Breeding for thermal tolerance in farmed atlantic surfclams (Spisula solidissima)

View the project final report

Commodities

• Animals: shellfish

Practices

• Animal Production: aquaculture, livestock breeding
• Crop Production: crop improvement and selection
• Education and Training: extension, participatory research
• Sustainable Communities: local and regional food systems, partnerships

Shellfish aquaculture is an important and rapidly expanding sector in US food production (FAO, 2016). Shellfish farmers in New Jersey and along the US east coast are eager to diversify their farm plan by cultivating new species. The Atlantic surf clam (Spisula solidissima) represents an ideal target species for diversification because it is native, grows rapidly, and its growing season complements the region’s established farming framework. However, the species is known to be vulnerable to high temperature conditions (Goldberg and Walker, 1990; Weinberg 2005) – an issue that will be exacerbated by rising temperatures (Munroe et al., 2016), and one that will be problematic on shallow coastal farms. Data from our previous and ongoing studies examining optimal nursery and grow-out conditions for surfclams suggest that thermal tolerance may be a heritable trait (Acquafredda et al., in prep). The purpose of this proposed project is to evaluate whether selective breeding for a heat-tolerant surfclam stock is a viable strategy for enhancing the survival of cultivated surfclams exposed to high temperatures on the farm. To accomplish this goal, hatchery-reared surfclams will be challenged with sustained thermal stress and the most heat-tolerant survivors will be selected and bred. The growth, survival, and health of the heat-tolerant progeny will then be compared to non-selected surfclams using two experiments: (1) a common garden experiment on a farm where water temperature will fluctuate naturally, and (2) a controlled laboratory experiment where warm and ambient water treatments will be applied.
 

Surfclams are known to be vulnerable to high temperature conditions (Goldberg and Walker, 1990; Weinberg 2005) – an issue that will be exacerbated by rising temperatures (Munroe et al., 2016), and one that will be problematic on shallow coastal farms. The goal of this project is to assess whether thermal tolerance is a potentially heritable trait in the Atlantic surfclam and to take the first steps towards developing a stock of selectively bred heat-tolerant surfclams. These goals will be achieved by comparing growth, survival, body condition, and overall performance of first-generation offspring of thermally-selected surfclams to that of offspring from non-selected surfclams.

Objective 1: Select heat-tolerant brood stock. Selecting the appropriate brood stock is paramount to any successful breeding program. We will select individuals from a large cohort of clams derived from a mix of wild stock parents. This cohort will be split into two groups: one that will be exposed to thermal stress, from which the heat-tolerant survivors will be selected, and a second that does not experience thermal stress and will act as control brood stock.

Objective 2: Produce heat-tolerant and control progeny. We will spawn and back-cross the heat-tolerant and control brood stocks to produce a thermally-selected cohort (TS-cohort) and a non-selected control cohort for comparison (NS-cohort). Through experimentation (Objectives 3 and 4), these progeny will allow us to determine if the heat-tolerance observed in the parent stock was transmitted to their offspring.

Objective 3: Evaluate survival, growth and performance of selected progeny on the farm. Clam farms experience fluctuating temperatures over tidal, diel, and seasonal temporal scales. By growing these surfclam cohorts on an actual farm for the entirety of the grow-out phase, we will be able to assess whether the thermally-selected progeny perform better than the non-selected progeny during both optimal (cooler water of late fall through early spring) and suboptimal conditions (summer), and determine differences in yield during the final harvest of market size animals.

Objective 4: Evaluate heat-tolerance of selected progeny in the laboratory. When the thermally-selected and non-selected cohorts are ready to be deployed to the farm, a portion of each cohort will be retained in the laboratory in order to assess the thermal tolerance of each group in a highly-controlled setting. By exposing the animals to more severe conditions than they would experience on the farm, we will be able to precisely determine the upper thermal tolerance of each cohort.