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The Resilience of Sea Urchin Larval Settlement Under Ocean Acidification

Paper Reviewed
Espinel-Velasco, N., Agüera, A., Lamare, M. 2020. Sea urchin larvae show resilience to ocean acidification at the time of settlement and metamorphosis. Marine Environmental Research 159: 104977.

Introducing the subject of their analysis, Espinel-Velasco et al. (2020) write that although many experiments to date have examined the potential impacts of so-called ocean acidification on marine life, "little is known, however, on how ocean acidification may affect larval settlement processes in marine invertebrates, and the mechanisms that might drive it." And so it was that this team of three researchers set out to determine "whether ocean acidification 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."

To accomplish their objective Espinel-Velasco et al. conducted four separate experiments. In the first, they exposed competent larvae to either bare rocks or rocks covered with crustose coralline alga (CCA) under three seawater pH treatments (pH of 7.7, 7.9 or 8.1) in order to study larval substrate preference. In the next two experiments they exposed larvae to six seawater pH levels (from a pH range of 7.0 to 8.1) at the time of settlement to assess the direct effects of ocean acidification, and in the final experiment they exposed competent larvae to CCA settlement substrates that had previously been exposed to reduced seawater pH for 28 days.

In discussing the outcome of their work, the authors report the following key findings: (1) "the range of experiments performed here showed no indication of an influence of reduced seawater pH on the settlement and metamorphosis in E. chloroticus larvae," (2) "our experiments did not detect any effects of ocean acidification on the larval settlement that would be consistent with reduced seawater pH altering the physiology or sensory capacity of the larvae in a way that influences their settlement behavior," and (3) "we found no indication that short-term exposure of CCAs to reduced pH altered the larval settlement success in E. chloroticus."

Commenting on these findings -- or rather the lack thereof -- Espinel-Velasco et al. conclude "our results indicate that E. chloroticus larvae reared under laboratory conditions are resilient to reduced seawater pH levels at settlement (direct effects), even at levels beyond the future predictions of reductions in ocean pH (i.e. pH < 7.6)." Consequently, it is highly likely that E. chloroticus will remain the key ecological, economic and culturally important species to New Zealand in the future that it is today.

Posted 16 October 2020