Elevated temperature and ocean acidification alter mechanics of mussel attachment
Newcomb, Laura Anne
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Global climate change by way of warming ocean temperatures and ocean acidification threatens the survival of marine organisms. For mussels, survival is tightly tied to byssal threads they form that anchor them to substrates, from the rocky intertidal to mussel aquaculture lines. Weakened byssal threads increase the likelihood of “fall-off” or “sloughing” from rocks and aquaculture lines, disturbing intertidal communities and reducing aquaculture yields. Seasonal variation in mussel attachment strength suggests environmental conditions may alter byssal thread strength and production. In this dissertation, I explore the role of rising temperature and ocean acidification on the mechanical performance of mussel byssal threads to improve predictions of what environmental conditions may precede fall-off events. In Chapter 1, I expose mussels (<i>Mytilus trossulus</i>) to a range of pH (7.3 – 8.2, total scale) and temperature conditions (10 – 25˚C) in a full factorial cross. Elevated temperature dramatically weakens mussel attachment: mussels produce 60% weaker and 65% fewer threads at 25˚C in comparison to 10˚C. The effects of temperature are strongest in the proximal region of the threads. Low pH (7.3) strengthens the plaque region of the thread by 20%, but has no effect on overall byssal thread strength. Since a thread is only as strong as its weakest region, these stressors do not act synergistically with each other; the strongest negative effect dominates, in this case temperature. Chapter 2 expands on the impacts of temperature on attachment strength, finding species-specific temperature effects. In the northeast Pacific, the warm-adapted mussel <i>M. galloprovincialis</i> and cold-adapted mussel <i>M. trossulus</i> compete for space on shore. While the attachment strength of these two closely related species does not differ from 11 - 18˚C, at temperatures from 18 - 24.5˚C, <i>M. trossulus</i> attachment strength decreases while <i>M. galloprovincialis</i> attachment strength increases. At temperatures greater than 18˚C <i>M. trossulus</i> produces fewer and weaker byssal threads with attachments that were up to 93% weaker than <i>M. galloprovincialis</i>. Chapter 3 follows up these laboratory studies using the field setting of a mussel farm to examine correlations between ocean conditions and attachment strength in <i>M. trossulus</i>. In the field, weak attachment strength in <i>M. trossulus</i> is best predicted by high temperature >14˚C and low pH, <7.5. Similar to the lab study, the effects of these two stressors are independent of each other. Altogether, these results find mussels and the communities they support are vulnerable to multiple aspects of future ocean conditions. Warming oceans may increase the competitive advantage of <i>M. galloprovincialis</i> in more northern latitudes at the expense of native <i>M. trossulus</i> populations. Monitoring these conditions near farms can signal periods where attachment is expected to be weak in order to best adapt farming practices.
- Biology