Regional variation in the impact of climate change: evidence that bottom-up regulation from plankton to seabirds is weak in parts of the Northeast Atlantic

Abstract

Climate change has profoundly altered the structure and biodiversity of marine ecosystems worldwide, and for many upper-trophic-level predators changes in lower-trophic- level prey has been the main driver of this alteration. To better understand the nature of marine ecosystem response to global change requires detailed knowledge of predatorprey dynamics, but this is hampered by our poor understanding of spatial variation in the strength of trophic link- ages. The aim of this study was to test for bottom-up effects across 4 trophic levels (phytoplankton, zooplankton, fish larvae and seabirds) over 17 yr, as well as testing for regional differences in 3 distinct marine ecosystems of the Northeast Atlantic: the Irish Sea, the Celtic Sea and the English Channel, where sea surface temperature has increased substantially in recent decades. Our results showed little evidence of bottom-up regulation from phytoplankton, zooplankton, fish larvae and seabirds, which is in contrast with the nearby North Sea, probably due to different oceanographic conditions. Despite this, we found a significant positive relationship between kitti- wake productivity and the abundance of fish larvae at one colony in the Irish Sea. We speculate that during the period 1991 to 2007 these ecosystems were weakly regulated by climate change, and seabird populations in these regions might be more heavily influenced by other extrinsic factors. The spatial effects of climate change appear to vary across ecosystems, even within a relatively small geographic area. In this context, we urge complex multi-trophic-level studies to elucidate the effect of climate impacts on marine ecosystems.