BORGIANINI, SA*; JURISA, J; STYLES, R; BRODIE, RJ; Univ. of South Carolina; Univ. of South Carolina; Univ. of South Carolina; Univ. of South Carolina: A Model Describing the Dispersal Capabilities of the Red-Jointed Fiddler Crab (Uca minax LeConte) Postlarvae in a River-Dominated Estuary.

Long-term and short-term human disturbances of river hydrology can significantly affect net flow into estuaries such as in Winyah Bay near Georgetown, South Carolina. The effects of changing river flow will have an impact on the recruitment of Uca minax postlarvae (megalopae) to freshwater upriver areas where they settle into adult habitats and metamorphose. Brachyuran megalopae have been shown to utilize flood-tide transport (FTT) to migrate to nursery areas upstream where cover and potential food sources are plentiful. The FTT model adequately explains recruitment of megalopae in well-mixed, tidally-dominated estuaries. In these estuaries the difference in duration and intensity of ebb tidal and flood tidal currents is not significant. However, applying the FTT model may be problematic in narrow, river-dominated estuaries that have significant net downstream flow, such as Winyah Bay. We developed an empirical two-dimensional flow model for the freshwater, tidal portion of the Great Pee Dee River that discharges into Winyah Bay. Our model is predictive of potential human-induced changes in flow (from increased upriver water usage) or eustatic sea level rise (due to affects of global warming) that will amplify the intensity and duration of flood tidal currents that transport marine larvae upstream. The flow model we developed can be used to assess the potential impacts of changing river flow and sea level on larval recruitment and dispersal of many types of planktonic larvae to upstream areas of coastal rivers. The model may also be used by scientists, resource managers and stakeholders when making decisions about minimum river flow allocations.