Natural and anthropogenic alteration of habitat in the Gulf of Mexico impacts every stage of the crab life cycle. Activities that can contribute to habitat loss include but are not limited to pollution, eutrophication, and alterations in freshwater and sediment flow (Guillory, Perry and VanderKooy 2001). Blue crabs depend on the quality and quantity of estuarine marshes, mangrove areas, submerged vegetation, and nearshore soft sediment habitats to successfully reproduce and grow (Guillory, Perry and VanderKooy 2001).
Habitats may be altered by human activity through freshwater control. Wetlands are created by and maintained through nutrients and sediments transported to them by river systems; the damming, channelization, and leveeing of rivers can affect the timing and flow of freshwater to a wetland estuary and greatly affect the composition of the habitat (Guillory, Perry, and VanderKooy 2001). Mississippi lost over 50% of its emergent wetland habitat from 1979-2007 and seagrass coverage has declined 50% (Handley et al. 2013, Moncreiff et al. 2006).
Current research in the Gulf of Mexico has identified freshwater inflow to be a critical driver of blue crab population dynamics (VanderKooy 2013). Low flow conditions hav ebeen found to negatively affect juveniles blue crabs in teh Apalachicola River estuary (Wilbur 1994). Sanchez-Rubio et al. (2011) related abundance of juvenile blue crab to the influence of global climate factors on regional hydrology and how climate and hydrology structure habitat. Riedel et al. (2010) highlights the correlation between significant downward trends in abundance of juvenile blue crabs and a period characterized by drought and habitat changes from both natural and man-made alterations to coastal wetlands. High river flows have also been linked to increased commercial landings in Florida and Texas (More 1969, Wilbur 1994).
Fluctuations in freshwater inflow and resulting changes in salinity may also have secondary effects on blue crab abundance due to predation (Bourgeois, Marx, and Semon 2014). Predation is a factor influencing blue crab abundance, and changes in salinity influence the presence or absence of predators. During periods of high freshwater inflow and low salinity, many predators remain offshore in higher salinity waters, while low rainfall will increase salinity, causing predators to move inshore and overlap with blue crab habitats.
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