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Ocean Acidification Effects on Copepod Egg Hatching Success

Paper Reviewed
Preziosi, B.M., Runge, J.A., Christensen, J.P. and Jones, R.J. 2017. Effects of pH and temperature on egg hatching success of the marine planktonic copepod, Calanus finmarchicus. Marine Biology 164: 218, doi: 10.1007/s00227-017-3243-5.

Calanus finmarchicus is a planktonic copepod that predominately inhabits waters of the northern North Atlantic Ocean. As a species, it is important to the food web, transferring energy from primary producers to higher tropic levels.

A number of researchers have examined the impacts of potential climate change on C. finmarchicus. Multiple studies have separately investigated the impacts of rising temperature or ocean acidification (reduction in seawater pH) on this marine species. However, few have studied the interactive effects of both warming temperature and a reduction in seawater pH.

Seeking to fill this data void, Preziosi et al. (2017) collected C. finmarchicus females at the Coastal Maine Time Series Station (43.75°N, 69.50°W, 110 m depth) and returned them to the Darling Marine Center of Walpole, Maine (USA). There, under controlled environment conditions, they conducted a study to determine the impacts of ocean acidification and temperature on the hatching success of C. finmarchicus eggs. Temperature treatments included current (3.5, 6.0 °C) and elevated (15.0 °C) habitat temperatures, while seawater pH treatments included a range of values from normal (8.0) to extremely severe conditions of ocean acidification (6.6).

Results of the experiment revealed that C. finmarchicus egg hatching success was unaffected by pH in both the 3.5 and 6.0 °C temperature treatments. At the 15.0 °C treatment, two of the nine pH treatments were significantly different from ambient conditions, the 7.0 and 6.8 treatments. However, Preziosi et al. were quick to point out that eggs in the lower 6.6 pH treatment experienced a hatching success that was not significantly different from that observed under ambient seawater conditions, suggesting that the 6.8 and 7.0 treatment results were anomalous, potentially caused by the fact that the eggs in these two treatments came from females immediately after their capture from the wild, whereas eggs in other pH treatments were from well-fed laboratory-acclimated females. Thus, Preziosi et al. hypothesize that parental history and possibly maternal provisioning influenced the egg hatching differences observed in the two anomalous treatments.

Notwithstanding these anomalies, the team of four researchers conclude that "consistent with previous studies of C. finmarchicus, our results indicate no effect on hatching success of eggs of C. finmarchicus at pH levels well below those predicted for surface waters and temperatures within its normal habitat range." And that is welcomed news with respect to the future well-being of this northern North Atlantic Ocean food web.

Posted 1 June 2018