Field Mark-Recapture of Calcein-Stained Larval Oysters (Crassostrea virginica) in a Freshwater-Dominated Estuary

Abstract

Knowledge of larval transport is important for restoration and management efforts; yet, there are no established methods to determine larval transport in situ. Calcein staining of oyster larvae may help fill this void, and a two-part study was conducted to determine its effectiveness at tracking larval oyster transport in the field. First, it was tested whether oysters could be successfully stained, survive, and grow at estuarine salinities (15, 20, 26), and at sufficiently large numbers (millions of oysters) to support field mark-recapture studies. Second, the field-based application was tested by releasing 22 million stained larvae twice (high and low salinity) into a major estuary, and two methods (fluorescent microscopy and FlowCam) were used to detect recaptured larvae. Results were compared with expected larval movement patterns simulated by an existing larval transport model. Calcein concentrations (100 mg L−1) did not affect larval growth or survival, but handling conditions (water salinity manipulations and tank size) did affect growth and survival during the post-staining period. Microscopy had double the detection capacity, but FlowCam was more practical and time efficient for the large-volume, high particulate load field samples. Larvae (n = 2) were recaptured during the second, higher salinity release, and model comparison showed a 1–2-day time-lag between field recapture and model predictions, suggesting need for model refinement. Calcein has potential to be a useful marker to track larval movement at large scales needed for field-based studies, providing critical information to aid in selection of restoration sites and management of commercially important shellfish species.