Altered mangrove wetlands as habitat for estuarine nekton: are dredged channels and tidal creeks equivalent?
Abstract:Hasty decisions are often made regarding the restoration of "altered" habitats, when in fact the ecological value of these habitats may be comparable to natural ones. To assess the "value" of altered mangrove-lined habitats for nekton, we sampled for 1 yr within three Tampa Bay wetlands. Species composition, abundance, and spatial distribution of nekton assemblages in permanent subtidal portions of natural tidal creeks and wetlands altered by construction of mosquito-control ditches and stormwater-drainage ditches were quantified through seasonal seine sampling. Results of repeated-measures analysis of variance and ordination of nekton community data suggested differences in species composition and abundance between natural and altered habitat, though not consistently among the three wetlands. In many cases, mosquito ditches were more similar in assemblage structure to tidal creeks than to stormwater ditches. In general, mosquito ditches and stormwater ditches were the most dissimilar in terms of nekton community structure. These dissimilarities were likely due to differences in design between the two types of ditches. Mosquito ditches tend to fill in over time and are thus more ephemeral features in the landscape. In contrast, stormwater ditches are a more permanent altered habitat that remain open due to periodic flushing from heavy runoff. Results indicate that environmental conditions (e.g., salinity, current velocity, vegetative structure) may provide a more useful indication of potential habitat "value" for nekton than whether the habitat has been altered. The type of ditching is therefore more important than ditching per se when judging the habitat quality of these altered channels for fishes, shrimps and crabs. Planning should entail careful consideration of environmental conditions rather than simply restoring for restoration's sake.
Document Type: Research Article
Publication date: May 1, 2007
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