Near-future extreme temperatures affect physiology, morphology and recruitment of the temperate sponge Crella incrustans

Abstract

Current rates of greenhouse gas emissions are leading to a rapid increase in global temperatures and a greater occurrence of extreme climatic events such as marine heatwaves. In this study, we assessed the effects of thermal conditions predicted to occur within the next 40 years (SSP3-7.0 scenario of IPCC, 2021) on the respiration rate, buoyant weight, morphology and recruitment of the temperate model sponge Crella incrustans. Under predicted average temperatures (+ 2.5 °C, over the local mean), C. incrustans did not show any physiological and morphological changes compared to current conditions. However, when exposed to a simulated marine heatwave (16 days duration and a thermal peak at 22 °C), there was a large increase in sponge respiration rate, significant weight loss resulting from tissue regression, and sponge mortality. The simulated marine heatwave resulted also in a shorter period of recruitment, lower recruitment rate and higher mortality of settlers. Despite the tissue regression, the majority of sponges that survived the extreme temperatures showed respiration rates similar to controls 13 days after the thermal peak, indicating some resilience of C. incrustans to extreme thermal events. Our study shows that marine heatwaves will significantly impact the physiology, morphology, and recruitment of temperate sponges under near-future conditions, but that these sponges are likely to persist in warmer oceans.

Keywords: Climate change; Marine heatwave; Ocean warming; Porifera; Reproduction; Respiration rate.