Ocean acidification creates legacy of stress for red abalone, study finds

A stressful childhood can affect an individual’s adult years and influence future generations. Scientists at the University of California, Davis, found a similar pattern for red abalone exposed as infants, and then again as adults, to the stress of ocean acidification.

Their study, published in the journal Biology of global change, found that the negative impacts of ocean acidification – a byproduct of carbon dioxide emissions – on red abalone can persist within and between generations. According to the study, addressing ocean acidification at crucial life stages can help mitigate these effects on captive and commercially raised red abalone, while also informing conservation efforts for wild abalone.

“For red abalone, if your parents were exposed to ocean acidification, that impacts your ability to handle stress,” said lead author Isabelle Neylan, a doctoral student. student at the UC Davis Bodega Marine Laboratory when the study was conducted and currently a postdoctoral researcher at Louisiana State University. “It carries over within this generation and onto the next generation.”

The research is part of a larger effort to save this troubled species, endemic to California and listed on the International Union for Conservation of Nature’s red list as critically endangered. Giant sea snails with iridescent shells are the most common of eight species of abalone found off the coast of California, but habitat degradation and the effects of climate change have decimated their numbers.

Generate, expose, repeat

For the study, scientists first bred adult red abalone. They then exposed about half of the offspring to current ocean conditions and the other half to highly acidic conditions in the near future for the first three months of their lives.

They raised the surviving animals for four years before exposing them again to high or low acidity treatments for 11 months as adults. They then measured their reproductive potential by ultrasound as well as their growth.

Finally, they bred these animals and exposed the second generation’s offspring to high or low acidity to analyze the impacts of ocean acidification over multiple generations.

Scientists found that exposure to ocean acidification early in life decreased the adult growth rate of abalones, even after five years, particularly when they were re-exposed as adults. Ocean acidification has reduced the ability of adults to reproduce, even for those who were not exposed to it as babies. Additionally, negative effects experienced by parents trickled down and reduced the survival and growth of the next generation.

The experiment found that baby abalones were resistant to ocean acidification for two to three weeks, but three months of exposure to ocean acidification led to stress and death. This finding gives abalone producers – for commercial aquaculture or captive breeding recovery programs – a clearer indication of when they should buffer water chemistry to help protect abalone.

The future is (sometimes) now

“We were looking to see if your parent was exposed, does that protect you from the impacts? It didn’t,” Neylan said. “The more you are affected, the worse it is, but there are glimmers of hope.”

For example, Neylan said some families of red abalone do better than others. Adults, on the whole, were quite resistant to ocean acidification. The adults were smaller, but they successfully spawned without significant mortality. However, as with many forms of life, young people are the most vulnerable. In nature, strong coastal upwellings that bring acidic water from the depths of the ocean to the surface often occur at the same time that red abalone spawn.

Upwelling is generally intermittent and driven by coastal surface winds. But highly acidic conditions, or “high pCO₂“, felt by the abalones in the experiment, are already occurring in short bursts during upwelling events off the coast of California. Climate models predict that high levels of upwelling are expected to become more common and last longer, as carbon dioxide emissions continue to fuel ocean acidification and strengthen coastal winds that trigger upwelling.

A Californian icon

Red abalone can live 50 years or more and are an important forest kelp species. For thousands of years, they have played a central role in the diet and cultural history of the region’s coastal indigenous people.

“Red abalone is a California icon,” said co-author Daniel Swezey, a research scientist at the UC Davis Institute of Coastal and Marine Sciences and its Bodega Marine Laboratory. “As well as being beautiful, large and durable, they have enormous cultural cachet and deep history. They mean a lot to a lot of people.”

But they face multiple, often interrelated threats: from warming ocean temperatures and disease to collapsing kelp forests, voracious purple sea urchins and habitat degradation. These factors led to the closure of the red abalone fishery in 2018 until at least 2026.

“The fishery is in poor shape; the kelp hasn’t really recovered; sea urchin populations are incredibly high,” Swezey said. “The question now is, what dents can we make to give the abalone a chance to recover? It’s a tall order, but we’re on it.”