Foraminifera with Chlorophyte Endosymbionts: Habitats of Six Species in the Florida Keys

Three species, Androsina lucasi, Archaias angulatus , and Cyclorbiculina compressa , all members of the subfamily Archaiasinae, are among the largest and most abundant benthic foraminifera in the Florida Keys. Each species harbors a different chlorophyte endosymbiont, and each species thrives in a different habitat. Androsina lucasi is the most euryhaline species. It is found in exceptional abundance in open, dwarfed-mangrove flats in water commonly less than 0.2 m in depth, growing on mangrove roots and propagules, and algae such as Batophora oerstedi, Archaias angulatus is moderately euryhaline, thriving at sites in Florida Bay and Largo Sound at depths less than 2 m, where temperatures range from 14°C in winter to 33°C in summer and salinities range from 29 to 39‰. Substratum includes rubble, seagrass ( Thalassia testudinum ), Halimeda and a variety of other macroalgae, especially when overgrown by epiphytes. Archaias is also common in open shelf and shelf-margin settings. Cyclorbiculina compressa is the most stenohaline, occurring in open shelf settings typically at depths of 5–30 m. Optimum habitat appears to be short (∼ 1 cm) filamentous algal turf on limestone pavement or reef rubble. Three other chlorophyte-bearing species, Broeckina/Parasorites orbitolitoides, Laevipeneroplis proteus and L. bradyi , are also common in this habitat.

Chlorophyte-bearing taxa are the most abundant and diverse group of larger foraminifera in the Holocene western Atlantic. Despite widespread occurrence throughout the Tethyan region during the Miocene, this group is represented in the Holocene Indo-Pacific by only two species. The decline of this lineage in the Indo-Pacific and its success in the tropical western Atlantic is opposite of biogeographical trends typically reported for shallow-water tropical taxa through the Neogene.