Award: OCE-2346837

Title: RAPID: A subtle epidemic: unique mortality of Mytilus californianus on the Oregon coast

Importance and General Significance. Environmental change and its alteration of environmental conditions has refocused the attention of the ecological community on ecosystem stability. On temperate rocky shores, mussels are a “foundation” species, serving as prey for multiple predators, able to filter particles out of huge volumes of water, and harboring hundreds of other species, thereby serving a central role in community function. Hence, threats to their abundance and persistence are of significant ecological and societal concern. Past research has shown that mussels are highly resilient and well-adapted to acute, short-lived stresses such as disturbance from winter storms or short-term warming. In summer 2023, a novel pattern of mortality was discovered during routine field research: high numbers of dead mussels, many with tissue remaining in the shell were observed in a scattered pattern. That is, rather than a mass mortality (i.e., all mussels in a large area are killed), single dead mussels surrounded by live and apparently healthy mussels occurred, with multiple dead individuals per square meter. This scattered mortality event was the most recent and most visually obvious sudden change observed in what have been seemingly stable and resilient rocky intertidal communities. With discoveries such as declining rates of recovery from disturbance and declining performance of mussels and sea stars, arguably the two most critical species in these systems, scattered mussel mortality may be another expression of increasing sensitivity to direct and indirect consequences of environmental warming. 

After evidence available allow rejection of alternative hypotheses, our studies tested the hypothesis that mortality was due to water-borne toxins from a bloom of toxic phytoplankton coupled with individual variation among mussels in susceptibility to these toxins. Water samples during the event revealed that toxic phytoplankton was present in the adjacent waters, and histological sampling showed that mussel digestive tracts showed signs of modified cell structure consistent with mussel consumption of a toxic algae. That is, the food that mussels were filtering out of the water suppressed their ability to assimilate the particles they were eating.

Broader Impacts. Environmental change is an existential threat to human society, and ecologists are among those called upon to help understand, mitigate and ideally reverse its effects. This research benefits society by providing insight into a novel, heretofore unrecorded event in the diverse and productive rocky intertidal communities of the Pacific Northwest. By detecting this event and identifying a possible causal agent, thereby alerting the public and managers to its occurrence, such information will be useful in coastal conservation and management. Our work also built scientific capacity through training of future contributors to improved understanding of ecosystem responses to climate change. Specifically, the primary technician supported by this award has moved on to work on an advanced degree at the University of Washington.

 

Last Modified: 11/23/2025
Modified by: Bruce A Menge