How Red Sea Urchin Populations in Northern and Southern California Are Adapted To Different Environmental Changes

A new study of red sea urchins, a commercially valuable species, looked at how different populations react to environmental changes.

The findings show that red sea urchin populations in Northern and Southern California are well adapted to their local environments, but differ in their vulnerability to future environmental changes caused by global climate change and ocean acidification.

Southern California's red sea urchin populations may be more vulnerable to climate change than those in Northern California.

Vulnerability of red sea urchins to climate change

(Photo : XAVIER LEOTY/AFP via Getty Images)

The new findings, published in Science Advances on January 20, suggest that red sea urchin populations in Southern California may be more vulnerable to climate change than those in Northern California, as per ScienceDaily.

Although sea urchins in Southern California are already adapted to warmer temperatures, the researchers believe that further warming of their environment may be too much for them.

The Southern California population of red sea urchins was much more sensitive to environmental changes than the Northern California population, and they believe this is because they are already closer to some kind of thermal limit, according to senior author Kristy Kroeker, professor of ecology and evolutionary biology at UC Santa Cruz.

Emily Donham, who led the study as a UCSC graduate student and is now a postdoctoral scholar at UC Santa Barbara, is the first author.

Red sea urchins are an important fishery species along our coast, so understanding how climate change will affect them is critical.

The researchers investigated the effects of three key environmental variables in the coastal habitat of sea urchins: water temperature, dissolved oxygen, and pH. (a measure of ocean acidification).

Climate change caused by increased carbon dioxide levels in the atmosphere warms the oceans and reduces oxygen levels in the water, while increased carbon dioxide absorption by seawater causes ocean acidification.

According to Kroeker, most studies on species adaptation to climate change have concentrated on a single aspect of environmental change, such as warming or ocean acidification.

"However, all of these species that we are concerned about are embedded in environments that have multiple variables that will be impacted by climate change," she explained.

The researchers first characterized the current conditions in Northern and Southern California kelp forests using a network of sensors deployed along the coast.

Because of strong seasonal upwelling in the north, which brings cold deep waters with low dissolved oxygen and pH to the surface, there are significant differences between the coastal waters of Northern and Southern California (closer to the acidic end of the scale). Southern California has much weaker coastal upwelling.

As a result, Northern California sea urchin populations are already subjected to more acidic, less oxygenated, and colder conditions than Southern California waters.

In the future, however, both regions will have warmer, more acidic, and less oxygenated waters than they do now.

The researchers grew juvenile sea urchins from the two regions in outdoor tanks at UCSC's Long Marine Laboratory, where they could control the conditions in each tank, to study the sensitivity of red sea urchins to changing conditions.

The experiments exposed sea urchins from both populations to the average conditions for temperature, dissolved oxygen, and pH in each of the two regions, and the results clearly showed that red sea urchin populations are adapted to their home environments and experience increased mortality when raised in different conditions. Under Northern California conditions, Southern California sea urchins fared poorly, and vice versa.

Red sea urchins were also exposed to future conditions expected for their home regions based on regional climate projections for the year 2100.

These future conditions do not generally overlap with the current range of conditions measured along the coast.

Despite the fact that mortality increased in both populations under the projected future conditions, Northern California sea urchins had lower mortality and better body condition than Southern California sea urchins

Life history of urchins

The spawning of red sea urchins peaks in southern British Columbia between June and September. The fertilized eggs hatch into planktonic larvae before settling on the seafloor and maturing into tiny juvenile sea urchins, as per Marine Bio.

This population replenishment, or "recruitment," appears to occur annually in local waters. New recruits must hide from predators, and many seek refuge under the spines of adult sea urchins with test diameters of 9.5 cm or greater.

Young sea urchins emerge from their shelter when they are about 4 cm in diameter and forage freely on the rocky sea floor.

Adulthood is reached at about 5 cm in diameter, and a legal size of 10 cm is reached in 4-5 years. Their life span is reported to be more than 100 years.