OA effects on mussel attachment strength

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

This project will expand on ocean acidification and temperature research relating to local mussel species to test for causes of seasonal weakening of mussel attachment.

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 will assess 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 will also quantify the environmental conditions native and naturalized mussels encounter at both the macro- and micro-habitat levels, and develop a high school curriculum on ocean acidification.

Research Updates

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 suggest 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 warms.