Interactions between Shellfish Aquaculture and Submerged aquatic vegetation (Sav): A State of Science Assessment to Inform habitat equivalency and more

Shellfish growers utilize a diverse array of culture methods to produce clams, oysters, geoduck, and scallops in every coastal state of the U.S. Cultivation methods vary significantly, including on-bottom and off-bottom (suspended) practices, from large corporate farms comprising hundreds of acres to small family-based operations of less than an acre. Shellfish aquaculture is the largest and fastest growing coastal aquaculture industry in the U.S. Cultured filter-feeding bivalves with gear can improve local water quality and provide additional ecosystem services, even when cultivated intensely. In planning for and regulation of aquaculture-industry development, coastal managers must weigh environmental benefits and costs in tandem with a growing number of other activities within the coastal zone. One such conflict includes the interactions between shellfish aquaculture and submerged aquatic vegetation (SAV). Due to the importance of SAV as essential fish habitat and the global decline in seagrass ecosystems, managers are concerned with how shellfish cultivation techniques impact sensitive SAV communities. Industry-wide monitoring reports and research findings suggest that shellfish aquaculture can have variable impacts on SAV depending on the cultivation technique and health of surrounding SAV communities. In many cases, shellfish aquaculture is identified as providing ecosystem services similar to SAV such as habitat provisioning, improving water clarity, inducing sedimentation, and carbon sequestration. To better understand these interactions, the NOAA National Ocean Service's Coastal Aquaculture Planning and Environmental Sustainability (CAPES) program is conducting a State of Science Assessment. This assessment provides a review of regulatory mandates, shellfish cultivation practices, SAV interactions (both negative and positive), and approaches for habitat equivalency analysis. In cases where net positive effects on SAV occur, we propose a metric and analysis framework capable of calculating net ecosystem effects. This approach allows the coastal manager to consider trade-offs and benefits at the ecosystem level.