Ultilization of a seagrass meadow and tidal marsh creek by blue crabs Callinectes sapidus. I. Seasonal and annual variations in abundance with emphasis on post-settlement juveniles

Abstract

Blue crabs Callinectes sapidus Rathbun were sampled in a lower Chesapeake Bay seagrass bed and adjacent tidal marsh creek from October 1982 through December 1986, using a drop net and suction sampler. Suction sampling was 88 % efficient and provided more accurate estimates of juvenile blue crab abundance, that were at least an order of magnitude greater than those obtained by conventional trawl gear For data analysis, C. sapidus were separated into 4 size classes by carapace width--54.25 mm (recently settled 1st and 2nd juveniles); 4.25 to 11.00 mm (3rd through 7th juvenile crabs); > 11.00 to 525.00 mm (8th through 12th juvenile crabs); and >25.00 mm (older juveniles and adults). Seasonal and annual cycles of C. sapidus abundance were observed in both habitats with annual differences most pronounced in the grassbed. Densities of C. sapidus were significantly greater in the grassbed in all but 2 of the 48 sampling dates. Settlement of the new year class appeared to be by megalopae and occurred from August through December A pulse of small C. sapidus C4.25 mm was observed in the grassbed from early to mid-September, whereas in the marsh creek this pulse occurred 2 to 4 wk later and consisted of 3rd stage and generally larger crabs (>4.25 mm). The small numbers of 1st and 2nd stage juvenile crabs (<4.25 mm) in the marsh creek in contrast to their abundance in the grassbed may result from increased predation in the tidal marsh creek or selective settlement into the grassbed. C. sapidus were rare in the marsh creek in winter but densities of crabs 5 2 5 mm remained high in the grassbed from fall through early spring. Densities decreased gradually in both habitats to lowest levels by mid-August. Approximately 90 '10 or more of C. sapidus collected at both sites from late August to June were 5 2 5 mm in carapace width. Densities of individuals 11 to 25 mm and >25 mm throughout the study period did not differ significantly among years (1983 to 1986) even though there were significant differences in the abundance of smaller sized individuals between 1983-84 and 1985-86. This suggests mortality within or emigration from grassbeds around this size. A possible ontogenetic shift in habitat use by crabs 11 to 25 mm may reflect a refuge in size from predation.

Time to metamorphosis of blue crab Callinectes sapidus megalopae:effects of benthic macroalgae

“…The exact mechanism for this reinvasion is not known, but may be the result of a combination of changes in postlarval behavior and physical transport by wind-driven and tidal currents (Sulkin et al 1980, Johnson et al 1984, Brookins & Epifanio 1985, Goodrich et al 1989, Forward & Rittschof 1994, Olmi 1994. In Chesapeake Bay, USA, newly recruited blue crab megalopae appear to settle preferentially into seagrass (Zostera marina) beds (Orth & van Montfrans 1987). In the back-barrier lagoons along the outer coast of Virginia, USA, seagrasses are largely absent, and megalopae must settle on alternative substrates such as benthic macroalgae.…”

Recruitment of shore crabsCarcinus maenas on tidal flats: Mussel clumps as an important refuge for juveniles

“…This implies that shore crabs, like other invertebrates, benefit from protection in such highly structured habitats as mussel or seagrass beds (see also Summerson & Peterson, 1984;Reise, 1985;Mattila, 1992). The availability of spatial refuges is particularly important to decapod crustaceans during their early benthic phases (Heck & Thoman, 1981;Armstrong & Gunderson, 1985;Wilson et al, 1986;Orth & Montfrans, 1987;Barshaw & Bryant-Rich, 1988;Wahle & Steneck, 1991.…”

Testing a selective tidal‐stream transport model: Observations of female blue crab (Callinectes sapidus) vertical migration during the spawning season

“…If oceanic conditions are favorable, the larvae are transported offshore, where higher salinities and decreased predation are more conducive to development (e.g., Smyth 1980;McConaugha et al 1983;Epifanio et al 1989). After a 4-to 7-week period as offshore meroplankton (Costlow and Bookhout 1959), blue crabs molt to a megalopae stage and return to estuarine nursery areas (e.g., Orth and van Montfrans 1987;Olmi et al 1990). When blue crab larvae are first released, they are transported passively by currents.…”