The Distribution of Blue Crab (Callinectes sapidus) Megalopae at the Mouths of Chesapeake and Delaware Bays: Implications for Larval Ingress

Abstract

Transport of Callinectes sapidus (blue crab) megalopae from the continental shelf into estuaries may influence recruitment variability of this species. Observations of the vertical distribution of C. sapidus megalopae near the mouths of Chesapeake and Delaware Bays were used to infer vertical swimming behaviors that may influence ingress to these estuaries. Megalopae and oceanographic conditions were sampled at locations from~10 km inshore of the estuary mouths to~40 km offshore in coastal shelf waters on September 7-13, 2005 and September 3-7, 2006. Megalopae were present in greater abundance and at shallower depths during night compared to day at all locations in Chesapeake and Delaware Bays, suggesting that megalopae make diel vertical migrations within the estuary and on the continental shelf near the estuarine mouths. Within the mouth of the estuaries, only limited evidence suggests that megalopae increase in abundance in the upper water column during nocturnal flood tides in Delaware Bay. These findings suggest that wind forcing and density-induced subtidal flows are more likely mechanisms for ingress to Chesapeake and Delaware Bays than tidal transport.

Blue crab larval dispersal highlights population connectivity and implications for fishery management

“…Megalopae reenter estuaries and settle in nursery habitats containing submerged aquatic vegetation (Perry et al 2003, Spitzer et al 2003. Blue crab larvae display distinct patterns of vertical distribution in the water column throughout ontogeny (Epifanio 1988, Biermann et al 2016). Sulkin et al (1980) studied the behavior of blue crabs under laboratory conditions and found that early zoeae I occurred high in the water column and late zoeae IV-VII occurred in deeper vertical positions, suggesting a daily vertical migratory (DVM) behavior.…”

“…However, field observations did not coincide with these findings because zoeae have been found near the surface throughout all development stages (Epifanio et al 1984, Epifanio 1988, Little & Epifanio 1991. On the other hand, a DVM behavior for megalopae was observed by Epifanio et al (1984) and Biermann et al (2016). Near the estuaries, megalopae perform vertical migrations synchronized with the flood phase of the tide to complete their ontogenetic migrations between oceanic and estuarine habitats, a mechanism known as selective tidal stream transport (STST) (see Forward & Tankersley 2001 for review).…”

“…To cover the 55 d larval dispersal, simulations started in November of the previous year. Vertical distribution data of the blue crab larvae in GOM waters were not available; therefore, larval behavior was parameterized using results from vertically stratified plankton surveys conducted at Chesapeake and Delaware bays (Epifanio et al 1984, Epifanio 1988, Biermann et al 2016). Larval vertical distribution patterns observed in the plankton surveys were used to create a vertical matrix (z, Dt ), in which the probability density distributions in the water column (z) were calculated through time intervals (Dt ) for each developmental stage (zoea and megalopae) ( Table 1).…”

Vertical distribution of larval Atlantic menhaden (Brevoortia tyrannus) and Atlantic croaker (Micropogonias undulatus): Implications for vertical migratory behaviour and transport

“…have documented a diel pattern in activity suggesting transport is reliant on wind forcing and density driven flows into Delaware Bay (Biermann, North, & Boicourt, 2016). Previous studies on menhaden suggest larvae engage in diel migratory behavior (e.g., Forward, Tankersley, & Burke, 1996;Forward et al, 1999;Hoss, Checkley, & Settle, 1989).…”

The ontogeny of larval swimming behavior in the crab Hemigrapsus sanguineus: Implications for larval transport

“…These thresholds determined in the present study should not be viewed as definitive because they depend on the stimulus resolution used in behavioral experiments, which was purposefully kept at half-log steps to limit light exposure of dark-adapted larvae. Nevertheless, the relative difference observed between photoresponse thresholds for Z3 stage larvae (5.8 × 10 12 photons m − 2 s − 1 ) and Z5 stage larvae (1.2 × 10 14 photons m − 2 s − 1 ) would result in later-stage larvae residing~10 m shallower during the daytime than earlier-stage larvae given optical properties of the Delaware Coastal Current (e.g., Biermann, 2009). A shallower daytime vertical distribution of Z5 stage H. sanguineus larvae, the depth of which is set by the lower visual threshold (Sulkin, 1984), would lead to even greater transport northward toward source populations by upwelling wind-driven surface currents than for deeper-dwelling Z3 stage larvae.…”