Date of Award

Summer 2020

Document Type

Open Access Thesis


Marine Science

First Advisor

James L. Pinckney


Benthic microalgae (BMA) play essential roles in food webs and regulating nutrient exchange at the sediment-water interface in continental shelf ecosystems. However, shelf BMA are not widely studied due to the difficulties sampling the upper few millimeters of shelf sediments. A few published studies have highlighted the high spatiotemporal distribution of BMA, but detailed explanations for this known variability are limited. The objectives of this study were to quantify BMA biomass variability on scales of cm to km and relate these measurements to in situ nutrient concentrations, sediment grain size, in situ irradiance, depth, and other environmental factors. Water and sediment samples for BMA and porewater nutrient analyses were collected by SCUBA divers on 11 nearshore cruises in 2018-2020 off Charleston, SC. BMA accounted for over half of total microalgal chlorophyll a, with BMA biomass reaching as high as 10 times that of phytoplankton in the overlying waters. High variability in BMA biomass was observed between and within sites, indicating BMA are likely influenced by small-scale (<1 >m) environmental differences. BMA biomass was positively correlated with percentage of fine grain sediments, but not with dissolved inorganic nitrogen (DIN) concentrations in either the water column, porewater, or submarine groundwater. However, porewater DIN was much higher than in the water column, suggesting that higher BMA biomass may be more dependent on N from the sediments rather than the overlying waters. Understanding how BMA vary spatially can be useful for making larger generalizations about BMA distribution over continental shelves and for modeling BMA biomass, production, and contribution to both benthic and pelagic food webs.


© 2020, Sarah N. Zaunbrecher