Effects Of Acidification And Salinity On Callinectes Sapidus, Mercenaria Mercenaria, And Their Interactions

Ocean acidification (OA) coupled with other stressors, will be detrimental at the species and ecosystem levels. Decreased carbonate ion concentrations negatively impact calcifying species, yet the combined effects of OA and other stressors are less well known, and many studies disregard species interactions. Multi-species studies involving OA and other stressors are crucial to comprehend the full threat of OA. Understanding how OA interacts with other stressors to affect species responses is necessary for future management of exploited species in an altered ecosystem. The objectives of my study were to assess: 1) the effects of long-term exposure to decreased pH and salinity on juvenile blue crab (Callinectes sapidus) carapace strength and pinch force and juvenile hard clam (Mercenaria mercenaria) armor and growth; and 2) the blue crab and hard clam predator-prey interactions under low pH and salinity via filmed mesocosm trials. In 2018 and 2019, I held juvenile blue crab (n = 24–40; 50–80 mm carapace width) and juvenile hard clams (n = 112; 10–15 mm shell length) in mesocosms with crossed pH and salinity treatments for 10 – 11 weeks. I regularly monitored water quality and chemistry and measured clams weekly. After treatment exposure, I assessed crab carapace and claw strength using force meters and imaged clam shells using a scanning electron microscope (SEM) for shell structure and ridge rugosity. In 2018, crab carapace strength increased with size, decreased with treatment exposure time, and was overall stronger after exposure to low pH. In 2019, crab carapace strength was weakest in the low-pH, high-salinity treatment and strongest in the low-pH, low-salinity treatment. In high-pH treatments, carapace strength was similar regardless of salinity. Claw pinch force also increased with size but was weaker in low-pH, in both 2018 and 2019. Moreover, male crabs in 2019 had stronger pinch force than females. Clam growth was negatively impacted by low pH in both years; however, salinity had a more negative impact in 2019 than in 2018. Clam survival followed a similar trend in both years, with survival being lowest in the low-pH, low-salinity treatment and highest in the control treatment. Deterioration of clam shell structure and ridge rugosity (indicative of damage) were also correlated, as both were greatest in the low-pH, low-salinity treatment and lowest in the control treatment. Finally, in 2019, filmed predator-prey mesocosm trials assessed the interaction between blue crabs and hard clams after treatment exposure. Low sample sizes precluded statistical analyses, but trends indicated there was no alteration in the predator-prey relationship under multiple stressors