Diversity of apex predators and ecosystem stability:spatial dynamics of predators and forage fish in the marine pelagic ecosystem

Intensive harvesting combined with changes in ocean climate have generated large fluctuations in northern marine shelf ecosystems. The link between zooplankton and apex predators in these systems is occupied by a few key species of small pelagic schooling fish. These stocks which sustain a large and diverse group of predators, are characterised by a variable and complex distribution in densities in space and time. In this proposal we argue that the highly dynamic and scale-dependent spatial pattern of for age fish species is a key factor in shaping the top predator community and determining the trophic interaction between forage fish and apex predators. To evaluate the role of this hypothesis on the ecosystem processes, we propose a study that aims at expl oring the spatial pattern in predator-prey interactions and competition. Data on spatial distribution of apex predators, forage fish species and zooplankton will be collected during regular cruises in the Barents Sea. Data will be analysed by using a recently developed multi-scale statistical method that separate patterns on different hierarchical spatial scales. We will quantify the scales of the spatial pattern and the spatial overlap of the different predator-prey groups. We wil l furthermore examine the spatial response of the apex predator community to changes in the abundance and spatial pattern of prey. Finally, we will quantify the temporal stability and predictability in the observed spatial pattern within and between years .