SPATIAL STRUCTURE OF THE SOUTHERN-OCEAN ECOSYSTEM - PREDATOR-PREY LINKAGES IN SOUTHERN-OCEAN FOOD WEBS

1. The food chain of the Southern Ocean has often been characterized a s simple and homogeneous. However, the population processes of a key p rey organism, krill Euphausia superba, operate over ocean basin scales and are strongly influenced by large scale abiotic factors. 2. A mode l was developed in which the local prey abundance was regulated by a c ontinuous, hydrodynamically mediated, supply rate and the concentratin g effects of abiotic-biotic interactions. This model was used with est imates of the annual predator demands and the prey concentration for t he South Georgia area to investigate the relationship between flow rat e and depletion in prey concentration as a function of distance from a predator colony. 3. The model results indicated that concentrating fa ctors need to be large to produce the build-up of krill densities of t he order estimated to occur in the South Georgia area, with the peak r etention rates required some distance offshore. It was, however, found that, for the estimated supply rates, the region does not need to be an area of particularly high prey concentration to support the estimat ed predator impact. 4. Differential predator foraging ranges produced a more complex response to the reduction of the abundance of particula r predators by harvesting, than in the situation where foraging ranges overlapped completely. In such a system the more inshore foraging pre dators encountered the greatest changes in prey abundance. 5. Random f luctuations in the interannual prey availability were introduced into the simulation of the flow system. This could lead to apparent populat ion cycling in predator and prey abundance due to the interactive form of the system, although the prey population dynamics were not involve d. The system enhanced variability such that inshore foraging predator s encountered greater variation in prey supply. 6. The model results e mphasize the importance of investigating the magnitude and timing of t he horizontal fluxes of secondary production in this spatially distrib uted ecosystem.