Effects of environmental variability on different trophic levels of the North Atlantic food web

The effects of environmental change on the biodiversity, structure and functioning of marine ecosystems is still poorly understood. In fact, very few studies have focused on changes in the at-sea foraging tactics of pelagic seabirds in relation to environmental stochasticity. Aiming at filling this knowledge gap, from 2005 to 2010 we directly measured the influence of climate (as driven by the North Atlantic Oscillation phenomenon) on (1) marine productivity (i.e. chlorophyll a concentration), (2) fish prey abundances and (3) the foraging behaviour of a top marine predator, the Cory's shearwater Calonectris diomedea borealis. There was a dramatic change in the foraging strategy of the birds during 2010, which seems to be mostly related to a climatic event that occurred during the winter of 2009 to 2010. This event had a negative impact on the productivity of the surroundings of the breeding colony and decreased the abundance of pelagic prey fish, which in turn altered the spatial, feeding and trophic ecology of Cory's shearwater and decreased their reproductive success. However, the negative trend in the abundance of pelagic prey (estimated from acoustic surveys and commercial fisheries landings) may be of concern because it does not seem to be only related to the climatic event of 2010. Long-term monitoring of the interactions between top predators, their prey and lower strata of the food web is crucial for a comprehensive assessment of the impacts that environmental variation may have on coastal ecosystems worldwide.