Benthic Superheroes: Living Foraminifera from Three Bays in the Mission-Aransas National Estuarine Research Reserve, USA

Abstract

Studies of living foraminiferal assemblages provide much information about their roles in present environments and a perspective on interpreting the past. Along modern coasts, benthic Foraminifera act as ecological indicators in their responses to different natural and anthropogenic conditions, such as food availability, oxygen concentrations, salinity, and trace metal concentrations. A detailed survey of foraminiferal populations was undertaken in the Mission-Aransas National Estuarine Research Reserve, Texas, close to the time of its establishment in 2006. The purpose was to gauge the overall status of populations and provide baseline data for future comparison. The arid south Texas Gulf Coast is a variable and often harsh environment where biota are subject to multiple anthropogenic stressors. Despite these rigors, living Foraminifera were prolific in the Reserve. This paper discusses the results from Mesquite (July 2008), Copano (May 2006), and Mission Bays (June 2006). Populations were robust in each bay, with Ammonia parkinsoniana, Ammotium salsum, and Elphidium excavatum being most abundant. Highest numbers corresponded mainly to areas of greater circulation. In Mission Bay, elemental analysis of shells, prompted by the presence of sulfur grains in sediments and by yellow tests, detected elevated levels of barium, strontium, and iron. Most sediment samples were black and sulfidic, and ubiquitous framboidal pyrite in sediment and shells suggests that forams were frequently subject to low-oxygen conditions. Abundant living numbers, tolerance of low-oxygen conditions, and the ability to cycle trace metals emphasize the resilience of Foraminifera in taxing environments and their integral position as lower trophic level members.