Phytoplankton abundance is regarded as a critical indicator of ecosystem status in coastal estuaries. Chlorophyll a concentration (used as a proxy for abundance) tracks trophic state and unusually high concentrations may reflect the onset of algal blooms. Our knowledge regarding phytoplankton variability in coastal estuaries comes in large part from monitoring studies which collect water samples at discrete locations at regular (usually monthly) intervals. These studies have provided insight into the seasonality and interannual variability associated with phytoplankton abundance across broad (> 10 km) geographic scales. In addition, we know from incubations and indirect observation that phytoplankton abundance is regulated on a micro-scale (< 1 m) level by nutrient availability, turbulence, and predation. The spatial distribution of estuarine phytoplankton at intermediate scales is less well known. In order to address this knowledge gap, we used an innovative water quality mapping technique to quantify the fine-scale distribution of phytoplankton in Florida Bay, USA on the scale of 10s of meters. We compared our observations against potential nutrient and climate drivers.
Patterns of phytoplankton abundance were markedly different within the open bay, coastal embayments, and nearshore lakes of Florida Bay. The highest observed chlorophyll concentrations occurred within the nearshore lakes. In contrast, the lowest concentrations were found in the open bay. Open Bay concentrations were generally less than 2.5 ug/L. Phytoplankton abundance in the coastal embayments decreased along a west-to-east geographical gradient. This gradient was coincident with decreasing phosphorus concentrations and increasing N:P ratios. Our results suggest that phytoplankton abundance is likely regulated by a different set of environmental drivers in each stratum of the Florida Bay ecotone. While our findings are consistent with studies using discrete sampling, we show that several basins have considerable intra-basin variation. This information will be critical for evaluating the performance of ecosystem modelling efforts aimed at predicting the incidence of future phytoplankton blooms under water management and environmental restoration scenarios.
Slides and related materials will be archived at http://doi.org/bcsg prior to the conference.