Fish Assemblage Shift Following Abrupt Seagrass Loss in a Southwest Florida Tidal Creek

Phase shifts can occur in ecosystems because of external stressors. Such transitions from one state (e.g., clear water, seagrass) to another (e.g., phytoplankton blooms, bare substrate) continue to be documented worldwide. In estuaries, stressors related to urban and suburban development are often implicated in phase shifts, including altered hydrology and eutrophication. Tidal creeks may be especially prone to phase shifts as their position in the landscape exposes them to the brunt of coastal development. In 2017, a precipitous seagrass decline occurred in a tidal creek downstream of coastal development in the Charlotte Harbor estuary, Florida (USA). Fisheries independent monitoring data (July 2014 to June 2022) from 21.3 m seines were used to investigate changes in fish assemblages. Multivariate analyses identified a fish assemblage shift that coincided with seagrass loss and increasing algal blooms. Reductions in seagrass-associated species (e.g., Rainwater Killifish Lucania parva ) were offset by increases in generalist and planktivorous taxa (e.g., Bay Anchovy Anchoa mitchilli ). Such changes did not occur in neighboring creeks downstream of more natural habitat. The present study is indicative of a potential phase shift. Tidal creeks serve as ‘sentinels’ for ecosystem change. Furthermore, similar patterns of seagrass loss and algal blooms are taking place in the open estuary; thus, the fish assemblage shift identified in the tidal creek may signal similar, widespread changes. Identifying shifts in biotic assemblages and predominant drivers can help guide resource planning to strengthen ecosystem resilience and recovery within Charlotte Harbor and other Florida estuaries.