Small-scale distribution of the sand dollars mellita tenuis and encope michelini (clypeasteroida, echinodermata) off the central florida gulf coast

Small-scale distributions of Encope michelini were quantified 27 km west of Captiva Island at 20 m depth and of Mellita tenuis 7 km west of Egmont Key at 6.5 m depth and at Mullet Key at 1.5 m depth during 2005. Encope michelini were aggregated in 33.3% of three plots in March. Off Egmont Key, M. tenuis were aggregated in 100% of four plots in March but in none of three plots in Sept. At Mullet Key, M. tenuis were aggregated in 37.5% of 16 plots in May, 12.5% of 16 plots in July, and 50.0% of 16 plots Sept Percentage of organic content was not correlated with sand dollar distribution, except for M. tenuis off Egmont Key. The distribution pattern of both species is dynamic. The pattern at Mullet Key changed within 2 to 5 hr after initial observations in two of eight plots in May and July and in five of eight plots in Sept. It is possible that aggregation is influenced by local, short-term concentration of food below the sensitivity of measurement of organic content and that dispersal to random distribution may occur when food concentration is decreased.