Trends in Ichthyoplankton Assemblage Structures in a Recovering Freshwater Tidal Embayment

Gunston Cove, VA, an embayment of the Potomac River, is a tidal freshwater system utilized by anadromous, estuarine and freshwater fish species for spawning and larval development. Historically polluted by point source pollution from a wastewater treatment facility, water quality has improved since nutrient loading from the effluent was significantly reduced in the 1980s. This improvement allowed for a transition from a phytoplankton dominated ecosystem to a system whose primary production is driven by submerged aquatic vegetation (SAV) in the last decade. This study aims to determine effects of observed trends in environmental quality on ichthyoplankton assemblage structures and abundances. Using data from bimonthly pelagic ichthyoplankton tows conducted since 1993, we employed multivariate statistical approaches to explore relationships between assemblages and environmental variables associated with nutrient loading. We found a significant difference between assemblage structures sampled within the cove during phytoplankton and SAV dominated time periods. Increases in abundance of fish species that utilize SAV habitats for spawning were found to be significant and correlated with decreases in total nitrogen, total phosphorus and total suspended solids. Outcomes from this analysis help broaden the understanding of the effects of point source nutrient reduction in ecosystems undergoing recovery