Citation:

Enzor, L., C. Hankins, M. Frazier, E. Moso, S. Raimondo, AND M. Barron. Elevated pCO2 and hypoxia alter the acid-base regulation of developing sheepshead minnows Cyprinodon variegatus. MARINE ECOLOGY PROGRESS SERIES. Inter-Research, Luhe, Germany, 636:157-168, (2020). https://doi.org/10.3354/meps13220

Impact/Purpose:

Estuarine fish are adapted to living in an environment with rapid and frequent changes in temperature, salinity, pH, and dissolved oxygen (DO) levels. While the adverse effects of low dissolved oxygen (hypoxia) on estuarine fish physiology has been well-documented, only recently has the interaction between low DO and elevated pCO2 become a research focus area. Sheepshead minnow, Cyprinodon variegatus, is an estuarine teleost which plays a critical role in estuarine food webs, and is tolerant to a wide array of environmental parameters, making them an ideal model species to study the impacts of projected environmental changes. We explored how the combination of hypoxia (2mg/L) and elevated pCO2 (2000uatm) altered the acid-base equilibrium of the fish as they developed from 24-hour old embryos to juvenile fish. While hypoxia and acidification delayed embryonic hatching, no life-stage was significantly impacted by acidification, hypoxia, or the combination of these stressors. These data indicate that sheepshead minnow are a robust species, and will likely not be impacted by projected environmental changes.

Description:

Lowered dissolved oxygen and pH levels are 2 environmental variables that concomitantly change in an estuarine environment and both are exacerbated by nutrient pollution and subsequent eutrophication. To better understand how estuarine residents compensate for daily fluctuations in these environmental variables, the interactive effects of elevated partial pressure of CO2 ( pCO2) and hypoxia were assessed in developing sheepshead minnows Cyprinodon variegatus using a 2 by 2 factorial design over a 42 d exposure. Embryos were exposed to either acidic ( pCO2: ~2000 µatm), hypoxic (reduced dissolved oxygen, ~2 mg l-1), or combined acidic and hypoxic conditions and monitored for development, hatch rate, and survival. Measurements of anaerobic pathway use, oxidative stress, and acid-base regulatory enzymes were evaluated at 3 life stages (embryo, larva, and juvenile) to discern if and how fish compensate for these stressors during development. The combination of elevated pCO2 and hypoxia delayed hatching in embryos but did not impact survival. Neither elevated pCO2, hypoxia, nor the combination of the stressors elicited an increase in anaerobic metabolic pathways or impacted oxidative stress of juvenile fish. Measurements of enzymes related to acid-base regulation were elevated in all 3 treatments in larval fish. Elevated carbonic anhydrase activity was observed in the multi-stress treatment in embryos and larval fish, but not in juvenile fish. These results show that developing sheepshead minnows can compensate for acidified and hypoxic waters.

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