Wind events and benthic-pelagic coupling in a shallow subtropical bay in Florida

Abstract

During the winter months (December to April), the SE United States is influenced by continental air masses from the north or northwest which pass at approximately 4 to 7 d intervals. These wind events can cause suspension of bottom sediments in Florida Bay. Over a 9 d period in March 2001, we examined the effects of a wind-mixing event on the pelagic system within the NW part of Florida Bay, where water depth is 2 to 3 m. This event caused significant suspension of bottom materials, large increases in NH 4 and PO 4 , smaller increases in NO 3 +NO 2 and Si(OH) 4 , a decrease in microzooplankton abundance, and an increase in benthic copepods in the water column. As wind speeds declined, there was a rapid decline in PO 4 concentration, gradual declines in suspended sediment, NH 4 and Si(OH) 4 , an increase in chlorophyll a (chl a) stock, an increase in phytoplankton growth and productivity, an increase in microzooplankton grazing rate, and a settling of the benthic harpacticoid community. No grazing response was apparent in the mesozooplankton community. The wind event clearly injected dissolved and particulate benthic materials into the water column, where they directly stimulated the bacterioplankton, phytoplankton and microzooplankton communities within 1 to 2 d after the event. The water column was strongly net heterotrophic at this time, suggesting a large input of dissolved organic matter from the bottom. Stimulation of the pelagic food web continued at least until we completed our study 6 d after the event. By the end of our study, the water column was net autotrophic.