Ecological Responses to Eutrophication and Restoration in a Shallow Subtropical Estuary

Abstract

Like many other estuaries in the world, the Indian River Lagoon (IRL) is experiencing serious environmental health challenges in recent years. Ecosystem challenges include the connected phenomena of Harmful Algal Blooms (HABs) due to eutrophication and accumulation of fine-grained organic-rich sediments on the benthos. Fine-grained organic-rich sediments, referred to as “muck”, is a source of nutrients and fuels algal blooms in the water column, and excess particles associated with algal blooms sink to bottom and contribute to muck. This dissertation aims to better understand these problems by addressing two main objectives: first, to determine whether key herbivorous mesozooplankton have the capacity to exert top-down control on the HAB species, and second, whether to explore alternative approaches of muck removal and ecosystem restoration to disrupt the vicious cycle of eutrophication perpetuated by organic sediments. For the first objective, grazing experiments revealed that Parvocalanus crassirostris, the dominant herbivorous copepod in the IRL, exerted some top-down control on the HAB species under laboratory conditions (Chapter 1). Additional laboratory grazing experiments on cell size and mucus effects were examined to better understand the low grazing rates (Chapter 2). For the second objective, estuarine ecosystems were monitored throughout a pilot aeration experiment to evaluate the feasibility and effectiveness of aeration for muck mitigation (Chapter 3). It was found that aeration facilitated benthic animal life, but only in the cold period when bottom waters held the most dissolved oxygen. Planktonic communities, on the other hand, displayed no significant responses to aeration.