Abstract

 Isla del Coco has one of the most diverse and well-conserved coral reefs in Costa Rica. These reefs have been extensively studied since the 1980’s, however those studies focused mainly on coral coverage. The aim of this study is to evaluate the coral reefs of the island, not only by the coverage of the substrate but also the composition of fish, invertebrates and reef complexity. A total of 17 sites around the island were sampled in July 2013 and in February-March 2014. At each site, we evaluated three depths (4-8 m, 9-12 m and 13-16 m), where three 10m long transects were sampled. Turf algae was the predominant substrate cover with 38.18±5.58 %. The crustose calcareous algae (Order Corallinales) had a 28.12±5.85 % cover and live coral was 18.64±3.55 %, with Porites lobata as the main reef builder. A total of 18 taxa of macroinvertebrates were observed in the study sites, of which 56 % of the species were not abundant, 33 % were common, and the sea urchin Diadema mexicanum was the only dominant species. The density of lobsters of the genus Panulirus was 388±385 ind ha-1, which is the highest density reported in the Eastern Tropical Pacific. Also we observed high densities of the sea cucumber Isostichopus fuscus (550 ind ha-1), which has a high commercial value. We recorded 45 338 fish individuals, distributed in 93 species, with an average of 1.2±8.5 tn ha-1. From the total of species, 51 % were uncommon, 31 % common, 11 % predominant and 8 % occasional. The fish community at Isla del Coco is represented by a large number of carnivorous species, followed by top predators, herbivores and planktivorous species. According to the fish categories of the IUCN Red List, 16 % of species are in threatened categories and represent 25 % of the total sampled biomass. When comparing with studies carried out from 1987 to the present, the recovery in coral cover over time is evident, mainly due to: 1) a decrease in the pressure of the bioerosive action of D. mexicanum; and 2) the conservation actions that have been taken on the island. This has been translated in complex and more rugose reefs. Isla del Coco reefs are healthy, with functional and complex food webs; where species of high commercial value have large populations. The effectiveness of conservation and management activities in Isla del Coco has resulted in the recovery of the reef communities.

Keywords: live coral cover, Diadema mexicanum, recovery, resilience, biomass, conservation.