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Pacific Northwest ecosystems are being tested by climate change

Over a 15-year period that concluded in 2020, the rocky shores of the Pacific Northwest underwent significant ecological changes. This time frame encompassed both a marine heat wave due to climate change and a devastating sea star wasting disease epidemic.

Researchers from Oregon State University have observed a dramatic shift in the composition of species along these shores, indicating potential vulnerabilities to ongoing climate fluctuations.

Ecosystems of the Pacific Northwest

The ecosystems of the Pacific Northwest are rich and diverse. This region includes dense forests, fertile valleys, and diverse marine environments.

Coastal forests, dominated by towering conifers like Douglas fir and western hemlock, provide habitat for numerous species, including the endangered spotted owl and marbled murrelet. The inland areas feature rivers and streams crucial for salmon runs, which in turn support predators such as bears and eagles.

In the marine environment, the Pacific Northwest is home to vibrant kelp forests, seagrass beds, and estuaries teeming with life. These habitats support a variety of marine mammals, including orcas, sea otters, and seals.

The region also faces challenges from climate change, pollution, and overfishing, which threaten its biodiversity. Conservation efforts are crucial for maintaining these ecosystems, ensuring that they continue to thrive and support the myriad of species that depend on them.

Climate change shifts in the Pacific Northwest

A recent study conducted in the region focused on various locations across Oregon and California.

The findings revealed that sessile invertebrates such as mussels and barnacles have increased in prevalence. In contrast, seaweed species, including kelps, have seen a decline.

This shift occurred after the significant loss of adult ochre sea stars, a key predator in these ecosystems, and during a period of unusually high water temperatures.

Zechariah Meunier, a doctoral graduate and the lead author of the study, explained the critical role of sea stars in this ecosystem.

“Sea stars are like the wolves of rocky shores because they normally eat enough mussels and barnacles to prevent these invertebrates from dominating the lower elevation areas. Many kelps did not survive the thermal stress during the heat wave,” noted Meunier.

Climate changes and resilience on Pacific shores

The end of the epidemic and the subsequent cooling of ocean temperatures did not lead to a recovery of the initial community structures.

This persistent change suggests a troubling low resilience among these communities to both temperature changes and alterations in predator populations.

Meunier expressed concerns over the long-term implications: “Diminishing resilience may lead to degraded rocky shore communities under future climate conditions.”

“And a warming climate will make restoring baseline conditions more difficult – regime shifts to degraded states are likely to last longer and put community structure and ecosystem function at risk.”

Broader impacts of climate change

The health of marine ecosystems is crucial, not only for biodiversity but also for their broader environmental roles.

The ocean, for instance, produces half of the oxygen we breathe and absorbs a significant portion of the carbon dioxide emitted annually.

However, marine ecosystems are now facing an onslaught of stressors, including harmful algal blooms, ocean acidification, and hypoxia. These challenges often exacerbate one another, leading to significant damage to marine habitats and loss of species diversity.

When these stressors become particularly severe, they can cause habitat transitions or regime shifts, such as the shift from kelp forests to urchin barrens observed in the Pacific Ocean.

“A classic example of multiple stressors causing a regime shift is the transition from kelp forests to urchin barrens in the Pacific Ocean off the west coast of North America,” explained Meunier.

This transition has been influenced by factors including a marine heat wave, urchin overgrazing, the historical removal of the sea otter, and the recent mass mortality of the sunflower star.

Hope for Pacific Northwest coastal ecosystems

Despite these challenges, there is some optimism. Adult ochre sea stars are beginning to recover in size and number to levels observed before the disease epidemic.

The resurgence offers hope that these predators may once again help regulate the expansion of barnacles and mussels, potentially aiding in the stabilization of these coastal ecosystems.

In conclusion, the resilience of rocky shore communities in the Pacific Northwest is being tested by climate change and environmental stressors. The ongoing research into these impacts is vital for understanding how to protect and restore these crucial natural habitats.

The study is published in the journal Nature Ecology & Evolution.


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