Seawater carbonate chemistry and development and growth in early‑stage larvae of the endemic New Zealand sea urchin, Evechinus chloroticus

Under the ocean acidification (OA) conditions predicted for 2100, the larval stages of temperate sea urchins are smaller, with reduced and abnormal skeleton and changes in metabolic rate. Here, we measure the impact of near-future and long-term predictions of atmospheric pCO2 levels on the early development of the echinometrid sea urchin Evechinus chloroticus using single male:female crosses, effect sizes and a within-study meta-analysis. Using the developmental signpost of the 16-cell stage, we show a mean delay of 5.11 min at pH 7.7 and 11.85 min at pH 7.5, which may have flow-on effects to later embryo and larval stages. Echinopluteus larvae raised in OA conditions (pH 7.7, 7.5) were 5–10% smaller in body length and 10–12% smaller in arm length than controls. Metabolic rate was highly variable between single male:female crosses—increasing in some crosses, decreasing in others—with a non-significant effect size in the meta-analysis. Preliminary experiments suggest that metabolic rate changes may be impacted by loss of mitochondrial function at low pH. Single male:female crosses showed variable OA responses in all measurements, suggesting that when assessing the population-level impacts of OA on early development of sea urchins there is a need to include high levels of biological replication.