Effects of freezing on the metabolic rate of the bay mussel, Mytilus trossulus

Abstract

Mussels that live in intertidal zones of temperate regions risk freezing at every
winter low tide as they are exposed to sub-zero temperatures. Therefore, they have
evolved the ability to tolerate freezing with a hefty energetic cost, as tissue and cellular
damage incurred must be repaired afterward. The metabolic costs of freezing have yet
to be investigated in an intertidal species, specifically whether a metabolic cost is
associated with crossing the freezing threshold. I hypothesized that animals that freeze
will experience relatively more damage than those which do not and will therefore
demonstrate a higher metabolic rate associated with repair immediately after freezing. I
exposed the intertidal mussel, Mytilus trossulus, to -5.5°C for 6 hours and found similar
oxygen consumption rates regardless of the outcome. This may indicate that the driver
for metabolic shifts is not attributed to the crossing of the freezing threshold but rather
the percentage of body water converted to ice. With the predicted increasing frequency
of cold snaps due to climate change, we can better predict how mussel populations will
respond to these events by understanding the fundamental mechanisms of freeze
tolerance.