Development of methods to track oyster movement under field conditions in North Inlet estuary, South Carolina

Eastern oyster (Crassostrea virginica) reefs provide important habitat structure and ecosystem services in saltmarsh tidal creek estuaries. Reef persistence depends on growth of resident individuals and regular recruitment to maintain suitable shell substrate. Boat wakes potentially physically displace oyster clumps. The objective of this research was to develop methods to track oyster clump position and biomass on two natural fringing oyster reefs in North Inlet estuary, South Carolina. Boat traffic (number of boats making wakes per day), oyster clump displacement (cm/d) over time, oyster biomass (g dry tissue), and condition index (biomass/g dry shell weight) were quantified from August 2019 through March 2020 at Clambank (high) and Bly (low) boat traffic reefs. More boats were observed in Clambank Creek (2.91±2.99 wakes/d) compared to Bly Creek (0.04±0.20 wakes/d). Oyster clumps were displaced over time at both Bly (median = 0.39 cm/d) and Clambank (median = 0.49 cm/d) Creek reefs. Predicted biomass of standard 50 mm and 76 mm shell height animals ranged from 0.19 to 0.81 g at both reefs. The allometric equation b coefficient varied seasonally from 1.63 to 2.49, at Clambank Creek (9/29/2019) and Bly Creek (1/28/2020), respectively. Condition index values within reefs ranged from 1.41 to 77.66 and 4.49 to 102.24 at Bly and Clambank Creek, respectively. Suggestions for refinement of these image analysis methods for estimating clump displacement rates incorporate date, location, and image specific calibration factors as well as extension from the current one dimension to two dimensions