The response of two ecologically important Antarctic invertebrates (Sterechinus neumayeri and Parborlasia corrugatus) to reduced seawater pH: effects on fertilisation and embryonic development |
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Authors: | Jessica A Ericson Miles D Lamare Simon A Morley Mike F Barker |
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Institution: | (1) Department of Marine Science, University of Otago, PO Box 56, Dunedin, New Zealand;(2) British Antarctic Survey, NERC, High Cross, Madingley Road, Cambridge, CB3 0ET, UK; |
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Abstract: | Ocean acidification, or the lowering of seawater pH, is caused by sequestration of atmospheric CO2 into the oceans. This study investigated the effects of present-day pH 8.0, predicted ocean surface pH for the years 2100
and 2300 (pH 7.7 and pH 7.3, respectively) and an extreme pH (pH 7.0) on fertilisation and embryogenesis in the Antarctic
nemertean worm Parborlasia corrugatus and sea urchin Sterechinus neumayeri. Fertilisation success was not affected by pH in P. corrugatus across a range of sperm concentrations. Fertilisation success in S. neumayeri declined significantly in pH 7.0 and 7.3 seawater, but only at a low sperm concentration. Seawater pH had no effect on the
rate of egg cleavage in S. neumayeri, or the proportion of abnormal embryos 1-day post-fertilisation. P. corrugatus embryogenesis was also relatively robust to pH changes, with a significant effect detected only when the seawater pH was
decreased to 7.0. While fertilisation and early cell division were relatively robust, later development through to the gastrula
was sensitive to pH. In S. neumayeri, an effect of pH on development was evident by the gastrula stage, while there were significantly more abnormal P. corrugatus embryos in pH 7.0 up to the blastula stage, and in pH 7.0 and pH 7.3 at the coeloblastula stage. Our results are similar
to the observations on other marine invertebrate species where fertilisation and early embryonic development are generally
robust to lowered seawater pH, while the older coeloblastula and gastrula stages are more responsive. We also found no evidence
to suggest that Antarctic species are more adversely affected by lower seawater pH compared with the findings for non-Antarctic
counterparts. We conclude that in the two species we examined, near-future decreases in pH (decreases of ≈0.3–0.5 pH units)
may not have a significant effect on fertilisation and early embryogenesis, while predicted longer term decreases (decreases
of ≈0.7–0.77 pH units) could reduce fertilisation success in S. neumayeri if sperm concentrations are low and may increase abnormalities in P. corrugatus during later embryogenesis. |
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