MEPS 452:179-191 (2012)  -  DOI: https://doi.org/10.3354/meps09605

ABSTRACT: In river-dominated estuaries such as Winyah Bay at the base of the Pee Dee River in South Carolina, USA, the net movement of water and pelagic larvae is toward the ocean. Larvae of many decapods are hypothesized to recruit back into estuaries using a complex behavior termed flood-tide transport (FTT). A pattern of late-stage larval behaviors in concert with daily tidal rhythms yields net larval transport upstream into the estuary. Tidal currents in narrow river channels exhibit little distortion of flow, resulting in near linear flows. This means that there is a linear decay in tidal current amplitude over the last few kilometers of the upper estuary that can be easily modeled with a simple 1-dimensional (1D) model. With our 1D model, we demonstrate that ebb and flood currents can be modeled accurately near the limit of maximum upstream tidal influence within narrow river-dominated estuaries. Our model predicts the damping of flood tidal current in the face of river discharge. This dampening restricts the upriver migration potential of larvae that use FTT to return to adult habitats, or colonize new habitat. When our model is coupled with FTT behavior, we can predict the ability of red-jointed fiddler crab Uca minax (LeConte 1855) larvae to recruit back to the freshwater reaches of the Pee Dee River estuary for any combination of river discharges or tidal amplitudes. The flow model we developed can be used to assess the potential impacts of changing river flow and sea level on larval recruitment to upstream areas of coastal rivers.

KEY WORDS: Larval transport · Decapod larvae · Tidal currents · River discharge · Tidal freshwater · Modeling · Uca minax · Global warming