Diatom assemblages from sediment traps in response to large seaweed Gracilaria cultivation off Nan'ao island, South China

Abstract

Most previous studies on seaweed bioremediation largely focus on laboratory control tests or short-time, in-situ field experiments. Here we present a dataset from 4-year-long field monitoring (2014–2018) in a mariculture area of the Baisha Bay off Nan'ao Island, South China, attempting to examine how the large seaweed Gracilaria lemaneiformis cultivation affects a mariculture ecosystem. The temporal variation in seawater physicochemical properties (TN, TP, Reactive silicate, CODMn, and chlorophyll α) and sediment proxies (TN and TP) suggest that the Baisha Bay maintained a better water quality during the Gracilaria cultivation periods (December–May) than other months. Additionally, sedimentary diatom assemblages during the Gracilaria cultivation periods showed an increase in Shannon-Wiener values, but a decrease in the dominant Thalassionema nitzschioides abundance, total diatom abundances and P/(A + B) ratios [Planktonic/(Attached + Benthic)]. These changes consistently suggest that Gracilaria cultivation may have helped improve seawater quality and phytoplankton diversity, thereby maintain a healthy mariculture ecosystem.