at the three reef areas; these two species can subtidal community was dominated (about influence the cornmunity structure of the coral 95 % of the live coral cover) by the massive reefs in the eastern Pacific (Gly nn 1974, coral Porites lobata Dana (erroneously 1985a, b, Guzmán 1988, Guzmán and identified as P. californica). In 1987 the Robertson 1989). All individuals encountered reefs at Punta Presidio and Punta Pacheco on an estimated 15 m wide independent belt­ had a continuous reef framework, while the transect were recorded. The transects (census), Chatham reef framework was solid from 3 four and five for A.planci and A. meleagris to 7 m in depth and was then formed by respectively at Presidio reef (each 180 m long), large coral patches intermixed with sand and four at Pacheco (each 235 m) and 4 at coral rubble down to 20 m. 312 REV ISTA DE BIOLOGIA TROPICAL TABLE I Sc/eractinian corals from Cocos Island, Costa Rica Suborder ASTROCOENIINA Family THAMNASTERIIDAE l. Psammocora stellata Verrill a, d, g 2. Psammocora supeificialis (Gardiner) b Family POCILLOPORIDAE 3. Poci/lopora capitata Verrill e 4. Poci/lopora damicornis (Linnaeus) b, d 5. Poci/lopora elegans Dana b, d 6. Pocillopora eydouxi Milne Edwards & Haime d 7. Pocillopora meandrina Dana b, d g 8. Poci/lopora verrucosa Squires b Suborder FUNGIINA Family AGARICIIDAE 9. Pavona c/avus Dana d, g lO. Pavona gigantea Verrill g 11. Pavona varians Verrill b, d, g 12. Gardineroseris planulata (Dana) a, b, g 13. Leptoseris papyracea (Dana) a, e Family FUNGIIDAE 14. Fungia (Cyc/oseris) curvata (VerriU) e 15 . Fungia (Cyc/oseris) distorta Michelin a, e Family PORITIDAE . 16. Porites lobata Dana' b, e, g Suborder FAVIINA Family FAVIIDAE * 17. Cladocora debilis Milne Edwards & Haime a * 18. Cladocora pacifica Caims f Family RHIZANGIIDAE 19. Astrangia dentata Verrill b 20. Culicia rubeola Dana f Suborder CARYOPHYLLIINA Family CARYOPHYLLIIDAE * 21. Anomocora carinata Cairns f * 22. Caryophy/Jia diomedeae Marenzeller f * 23. Desmophyllum cristagalli Milne Edwards & Haime f * 24. Polycyathus hondaensis (Durham & Bamard) a Family FLABELLIDAE * 25. Javania cailleti (Duchassaing & Michelotti) f Suborder DENDROPHYLLIINA Family DENDROPHYLLIIDAE * 26.