The vulnerability of Red Sea urchins to climate change depends on location

A new study of Red sea urchins, a species of commercial value, looked at how different populations respond to changes in their environment. The results show that red sea urchin populations in northern and southern California are adapted to their local conditions but differ in their vulnerability to projected future environmental changes due to global climate change and ocean acidification.

New findings published on January 20 in the Scientists advance, suggest 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 have already adapted to warmer conditions, researchers believe the warming of their environment may be more than they can handle.

“Red hedgehogs from Southern California were more sensitive to environmental changes than those from Northern California, and we think this is likely because they are already closer to some kind of thermal limit,” said lead author Kristi Crocker, professor of ecology and evolutionary biology at UC Santa Cruz. .

First author Emily Dunham led the study as a graduate student at UCSD and is now a postdoctoral researcher at UCSB. “Red sea urchins are an important species for fisheries 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 major environmental variables in sea urchin coastal habitats: water temperature, dissolved oxygen, and pH (a measure of ocean acidity). Climate change caused by an increase in atmospheric carbon dioxide is warming the oceans and reducing oxygen levels in the water, while seawater absorption of carbon dioxide is causing ocean acidification.

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

Using a network of sensors scattered along the coast, the researchers first determined current conditions in kelp forests in northern and southern California. Significant differences exist between the coastal waters of northern and southern California because of the strong seasonal upwelling to the north, which brings to the surface cooler, deep waters with lower levels of dissolved oxygen and a lower pH (closer to the acidic end of the scale). Coastal sewage is much weaker in Southern California.

As a result, sea urchin populations in Northern California are already exposed to conditions that are more acidic, less oxygenated, and cooler than Southern California waters. However, in the future, both regions will see 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 raised juvenile sea urchins from the two regions in tanks outside UCLA’s Long Marine Laboratory, where they could control the conditions in each tank.

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

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The researchers also revealed Red Sea Urchins projected future conditions for their home regions based on regional climate projections for the year 2100. These future conditions do not generally overlap with the set of conditions currently measured along the coast.

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

“Although Northern Californians will be in more acidic conditions with less oxygen in the future, Southern Californians will be hardest hit,” Crocker said.

This was a surprise, she says, because Northern Californians adjust to seasonal changes as temperature, dissolved oxygen, and pH all drop, while with climate change that variability, or “structure heterostructure,” narrows. . The dissolved oxygen and pH will drop further, but the temperature will rise.

“It breaks the ecological heterogeneity structure that they adapt to, so our expectation was that it would make them more vulnerable. But that’s not what we found,” Crocker said.

The results indicate that water temperature is an important environmental variable for red sea urchins. As temperatures begin to get warmer, southern California coastal waters may not need much warming to reach temperatures unsuitable for red sea urchins.

“We should not assume that the vulnerability of species to climate change is the same across their range,” Crocker said. “Each population group adapts to local conditions, and not all populations will react the same way to global climate change.”

In addition to Dunham and Crocker, co-authors include Iris Flores, Alexis Huber, and Evan O’Brien of the University of California, Santa Cruz; Kate Villette and Jan Freywald of the Reef Check Foundation; and Yoichiro Takeshita at the Monterey Bay Aquarium Research Institute. This work was supported by the UCLA Institute for the Study of Environmental and Evolutionary Climate Impacts (ISEECI) and the California Ocean Conservation Council.

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