OA effects on mussel attachment strength

Impacts of Ocean Acidification on Wild and Farmed Mussels in Puget Sound

Research on three mussel species identified increased temperature and acidification as detrimental to byssal thread strength and, therefore, mussel survival.

Principal Investigator

Emily Carrington, University of Washington, Friday Harbor Laboratories

Co-Principal Investigator

Carolyn S. Friedman, University of Washington, School of Aquatic and Fishery Sciences


The rapid onset of ocean acidification (OA) presents an important new environmental stressor for commercially and ecologically important mussels in Puget Sound. Through laboratory studies and field observations of various local mussel species, this project assessed the synergistic roles of OA, temperature change, food rationing, and seasonal spawning cycles in byssal strength and dislodgement, a major cause of mussel mortality. It also quantified the environmental conditions native and naturalized mussels encounter at both the macro- and micro-habitat levels, and developed a high school curriculum on ocean acidification.


Washington Sea Grant-supported researchers studied the effects of temperature and pH changes on byssal strength in two native mussel species, Mytilus trossulus and M. californianus, and the introduced species, M. galloprovincialis. They assessed: mussel attachment and condition at three far-flung Puget Sound aquaculture sites; byssal strength in wild mussels in Olympic National Park; and byssal effects of varying food supply, temperature and pH.

Two years of observations revealed a pronounced seasonal cycle in attachment strength, with attachment stronger in winter and weaker in summer, especially in surface waters. Preliminary analyses suggested warming and pH are the best predictors of weak attachment. But responses to acidification varied seasonally according to the three species’ different breeding schedules. Effects on byssal strength were less obvious during breeding, when the animals were already nutritionally stressed. M. galloprovincialis adapted better than M. trossulus in higher salinity. When temperature exceeded 20 degrees Celsius, M. trossulus produced fewer byssal threads and M. californianus production held steady; M. galloprovincialis produced more, giving it a competitive advantage as oceans warm.

Observations suggest both warming and acidification reduce byssal strength but do not compound each other’s impacts; for example, increased temperatures and average pH can be just as damaging as increased temperatures and low pH. Weak attachments are most prevalent during the summer, when the water is warmer and more acidic. Mussels can manage subpar environmental conditions of relatively short duration by waiting to make new byssal threads until conditions improve, but if subpar conditions persist, the existing byssal threads weaken and newly formed threads never strengthen. M. galloprovincialis was the least affected by warming waters, indicating that growers who focus on this species could have a competitive advantage as the climate changes. The researchers hope to develop tools to predict the occurrence of harmful conditions to help growers mitigate potential profit losses. The growers with whom the researchers collaborated have already found the work useful for farm management.

Annual Reports

Final Report

2016 Progress Report

2015 Progress Report

2014 Progress Report