Humans redistribute habitats through climate-driven changes in the ranges of habitat-forming species, such as plants and corals. The maintenance of inhabitant communities in shifting systems will depend on organisms’ abilities to associate with their preferred habitat in patchy and dynamic landscapes. Globally, mangroves are shifting poleward – displacing temperate grass marshes – with unknown consequences for wetland inhabitants. Where mangroves encroach into temperate salt marshes, the change in foundation species and accompanying structure and production likely alters the habitat landscape for marine communities. Along one mangrove-marsh ecotone on Florida’s Atlantic coast, we investigated nekton community structure across spatial scales. We used a spatially-nested field experiment to isolate physical structure from production and investigated their independent influences on community organization and associations of component species. We monitored nekton composition on an array of retrievable panels biweekly for six months at two mixed mangrove-marsh sites. We evaluated whether associated communities differ between mangroves and marshes and at what scale (landscape, patch, sub-patch vegetation structure). We expected community composition to depend on vegetation type; if physical structure alone is influential, then the community should be distinguishable at the sub-patch scale; if productivity drives community patterns, they should emerge at the patch scale.
Results/Conclusions
The optimized multivariate GLMM revealed that nekton communities are most distinctive by site but are also distinguishable at patch and sub-patch levels, indicating detectable structuring from the scales of kilometers to less than a meter. Each level – corresponding to dominant landscape vegetation (or geographic location), vegetation patches, and physical habitat structure – explains significant compositional patterns not accounted for in the other spatial scales. Differences are driven by a small subset of well-sampled species among the ~25 encountered. Strongly associated species are often present even in small, emergent mangrove patches. Among the responding species, a complimentary set of formative processes are shaping the nekton community across spatial scales in a dynamic, patchy landscape. The composition patterns suggest influences of environmental filtering and/or niche-based sorting – particularly for specialists – helping to explain efficient habitat tracking along the expanding mangrove edge. The nested community structure also indicates a hierarchy of associations (from sub-patch up to landscape), which may emerge differently depending on the extent of habitat shift and the scale of sampling. The pattern in this system likely stems from high propagule pressure due to pelagic larval dispersal; similar patterns could be expected in other systems that lack acute dispersal limitation.