Abstract
In order to evaluate their tolerance to low salinities, zoeae of the fiddler crab Uca tangeri from the Rio San Pedro population (southwestern Spain) were reared in the laboratory at 20oC and at three salinities (16, 24 and 32). The zoeal development was completed at 24 and 32 but the crabs died as zoea I or zoea II, and very rarely as zoea III, at 16; tolerance to low salinities varied among clutches produced by different females. The duration of the first zoeal stage and of the complete zoeal development was shorter at 32. Our observations showed that the zoeae of U. tangeri could not tolerate retention in the mesohaline water of estuaries, and that export to oceanic waters would be optimal for their successful development. Survival at 24 suggests that larvae could also develop in polyhaline conditions if they were retained in the ocean-estuary interface. The presence of an additional zoeal stage (zoea VI) was observed in some individuals and associated with unfavourable combinations of temperature and salinity. In addition, some previously omitted aspects of zoeal morphology were re-described and illustrated, providing new evidence which supports the basal position of this species in a proto-Atlantic origin of the genus Uca. It is proposed that the differences between Uca tangeri and the rest of the Uca species should be highlighted, and that it should be placed in its own genus as Afruca tangeri .
Highlights
The ontogeny of most estuarine crabs includes a free larval phase
The original objective of the present study was to evaluate the tolerance of Uca tangeri zoeae to low salinities, and to determine whether this tolerance varies among clutches produced by different females
From 11 zoeae VI obtained in the 4 clutches, 81.8 % were observed at salinity 24
Summary
Two developmental strategies were described in larvae of species whose adults live in brackish waters: retention in the parental habitat, and exportation to the more stable conditions of coastal or oceanic waters (Anger, 2001). When the tolerance range of larval stages to salinity is narrower than that of adults, the exportation strategy allows larvae to develop in a less stressful environment. Once in the ocean, exported larvae may face a reduced predation pressure and play an important role in the dispersal of a species. The tolerance to reduced salinities is not an “all or not” trait: it has been demonstrated that genetic variability at the clutch level, individual variability in the provisioning of eggs with yolk, and salinity prevailing during embryonic development could affect salinity tolerance during crustacean development (e.g. Lee and Petersen, 2002; Giménez and Anger, 2003; Devreker et al, 2004)
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