Sea urchin larvae show resilience to ocean acidification at the time of settlement and metamorphosis

Highlights

• Settlement success in Evechinus chloroticus larvae was unaffected when presented with a range of reduced seawater pH (pH 7.0 to ambient) at the time of settlement (no direct effects).

• When presented with crustose coralline algae (CCA) pre-conditioned at either ambient pH or reduced pH 7.7 for 28 days (no indirect effects) at the time of settlement, larval settlement success in E. chloroticus remained unaltered.

• E. chloroticus larvae did not lose their ability to recognize their preferred settlement substrate when exposed to reduced seawater pH at the time of settlement.

• No interactions were observed between the direct (seawater pH) and indirect (preconditioned substrates) effects of reduced pH on E. choroticus settlement success.

Abstract

Extensive research has shown that the early life stages of marine organisms are sensitive to ocean acidification (OA). Less is known, however, on whether larval settlement and metamorphosis may be affected, or by which mechanisms. These are key processes in the life cycle of most marine benthic organisms, since they mark the transition between the free swimming larval stage to the benthic life. We investigated whether OA could affect the larval settlement success of the sea urchin Evechinus chloroticus, a key coastal species with ecological, economic and cultural importance in New Zealand. We performed four settlement experiments to test whether reduced seawater pH (ranging from 8.1 to 7.0, at an interval of ∼0.2 pH units) alters larval settlement and metamorphosis success. Our results show that settlement success was not significantly reduced when the larvae were exposed to a range of reduced seawater pH treatments (8.1–7.0) at time of settlement (direct effects). Similarly, when presented with crustose coralline algae (CCA) pre-conditioned in different seawater pH of either pH 8.1 or 7.7 for 28 days, larval settlement success remained unaltered (indirect effects). We conclude that competent larvae in this species are resilient to OA at time of settlement. Further research on a range of taxa that vary in settlement selectivity and behaviour is needed in order to fully understand the effects of OA on the life cycle of marine invertebrates and the consequences it might have for future coastal marine ecosystems.

Espinel-Velasco N., Agüera A. & Lamare M., in press. Sea urchin larvae show resilience to ocean acidification at the time of settlement and metamorphosis. Marine Environmental Research. Article (subscription required).

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