The vulnerability of red sea urchins to climate change depends on location

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

New findings published on January 20 Scientists are moving forward, suggesting that red sea urchin populations in Southern California may be more sensitive to climate change than those in Northern California. Although southern California sea urchins have already adapted to warmer conditions, researchers suspect that further warming may be more than they can handle.

“Red hedgehogs from the Southern California population were more sensitive to environmental changes than those from Northern California, and we think this is because they were already closer to some sort of thermal threshold.” says Kristy Kroeker, 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 currently a postdoctoral researcher at UC Santa Barbara. “Red sea urchins are an important fishery along our coast, so understanding how they will be affected by climate change is critical,” he said.

The study looked at the effects of three key environmental variables on sea urchin coastal habitat: water temperature, dissolved oxygen and pH (a measure of ocean acidity). Climate change caused by increased carbon dioxide in the atmosphere warms the oceans and reduces oxygen levels in the water, and the increase in carbon dioxide with seawater causes ocean acidification.

According to Kroeker, most studies looking at species adaptation to climate change have focused on one aspect of environmental change, such as ocean warming or acidification. “But these species of concern to us are all placed in environments where there are many variables that will be affected by climate change,” he said.

Using a network of sensors deployed along the coast, the researchers first characterized the current state of kelp forests in 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 dissolved oxygen levels and low pH (near the acid end of the scale). ). Coastal upwelling is 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, both regions will have 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 both regions in tanks outside UCSC’s Long Sea Laboratory, where they could monitor the conditions in each tank.

The experiments exposed sea urchins from 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 adapting to their native environments and increased mortality when reared under different conditions. Southern California sea urchins performed poorly under Northern California conditions and vice versa.

The researchers also exposed the red sea urchins to expected future conditions for their region, based on regional climate projections for the year 2100. These future conditions generally do not coincide with conditions currently measured along the coast.

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

“Although the population of northern California will live in more acidic, low-oxygen conditions in the future, it is the population of southern California that will be most affected,” Kroeker said.

This came as a surprise, he said, because populations in northern California have adapted to seasonal changes in temperature, dissolved oxygen and pH concentration, and with climate change, this variation has been compounded and narrowed, or the “covariance structure” disrupted. . Dissolved oxygen and pH will further decrease, but temperature will rise.

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

The results indicate 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 temperatures unfavorable for red sea urchins.

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

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 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 Effects (ISEEECI) and the California Ocean Conservation Council.

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