Native species in California estuaries are expected to decline more sharply as invasive species interact with climate change.

A study published in the journal Ecology of the Environmental Society of America states that this decline is expected due to climate stress and the increasing influence of new invasive predators, whose effects are much more pronounced in estuaries.

"Our study finds that climate change and biological invasion of coastal estuaries may interact in unexpected ways," said lead author Benjamin Rubinoff, Ph.D. was a student in the Department of Environmental Science and Policy at UC Davis at the time of the research. "This increased predation risk discourages native species already facing increasingly stressful environmental conditions."

Researchers tested the effects of environmental stress and predation on sedentary invertebrates in Tomales Bay, California, in the summer of 2019. Sedentary invertebrates are vertebrates that cling to coral reefs or seagrass and rarely move, such as bryozoans and sea squirts. Their predators include starfish, crabs, and snails.

In estuaries, changes in salinity also water temperature significantly impact the distribution of many invertebrate species, from clams to crustaceans to sea spray. This gradient can be incredibly steep in estuaries in California, which are highly vulnerable to climate change and invasive species.

In most estuaries, stressful conditions for marine life, such as low salinity and high temperatures, increase as you move inland. Under increased pressure, native predators usually consume less prey.

However, studies have found that biological invasion changes this equation, as many non-native predators are more stress-tolerant than native predators. Such highly stressed native prey species face large numbers of stress-resistant invaders who compete with them for resources when they are not eating them.