DEMOGRAPHY OF THE EPIPHYTIC FORAMINIFERAN SORITES DOMINICENSIS IN BELIZE, C.A

Sorites dominicensis is an evolutely-coiled, disk-shaped Soritacean species with dinoflagellate endosymbionts that lives as an epiphyte on the seagrass Thalassia testudinum throughout the shallow waters of the subtropical to tropical Western Atlantic. Populations of S. dominicensis were censused from seagrasses growing in the mangrove lagoons and channels of the Twin Cays in Belize, C.A. Static life tables were constructed for this species using chamber number as a proxy for age. Survivorship curves generated from the life tables demonstrate that S. dominicensis has a survivorship curve that is intermediate between Type I and Type II curves, with relatively constant survivorship in the juvenile and intermediate stages, followed by a steep drop-off as individuals approach maturity. Other values calculated for this population include: generation time (T_G=25.273 chambers); net reproductive rate (R₀=8.214); and instantaneous rate of increase (r=0.8). The relatively low value of r calculated for S. dominicensis is consistent with previous characterizations of “larger” endosymbiont-bearing foraminiferans as being K-selected. Some of the traits typically expected under K-selection are seen in S. dominicensis, such as a large “body,” or cell size, and delayed reproduction. Other life history traits of S. dominicensis, such as a large number of offspring and semelparity, are characteristic of r-selected species with Type III survivorship curves. Most, if not all, foraminiferans undergo semelparous reproduction. Parental cell size is correlated with the number of offspring produced during reproduction by multiple fission; thus, larger parent cells have the capability of producing more progeny.