PARENT SESSION
Poster Session # 19: Insect and Invertebrate Ecology.

Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

The ectosymbiont crab Dissodactylus mellitae-sand dollar Mellita isometra relationship.

George, Sophie^*,1, ¹ Georgia Southern University, Statesboro, Georgia, USA

ABSTRACT- This study investigated dispersion and reproduction of a small commensal crab and their effects on the sand dollar Mellita isometra. The number of crabs found on the sand dollar, stage of maturity, sex, numbers of eggs, and size of eggs produced by crabs were noted over a two year period. The test diameter of 2648 sand dollars, the number of eggs produced, and the diameter of 4259 eggs was also noted. Infestation rates of crabs on sand dollars varied over time. The three types of population dispersion; random, uniform, and clumped were observed for crabs on sand dollars throughout the sampling period. Clumped distribution was observed when juvenile crabs were abundant, uniform and random distribution when adult crabs were abundant. Female crabs were significantly larger than male crabs. Crabs produced between 80 and 300 eggs ranging from 0.188 mm to 0.291 mm in diameter. Bigger crabs produced significantly more eggs than smaller crabs. The presence of crabs on sand dollars affected total egg production of sand dollars in May, the peak of the spawning season, with sand dollars carrying one or two crabs having a lower egg production than those without crabs. The present study though not conclusive clearly demonstrates that a small percentage of the variation in egg size observed for M. isometra might be due to seasonal variation in the distribution and abundance of the commensal crab Dissodactylus mellitae.

Key words: commensal crab, sand dollar, population dispersion, egg production