Seasonal and tidal abundance patterns of decapod crustacean larvae in a shallow inlet (SW Spain)

Planktonic larvae of decapod crustaceans were collected monthlyfrom July 1991 to June 1992 by pumping during nocturnal floodand ebb tides to establish seasonal larval abundance patternsin an inlet of the Bay of Cdiz. Additional 24 h series of sampleswere collected seasonally (July 1991, October 1991, January1992 and May/June 1992) during spring and neap tides to analyselarval abundance in relation to the main environmental cycles(diel, tidal and lunar phases) and vertical position in thewater column. First zoeae were the most abundant stage for mostspecies, representing 97.6% of all individuals collected. ZoeaI abundance was higher in spring and swmner and, on most samplingoccasions, there was a net output from the inlet to the bay.Five species (Liocarcinus arcuatus and Liocarcinus vernalis,Uca tangeri, Diogenes pugilator and Panopeus africanus) represented60% of total individuals caught. The seasonal occurrence offirst zoeae of the most abundant species indicated two differentreproductive patterns: species with a short reproductive periodand species spawning year round. Zoea I of several species (Panopeusafricanus, Uca tangeri, Pachygrap sus marmoratus, Processa spp.)were significantly more abundant during ebb tides and theirlater larval stages were scarcely collected, suggesting thatthese larvae are released in the inlet and exported to the bay.Conversely, a net input of first zoeae was observed for otherspecies (D.pugilator and Pinnotheres pinnotheres), but theirlater larval stages were also scarcely collected. Such importationcould be a larval rhythm artifact due to release of larvae inthe bay that drifted into the inlet by tidal currents. The crabIlia nucleus, whose later larval stages were collected frequently,was the only species that seemed to complete its life cyclewithin the bay. These results suggest that the studied inletwas primarily used by decapods as an adult habitat and spawningground, while larval development occurred in open sea. Sincevertical migration was not observed for exported larvae, thetidal synchronization of female release seemed to be the mostprobable mechanism of larval exportation. There were no significantdifferences between larval release during spring and neap tides.