Graduation Year


Document Type




Degree Granting Department


Major Professor

John Lawrence, Ph.D.

Committee Member

Susan Bell, Ph.D.

Committee Member

Ron Sarno, Ph.D.


nonrandom, aggregation, density, nearest neighbor, percent organic content


Small scale distributions of Mellita tenuis and Encope spp. were quantified at Fort De Soto Park on Mullet Key, off Egmont Key and off Captiva Island, Florida during 2005. Off Captiva Island, Encope spp. were aggregated in 33.3% of plots in March. Off Egmont Key, M. tenuis were aggregated in 100% of plots in March but in no plots in September. At Fort De Soto Park, M. tenuis were aggregated in 37.5% of plots in May 12.5% in July and 50.0% in September. Sand dollars in 6.3% of the plots in September at Fort De Soto had a uniform distribution. Individuals in all other plots at all sites had random distributions. At Fort De Soto, each plot was revisited a few hours after the initial observation; 37.5% of plots had a different distribution at the second observation.

Percent organic content of the smallest sediment grains (<105 >μm) was not correlated with sand dollar distribution, except off Egmont Key. There was a significant negative correlation between nearest neighbor index and percent organic content. Mellita tenuis do aggregate on occasion. The cause of aggregation is not known. If localized differences in percent organic content of the sediment influence distribution, then homogeneity in the percent organic content of the sediment, as found in the majority of plots, would suggest random distribution of sand dollars.