A scoping review on the ecophysiology of the hard clam, Mercenaria mercenaria

ABSTRACT In this scoping review, we synthesize information available on the physiological ecology of the hard clam (Mercenaria spp.). This review builds on chapters within the Biology of the Hard Clam, summarizing research conducted in the 25 years since publication, and broadens the scope to include all physiological responses to environmental stressors. This comprehensive literature review was conducted to determine the effects of environmental stress on the physiological ecology of Mercenaria mercenaria and M. campechiensis to improve restoration efforts, our understanding of natural populations under future climate scenarios, and aquaculture. We searched Scopus, Web of Science Core Collection, ProQuest Dissertations & Theses Global, ProQuest Science & Technology Database Collection, Google Scholar and articles from the National Oceanic and Atmospheric Administration (NOAA) website based on target keywords related to physiological responses and environmental parameters of interest. Our search identified 2,406 potential studies that were then screened by title and abstract, then full text to determine eligibility based on inclusion and exclusion criteria. Ultimately, 219 papers were synthesized that evaluated the response of hard clams to temperature, food availability, pH, dissolved oxygen, salinity, nutrients, turbidity and multiple stressors. The individual response was quantified based on survival, growth, metabolism, reproduction, feeding or behaviour. Most research focused on the effects of temperature and food on the northern quahog, Mercenaria mercenaria, with an emphasis on growth and survival of larger individuals. A paucity of research exists on the southern quahog and early life stages of hard clams, as well as the impacts of environmental stress on reproduction, metabolism and behaviour. As many of these parameters contribute to the ecosystem services provided by hard clam, filling the research gaps identified in this review will improve hard clam restoration efforts, aquaculture and our understanding of the physiological capacity of these congeners in modified habitats.