Expanding aquaculture opportunities in the Northeastern United States through ecologically-sound diversification
Creators: name: Acquafredda, Michael
Publisher: name: No Publisher Supplied
Year: 2021

description: The goal of this dissertation was to investigate ways to expand bivalve aquaculture opportunities in the northeastern United States through ecologically-sound diversification (ESD). In an aquaculture context, ESD is defined as the practice of cultivating multiple species in a manner that minimizes negative impacts on the surrounding ecosystem while remaining adaptive and resilient to environmental change. Bivalve aquaculture is among the least environmentally damaging forms of food production and many of its impacts serve a net benefit to surrounding ecosystems, making it an ideal starting point for ESD. In the Northeast, production is dominated by the Eastern oyster (Crassostrea virginica) and the hard clam (Mercenaria mercenaria), and high-efficiency yet risk-prone monoculture is the norm. In the first unit (Chapters 2 and 3), various aspects of Atlantic surfclam (Spisula solidissima) husbandry were evaluated to test whether this species can become an alternative species for shellfish growers. In Chapter 2, the effect of rearing temperature on the survival and growth of early juvenile surfclams was investigated. The results show that of the temperatures tested, 20˚C was optimal for promoting survival and growth. In Chapter 3, a series of controlled experiments were conducted to evaluate the efficacy of various surfclam nursery and grow-out techniques. In the nursery phase, juvenile surfclams were reared in various gear types. In the grow-out phase experiments, surfclam growth, survival, and condition were evaluated at three New Jersey farms. Results show that multiple rearing methods can effectively produce surfclams, but flow rate, food availability, and temperature are important factors that affect gear efficiency. In the grow-out experiments, survival varied across farms and across years; growth and condition were consistent across farms but varied seasonally. The second unit (Chapters 4 and 5) expands upon the results of the previous chapters, which demonstrated the vulnerability of surfclams to heat stress. Research presented in Unit 2 takes a proactive approach towards climate-informed aquaculture. In Chapter 4, the feasibility of breeding surfclams for greater heat tolerance is explored. The results indicated that when juvenile surfclams were exposed to prolonged lethal temperatures, the adult survivors withstood subsequent heat stress for significantly longer than individuals that did not experience heat stress as juveniles. Additionally, selective breeding enhanced heat tolerance in first-generation surfclam progeny. To understand how selection via heat stress could alter the gene expression of a surfclam population, a transcriptomics study was conducted (Chapter 5). The results show that randomly selected (control) clams differentially expressed more genes in response to heat stress than the heat-selected clams, yet the latter group exhibited significantly stronger expression of heat shock proteins and other stress-response genes. In the third and final unit (Chapter 6), the efficacy of bivalve polyculture was evaluated using four cultured species: the Eastern oyster (C. virginica), the Atlantic surfclam (S. solidissima), the hard clam (M. mercenaria), and the softshell clam (Mya arenaria). Three particle depletion experiments were conducted to determine if more diverse bivalve assemblages had greater clearance rates than those which were less diverse. Likewise, the effect of species richness on bivalve productivity (growth and survival) was evaluated. When supplied with natural seston, the four-species polyculture demonstrated a significantly greater tank-level clearance rate for particles &lt;25 µm compared to most monocultures. However, nearly all productivity metrics were unaffected by species richness. Overall, this dissertation finds that the surfclam is a good candidate for species diversification in the Northeast, and the species fits well into the region’s established farming framework. Despite the current and future risks that the warming climate poses for the surfclam, this dissertation also finds that selective breeding may be a viable strategy for enhancing the survival of cultured surfclams. Finally, this dissertation provides some of the first evidence for niche complementarity among four cultured bivalves and demonstrates that in non-food limited systems, the focal species can be co-cultured without outcompeting one another. Taken together, this dissertation concludes that ecologically-sound diversification can be achieved spatially, temporally, and genetically in the northeastern United States.