Assessing the net effect of anthropogenic disturbance on aquatic communities in wetlands: community structure relative to distance from canals |
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Authors: | Jennifer S Rehage Joel C Trexler |
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Institution: | (1) Department of Biological Sciences, Florida International University, Miami, FL 33199, USA |
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Abstract: | Anthropogenic alterations of natural hydrology are common in wetlands and often increase water permanence, converting ephemeral
habitats into permanent ones. Since aquatic organisms segregate strongly along hydroperiod gradients, added water permanence
caused by canals can dramatically change the structure of aquatic communities. We examined the impact of canals on the abundance
and structure of wetland communities in South Florida, USA. We sampled fishes and macroinvertebrates from marsh transects
originating at canals in the central and southern Everglades. Density of all aquatic organisms sampled increased in the immediate
proximity of canals, but was accompanied by few compositional changes based on analysis of relative abundance. Large fish
( >8 cm), small fish ( <8 cm) and macroinvertebrates ( >5 mm) increased in density within 5 m of canals. This pattern was
most pronounced in the dry season, suggesting that canals may serve as dry-down refugia. Increases in aquatic animal density
closely matched gradients of phosphorus enrichment that decreased with distance from canals. Thus, the most apparent impact
of canals on adjacent marsh communities was as conduits for nutrients that stimulated local productivity; any impact of their
role as sources of increased sources of predators was not apparent. The effect of predation close to canals was overcompensated
by increased secondary productivity and/or immigration toward areas adjacent to canals in the dry season. Alternatively, the
consumptive effect of predatory fishes using canals as dry-season refuges is very small or spread over the expanse of marshes
with open access to canals.
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Keywords: | wetlands canals anthropogenic disturbance density community structure |
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