An Absence of Ocean Acidification Impacts on Two Marine Copepods

Copepods are small crustaceans and encompass a major group of secondary producers in the planktonic food web, often serving as a key food source for fish. And in the words of Isari et al. (2015), these organisms “have generally been found resilient to ocean acidification levels projected about a century ahead, so that they appear as potential ‘winners’ under the near-future CO2 emission scenarios.” However, many copepod species remain under-represented in ocean acidification studies. Thus, it was the goal of Isari et al. to expand the knowledge base of copepod responses to reduced levels of seawater pH that are predicted to occur over the coming century.

To accomplish this objective, the team of five researchers conducted a short (5-day) experiment in which they subjected adults of two copepod species (the calanoid Acartia grani and the cyclopoid Oithona davisae) to normal (8.18) and reduced (7.77) pH levels in order to assess the impacts of ocean acidification (OA) on copepod vital rates, including feeding, respiration, egg production and egg hatching success. At a pH value of 7.77, the simulated ocean acidification level is considered to be “at the more pessimistic end of the range of atmospheric CO2 projections.” And what did their experiment reveal?

In the words of the authors, they “did not find evidence of OA effects on the reproductive output (egg production, hatching success) of A. grani or O. davisae, consistent with the numerous studies demonstrating generally high resistance of copepod reproductive performance to the OA projected for the end of the century,” citing the works of Zhang et al. (2011), McConville et al. (2013), Vehmaa et al. (2013), Zervoudaki et al. (2014) and Pedersen et al. (2014). Additionally, they found no differences among pH treatments in copepod respiration or feeding activity for either species. As a result, Isari et al. say their study “shows neither energy constraints nor decrease in fitness components for two representative species, of major groups of marine planktonic copepods (i.e. Calanoida and Cyclopoida), incubated in the OA scenario projected for 2100.” Thus, this study adds to the growing body of evidence that copepods will not be harmed by, or may even benefit from, even the worst-case projections of future ocean acidification.

 

References

Isari, S., Zervoudake, S., Saiz, E., Pelejero, C. and Peters, J. 2015. Copepod vital rates under CO2-induced acidification: a calanoid species and a cyclopoid species under short-term exposures. Journal of Plankton Research 37: 912-922.

McConville, K., Halsband, C., Fileman, E.S., Somerfield, P.J., Findlay, H.S. and Spicer, J.I. 2013. Effects of elevated CO2 on the reproduction of two calanoid copepods. Marine Pollution Bulletin 73: 428-434.

Pedersen, S.A., Håkedal, O.J., Salaberria, I., Tagliati, A., Gustavson, L.M., Jenssen, B.M., Olsen, A.J. and Altin, D. 2014. Multigenerational exposure to ocean acidification during food limitation reveals consequences for copepod scope for growth and vital rates. Environmental Science & Technology 48: 12,275-12,284.

Vehmaa, A., Hogfors, H., Gorokhova, E., Brutemark, A., Holmborn, T. and Engström-Öst, J. 2013. Projected marine climate change: Effects on copepod oxidative status and reproduction. Ecology and Evolution 3: 4548-4557.

Zervoudaki, S., Frangoulis, C., Giannoudi, L. and Krasakopoulou, E. 2014. Effects of low pH and raised temperature on egg production, hatching and metabolic rates of a Mediterranean copepod species (Acartia clausi) under oligotrophic conditions. Mediterranean Marine Science 15: 74-83.

Zhang, D., Li, S., Wang, G. and Guo, D. 2011. Impacts of CO2-driven seawater acidification on survival, egg production rate and hatching success of four marine copepods. Acta Oceanologica Sinica 30: 86-94.