Abstract
Multiple changes to the marine environment under climate change can have additive or interactive (antagonistic or synergistic) effects on marine organisms. Prompted by observations of anomalously warm sea temperatures and low chlorophyll concentrations during the 2013–2016 warm “Blob” event in the Northeast Pacific Ocean, we examined the combined effects of thermal stress and a shift in food resources on the development of a larval echinoid (Strongylocentrotus droebachiensis) in the laboratory. A high concentration of phytoplankton yielded faster echinus rudiment development at warm versus historical temperature, indicating a mitigating effect of abundant food on thermal stress; however, low phytoplankton concentration or a shift in diet to suspended kelp detritus, yielded slow development and high mortality at warm temperature. The results indicate a synergistic negative effect of thermal stress and altered food resources on larvae of a keystone marine species.
Highlights
Under climate change, extreme events such as heatwaves are predicted to increase in frequency and intensity[1]
Combined stressors of warm sea temperature and low phytoplankton concentration may impact the planktonic larval stage of benthic marine invertebrates, such as sea urchins, that rely on phytoplankton as a source of food[5]
On both sides of the North Atlantic and in the Northeast Pacific, recruitment pulses of green sea urchins Strongylocentrotus droebachiensis into kelp beds have led to destructive grazing of kelps, and ecosystem phase shifts from kelp beds to sea urchin barrens[6,7,8,9,10]
Summary
Age (covariate), indicating heterogeneity of slopes and an interactive effect of treatments on rudiment development rates (Supplementary Table S1). Slopes did not differ among low ration food treatments at 9 versus 17 °C (Fig. 3) These results indicate that a high concentration of phytoplankton mitigated a negative effect of warm temperature on larval development (antagonistic effect), while a high concentration of kelp detritus exacerbated the negative effect of warm temperature on larval development (synergistic effect). The presence of deleterious microbes could have contributed to slow growth of larvae due to the energetic cost of mounting an immune response This hypothesis assumes that deleterious microbes were most abundant in the warm, high ration kelp detritus treatment due to a higher dosage of microbes (i.e. greater volume of kelp detritus added as compared to the low ration diet) and faster growth of microbes at warm versus historical temperature. All other data analyzed are included in this article (and its supplementary information files)
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