SPATIAL AND TEMPORAL PATTERNS OF ENERGY FLOW IN A SEASONALLY VARIABLE MARINE ENVIRONMENT

Food web theory has uncovered several structures, or patterns of carbon flow, that increase food web persistence. However, empirical studies focused on these structures have been largely restricted to temperate and tropical areas. In the present dissertation, I sampled the food web of Cumberland Sound, Nunavut during summer (August) and winter (April) of 2007-2009 and used stable isotopes (SI: d15N, d13C) and fatty acids (FA) to identify whether this arctic food web exhibited the following structures: 1) spatial resource coupling, 2) individual diet specialization and 3) temporal resource coupling. I first identified that the FA profile of a key arctic herbivore (Calanus hyperboreus) consistently differed between summer and winter over two years (e.g. higher 18:1n-9 in winters vs. summers), which aided in the interpretation of FAs in upper trophic levels. I then tested for the presence of spatial resource coupling in the summer food web. Based on d15N-derived trophic positions and d13C-derived % reliance on phytoplankton (vs. macroalgae), lower trophic levels fed predominantly on one of two resources and upper trophic levels used multiple resources, supporting the existence of spatial resource coupling. Following a preliminary analysis comparing Greenland shark (Somniosus microcephalus) and prey FAs, inter-tissue differences in Greenland shark 22:5n-3 among muscle, liver and plasma revealed that some individual sharks fed on consistent resources, but that the extent of individual diet specialization varied over time. Individual Greenland sharks were therefore concluded to feed as generalists, which is consistent with the finding that Cumberland Sound consumers acted as spatial resource couplers. Finally, SIs and FAs revealed that ~50% of Cumberland Sound species switched their diet between summer and winter. A literature review confirmed this temporal resource coupling by consumers on a pan-arctic scale. Overall, structures of an arctic food web agreed with those predicted by recent food web theory, such that spatial and temporal variability in resource abundance and consumer feeding behaviour are likely important for arctic food web persistence. In this context, any result of climate warming that acts to synchronize resource dynamics or remove consumer resource coupling could decrease the persistence of arctic food webs