Spatial Dynamics and the Protection of Critical Habitats for the Blue Crab

Protection of critical spawning, mating, feeding, and nursery habitats is a key element of management strategies that seek to conserve exploited marine species, such that recruitment overfishing and population collapse are averted. The use of marine protected areas (sanctuaries, corridors) is a potentially powerful tool for the conservation of critical habitats and heavily exploited species through effort control.

Although essential habitats have been readily identified for many exploited marine species, determination of the optimum quantity and spatial distribution (i.e., seascape) of essential habitats requiring protection to conserve spawning stock and recruitment remains largely theoretical. Using the blue crab Callinectes sapidus, a species with wide dispersal that supports the world’s second largest crab fishery, we examine the influence of recruitment processes, habitat quality, food availability, environmental stress, exploitation, and spatial distribution of protected critical habitats to the conservation and enhancement of spawning stock and recruitment.

My role in this multi-investigator project is to evaluate the relative roles of food and refuge in determining the value of essential habitats to the distribution and abundance of crabs in nursery habitats and dispersal corridors. Distribution of the blue crab can be affected by several factors including abundance of food, habitat type or complexity, and proximity to favorable currents. Larger blue crabs are not likely to be controlled by top-down factors  (i.e., predation) in many habitats, since they obtain a size refuge at about 90-mm carapace width. Alternatively, bottom-up factors (i.e., food availability) may affect crab abundance. Specifically, bivalves comprise approximately 50% of the blue crab diet, although crabs secondarily consume conspecifics, polychaetes, amphipods, and other benthic prey. Recent work indicates that blue crab densities are higher in areas with elevated clam densities, suggesting that habitats with abundant food are essential and should be protected.

This research is supported by NOAA - National Sea Grant.