Diversity, taphonomy and behavior of encrusting foraminifera on experimental shells deployed along a shelf-to-slope bathymetric gradient, Lee Stocking Island, Bahamas

Abstract

Encrusting foraminifera that settled on experimental arrays deployed for 2 years in shelf (15 m–30 m), shelf edge (70 m) and slope (183–253 m) environments off the carbonate platform of Lee Stocking Island, Bahamas, were found to occur in four environmental-indicator guilds, each with common and unique encrusting species. These guilds can be used as paleobathymetric and temporal guides, indicating how long a substrate was exposed on the sea floor prior to burial. Taphonomic signatures of encrusting foraminifera also changed with depth, resulting in four foraminiferal taphofacies that varied from corrasion (dissolution and abrasion) at shallow sites to pristine tests at the deepest sites. The taphonomic processes for encrusting foraminifera were found to be decoupled from those reported for invertebrate hardparts in this region, perhaps related to their ability to nestle within sutures or other depressions (deemed taphonomic refugia) on the shell substrates. The shelf-edge site had the highest foraminiferal diversity associated with the highest physical damage to the tests, which is counter-intuitive to the Intermediate Disturbance Hypothesis (IDH), which posits that high physical disturbance leads to low species diversity. While the IDH appeared true for the shallowest sites, it does not completely explain the high foraminiferal diversity at the shelf edge where physical taphonomic factors were high. Behavioral interactions, such as overgrowth interactions, also varied with depth, and these can be used to examine depth-related paleobehavioral patterns in the past. Thus, the often overlooked encrusting foraminifera are excellent candidates for paleocommunity and paleoenvironmental analyses.