Seasonal and tidal abundance of crab larvae in a tropical mangrove system, Gulf of Nicoya, Costa Rica

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Abstract
Crab larvae were collected from a platform moored in the mouth of a mangrove estero (= tidal creek) in the Gulf of Nicoya on the Pacific coast of Costa Rica, Central America. Eight observation periods encompassed both spring and neap tides and covered all season of the year. During each observation period, samples were collected every 2 h over 5 consecutive tidal cycles. Samples were collected from a depth of 1 m with a gasoline-powered impeller pump; total volume of each sample was 10 to 12 m3. The gross taxonomic composition of the observed larval assemblage was similar to that seen in temperate estuaries along the Atlantic coast of North America. Larvae of Uca spp., Grapsidae, Xanthidae and commensal crabs such as Pinnotheres spp. were the most common. However, abundance of individual taxa was greater than that seen in temperate estuaries with common forms in excess of 1000 larvae m-3. In contrast to temperate estuaries, spawning occurred year-round, but individual taxa showed distinct seasonality. As in temperate estuaries, spawing in the estero was also influenced by lunar cycles and larvae of several taxa showed tidally rhythmic changes in abundance. Zoea I of Uca spp., Grapsidae, Xanthidae, Pinnotheres spp. and Petrolisthes spp. were significantly more abundant during ebb tides suggesting that these larvae were spawned in the creek and exported to the open Gulf. Advanced zoea and megalopae appeared to take advantage of nocturnal flood tides to be recruited back into the estuary. Export of early stages did not occur in all taxa. Abundance of early zoeal stages of Pinnixa spp. was not affected by tidal phase suggesting that early stages were not exported from the estero.