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Copepod Response to Ocean Acidification and Salinity Stress

Paper Reviewed
Hemraj, D.A., Allais, L. and Leterme, S.C. 2017. A combination of salinity and pH affects the recruitment of Gladioferens pectinatus (Brady) (Copepoda; Calanoida). Limnology and Oceanography 62: 1799-1809.

Gladioferens pectinatus is a marine copepod species commonly found in estuaries across south-eastern Australia and New Zealand. As an inhabitor of such environments, G. pectinatus is frequently subjected to variations in salinity and pH. Yet, to date, there have been no studies exploring the reproductive response of G. pectinatus to these two variables. Thus, it was the objective of Hemraj et al. (2017) to investigate the combined impact of changes in salinity and pH on several reproductive parameters of this euryhaline copepod species, including brood size, embryonic development, hatching success, sex ratio, mortality rate, development time and percent of nauplii reaching adulthood.

In accomplishing their design, the scientists cultured breeding pairs of adult copepods at two salinities (2 and 10) and four pH levels (7.77, 7.51, 7.29 and 7.18 in the salinity 2 treatment and 8.09, 7.86, 7.68 and 7.41 in the salinity 10 treatment). Once the female had egg sacs, the male was removed and after the last eggs were hatched the female was removed. The experiment concluded when all copepods reached adulthood.

With respect to their findings, Hemraj et al. report they observed "no impairment in the brood size, embryonic development time and hatching success under low pH levels at either salinities." Rates of mortality did not vary by pH in the two salinity treatments either. Neither were there any significant differences among mean development time and stage durations for nauplii and copepodites. However, the percent of nauplii that reached adulthood declined at low pH in the salinity 2 treatment, but was not affected by pH at salinity 10.

In light of the above findings, it is clear that G. pectinatus "did not show any major impairment in reproduction and development when exposed to low pH" when grown at salinity 10; and it was mostly indifferent to changes in pH at salinity 2. Consequently, it would appear that, as stated by the authors, "resilience and phenotypic plasticity highly influence the ability of different copepod species and populations to reproduce and grow under stressful combinations of environmental parameters," including reduced salinity and pH.

Posted 7 February 2018