or this regime shift has influenced the frequency of
occurrence of jellyfish across the North Sea, covering six
standard CPR sectors (Fig. 1a), but focusing on areas of
previous study to validate trends (C2). Additionally, we
investigated past relations between North Sea pH and
jellyfish frequency to test the prediction that future
increasing acidity due to higher levels of CO2 in the
atmosphere (Calderia and Wickett 2003) may be detrimental
to calcareous, skeleton-forming plankton (Riebesell et
al. 2000; Hays et al. 2005) and thus allow proliferation of
gelatinous organisms. Finally, we utilized the output from
climate models (Osborn 2004) to explore possible future
trends (Arau´ jo et al. 2005) in jellyfish frequency