Investigating the impacts of transplantation techniques and hard clam presence on subtropical seagrass restoration

Introduction Seagrass restoration has historically been difficult and expensive. Recently, there has been interest in co‐restoring seagrasses with Hard clams ( Mercenaria spp.) to improve seagrass restoration through nutrient enrichment and water filtration. Objectives To examine the effects of clam co‐restoration and transplantation techniques on seagrass ( Halodule wrightii ) growth, two experiments were conducted in the Indian River Lagoon (IRL), Florida, from May through November 2023. One experiment compared transplantation techniques (non‐anchored, staples, burlap mats, and jute mats) with and without juvenile clams, while another experiment investigated the effects of juvenile versus adult clams to determine size effects of clams on planting success. Methods Treatments were monitored for seagrass cover, shoot count, and canopy height. Clam measurements and seagrass nutrients were measured to determine differences driven by treatments. Results Juvenile clams in both experiments died weeks after deployment, possibly from predation and transplantation stress. In the transplantation experiment, clam presence had no significant effect on seagrasses due to mortality. Plots planted with burlap had higher cover versus all other techniques ( p ≤ 0.0133) and higher shoots versus all techniques except jute ( p ≤ 0.0048). The clam maturity experiment found that no clam and adult clam plots had higher cover ( p ≤ 0.0462) and shoots ( p ≤ 0.0358) versus juvenile clams. Conclusion While no relationship between clams and seagrass growth was found due to clam mortality (and possibly algae bloom‐related stress for adult clams), the study determined burlap as the optimal restoration technique of the methods tested in the IRL.