Homotrema rubrum (Lamarck): distribution and biology of a potential reef bioindicator and underwater angler

Homotrema rubrum is a species of encrusting foraminifera that reinforces the coral-reef framework by calcifying in cracks, crevices and under-populated parts of reefs. H. rubrum secretes a hard skeleton that is well preserved in the fossil record and, thus, has the potential to be important in paleoecological analyses. The distribution of this species along transects across Tennessee Reef (Florida Keys, USA) reveals an abundance of encrusting, knobby and hemispherical morphologies on the reef flat. Feeding experiments dispute previous claims of H. rubrums sole reliance on photoendosymbionts by demonstrating that H. rubrum can be an active and efficient carnivore. Photo and Scanning Electron Micrographs reveal that H. rubrum utilizes sponge spicules collected from the environment in combination with reticulopodia to trap and consume living prey. Close observation and epifluorescence microscopy suggests H. rubrum is capable of calcifying under controlled laboratory conditions.