A coastal ecosystem destabilized by climate change, according to a study

Ecological communities on the Oregon coast are being subtly destabilized by the pressures of climate change despite an appearance of resistance to stress, according to new research from Oregon State University.

The results are important because assessing and understanding how plants, animals and other life forms respond to global warming are essential for human well-being, said lead author Bruce Menge.

The study published today in the Proceedings of the National Academy of Sciences shows that ecological communities in the rocky intertidal zone of Oregon have become less stable over the past decade or more, although their structure – the organisms that make them up – has essentially remained the same.

The destabilization of the community stems from the decrease in resilience, that is, the ability to bounce back from disturbances. The results suggest that other ecological communities around the world that project an appearance of stability would not appear this way upon close inspection of how their member organisms collectively respond to disturbances.

“Climate change threatens to destabilize ecological communities,” said Menge, a professor of integrative biology at OSU who has been researching the coast for four decades. “One possibility is that they stop being persistently occupied, what we call pools of attraction, and move to other states.”

Menge, postdoctoral researcher Sarah Gravem, and colleagues at the College of Science examined a total of six sites in three separate regions of Oregon’s lower intertidal zone from 2011 to 2019. The regions are Cape Perpetua on the central coast, Cape Foulweather to the north and Cap Blanco to the south.

At each site, scientists created five “disturbed plots”, each half a square meter in size. Once a year, these plots were cleared of all forms of life large enough to be seen with the naked eye: limpets, mussels, sea anemones, barnacles, seagrass, sponges, snails, crabs, starfish, etc.

The plots were photographed regularly and from these images, the researchers were able to assess the quantity of taxa on each plot.

If the ecological communities surrounding the plots were stable, the plots would exhibit consistent recovery patterns after each clearing. This is not what happened, the researchers found.

In general, disturbances have caused communities to move to structures dominated by open space and more “weedkiller” taxa such as barnacles and filamentous algae.

“And in any case, over time the recovery rates slowed down and also became more variable,” Gravem said. “Increasing variation in key ecological processes can indicate that an ecosystem is about to change state. On the Oregon coast, the factors behind this increasing variation appear to be from changes in ocean currents and thermal disturbances such as marine heat waves. , which can impair growth, decrease colonization rates and kill organisms. “

The research does not necessarily indicate that the iconic rocky regions of the Oregon coastline are approaching an ecological tipping point where sudden and often irreversible ecosystem changes are occurring, scientists say. But the results aren’t good news either, they say.

“On land, extreme forest fires illustrate how gradual changes in temperature or precipitation can eventually lead to catastrophic events,” Menge said. “In the ocean environment, new events such as marine heat waves and disease epidemics are new and acute threats that add to the gradual increases in water temperature and generally ocean acidification. associated with climate change. “

Scientists say that while it’s difficult to predict exactly when a sudden ecosystem change will occur, systems close to the edge of one can send warning signals. The increasing variability in community structure is believed to be one of them, and another is the system that is slowly recovering from small disturbances.

“Resilient systems can quickly return to their original configurations after a disruption,” Gravem said. “The intertidal rock systems are very dynamic, but the Oregon one has started to show signs of loss of resilience, possibly in response to unprecedented stresses from acute warming events. Even the intact communities we studied next to cleared plots have become more variable, which we believe is a harbinger of instability and a harbinger of a change in community state. “

Angela Johnson, Jonathan Robinson, and Brittany Poirson from OSU College of Science were also involved in the research.