Benthic Foraminiferal Distributions in a Shallow Subtropical Estuary and the Influence of Environmental Factors
Zamora Duran, Maria Angelica
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Benthic foraminiferal communities are potentially useful tools for assessing and monitoring estuarine ecosystems and as bioindicators of water quality and pollution. To evaluate this indicator for the Indian River Lagoon (IRL) benthic ecosystem, the densities and distributions of Foraminifera were measured in Turkey Creek (Palm Bay, Florida), Crane Creek (Melbourne, Florida), and the adjacent IRL. Spatial population patterns were compared with parameters characterizing benthic sediments, including silt and clay content, organic matter (OM), and associated boundary water column conditions including salinity, temperature, and dissolved oxygen (DO. Samples (n=145) were collected from October 2015 to December 2015 at 12 locations. Four species, Ammonia tepida, Ammonia parkinsoniana, Elphidium excavatum, and Quinqueloculina seminula made up >90% of the foraminiferal assemblages, with A. tepida dominating at all sites. The highest average densities were found in the intermediate sediments of Turkey Creek. The average foraminiferal density was between 124 (±35 SE) and 291 (±91 SE) individuals ml⁻¹ in the low (OM <2%) organic matter sediments of the IRL near Crane Creek and Turkey Creek, respectively. This was significantly lower (p<0.01) than the 750 (± 180 SE) individuals ml⁻¹ in the intermediate organic sediments in Turkey Creek, and significantly higher (p<0.01) than the 20 (±19 SE) individuals ml⁻¹ in the deep channels containing the highest amounts of fine-grained, organic-rich sediments (OM >10%, “muck”). In general, foraminiferal densities correspond strongly to OM and DO, with the highest densities occurring between 2-4 mgl⁻¹ DO and 1-5% OM. Paleoecological data from foraminiferal tests provide insight into how foraminiferal communities may respond to the changing estuary over decades. No foraminiferal community shifts were observed in the intermediate organic sediments (TC). There is, however, an increasing abundance of Quinqueloculina seminula in shallower, more recent TC sediments, possibly due to recent increases in sediment organic content.