Though the crabs arent killing existing populations of oysters, their long-term impact could still be significant. For instance, Hay noted, their availability as food could potentially increase the population of native crabs, disrupting the delicate balance between those predators and the oysters.
But assessing the long-term impact of the crabs has been difficult because the creatures reproduce and grow rapidly, flooding the shallow coastal waters with their young. In research conducted off Skidaway Island and Sapelo Island on the Georgia coast, the researchers found extraordinarily high populations of the crab as many as 11,000 individuals per square meter.
To assess the impacts of the non-native crab population, graduate student Amanda Hollebone placed oysters and mussels into large baskets and located them on mud flats away from existing oyster reefs. Some of the baskets contained only oysters and mussels and were intended to serve as controls, some had a community of oysters, mussels, oyster drills and native mud crabs, while others had the same community spiked with non-native crabs. The distance from the existing oyster reefs was expected to prevent adult green porcelain crabs from reaching the baskets.
However, the researchers found that within a month, the control baskets also had large populations of the green porcelain crabs that had reached the containers as juveniles settling from the water column. Entry of the crabs to the control baskets interfered with the researchers ability to compare the traits of communities with and without the non-native crabs.
You get a true understanding of the sheer densities of these crabs only when you actually pick up or dig through clumps of oysters and oyster shell hash, said Hollebone, who is
|Contact: John Toon|
Georgia Institute of Technology Research News