Setilement of Blue Crab Postlarvae in Western North Atlantic Estuaries
Abstract:We quantified variability in daily settlement of blue crab postlarvae (megalopae) on identical artificial settlement substrates at up to 6 sites concurrently over a broad geographic expanse (∼1300 km) of the western North Atlantic (Delaware–South Carolina, USA). The 4-year study encompassed the blue crab recruitment season (generally July–November) from 1989–1992. Regional settlement was characterized by: (1) constant low levels of daily settlement punctuated by significantly non-random, episodic peaks of variable duration and intensity with peaks collectively accounting for at least half the total annual settlement at a site; (2) spatial and temporal variability leading to a general lack of coherence between sites in a given year and across years within a site; (3) occasional coherence in patterns between sites during a given year, suggesting linkages in regional processes affecting settlement; and, (4) significant semilunar patterns of episodic settlement pulses at the York River and Charleston Harbor sites over a 4-year period. Thus, regional settlement patterns exhibit both consistent (i.e., semilunar periodicity, episodic pulses) and variable (i.e., temporal and spatial variation) elements, which are likely due to a combination of stochastic and deterministic processes. Such patterns may impart an ecological advantage to crabs settling en masse (i.e., reduced encounter rate with predators through predator swamping) or at continuous low levels (i.e., below a density-dependent threshold) during the recruitment season. An identical study illustrated that settlement in Gulf of Mexico estuaries exhibited similarly episodic and highly variable patterns. Daily mean and total annual settlement were up to a hundred-fold greater for gulf than Atlantic Coast estuaries implying population limitation by post-settlement processes in the gulf and greater recruitment limitation in the Atlantic. These studies emphasize the merit of conducting research over a broad geographic range using standardized techniques to attempt meaningful ecological comparisons.
Document Type: Research Article
Publication date: November 1, 1995
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