Potential Influence of Phytoplankton Communities on the Growth of Farmed M. mercenaria in Southern New Jersey: A Pilot Study

As a family business established in 1909, Parsons Seafood and Mariculture has over a century of practical experience devoted to the farming and harvesting of bivalves in waters local to Tuckerton, NJ. Extensive knowledge of aquaculture farming practices allows 5th generation owner, Dale Parsons, to adjust planting and harvesting routines based on a multitude of conditions including but not limited to weather, water characteristics, and tidal patterns. This ability to modify practices based on farmer knowledge and hands-on experience has allowed the Parsons business to flourish and become a multifaceted enterprise while remaining connected to the generations that came before.

Although continuing to operate a successful multigenerational aquaculture business, it is evident that the growth rate of farmed hard clams, M. mercenaria, has decreased significantly in recent years. While planted clam seed do not seem to be experiencing a noticeable reduction in juvenile development there has been a remarkable decline in growth rate once clams begin to enter the size in which they would be considered mature. Not solely limited to the farmed leases that Parsons maintains, other aquaculture businesses local to the Tuckerton area and beyond have experienced a similar decrease in the rate growth for their clams. The reduction in growth directly impacts aquaculture farm profit as restricted growth results in less harvested clams available for the wholesale and retail market. If the rate of clam growth continues to decline, aquaculture farms in New Jersey may very well be compromised with the loss of their primary harvest species.

Having already experimented with altering various aspects of the aquaculture process, the question of what is influencing the apparent decrease in the growth of clams remains unanswered. A previous study in the same region resulted in findings that indicated a significant negative linear relationship between the growth of hard clams and the presence of cyanobacteria species (Fantasia, Bricelj, & Ren, 2017). Although this study was conducted in an area with close geographic relation to Parsons there is a profound lack of current knowledge regarding phytoplankton communities in waters surrounding the aquaculture farms involved in this study. Middle Island Channel and Dry Bay are located in adjacent waterways and have both experienced a continuous decrease in growth rates for clams while Great Sound, a waterbody located roughly 50 miles south, has exhibited consistency with hard clam growth rate. Sampling conducted during this pilot study will focus on analyzing the presence and differences of phytoplankton communities between Middle Island, Dry Bay, and Great Sound. Obtaining knowledge concerning phytoplankton communities in various water bodies will provide valuable information for potential additional studies surrounding the decrease in growth rate for hard clams. As stated through research performed by Sea Grant New York, “evidence suggests that hard clams are growing slower…than they did in the past, potentially due to brown tides…or changes in the plankton community due to variable plankton size and type” (2007).

With the findings of this study and studies that will potentially follow, aquaculture farmers that have experienced a continued decrease in the growth rate of their product may be able to mitigate the compromise of their businesses through alteration of their brood stock.  If, among other factors, it is a possibility that the presence of specific communities of phytoplankton are hindering clam growth, aquaculture farmers will have a recent and thoroughly assessed collection of data indicating the concentration and location of where these species may be found. Without knowledge of what phytoplankton species are present in the water column there is not enough information available with which farmers can make an educated decision on where to place their focus when attempting to mitigate the decline in growth that has been noticed. Additionally, if analysis of samples taken during this study indicates that there are different densities of harmful or beneficial phytoplankton found in certain areas of the waterbody, changing the location of the farmed leases could prove to be advantageous. There are multiple approaches that shellfish farmers could pursue in efforts to continue the success of their business, but without the knowledge that this study will aid in providing it is impossible for an informed decision to be made. In short, finding out the “where?” “what kind?” and “how much?” regarding phytoplankton communities around aquaculture farms could effectively assist in the persistence of multiple threatened businesses.