Vulnerability of red sea urchins to climate change depends on location

A new study of red sea urchins, a commercially valuable species, has investigated how different populations respond to changes in their environment. Results show that red sea urchin populations in northern and southern California are adapted to their local conditions but differ in their vulnerability to environmental changes expected in the future due to global climate change and ocean acidification. .

The new findings, published on January 20 in Scientists progress, indicate that red sea urchin populations in southern California may be more vulnerable to climate change than those in northern California. Although Southern California sea urchins are already adapted to warmer conditions, researchers suspect that further warming of their environment could be more than they can tolerate.

“Red urchins from the Southern California population were much more sensitive to environmental changes than those from Northern California, and we think that’s likely because they’re already closer to some sort of thermal limit. said lead author Kristy Kroeker, a professor of ecology. and evolutionary biology at UC Santa Cruz.

First author Emily Donham led the study as a graduate student at UCSC and is now a postdoctoral researcher at UC Santa Barbara. “Red sea urchins are an important fishery species along our coast, so understanding how they are likely to be affected by climate change is very important,” she said.

The study looked at the effects of three key environmental variables in the sea urchins’ coastal habitat: water temperature, dissolved oxygen, and pH (a measure of ocean acidification). Climate change driven by increased carbon dioxide in the atmosphere is warming the oceans and reducing oxygen levels in the water, while increased uptake of carbon dioxide by seawater is leading to acidification oceans.

According to Kroeker, most studies looking at the adaptability of species to climate change have focused on one aspect of environmental change, such as ocean warming or acidification. “But all of these species that we are concerned about are embedded in environments with multiple variables that will be affected by climate change,” she said.

Using a network of sensors deployed along the coast, researchers first characterized current conditions in the kelp forests of northern and southern California. There are large differences between the coastal waters of northern and southern California due to the strong seasonal upwelling in the north, which brings to the surface cold deep waters with reduced levels of dissolved oxygen and a Lower pH (closer to the acid end of the scale). Coastal upwelling is much weaker in southern California.

As a result, northern California sea urchin populations are already exposed to more acidic, less oxygenated, and colder conditions than southern California waters. In the future, however, both regions will experience warmer, more acidic, and less oxygenated waters compared to current conditions.

To study the sensitivity of red sea urchins to these changing conditions, the researchers bred juvenile sea urchins from both regions in tanks outside UCSC’s Long Marine Laboratory, where they could control the conditions in each tank.

The experiments exposed the sea urchins of the two populations to the average conditions of each of the two regions for temperature, dissolved oxygen and pH. The results clearly showed that red sea urchin populations are adapted to their native environment and experience increased mortality when reared under different conditions. Southern California sea urchins performed poorly in Northern California conditions, and vice versa.

The researchers also exposed the red sea urchins to expected future conditions for their home regions based on regional climate projections for the year 2100. These future conditions generally do not overlap with the range of conditions currently measured along the coast.

Although mortality increased in populations in both regions under projected future conditions, northern California sea urchins experienced lower mortality and had better body condition than southern California sea urchins.

“Although northern California populations will be in more acidic, low-oxygen conditions in the future, it’s southern California populations that have been much more affected,” Kroeker said.

This was a surprise, she says, because northern California populations are adapted to seasonal changes in which temperature, dissolved oxygen and pH all decline in concert, whereas with climate change this variation narrows coupled, or “covariance structure”, will be broken. . Dissolved oxygen and pH will decrease further, but temperature will increase.

“It breaks down the environmental covariance structure they are adapted to, so our prediction was that it would make them more vulnerable. But that’s not what we found,” Kroeker said.

The results suggest that water temperature is a critical environmental variable for red sea urchins. With warmer temperatures to begin with, southern California coastal waters may not need to warm much further to reach inhospitable temperatures for red sea urchins.

“We shouldn’t assume that a species’ vulnerability to climate change is the same across its range,” Kroeker said. “Each population is adapted to local conditions, and not all populations will react in the same way to global climate change. »

In addition to Donham and Kroeker, co-authors include Iris Flores, Alexis Hooper, and Evan O’Brien of UC Santa Cruz; Kate Vylet and Jan Freiwald of the Reef Check Foundation; and Yuichiro Takeshita at the Monterey Bay Aquarium Research Institute. This work was supported by the UC Institute for the Study of Ecological and Evolutionary Climate Impacts (ISEECI) and the California Ocean Protection Council.

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