| Great Lakes coastal wetlands are highly productive environments, vital to the health of the aquatic food web, yet threatened by shoreline development that fragments them. Little is known about the effects of fragmentation on Great Lakes' fishes, which utilize coastal marshes during different life history stages. Fragmentation alters the geometry and patchiness of coastal marshes, changing contiguous waterscapes into smaller, isolated fragments with more edge habitat.; I assayed the biotic and abiotic characteristics of the littoral marsh in Mismer Bay, Lake Huron, USA, sampling physical habitat features and fish assemblages, and establishing their spatio-temporal variation. Fish species richness decreased with increasing water depth, and species' abundances corresponded with the percent cover of emergent, floating, and submergent macrophytes. Four natural marsh patches were visually and statistically identifiable. The consequence of decreased patch size was evaluated from fish species-area curves measured for three emergent marsh patches. Using a threshold of 80% natural richness, minimum area was 205 m2 in single patches and was 500 m2 for all emergent patches combined. However, these areas underestimated contributions of finer-scale habitat heterogeneity to fish diversity, subsequently illustrated by dispersal and behavior patterns. The consequences of isolation were evaluated from intra- and inter-patch mobility patterns, determined from tagged and recaptured individual fish. Mobility metrics (e.g., net distance traveled, number of boundaries crossed) were used to construct an explanatory index to rank species according to their relative sensitivity to patch isolation. Pimephales notatus and Culaea inconstans showed greatest inter-patch mobility while Cottus bairdii showed the least. The consequences of increasing edge habitat were evaluated by comparing behavior at edges to that in patch cores. Behavioral observations indicated a positive edge response whereby more species and individual fish were detected at edges than in patch cores. Relatively more feeding and shoaling were observed at edges as well, suggesting that P. notatus and Notropis stramineus would be least affected by patch boundaries and fragmented edges. In general, these mobile, edge-utilizing species would be least vulnerable to fragmentation. |
