Trophic Cascades and Marine Reserves: Dual Indicators of Fishery and Climate Change Disruption in Pelagic and Benthic Ecosystems

Abstract

Trophic cascades occur when a reduced abundance of a keystone species, such as a top predator, causes changes in their prey abundance, which in turn affects other trophic levels, such as mesopredators, herbivores and/or plants. They are reported from freshwater, terrestrial, and marine environments. This article describes examples of pelagic and benthic trophic cascades, and of how no-fishing marine reserves enabled the realization that fisheries have widespread impacts on food webs leading to noticeable ecosystem changes such as in the cover of seaweed habitats. Marine reserves thus provide “control” and “reference” areas to investigate the effects of fishing, and can also help discriminate the effects of fishing from climate change. While an indicator of fishing effects, the significance of trophic cascades for species extinction risk is unclear. However, it has been hypothesized that trophic cascades are stronger and food webs less stable in species poor ecosystems. If so, changing latitudinal gradients in species richness due to climate change may result in changes in trophic cascades in high and low latitudes, with lower occurrence and intensity in the former and higher in the latter than in the past.