No abstract

Marine heatwaves (MHWs) are increasing in both intensity and frequency against a backdrop of gradual warming associated with climate change. In the context of MHWs, animals are likely to experience sub-lethal rather than lethal effects, defining long-term limits to survival and/or impacting individual and population fitness. We investigated how functional sub-lethal limits track critical thresholds and how this relationship changes with warming rate. To this end, we monitored basic functioning, specifically the ability to right, feed and assimilate energy, as well as oxygen consumption rate in the common Antarctic sea urchin Sterechinus neumayeri. Water temperature in experimental systems was increased at rates of 1, 0.5 and 0.3°C d-1, in line with the characteristics of MHW events previously experienced at the site where the study urchins were collected on the Antarctica Peninsula. Functioning was assessed during the simulation of MHWs, and sub-lethal limits were determined when the rate of functional degradation changed as temperature increased. Results suggest that thermal sensitivity varies between the key biological functions measured, with the ability to right having the highest thermal threshold. Functions deteriorated at lower temperatures when warming was more rapid (1°C d-1), contrary to lethal critical thresholds, which were reached at lower temperatures when warming was slower (0.3°C d-1). MHWs and their impacts extend far beyond Antarctica, and in this context, our analyses indicate that the onset rate of MHWs is critical in determining the ability of an organism to tolerate short-term elevated temperatures.

Ecosystems and their biota operate on cyclic rhythms, often entrained by predictable, small-scale changes in their natural environment. Recording and understanding these rhythms can detangle the effect of human induced shifts in the climate state from natural fluctuations. In this study, we assess long-term patterns of reproductive investment in the Antarctic sea urchin, Sterechinus neumayeri, in relation to changes in the environment to identify drivers of reproductive processes. Polar marine biota are sensitive to small changes in their environment and so serve as a barometer whose responses likely mirror effects that will be seen on a wider global scale in future climate change scenarios. Our results indicate that seasonal reproductive periodicity in the urchin is underpinned by a multiyear trend in reproductive investment beyond and in addition to, the previously reported 18–24 month gametogenic cycle. Our model provides evidence that annual reproductive investment could be regulated by an endogenous rhythm since environmental factors only accounted for a small proportion of the residual variation in gonad index. This research highlights a need for multiyear datasets and the combination of biological time series data with large-scale climate metrics that encapsulate multi-factorial climate state shifts, rather than using single explanatory variables to inform changes in biological processes.