Spatial and Temporal Variation of Fish Communities in Constructed Tidal Wetland Ponds within Humboldt Bay, California

The widespread loss of coastal wetlands over the past century has led to increased use of constructed wetland systems. In Humboldt Bay, California, where over 90% of tidal wetlands have been lost, several constructed wetlands with tide gates have been created to provide ecosystem services including wastewater treatment and habitat provision. However, differing management strategies may alter fish usage of these habitats, which most monitoring programs lack robust baseline data to assess. This study explored fish community composition across three constructed wetland ponds with tide gates over a 10-month period in 2024. Using a multi-gear approach including beach seines, fyke nets, and light traps, we documented 20 fish species across varying life stages, including one endangered, one threatened, and two invasive. There was significant variation in community composition and environmental conditions among and within ponds, and seasons, likely influenced by tide gate design and management. The pond with the most consistent tidal exchange during the study period supported higher species richness, greater larval recruitment, and more consistent fish movement, while ponds with restricted connectivity exhibited dominance by fewer species and lower diversity. Differences among ponds were strengthened during spring and summer, when reduced freshwater flows heavily influenced environmental conditions. These findings demonstrate the value of monitoring constructed wetlands across species and life stages and the critical role of restoring connectivity in human-made habitats. The resulting baseline dataset documents key factors potentially influencing community structure which can be utilized in the future design, creation, and continued management of constructed wetland systems.