Do Indian River Lagoon Wetland Impoundments (Eastern Florida) Negatively Impact Fiddler Crab (Genus Uca) Populations?

Abstract

Quantitative sampling of fiddler crabs was performed in June– July between 1992 and 1994 along transects at three St. Lucie County mosquito impoundments, Florida, running from the Indian River Lagoon (IRL) shore and across the impoundment perimeter dikes, and in one impoundment across the perimeter ditch. A total of 929 specimens representing four species were found: Uca pugilator, Uca rapax, Uca speciosa, and Uca thayeri. The quantitative sampling showed that there was no correlation between the number of Uca burrow openings on the sediment surface and the actual number of crabs in the sediment. Differences were recorded in abundance and distributional patterns between impoundments, but no correlation was recorded between substrate organic content and species distributional patterns. The male/female ratio was close to 1 for all species, except for U. thayeri; the males dominated for this species (ratio, 1.8:1). High water temperatures potentially lethal to fiddler crabs occurred in the impounded marsh in the summer. U. pugilator and U. rapax were unlikely to be impacted by the impoundment flooding as they are highly motile and not very site specific. U. speciosa and U. thayeri were more restricted to the very soft, dark, and wet substrate along perimeter ditch banks and may therefore be impacted during periods of flooding because they are dependent on nonflooded areas for feeding and reproduction.