DISTRIBUTION, ABUNDANCE, AND LABORATORY CALCIFICATION OFHOMOTREMA RUBRUMFROM TENNESSEE REEF, FLORIDA KEYS, USA

Abstract

Homotrema rubrum is a (sub)tropical, sessile foraminiferan that reinforces the coral-reef framework by calcifying in cracks, crevices and on the cryptic undersides of coral colonies and other reef substrata. It secretes a pigmented carbonate skeleton that can be well preserved in the fossil record and, thus, has the potential to influence paleoecological analyses. In an effort to gain insights about the ecology and laboratory maintenance of this species, we studied its distribution in the field as well as its survival in the laboratory under different environmental conditions. The distribution of H. rubrum along transects across Tennessee Reef (Florida Keys, USA) revealed an abundance of encrusting, knobby and hemispherical morphologies on the reef flat, and all five of the morphotypes delineated by others were identified. The highest abundances of H. rubrum occurred on the reef flat, shoreward of the living reef, attached to non-living, detrital coral, most of which was covered by a veneer of coarse carbonate sediment. Direct observation of living individuals and epifluorescence microscopy of specimens incubated with calcein demonstrate that H. rubrum can calcify under controlled laboratory conditions. Calcification is not limited to chamber formation, but rather occurs differentially over the surface. Of the five distinct designs tested for laboratory maintenance of this species, the quasi-static aquarium in indirect natural light proved the most effective. Together, these findings help establish H. rubrum as a useful model for studying natural environmental changes and anthropogenic impacts on marine ecosystems.