UC Davis study: North Coast water changes affecting marine life

Scientists at the UC Davis Bodega Marine Laboratory say a new study shows that the response by certain aquatic animals to warming ocean temperatures may make them more vulnerable to growing acidification, a secondary effect of climate change already measurable off the Sonoma Coast.

The research showed that organisms called bryozoan changed the composition of their skeletons in warm water to ones that quickly dissolved when exposed to water of higher acidity, causing the animals to shut down, lead author Dan Swezey said. He said the study mimicked conditions expected to be widespread by the end of the century.

The findings suggest that some marine life faced with adapting to a shifting ocean environment may be in a double bind when confronted with the “one-two punch” of global warming, a university representative said, with implications for sea stars, sea urchins, coralline algae and other ecologically significant marine life that depend on mineralized skeletons containing magnesium.

UC Davis spokeswoman Kat Kerlin likened the bryozoan to a “canary in a coal mine.”

“Our results add to this growing body of evidence that ocean acidification is a threat for lots of marine animals that are producing hard shells and skeletons,” said the study’s co-author, Eric Sanford, a professor of evolution and ecology. “But that might be increasingly true if the trend of acidification is combined with this trend of warming oceans.”

The research involved a particular species of a widespread yet little-known type of invertebrate common to the kelp forests of the North Coast. The whole colony spread across a blade of bull kelp more closely resembles a crusty white coating or even frost than a living animal.

But under magnification, the rigid, white honeycomb structure on which the softer parts of the animal depend is clearly visible. Each dark cell - about a half-millimeter wide - is occupied by a translucent, spherical feature with flower-like tentacles used to gather food.

Bryozoans, sometimes called moss animals, build their skeletons of calcium carbonate and some magnesium. Samples for the study were collected off Dillon Beach near Tomales Bay, where several species can be found growing seasonally on the branching stems of red algae in the intertidal zone.

But when exposed in the lab to water just a few degrees warmer than usual - similar to conditions existing off the coast of North America during a recent phenomenon commonly known as the Warm Blob - the bryozoans built higher levels of magnesium into damaged areas and new skeleton growth for reasons that are unknown. The stress of poor nutrition, which also was manipulated in the study, similarly caused magnesium levels to rise.

Then, when bathed in water of lower pH mimicking conditions that sometimes exist in waters off the North Coast, the skeletal structures, which were predicted to thin or diminish, actually dissolved, scientists said.

“They are literally disappearing,” Swezey said.

Bodega Bay provided an interesting location for the research because of unique characteristics reflecting forecast conditions for the larger ocean in the coming decades and those simulated in the study, Swezey said.

The area was deeply affected by the Warm Blob that persisted along the West Coast for three years, raising ocean temperatures as much as?4½ degrees Fahrenheit and altering the food web sufficiently to spread starvation among many species of wildlife.

It also experiences the impact of strong coastal upwellings that bring nutrient-rich, cold water up from the ocean depths seasonally, water so acidic it simulates what the larger ocean will look like within the next century, thanks to increased absorption of excess carbon dioxide from the atmosphere, Swezey said.

In the meantime, the warming land mass is expected to cause more abrupt and erratic coastal winds, intensifying upwelling frequency and duration, he said.

“Those swings back and forth that we are worried are going to be more common are what we wanted to test in this study,” Swezey said.

There is emerging research that indicates other invertebrates similarly respond to warm water by increasing the content of magnesium in their skeletons, though much more research needs to be done, Swezey said. What hasn’t been shown is the tendency for those skeletons to then dissolve, he said.

But if the same effects occur in other types of marine life the repercussions could be profound.

Coralline algae, and pink or reddish organisms, for example, many of which exist in abundance along the North Coast, provide food, habitat and biological cues to juvenile abalones to settle and grow into mature shellfish, Swezey said.

“They are the foundation of a lot of ecosystems,” and they have high magnesium concentrations, he said.

Bryozoans were chosen for the study for a variety of reasons, including their rather short life cycle and the reliability with which they can be cultured in a lab. A key benefit is that they produce the interconnected units of each colony asexually, meaning each part of a colony is a genetically identical clone, Sanford said.

Sanford said the study reflects the importance of analyzing the combined impacts of multiple environmental stressors, many of which have been present along the North Coast in recent years, on the health of local fisheries and the kelp forest.

“In reality, life in the sea is increasingly facing many changes at once in terms of changing temperature and acidity and nutrients and pollution, for example, so I think marine scientists are increasingly trying to understand how species react to multiple changes in the ocean at once,” he said.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.