A new study shows that tropical sea urchins are vulnerable to global warming. Sea urchin eggs and larvae may not be able to survive even a small temperature increase. The findings are in a paper just published in the journal Ecology and Evolution.
Sea urchins are spiny, aquatic invertebrates that graze on algae. Their spines protect them from some predators but they’re a major food source for animals such as otters, eels, and crabs. Sea urchin offspring are tiny, free-floating larvae that barely resemble their adult forms. While sea urchin adults may be able to tolerate temperature changes, the eggs and larvae are more sensitive to water conditions.
A team of researchers studied green sea urchins (Lytechinus variegatus) at the Smithsonian Tropical Research Institute. They exposed different life stages to high temperatures to determine what the urchins could tolerate. Adult urchins tolerated temperatures of up to 34.8°C but the other life stages were much more vulnerable. Sea urchin larvae did poorly at temperatures above 30.5°C, with many dying or showing signs of improper growth. They were not able to survive chronic exposure to temperatures above 32.3°C. These temperatures are not much higher than the current temperature range of their home in Bocas del Toro, Panama. The lagoons in the area already experience temperatures from 27°C to 29°C.
As temperatures rise due to climate change, sea urchins may be in trouble. While the adults can handle slightly higher temperatures, their larval forms are much more sensitive. Green sea urchin larvae were negatively impacted when temperatures were raised by just a few degrees compared to their natural habitat. According to climate change models, the lagoons will reach fatal temperatures by 2084. The loss of sea urchins could damage the local ecosystem. Urchins are major predators of algae; without them, algae can take over and smother other forms of marine life. The authors are now investigating how other urchin species deal with heat stress.
Rachel Collin et al. The sea urchin lives close to the upper thermal limit for early development in a tropical lagoon. Ecology and Evolution (2016).