Complex Tidal Marsh Dynamics Structure Fish Foraging Patterns in the San Francisco Estuary

Abstract

Mechanisms driving the consumption and transport of tidal marsh nutrients and energy by fishes are of key interest in the San Francisco Estuary, CA, USA. By combining multiple data sources (gill-net catches, gut contents, channel morphology, tides), we modeled spatial and temporal patterns of fish abundance and gut fullness across a tidal marsh elevation gradient. Channel depth, microhabitat, and tide were important predictors of fish abundance and gut fullness. Species, feeding guild, and season were also important to fish abundance but not to gut fullness, suggesting that abundance was more related to physical constraints of shallow water than to prey availability. Multiple feeding guilds overlapped in space and time at interaction hotspots in subtidal channel habitat near the marsh entrance. In contrast, fish use of shallow intertidal marsh channels was more variable and indicated tradeoffs between foraging and predation. Gut content analysis revealed moderate-to-high gut fullness for all feeding guilds and models predicted high gut fullness in subtidal reaches during tidal flooding, after which fish fed intensively throughout the marsh. While mysids, amphipods, and detritus were common prey among feeding guilds, variation in prey consumption was apparent. Overall, complex tidal marsh hydrogeomorphology driving land-water exchange and residence time may diversify and enhance benthic and pelagic food web pathways to fishes and invertebrates. Furthermore, these findings substantiate the notion that dynamic tidal marshes in this system can support robust secondary production, foraging by multiple feeding guilds, and trophic transfer by fishes to the estuarine mosaic.

Climate Change Impacts on San Francisco Estuary Aquatic Ecosystems: A Review

“…the upper estuary and have received less attention from long-term aquatic monitoring programs (Brown 2003). Nevertheless, there is a growing recognition of the role that tidal marsh plays in the estuary food web and as key habitat for species of concern (Davis et al 2019;Hammock et al 2019;Colombano, Handley, O'Rear et al 2021). Because of the various ecosystem services that tidal marsh can provide, extensive marsh restoration planning and implementation throughout the estuary is now underway (Herbold et al 2014;Sherman et al 2017).…”

South West Atlantic salt marshes as model systems for community and ecosystem ecology

“…Subsidies can occur via direct transportation of salt marsh detritus through tidal or fluvial flooding (Teal 1962;Nixon 1980;Odum 2000), or it can involve an indirect increase of marine primary production through an enhanced supply of dissolved nutrients, in the form of reactive inorganic N generated by organic matter decomposition in marsh sediments (e.g., Krest et al 2000;Santos et al 2019). Another usual but indirect mechanism involves the flux of energy through animal movements between environments, as marine juvenile fishes feeding on salt marsh habitats (Colombano et al 2021). This hypothesis of salt marshes as supporters of the secondary production of ₈₁₆ P D���� �� �� Ecología Austral 32:806-820 marine environments (especially fisheries of commercial interest) was, for years, the most important argument for the conservation and restoration of these habitats worldwide.…”

Climate Change Implications for Tidal Marshes and Food Web Linkages to Estuarine and Coastal Nekton

“…Due to the fact that marshes are embedded in seascape mosaics linked by an overlying water column that integrates multiple interacting processes (Childers et al 2000), consumers that are able to exploit different resources in space and time may be more resilient to change (Young et al 2020). However, if consumers are reliant on marsh-derived organic matter, a reduction in its availability resulting from marsh plant loss could have cascading effects on nekton growth and recruitment (Litvin and Weinstein 2004;Litvin et al 2018), foraging success (Colombano et al 2021), energy reserves (Litvin et al 2014), and trophic relays (Childers et al 2000;Deegan et al 2000;Kneib 2000).…”