Abstract
The deepwater faunas of oceanic islands and seamounts of the Eastern Tropical Pacific are poorly known. From 11-22 September 2009 we conducted an exploration of the deepwater areas of the Isla del Coco Marine Conservation Area, Costa Rica and a nearby seamount using a manned submersible. The goal of the exploration was to characterize the habitats and biota, and conduct quantitative surveys of the deepwater portions of Isla del Coco National Park and Las Gemelas Seamount, located about 50km southwest of Isla del Coco. We completed a total of 22 submersible dives, spanning more than 80hr underwater, and collected a total of 36hr of video. We surveyed habitats from 50-402m and observed more than 45 species of fishes, some of which have not yet been described and are likely new to science. The diversity of fish species in deep water at Isla del Coco National Park was lower than the diversity of fishes in shallow water, and eight species groups accounted for more than 95% of the total fish biomass. The combined density of all fish species was higher at Las Gemelas Seamount (253 fishes/100m2) than at Isla del Coco National Park (138 fishes/100m2). The combined density of fishes in habitats comprised primarily of bedrock or large boulders outcrops was more than three times as high at Las Gemelas Seamount as it was at Isla del Coco National Park. This discrepancy was caused by the extremely high concentration of Anthiinae fishes in rocky habitats at Las Gemelas Seamount. Densities of fishes in the other habitats were similar between the two sites. Similarly, when estimates of fish density were plotted by slope categories the density was much greater on steep slopes, which were usually comprised of rock habitats. Also, the density of fishes was greatest on high rugosity habitats. Results of these submersible surveys indicate that seamounts in the tropical eastern Pacific Ocean may be an important source of biodiversity and that more quantitative surveys are needed to characterize the fauna of the region. Citation: Starr, R.M., K. Green & E. Sala. 2012. Deepwater fish assemblages at Coco Island National Park and Las Gemelas Seamounts, Costa Rica. Rev. Biol. Trop. 60 (Suppl. 3): 347-362. Epub 2012 Dec 01.
Highlights
Isla del Coco, known as Cocos Island, is located 550km southwest of the Pacific coast of Costa Rica and sits atop the Coco Volcanic Cordillera, a submarine mountain range that exists offshore of the southern part of Costa Rica (Cortés 2008, Alvarado 2009)
We conducted a total of four dives at the Las Gemelas Seamount and 18 dives around Isla del Coco National Park
An increasing amount of research has been devoted to studying the biological communities and patterns of benthic biodiversity of seamounts
Summary
Isla del Coco, known as Cocos Island, is located 550km southwest of the Pacific coast of Costa Rica and sits atop the Coco Volcanic Cordillera, a submarine mountain range that exists offshore of the southern part of Costa Rica (Cortés 2008, Alvarado 2009). A recent study reported that the average total biomass of reef fishes in the shallow waters around Cocos Island was 7.8t/ha, among the largest in the tropics worldwide (Friedlander et al Revista de Biología Tropical, this issue). This makes Isla del Coco National Park a place of unique global value, and Costa Rica provided further protection to the region in 2001 by placing a 22.2km no-fishing buffer surrounding the national park at Cocos Island. The objectives of the cruise with respect to fishes, were to gather quantitative information about species composition, numerical density, biomass, distribution and habitat associations of demersal fishes, and to compare the fish assemblages between Isla del Coco National Park and Las Gemelas Seamount
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