Because the green porcelain crabs quickly took over the control baskets, the researchers only had valid comparison data for 4-6 weeks. However, information from their baskets supported the observations made under more controlled but less natural conditions at Georgia Techs laboratory at the Skidaway Institute of Oceanography near Savannah.
As in the lab experiments, the researchers found that the crabs slowed the growth of small oysters, but not small mussels -- another common filter-feeder.
The long-term effects of the massive crab population are difficult to predict. Their large numbers could lead to population growth among the native crabs and fish that now prefer eating them instead of their normal diet. But if the predator population should grow large enough to control the non-native crabs, that could lead to a decline in their numbers and force the predators back to their traditional prey of oysters and mussels.
Were not sure whats going to happen, Hay said. We cant really raise the alarm because we dont have the data to say these crabs are doing something bad. Its possible that they will not have a huge effect at all.
Long-term observation of the oyster reefs may ultimately provide answers. We have observed both positive and negative impacts on oysters and oyster-related biota at small scales, but we cannot definitively answer our concerns about oyster reefs at larger scales, Hollebone added. With continued monitoring of large expanses of reefs, we may begin to understand the long-term, large-scale effects.
The green porcelain crabs were observed in Florida during 1990s, but have since appeared in large numbers in coastal waters of Georgia and South Carolina. Researchers
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Georgia Institute of Technology Research News