Eutrophication leads to food web enrichment and a lack of connectivity in a highly impacted urban lagoon

Abstract

Nitrogen (N) loading can affect estuarine food webs through alteration of primary producers. In the Indian River Lagoon (IRL), Florida there has been long-term N enrichment, worsening phytoplankton blooms, large-scale macroalgal blooms, and catastrophic seagrass losses. To investigate how N enrichment affects higher trophic levels and food webs in the IRL, nutrient availability was compared to primary producer and faunal stable N (δ15N) isotope values. Seawater samples were collected in the IRL for dissolved nutrient, chlorophyll-a, and particulate organic matter δ15N analyses. Macrophytes and fauna were also collected for δ15N analyses. Throughout the IRL, N was elevated but was highest in the northern IRL and Banana River Lagoon. δ15N was enriched in these segments for most samples to levels characteristic of human-waste impacted estuaries. Variability in δ15N among lagoon segments suggests a low level of trophic connectivity. Decreasing N loading to the IRL and other eutrophic estuaries may help improve resiliency.