Size differences in sand crabs living in the Gulf of Mexico and the Atlantic Ocean

Background/Question/Methods

Sand crabs (Decapoda: Albuneidae) are little known digging crustaceans that are dependent on fine sand. Surveys of one species, Lepidopa benedicti, in the Gulf of Mexico (South Padre Island, Texas) showed that individuals were significantly smaller than those recorded from the Atlantic coast of Florida. Additionally, no reproductive females had been found at the Gulf study site, suggesting the region may be a sink for the population. The Gulf and Atlantic populations appear to be separated by a gap hundreds of miles long, where no individuals have been recorded. To test whether this difference in size was due to the environmental differences, we examined the sizes of three other sand crab species that live in both the Gulf of Mexico and the Atlantic Ocean, using records in the published literature: L. websteri, Albunea catherinae and A. gibbesii. We predicted that if the size differences of L. benedicti populations due to environmental factors, the size differences would be reflected in the other three species, because all are obligate digging species with broadly similar ecology.

Results/Conclusions

Of the three tested species, only A. gibbesii showed the same pattern as L. benedicti, with significantly smaller individuals in the Gulf of Mexico than the Atlantic Ocean. Even so, the relative difference in size between the Gulf and Atlantic A. gibbesii individuals is smaller than seen in L. benedicti. This indicates that the size differences seen in L. benedicti populations are particular to that species, rather than the Atlantic coastline representing a superior habitat for sand crabs generally. An alternative hypothesis is that these populations are drifting apart due to isolation. Quantitative distribution models will be developed to test whether areas with no recorded individuals are due to unsuitable habitats.