Examining the 'global spreading hypothesis' using graph theory

Abstract

A persistent view, called the 'global spreading hypothesis', maintains that the frequency, magnitude and geographical extent of harmful algal blooms have increased in recent decades. These putative trends have been variously attributed to nutrient enrichment, climate change and inadequate databases. Biotic explanations for these trends have not generally been taken into account, but the recent tendencies of fisheries to graduate from predation to extermination are likely to have profound effects at all trophic levels of marine ecosystems, and need to be explored in this context. This study examines a model pelagic foodweb from the perspective of graph theory, and calculates the changes in the positional importance of phytoplankton in the interaction network. The positional importance of algae in foodwebs is quantified and community-wide effects on how their network position can change are demonstrated.