Large-scale blue crab recruitment: linking postlarval transport, post-settlement planktonic dispersal, and multiple nursery habitats

A large-scale study of early juvenile blue crab Callinectes sapidus recruitment within a shallow, predominantly wind-driven estuarine system demonstrated that distribution and abundance patterns were jointly influenced by location from oceanic sources of postlarvae, time period, habitat type, and post-settlement planktonic dispersal. The Croatan-Albemarle-Pamlico Estuarine System (CAPES) in North Carolina, USA, is a lagoonal body of water that is separated from the Atlantic Ocean by a chain of barrier islands, which are bisected by Oregon, Hatteras, and Ocracoke Inlets. For sampling purposes, the GAPES was divided into 4 regions that differed in distance and orientation from oceanic sources of postlarvae, as well as available complex benthic habitat types. The Eastern region was closest to oceanic waters, contained 3 major inlets, and harbored extensive seagrass beds. The Northern and Western regions were located along the inland boundary of the GAPES, and contained alternative habitat types including the submersed rooted vascular plant Myriophyllum spicatum and shallow detrital habitats. The Southern region was inshore and contained patchy seagrass. During a period that lacked storm events, virtually all juvenile recruitment occurred within seagrass beds at the Eastern region. Conversely, early juvenile blue crabs were distributed widely throughout the GAPES after the passage of tropical cyclones. The Eastern region appears to act as a relatively consistent initial recruitment site, whereas Northern and Western regions of the GAPES may act as episodic recruitment areas after the passage of tropical cyclones. Similar densities of early juveniles were found in different complex benthic habitats (seagrass, shallow detrital habitat, M. spicatum). A comparison of site-specific, settler-recruit densities (which represent distinct cohorts) suggested that post-settlement juveniles dispersed planktonically throughout the GAPES, most likely due to storm-driven transport. Post-settlement, planktonic dispersal altered the settler-recruit relationship, by both masking and potentially enhancing a density-dependent relationship between settlers and recruits. This study illustrates that ecological processes influencing recruitment, such as post-settlement dispersal, may be missed when studied at relatively small spatial scales, and that our interpretation of population regulation can vary depending on the scale of study. Studies conducted over broad spa tial scales can provide a more complete understanding of recruitment dynamics and can elucidate the interconnectedness of subpopulations by identifying potential 'source' areas in species with open populations.