Overwintering ecology and ecophysiology of Neocalanus plumchrus




Campbell, Robert William

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Neocalanus plumchrus is the most common copepod in the Northeast Pacific, and as such plays in important role in the ecosystems of that area. The bulk of N. plumchrus’ annual life cycle is spent in a dormant overwintering state, and little is known of its ecology, behaviour, or physiology during that period. The goal of this thesis is to describe the physiological changes that occur during the overwintering period, and explain how they interact with the physical environment to produce observed life history patterns. Lipid stores in N. plumchrus were primarily wax esters, and were in highest abundance in overwintering stage 5 copepodids. Consumption of wax ester stores began approximately two months prior to moulting in situ. Rates of lipid use in the in situ population and a number of laboratory incubations ranged from 0.3 - 1% d⁻¹ , with 22 - 60% of total wax ester reserves used prior to moulting, presumably to fuel gonadogenesis. Concurrent measurements of protein content and glutamate dehydrogenase activity (an enzyme involved in protein catabolism) did not show any significant protein use during overwintering. Incubation experiments suggest that N. plumchrus has some concept of the time of year (i.e. an endogenous clock), but the use of external cues cannot be ruled out. It is often assumed that the abundant lipids found in calanoid copepods play some role in buoyancy regulation. However, lipids are generally more compressible, and more thermally expansive than seawater, which means that neutral buoyancy will be inherently unstable. A simple model of mass density shows that (i) individuals will only be able to stay at depth if they are able to diagnose where they are neutrally buoyant, and (ii) the buoyancy properties of an individual are extremely sensitive to its chemical composition. In the Strait of Georgia, depth-specific measurements of abundance showed a shift towards deeper depth distributions over the course of the overwintering period. Model results suggest that lipid use could be responsible for those changes, though deep water renewal events that occur regularly in the Strait of Georgia in winter may also have been partially responsible.



Copepoda, Marine invertebrates