LAWRENCE, J.M.*; COBB, J; HILBER, SE; SWIGART, JP; Univ. of South Florida, Tampa; Fish and Wildlife Research Institute, St. Petersburg; Univ. of South Florida, Tampa; Univ. of South Florida, Tampa: Characteristics of populations of sand dollars Encope michelini and Encope aberrans off the central Florida gulf coast

A population of E. michelini ca. 30 km west of Sanibel Island at 20 m depth on shell substratum with a graphic mean of 1.59±0.63Φ was observed from 2003 to 2005. The density was 2.00±1.53 inds∙m^-2 and 1.03±1.00 inds∙m^-2 and the width between the anterior notches was 7.98±0.37 cm and 8.21±0.45 cm in 2003 and 2005, respectively. Aboral plates had 2 to 3 growth lines (2.7±0.5) in 2004. Analysis of distribution in spring 2005 showed one replicate with clumped distribution and two replicates with random distribution. 75% of the particles in the gut had a graphic mean of <6.8Φ, indicating smaller particle sizes than the substratum. A population of E. aberrans ca. 6.5 km west of Egmont Key at 6 m depth on sand substratum was observed from 1999 to 2005. The density was 2.00±1.41 inds m^-2 and 0.17±0.46 inds∙m^-2 and the width between the anterior notches was 8.02±0.98 cm and 10.49±0.73 cm in 2002 and 2005, respectively. Aboral plates had 3±0 growth lines in 1999 and 2 to 7 growth lines (3.8±1.4) in 2004. Both species occurred together ca. 9 km south of the population of E. michelini off Sanibel with sizes similar to those where they occurred alone. The uniformity of growth lines suggests sporadic, localized recruitment. This is supported by the absence of small individuals over space and time. The persistence of the populations and the near asymptotic size of individuals suggest low mortality at both locations.