Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


The Chesapeake Bay blue crab is in decline. One of the threats to it is the loss of its once plentiful nursery habitat, seagrass, due to baywide eutrophication and climate change. The emergence of the non-native benthic macroalga Gracilaria vermiculophylla may offer the blue crab an alternative nursery if it can provide juvenile crabs a refuge from predation. The ability of Gracilaria to protect juvenile blue crabs was investigated in mesocosm and field survival studies, which were combined into a larger dataset. All of these studies used tethering and therefore a tethering validation study in mesocosms accompanied these experiments. In the validation study, there was no evidence for treatment specific-bias due to tethering, and mortality of free crabs was approximately half that of tethered crabs. In mesocosms, survival in a large algal patch of 80-cm diameter was 42-69 % greater than that of crabs in a 10-cm algal patch or unvegetated habitat. In the field, the survival benefits of a 40-cm-diameter Gracilaria patch varied with the size of juvenile blue crabs. In the combined data, larger algal patches increased the survival of smaller juvenile crabs. This survival benefit of macroalgae decreased with increased crab size such that survival of larger juveniles was inversely related to Gracilaria patch diameter. Consequently, the non-native Gracilaria may serve as a nursery for the blue crab, but its benefits will depend on crab and algal patch size.



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