Noncalcifying larvae in a changing ocean: warming, not acidification/hypercapnia, is the dominant stressor on development of the sea star Meridiastra calcar

Abstract

Climate change driven ocean warming and acidification is potentially detrimental to the sensitive planktonic life stages of benthic marine invertebrates. Research has focused on the effects of acidification on calcifying larvae with a paucity of data on species with alternate developmental strategies and on the interactive effects of warming and acidification. To determine the impact of climate change on a conspicuous component of the intertidal fauna of southeast Australia, the development of the noncalcifying lecithotrophic larvae of the sea star Meridiastra calcar was investigated in the setting of predicted ocean warming (+2 to 4°C) and acidification (À0.4 to 0.6 pH units) for 2100 and beyond in all combinations of stressors. Temperature and pH were monitored in the habitat of M. calcar to place experiments in context with current environmental conditions. There was no effect of temperature or pH on cleavage stage embryos but later development (gastrula-larvae) was negatively effected by a +2 to 4°C warming and there was a negative effect of À0.6 pH units on embryos reaching the hatched gastrula stage. Mortality and abnormal development in larvae increased significantly even with +2°C warming and larval growth was impaired at +4°C. For the range of temperature and pH conditions tested, there were no interactive effects of stressors across all stages monitored. For M. calcar, warming not acidification was the dominant stressor. A regression model incorporating data from this study and projected increasing SST for the region suggests an increase in larval mortality to 70% for M. calcar by 2100 in the absence of acclimation and adaptation. The broad distribution of this species in eastern Australia encompassing subtropical to cold temperate thermal regimes provides the possibility that local M. calcar populations may be sustained in a warming world through poleward migration of thermotolerant propagules, facilitated by the strong southward flow of the East Australian Current.

The stunting effect of a high CO2ocean on calcification and development in sea urchin larvae, a synthesis from the tropics to the poles

“…We analysed data on arm length prior to commencement of feeding because after food is introduced to sea urchin larval cultures, comparisons between studies are confounded by the natural phenotypic plasticity in arm growth due to a feedback mechanism linking nutritive rstb.royalsocietypublishing.org Phil Trans R Soc B 368: 20120439 environment (food levels and larval density) and arm length, the expression of which differs among echinoid families [40,41]. Most studies report pH on the pH NIST (National Institute of Standards and Technology) scale, which is approximately 0.1 units lower than the pH t (total) scale ( [69], see also, [26,58]). To compare all data on the NIST scale, we added 0.1 pH units to the pH t values provided by studies that used this scale.…”

“…For the tropical sand dollar A. placenta, larval size increases with warming, but as the boundary of optimal temperature for development is approached and exceeded larvae are smaller [101]. For asteroid brachiolaria, near-future warming also stunted larval growth [26]. Understanding the potential interactive effect of concurrent ocean acidification and warming remains a significant challenge.…”

“…Thus far, the interactive effects of near-future ocean warming and acidification, on marine invertebrate development have been investigated for 23 species (three corals, nine molluscs, six echinoderms and five crustaceans) including three sea urchin species [67]. In several studies, near-future warming, not acidification, is the more important stressor, especially with regard to survivorship of early embryos [26,102]. For those embryos that develop through the early bottleneck of mortality to reach the larval stage, the effects of simultaneous exposure to warming and acidification differ depending on species and stressor levels used [67].…”

“…For instance, owing to natural variability in habitat temperature and pH, animals living in intertidal and estuarine environments may have some resilience to increased temperature and/or acidification [21,22,25,26,[30][31][32]. In these habitats, seawater pH fluctuates markedly in association with diurnal cycles of respiration and photosynthesis (figure 1).…”

Temperature modulates the response of the thermophilous sea urchin Arbacia lixula early life stages to CO2-driven acidification

“…Only 3 studies studied the combination between warming and acidification on echinoderm larvae. In seastar Meridiastra calcar larval growth rate decreased while temperature increased although there was not any effect from acidification treatment (Nguyen et al, 2012). Based on the theoretical framework developed by Pörtner and Farrell (2008) it was predicted that (i) response to ocean acidification is modulated by temperature and, (ii) ocean acidification can only drive negative response in animals.…”