An ecological model of the habitat mosaic in estuarine nursery areas: Part II—Projecting effects of sea level rise on fish production

Understanding the response of fish populations to habitat change mediated by sea level rise (SLR) is a key component of ecosystem-based management. Yet, no direct link has been established between habitat change due to SLR and fish population production. Here we take a coupled modeling approach to examine the SLR-habitat-fish relationship based on projections of habitat change resulting from a 0.26m increase in sea level by 2100 as input for a spatially-explicit individual-based model (SEIBM) of juvenile fish growth and mortality. This coupled modeling approach allows for an examination of both mechanistic and behavioral responses to habitat change, as well as the projected impact of these responses on population production. Habitat changes described with the Sea Level Affecting Marshes Model (SLAMM 6.0.1) in response to SLR included a conversion of marsh and higher elevation habitat types into other structural types and open water, and an increase in overall fragmentation. These habitat changes were combined with measures of temporal change in dynamic habitat variables to form a habitat mosaic. The impact of changes in this mosaic on juvenile fish growth and mortality was largely dependent on movement strategy employed in the SEIBM followed by changes in dynamic habitat, and then changes in structural habitat projected by the SLAMM model. Movement strategy and SLR effects interacted strongly, which suggests that how fish respond to habitat change is a critical factor to understanding population-level effects. Overall, projected SLR effects on fish distribution most consistent with field data were initially negative for net fish production, but became net positive by the terminal year of SLR as the positive effects of fragmentation became most important. These results are consistent with empirical studies of coastal marsh production in the Gulf of Mexico and demonstrate the importance of incorporating a holistic measure of habitat quality and fish behavioral responses into any projection of SLR effects on estuarine fish production.