Then and now: A comparison of patterns in blue crab post-larval abundance and post-settlement mortality during the early and late 1990s in the Mobile Bay System
Abstract:Two independent, yet identical blue crab studies were conducted five years apart (1990–1991 and 1997–1998) within the Mobile Bay system, providing the rare opportunity to compare patterns in post-larval settlement and post-settlement mortality within the same system over time. Patterns from the previously published study in 1990–1991 (Heck and Coen, 1995; Morgan et al., 1996; Heck et al., 2001) and patterns from the 1997–1998 study that were compared included: correlation between physical factors and post-larval settlement, the relationship between megalopal abundance and juvenile abundance, the abundance of juveniles within the system, and the role of refuge on early juvenile mortality. In 1990–1991, recruitment of megalopae into the Mobile Bay System was greater than in 1997–1998; however, peak recruitment was in late August–early September during both time periods. Recruitment was compared with juvenile abundance using 1-, 3- and 7-day lags to determine if there was an immediate or delayed relationship between these two factors. There were few significant correlations between megalopal abundance and juvenile abundance in either study, and most of the these occurred shortly after large recruitment events and disappeared within a few days. In both studies, juvenile abundance varied throughout the system, with most juveniles occurring in SAV (submerged aquatic vegetation) and in the lower portion of the bay. Early juvenile mortality was high (>80% d−1) during both studies. Although some differences were found between the two studies, the overall patterns in post-larval settlement and post-settlement mortality from the 1990–1991 study were qualitatively similar to those of the 1997–1998 study. The relative importance of post-larval abundance and post-settlement mortality did not change between the two time periods, confirming that the Mobile Bay system seems to be limited by high levels of post-settlement mortality and not post-larval abundance.
Document Type: Research Article
Publication date: March 1, 2003
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