Bottom water characterization of Atlantic surfclam habitats off New Jersey
Creators: name: Bramich, Charlotte
Publisher: name: No Publisher Supplied
Year: 2024

description: Shellfish aquaculture often occurs in shallow bays, which can have space constraints or unsuitable water conditions for some species. As opportunities to expand shellfish aquaculture into coastal habitats grow, it is important to evaluate the bottom water environmental conditions in those new habitats to assess potential for success. A site off the coast of New Jersey (39.4524 N, 74.2409 W) is being used as a pilot experiment for Atlantic surfclam (Spisula solidissima) aquaculture that aims to characterize inter-annual and seasonal patterns in bottom waters at this location. Ocean bottom water is understudied, creating a need for comprehensive coverage of parameters like temperature and dissolved oxygen as it relates to biological needs of the benthos. The goal of this study was to leverage existing datasets to characterize the bottom water conditions in and around a study site to determine if the area had suitable surfclam growing conditions. Parameters including temperature, salinity, density, and dissolved oxygen were sourced from modeled and glider-recorded datasets; model data provides a continuous historical estimated timeseries and the observational data provides observed measurements at isolated points in time. A literature review was conducted on the Atlantic surfclam to better understand the biological needs of juveniles and adults. The threshold for salinity for the Atlantic surfclam is above 28 ppt. Below 28 ppt, lab experiments have shown stress-induced behaviors, but this was closely related to dramatic salinity drops, which is not anticipated within the study area. Feeding and respiration rates decrease above 23-24 °C, and at 20 °C growth declines and burrowing is inhibited. Dissolved oxygen (DO) below 2.85 mg/L is lethal for surfclams, but oversaturation (DO over 10 mg/L) can also harm them. Physiological stress in mollusks occurs below 4 mg/L, which serves as the DO threshold in this study. A regional ocean model (Doppio) provided monthly averages of bottom water temperatures from 2007 – 2023 at the study location. The monthly averages were reviewed for seasonal trends and to assess changes across years. Glider observations were made within the bounds of the study area (116 km2), the center of which is 6 km off the coast of Atlantic City. All glider observations collected in the study area within 5 meters of the bottom were averaged daily to create a multi-year time series of observed bottom water conditions. Glider observations from 22 deployments were available between 2014 – 2023, spanning all seasons, with higher coverage during fallThe combined timeseries of bottom water conditions from the model output and glider observations provide a comprehensive hindcast of the conditions that long-lived surfclams have experienced at that location over recent decades. The summarized bottom water conditions were used in comparison to surfclam biological thresholds and suggest that bottom water temperature tends to exceed 20°C for about 80 days each year. While this is not a lethal threshold for Atlantic surfclams, physiological stress may increase during those times. The other water quality parameters (salinity and DO) remain within suitable levels. This approach, combining modeling and observations, can be utilized as framework in the future for large-scale bottom water mapping to identify suitable aquaculture sites for the Atlantic surfclam.