Florida has become a leading producer of hard clams in the nation with Cedar Key providing over 90% of the state’s production. Recently, clam growers have reported below average survivals or total losses during the prolonged hot summers. A variety of factors and stressors may contribute to these mortalities. However, diversity in farm location and operational scale has made it difficult to determine whether losses incurred can be traced to one or two over-arching causes, such as water temperature, or are the result of related or unrelated issues. In partnership with the clam aquaculture industry, a multi-step process was implemented to begin to identify contributing factors associated with mortality events experienced by growers and develop a working relationship with research and extension faculty in conducting preliminary research and monitoring activities over the summer of 2024.
A survey of members of the clam aquaculture industry in Cedar Key was conducted to gain an understanding of crop losses, contributing factors, and research and monitoring efforts needed.
Based on results of the growers’ survey and round table session with researchers, the following projects were conducted during the summer in 2024 to gain preliminary information or augment existing activities with funding through Florida Sea Grant. Final reports and workshop presentations for each project are provided.
Investigator: Shirley Baker, University of Florida (UF)/IFAS SFFGS Fisheries and Aquatic Sciences Program
Objectives: This study investigates the physiological responses of hard clams (Mercenaria mercenaria) to elevated summer temperatures, with a focus on oxygen uptake, behavioral stress indicators, and mortality. By examining how metabolism and chronic heat exposure intersect to challenge clam survival, this work aimed to inform research priorities, guide selective breeding efforts, and support the development of practical management strategies for shellfish aquaculture in a warming climate. Learn More
Investigator: Sarah Hutchins and Stephen Hesterberg, Gulf Shellfish Institute
Objectives: Hard clams that survived high thermal stress (>37°C) were spawned. This study monitors performance of the thermally exposed F1 progeny relative to conventional lines on commercial leases during the field nursery stage. Clam farmers with leases in different environmental contexts were provided with seed, supplies, and resources needed to culture both stocks. Differences in performance were evaluated on low salinity and high salinity leases. Learn More
Investigator: Leslie Sturmer, Natalie Anderson and Tracey Vlasak, UF/IFAS Shellfish Aquaculture Extension
Objectives: To increase insight into basic but key relationships between environmental factors and survival and health of cultured clams, this study increases water quality monitoring efforts. Chlorophyll sensors were added to existing monitoring stations to assess phytoplankton availability. In addition, surveillance of water temperature and salinity at lease areas was expanded. Growers can access real-time and archived data via the website, https://shellfish.ifas.ufl.edu/water-quality-monitoring/. Learn More
Investigator: Todd Osborne and Tracey Schafer, UF/IFAS Soil, Water and Ecosystem Sciences Department
Objectives: This study investigates the role of sediment organic matter (SOM) in temperature driven summer mortality events of hard clams. Mortality events could be due to low oxygen (hypoxia), hydrogen sulfide toxicity or a combination brought about by increased temperatures. The presence of organic matter influences hypoxia by stimulating respiration in microorganisms and can similarly fuel production of hydrogen sulfide. Thus, this work aims to test that SOM would result in clam mortality proportional to SOM concentration. Learn More
Investigator: Susan Laramore, Florida Atlantic University-Harbor Branch
Objectives: This study determines how environmental changes seen during summer impact clam health by employing bacterial and histological analysis. Taking an integrated approach, the presence of bacterial and other disease-causing organisms in clams in response to environmental changes that occur during the summer are documented at two lease areas. In addition, physiological condition and responses, such as changes in the digestive tract tubules and presence of food in the gut, are evaluated. Learn More
