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Climate change is altering naturally fluctuating environmental conditions in coastal and estuarine ecosystems across the globe. Departures from long-term averages and ranges of environmental variables are increasingly being observed as directional changes [e.g., rising sea levels, sea surface temperatures (SST)] and less predictable periodic cycles (e.g., Atlantic or Pacific decadal oscillations) and extremes (e.g., coastal flooding, marine heatwaves). Quantifying the short- and long-term impacts of climate change on tidal marsh seascape structure and function for nekton is a critical step toward fisheries conservation and management. The multiple stressor framework provides a promising approach for advancing integrative, cross-disciplinary research on tidal marshes and food web dynamics. It can be used to quantify climate change effects on and interactions between coastal oceans (e.g., SST, ocean currents, waves) and watersheds (e.g., precipitation, river flows), tidal marsh geomorphology (e.g., vegetation structure, elevation capital, sedimentation), and estuarine and coastal nekton (e.g., species distributions, life history adaptations, predator-prey dynamics). However, disentangling the cumulative impacts of multiple interacting stressors on tidal marshes, whether the effects are additive, synergistic, or antagonistic, and the time scales at which they occur, poses a significant research challenge. This perspective highlights the key physical and ecological processes affecting tidal marshes, with an emphasis on the trophic linkages between marsh production and estuarine and coastal nekton, recommended for consideration in future climate change studies. Such studies are urgently needed to understand climate change effects on tidal marshes now and into the future.

Climate change driven sea level rise and mangrove expansion are rapidly altering coastal systems in the northern Gulf of Mexico. Such substantial and wide-spread change will likely have substantial effects on the flow of energy through the food webs in these systems. Using stable isotopes and habitat cover maps, we built energetic landscapes (E-scapes) for three nekton species to determine how the landscape’s ability to produce energy changes with changing habitat cover over a 5-year period. Between 2015 and 2020, 25% (367.26 ha) of marsh habitat converted into mangrove habitat and 10% (144.93 ha) of marsh habitat transitioned into water. We observed an overall decrease in the energetic benefit to all consumers with increasing mangrove cover, due to the fact mangrove detritus is not used as a food source by consumers in our system. Edge habitat had a positive relationship with overall energetic production, likely due to the increase in available area for benthic algal production. The relationship between edge habitat and water habitat suggests that while these areas may initially increase in their ability to support consumer species, continued sea level rise will lead to reductions in the landscape’s ability to produce energy for consumers as land is converted to water. As these coastal areas experience rapid habitat cover changes, the reduction in energetic quality of habitats could lead to a reduction in the ability of these systems to support existing consumer species.

In New England saltmarshes, mummichogs (Fundulus heteroclitus) connect the vegetated marsh and creek food webs by opportunistically foraging on the invertebrate communities of the marsh surface when access is permitted by tidal flooding and marsh-edge geomorphology. Via their movements, mummichog represent a critical food web node, as they can potentially transport energy from the marsh surface food web to creek food web and exert top-down control on the communities of the vegetated marsh surface. Here, we demonstrate that access to the marsh surface (afforded by marsh-edge geomorphology) did not impact mummichog distribution across the marsh platform and exhibited no evidence of top-down control on their invertebrate prey. Thus, mummichogs function as initial nodes in the trophic relay, unidirectionally moving energy from the vegetated marsh to the creek food web. Reduced marsh surface access via altered marsh-edge geomorphology results in a 50% to 66% reduction in total energy available to aquatic predators via this route. Estuarine systems are intimately connected to coastal and offshore systems via consumer mediated flows of energy; thus, disruptions to the trophic relay from the marsh surface at the tidal creek scale can have far reaching impacts on secondary productivity in multiple disparate systems and must be accounted for in considerations of impacts to future food-web function.

The primary goal of habitat restoration is to recover the ecological structure, function, and services of natural ecosystems lost due to disturbance. Post-restoration success typically focuses on the return of a desired habitat type, consumer species composition, or abundance relative to a reference site. However, how energy flow responds to habitat restoration has not been widely studied, and there is a need to develop a better understanding of how energy flows through a restored vs reference ecosystem following restoration. We tested recently developed niche metrics as a tool to assess the degree of recovery of ecosystem energy flow and evaluate the success of habitat restoration. Using published stable isotope values from six systems, one to three years post-restoration, we used Bayesian mixing models to quantify resource use by consumers to generate food web hypervolumes for restored and reference habitats in each ecosystem and to quantify similarity in resource use between restored and reference systems. Our analysis showed that there were differences in restoration success at each restoration project between the restored and reference food webs, but two general patterns emerged in the early stages following restoration. Restoration efforts that restore biogenic habitats display lower levels of recovery of food web function than those that only restore abiotic habitat structural. Restoration increases the variability in basal resource use of consumers in food webs that rely heavily on one basal resource, while in food webs that relied on multiple basal resources consumers decrease variability in basal resource use. Our results demonstrate that hypervolume analysis is a powerful tool that can be used to quantify energy flow, the recovery of food web function, and measure restoration success.

Consumer-mediated movement can couple food webs in distinct habitats and facilitate energy flow between them. In New England saltmarshes, mummichog (Fundulus heteroclitus) use the flooding spring tides to access the high marsh platform and eat invertebrate prey, coupling the high marsh and aquatic creek food webs by gathering energy produced on the high marsh and making it available to the aquatic food web. Changes in the geomorphology of saltmarsh creek edges greatly influence the survival, biomass, and resource use of mummichog populations. Here, we use gut content analysis and field surveys to quantify the effect of altered creek edge geomorphology of mummichog predation on terrestrial invertebrate prey found on the high marsh surface. Fish populations in creeks with greater connectivity had a higher total biomass of terrestrial invertebrates in their guts. However, bomb calorimetry showed no difference in the average caloric content of mummichog individuals from creeks with different creek edge geomorphology. Additionally, we did not observe differences between the biomass and length distributions of mummichog in those creeks. While altered creek edge geomorphology has no effect the condition of the individual mummichog, it does decrease the total number of mummichog supported by a marsh creek and therefore decreases the total amount of high marsh production fluxed by mummichog to the aquatic habitat, decreasing coupling between the terrestrial and aquatic food webs.

In the Northern Gulf of Mexico, black mangroves (Avicennia germinans) are expanding their range and replacing smooth cordgrass (Spartina alterniflora) as the dominant foundation species in estuarine systems. The impact this habitat transition has on the sources of primary production that contribute to the food webs of these areas is as of yet unclear. Here, we used stable isotopes and Bayesian mixing models to determine the contributions of primary production sources to the food webs in Louisiana saltmarshes currently experiencing rapid mangrove encroachment. In addition, we determined how these contributions are altered as a function of foundation species cover, particularly for white shrimp (Litopeneaus setiferus). Species primarily rely on algae-derived and water-column derived production, not on production derived from the foundational macrophytes themselves. White shrimp trophic position increased in areas with higher mangrove cover at some locations; shrimp used more water column-derived production and less algae-derived production. Transition from Spartina to mangrove-dominated estuarine areas has little effect on the overall pattern of primary producer contribution to food webs in these areas. However, differences in the structural and substrate properties of these foundational species could be altering the way energy moves through food webs.