Marta Eckert-Mills - Crab Lab 

Warren Wilson College, Asheville, NC

                                           

 

Color change in aquacultured blue crabs ( Callinectes sapidus )

and effect of color on predation

Abstract

As part of a blue crab stock enhancement project in the upper Chesapeake Bay, the ability of juvenile blue crabs, Callinectes sapidus , to change carapace color to match substrate color was studied. Carapace color is a characteristic that potentially affects the survival of hatchery-raised individuals once released into the wild. Color differences were noticed between hatchery-raised and wild blue crabs, as were differences in survivorship. My goal was to examine the potential link between color difference and survivorship. Hatchery-raised juvenile crabs were exposed to differing substrates (white, brown, or sand) and were monitored for change in carapace color over a one to two week period. The overall hue of carapace color did not appear to be affected by substrate color, nor did the spottiness (variation in color) of the carapace. Color saturation (amount of color) and brightness, however, were affected by substrate color after two days of exposure to treatments. Crabs placed on white substrate were significantly higher in color saturation and brightness than those placed on sand substrate. This study shows that juvenile blue crabs do have the ability to alter their carapace color to match substrate color. The mechanism of this color change was not determined, although crabs did not need to molt in order to alter carapace color. I also determined the effect of carapace color on predation rates. Crabs were tethered in a tributary of the Rhode River and exposed to juvenile striped bass predators in lab trials. Crabs that had been on sand substrate had slightly, but not significantly, lower predation rates than crabs that had been on white substrate. My results indicate that carapace color change of juvenile blue crabs is easily induced by environmental cues and hatchery-raised individuals can be conditioned to look more like wild crabs. Further study may focus on the impact of color on overall survivorship of blue crabs in the wild and the biological effects of this morphological difference.

My post-graduation plans are to travel, working on organic vegetable farms around the world and then to return to the united states and become a cooperative agricultural extension agent and a vegetable farmer.  I also hope to conduct agricultural research through my job as an extension agent, building a bridge between researchers, farmers, and the public.

Bibliography

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Reid, D.G., P. Abello, M.J. Kaiser, and C.G. Warman. 1997. Carapace color, inter-moult duration and the behavioural and physiological ecology of the shore crab Carcinus maenas . Estuarine, Coastal and Shelf Science 44 : 203-211.

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