No maternal or direct effects of ocean acidification on egg hatching in the Arctic copepod Calanus glacialis

Abstract

Widespread ocean acidification (OA) is transforming the chemistry of the global ocean and the Arctic is recognised as the region where this transformation will occur at the fastest rate. Moreover, many Arctic species are considered less capable of tolerating OA due to their lower capacity for acid-base regulation. This inability may put severe restraints on many fundamental functions, such as growth and reproductive investments, which ultimately may result in reduced fitness. However, maternal effects may alleviate severe effects on the offspring rendering them more tolerant to OA. In a highly replicated experiment we studied maternal and direct effects of OA predicted for the Arctic shelf seas on egg hatching time and success in the keystone copepod species Calanus glacialis. We incubated females at present day conditions (pHT 8.0) and year 2100 extreme conditions (pHT 7.5) during oogenesis and subsequently reciprocally transplanted laid eggs between these two conditions. Statistical tests showed no effects of maternal or direct exposure to OA at this level. We hypothesise that C. glacialis may be physiologically adapted to egg production at low pH since oogenesis can also take place at conditions of potentially low haemolymph pH of the mother during hibernation in the deep.

Fig 1. Transplants of eggs among incubation buckets.

For clarity only transplants in one treatment group (High to low pH; HL) are shown. The table shows all transplants for each treatment group. Three flasks with eggs were transplanted along each of the arrows in the figure. In total, each treatment group contained nine transplants.

Fig 2. Cumulative egg hatching during the incubation period.

To enable comparison among flasks holding different initial numbers of eggs, egg counts were calculated as fractions of the number of eggs at the first count. Solid lines show mean predicted values from the Hill regressions on each individual flask. The vertical lines at t = 2 d is inserted as a guide to facilitate visual judgement of differences among treatments.