Meeting Abstract
In the intertidal zone, where waves impart lift and drag forces on stationary objects, mussels survive by forming aggregations, where individuals adhere to rocks and each other using fibers (byssal threads) tipped with a protein-based adhesive. Single protein adhesion models predict that a pH and oxygen differential imposed during secretion promotes adhesion with the substrate, while exposure to seawater facilitates the solidification and cross-linking of proteins to form a bulk solid. What remains unclear is to what extent pH and oxygen at the substrate, and in aggregations, differs from open ocean conditions, and to what extent this difference impacts adhesive strengthening. Here we present substrate level pH and oxygen measurements from mussel aggregations that are suspended during raft aquaculture operations at the Penn Cove Shellfish Farm, in the Puget Sound, Washington State. Field observations of pH and oxygen were used to inform fluctuating laboratory experiments, wherein byssus adhesive was incubated in seawater treatments, sampled over time, and pulled to failure using a tensile testing machine. Excursions below a pH of 7 were sufficient to arrest adhesive strengthening, which then resumed when seawater returned to a pH of 8. Oxygen fluctuations below 1 mg L-1 failed to stop adhesive strengthening over a three-day exposure, although the rate of strengthening was reduced. Results from these assays provide insights into what substrate-level micro-environment is required for secure mussel attachment, answers whether or not this interaction is reversible or temporally constrained, and can be used to inform a dynamic model that predicts the timing of “fall off” events at mussel farms given changes in future oceanic conditions.
