Abstract
The fiddler crab Uca rapax (Smith) feeds on microbes that colonize decaying cordgrass Spartina alterniflora Loisel. in the salt marsh. Crab-burrowing activity brings organic matter to the sediment surface. This fosters microbial growth on the organic matter and stimulates cordgrass growth. Food supply to the crabs is thereby directly and indirectly enhanced. Fiddler crabs may dig more burrows than they require for their protective and physiological needs. There may be a selective advantage in digging burrows in excess of one burrow per crab, because of the benefit of enhancing food supply and decreasing the competition for food. Fiddler crabs may dig burrows “in excess” even when empty burrows are available and they may adjust their burrowing in response to food supply. This hypothesis was examined by (a) comparing burrow and crab density in a salt marsh, then (b) manipulating burrow density and (c) food availability in the laboratory. Furthermore, females were hypothesized to be more sensitive to food availability than males, and small crabs more sensitive than large crabs. Results showed that (a) there were more burrows than fiddler crabs, (b) smaller crabs of both sexes dug new burrows despite the presence of unoccupied burrows and (c) burrowing activity of smaller crabs of both sexes varied with food availability. When food availability was lower, they excavated as much sediment and dug more burrows and burrow branches, while allocating less time to burrowing. They did so by burrowing faster and to lesser depths. Small crabs may be more sensitive to food availability and may be better capable of adjusting their burrowing to food supply.
Published Version
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