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Use of Non-Native Macroalgal Habitat by Hatchery-Reared and Wild Blue Crab Juveniles

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Author: Mahalak, Kristin
Advisor: Heideman, Paul D.
Committee Members: Seitz, Rochelle; Lipcius, Romuald; Chambers, Randolph M.
Issued Date: 2008-05-06
Subjects: Blue crab nursery habitat
Stock enhancement
Genetic tracking
URI: http://hdl.handle.net/10288/489
Description: Seagrass beds are considered the preferred nursery habitat for juvenile blue crabs, Callinectes sapidus, increasing both survival and growth in early juvenile stages. Degradation of this structured nursery habitat and a drastic decline in spawning stock, due to natural and fishing mortality, has many scientists concerned about the Chesapeake Bay's blue crab population. This study aimed to determine whether non-native macroalgae, Gracilaria spp., may function as an alternative nursery habitat for juvenile crabs and whether Gracilaria spp. may help to increase release success of hatchery-reared cohorts as part of stock enhancement efforts. In this study, ~28,000 hatchery-reared blue crab juveniles (mean size 7.15mm carapace width-CW) were released near the mouth of the York River in an unvegetated mud cove enhanced with ~3600 L of Gracilaria spp. Sampling was conducted in two areas of the cove using a basket apparatus. The number and size (carapace width-CW) of crabs were measured during each sampling. The crabs collected during sampling were identified as hatchery-reared or wild using genetic analysis. Crab density at each site suggests Gracilaria in the mud cove had a carrying capacity of ~4-8 crabs m-2. Genetic analysis determined that some hatchery-reared crabs remained within the mud cove for the entire 43 day study period. Mean carapace width for the hatchery-reared cohort increased from 7.15mm (SE+/- 0.0581) to 26.6mm (SE+/- 1.93). In addition, settlement of wild juvenile recruits in Gracilaria was observed in early August. These findings suggest that the non-native macroalgae, Gracilaria spp., serves as an alternative nursery habitat for blue crab juveniles and release of hatchery-reared juveniles into habitats containing Gracilaria may help to increase post-release success.
Degree: Bachelors of Science in Biology

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