Blooms in Lagoons:Different from Those of River-Dominated Estuaries
Coastal lagoons differ substantially from river-dominated estuaries in the type of high-biomass phytoplankton blooms that generally proliferate, the seasonal timing of the blooms, the forms of nutrients that support these blooms, and the influence of hydrology on blooms and their nutrient dynamics. Coastal lagoons often support blooms of picoplankton (<3 μm in size) that can be sustained for months to years, whereas riverine estuaries often support high-biomass spring diatom blooms. These picoplankton blooms are also more likely to be sustained on regenerated forms of nitrogen, such as ammonium, urea, or dissolved organic substrates, compared to riverine spring blooms, which are generally supported by seasonal nitrate inputs. Regenerated forms of nutrients can be sustained in lagoons due to the higher surface:volume ratios and long residence times of these systems, both of which lead to a strong coupling between benthic nutrient fluxes and the plankton. The picoplankton genera that dominate have physiological characteristics that make them well suited to compete effectively for these substrates, but they must have sustained nutrient sources and limited grazing losses to maintain bloom biomass for prolonged periods. Using long-term monitoring data as well as experimental results, these characteristics are illustrated for Florida Bay and the Maryland-Virginia Chincoteague Bay.