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

Date Published: February 7, 2018

Publisher: Public Library of Science

Author(s): Peter Thor, Fanny Vermandele, Marie-Helene Carignan, Sarah Jacque, Piero Calosi, Erik V. Thuesen.


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.

Partial Text

Uptake of anthropogenic CO2 is changing the chemistry of the global ocean [1]. When entering the sea, CO2 reacts with water to form carbonic acid, and this ocean acidification (OA) has lowered the global ocean mean surface pH from 8.13 during the pre-industrial age to the present day 8.05. This trend is predicted to continue and current models estimate a further decrease of up to 0.4 pH units by the year 2100 [2–4]. In this respect, the Arctic is a region of specific concern. OA is currently progressing at faster rates in many Arctic regions and is expected to continue to do so [1, 5–7]. This is partly due to rising temperatures generating increasing volumes of sea ice melt water, which holds low H+ buffering capacity [8]. Moreover, while the Arctic Ocean contains only 1% of the global ocean volume, it receives 11% of the global riverine discharge. This discharge not only carries low H+ buffering capacity but also contributes significant loads of terrestrial carbon, which increases CO2 production by promoting heterotrophic microbial respiration [9]. Finally, inflow from the North Atlantic transports increasing amounts of anthropogenic CO2 to the Arctic Ocean [10]. Arctic organisms are therefore the first to face the effects of OA and will continue to experience stronger OA in the future [7].

There were no significant differences in average temperature among the incubation buckets during the incubation period (Table 1; 1-factor PERMANOVA: Pseudo-F5,71 = 0.18, P = 0.98). pHT differed significantly between high and low pH treatments and there were no significant difference among buckets within treatments (1-factor PERMANOVA pair-wise tests: P > 0.05). There were no significant differences in diatom food concentration among buckets (1-factor PERMANOVA: Pseud-F5,59 = 0.29, P = 0.91).

In the study presented here, we did not detect any significant direct or maternally transferred effects of pH levels predicted for the Arctic Ocean in year 2100 on egg hatching success (EHS) or egg hatching timing (Km) of Calanus glacialis eggs.




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