Hatching rhythms and dispersion of decapod crustacean larvae in a brackish coastal lagoon in Argentina

摘要: Mar Chiquita, a brackish coastal lagoon in central Argentina, is inhabited by dense populations of two intertidal grapsid crab species,Cyrtograpsus angulatus andChasmagnathus granulata. During preliminary one-year study and subsequent intensive sampling programme (November–December 1992), the physical properties occurrence decapod crustacean larvae surface water were investigated. The characterized highly variable conditions, with oligohaline waters frequently predominating over extended periods. adjacent show complex pattern semidiurnal tides that often do not influence lagoon, due to existence sandbar across its entrance. Besides occurring (exclusively freshly hatched zoeae few megalopae) dominating species, those three other brachyurans (Plathyxanthus crenulatus, Uca uruguayensis, Pinnixa patagonica) one anomuran (the porcellanidPachycheles haigae) also found occasionally. Caridean shrimp (Palaemonetes argentinus) occurred moderate number samples, maximum density 800·m−3. highest larval abundance was recorded inC. angulatus, almost 8000°m−3. Significantly moreC. andC. granulata at night than during daylight more (statistically significant only former species) ebb (outflowing) flood (inflowing) tides. In consequence, most observed nocturnal ebb, least diurnal Our data suggest develop where adult live, but exhibit an export strategy, probably based upon exogenously coordinated egg hatching rhythms. Zoeal development must take place marine waters, from megalopa eventually returns for settlement metamorphosis lagoon. higher frequency ofC. low salinities (≤12‰) particular site may be related local distribution patterns reproducing population. Unlike larvae, (P. are retained inside they through metamorphosis. They significantly prefer salinity occur night. These cannot explained release rhythms like brachyuran crabs, reflect diel vertical migrations bottom. It concluded osmotic stress as well predation pressure exerted visually directed predators (small species or life-cycle stages estuarine fishes) principal selection factors evolution migration these characteristics retention mechanisms, respectively.