Sea urchin’s secret to surviving marine heatwaves

10 August 2022

Global ocean temperatures are increasing due to climate change, exposing ecosystems to extreme temperatures called marine heatwaves, which can increase the temperature of marine waters by 5°C higher than normal. These heatwaves can last several months and cause devastating effects on marine organisms.

Dr Bayden Russell from The Swire Institute of Marine Science and The University of Hong Kong, along with his research group, experimentally assessed whether adult sea urchins (Heliocidaris erythrogramma) that are exposed to marine heatwaves could pass beneficial protective mechanisms onto their offspring, thus ensuring the survival of the next generation. The findings have been published in Global Change Biology.

Sea urchins are both economically and ecologically valuable. They maintain the structure and function of benthic marine ecosystems by eating algae that would otherwise take over and make the ecosystem less biodiverse. This role is particularly important in ecosystems stressed by human activities like nutrient pollution or marine heatwaves, which benefit fast-growing algae that replace coral reefs or kelp forests. Therefore, the continued survival of sea urchins under global heating is key to the continued function of many marine ecosystems.

This current research exposed adult sea urchins to different strengths of marine heatwaves and then spawned the adults under these conditions. The offspring were then reared across a range of temperatures, and their development was tracked to assess for carryover effects from the parents to their offspring. Surprisingly, heatwave-conditioned parents produced faster growing, larger and more heat-tolerant offspring. If heatwaves continued, however, there was high mortality in offspring, showing that these carryover effects may not remain effective throughout the development and growth of juvenile urchins.

"If a marine heatwave occurs at any time during the spawning period of the urchins, these carryover effects could lead to increased survival of the juveniles under what would normally be stressful temperatures. But, if the heatwave continues throughout the larval development, these short-term physiological responses may lead to higher mortality and ultimately reduce the survival of the next generation," said Dr Jay Minuti, postdoctoral researcher at The University of Hong Kong’s Swire Institute of Marine Science.

Therefore, as these types of extreme events become more frequent and intense under climate change, the beneficial carryover effects of parental conditioning to marine heatwaves will only protect the more sensitive juvenile stage and enhance survival if ocean conditions return promptly to normal temperatures.

"These findings are key for our understanding of what some marine ecosystems might look like under climate change," said Dr Russell. “Unfortunately, it is clear that the only way to stop heatwaves from becoming worse is to reduce the effects of climate change by reducing carbon emissions. If we don’t, then it is becoming clear that heatwaves will devastate marine ecosystems which are important for human society."