Marine Biodiversity of Costa Rica: Perspectives and Conclusions

According to the numbers presented in the different taxonomic chapters of the present book, the marine biodiversity of Costa Rica comprises a total of 6,778 species, representing about 3.5% of all marine species reported worldwide (̃190,000 spp.: Reaka-Kudla 1997, www.marinespecies.org). Of these species, 4,745 spp. are reported from the Pacific and 2,321 spp. from the Caribbean of Costa Rica. A total of 288 species have been found on both coasts of the country. Costa Rica harbors a total of 85 species so far encountered exclusively in its waters. Arthropoda is the phylum with the highest number of endemic species (37 spp.). Regarding endemism, once again Isla del Coco plays an outstanding role with 41.2% of the country's endemics. The most species rich groups are Mollusca (2,170 spp.), Chordata (1,605 spp.), and Arthropoda (1,066 spp.), followed by benthic algae (420 spp.), Annelida (318 spp.), Cnidaria (290 spp.), phytoplankton (268 spp.) and Echinodermata (229 spp.) (Table V.1). The total number of species from the Pacific is more than double the number reported for the Caribbean (Fig. V.1a), and this situation occurs in most taxonomic groups, but there are several exceptions in which there are higher species numbers for the Caribbean: benthic algae (297 vs 175 spp.), sponges (65 vs 62 spp.), Anthozoa (83 vs 77 spp.), Trematoda (30 vs 21 spp.), Isopoda (46 vs 34 spp.), and Thaliacea (2 spp. vs 0 sp.). On the other hand, there are numerous groups with substantially more species reported from the Pacific coast, such as Polychaeta (317 vs 4 spp.), Hydrozoa (118 vs 14 spp.), Decapoda (437 vs 119 spp.), Copepoda (171 vs 47 spp.), and Echinodermata (187 vs 44 spp.).

Isla del Coco is of special importance for the marine biodiversity of Costa Rica. This fairly well-studied island contains 1,142 species; 35 of which have been reported so far exclusively from Isla del Coco and thus can be considered as endemic. Similar to the situation on the mainland, the most specious groups on the island are Mollusca (441 spp.), Chordata (355 spp., including 285 spp. of fishes), Arthropoda (128 spp., including 104 decapod species), and Echinodermata (124 spp.). Interestingly, 66.3% of all echinoderms reported from Pacific Costa Rica are from Isla del Coco. It is noteworthy that several taxa are underrepresented according to the compiled data: for example, for phytoplankton, marine macroalgae, pelagic opisthobranchs, copepods, and flatworms not even a single species has been reported, although they certainly occur around this island. Regarding other taxa, the differences in species numbers between Isla del Coco and the Pacific mainland, respectively, are striking: examples are benthic algae (0 sp. vs 175 spp.), sea slugs (11 vs 155 spp.), bivalves (65 vs 380 spp.), hydroids (12 vs 118 spp.), sipunculids (1 vs 15 spp.), polychaets (8 vs 317 spp.), and decapods (104 vs 437 spp.). These differences might be due to the absence or scarcity of these groups in Isla del Coco, but more likely reflect the lack of detailed studies concerning these taxa.