Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean

Abstract

Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.

Invasive species cause large-scale loss of native California oyster habitat by disrupting trophic cascades

“…But an invasive intermediate consumer capable of depleting an important foundation species appears to be excluded from the food web, because the invader's naivete prevents it from recognizing and successfully avoiding a native top predator before being consumed. Thus, echoing the conclusions of previous work on trophic cascades (Myers et al 2007), biological invasions (Parker et al 2006), and biodiversity-ecosystem function (Jackson et al 2001;Worm et al 2006), our results suggest that marine food webs can be conserved by protecting native top predators that simultaneously regulate the foraging of native intermediate consumers (via density-and trait-mediated cascades) and exclude invasive intermediate consumers (via density-mediated cascades). Furthermore, although native species extinctions at the local and regional scale can be balanced by invasions of functionally similar species (Sax and Gaines 2003), our results suggest that naivete can prevent top predators and/or intermediate consumers in invaded food webs from re-creating historically important trophic cascades that maintain biodiversity and ecosystem function (Schmitz 2008).…”

“…Trophic cascades indirectly maintain many important basal species including hardwood trees, kelps, salt-marsh plants, and scallops (Estes and Palmisano 1974;Myers et al 2007;Ripple and Beschta 2007;Silliman and Bertness 2002) when top predators reduce the foraging of intermediate consumers, either by eating them (Carpenter et al 1985;Hairston et al 1960;Paine 1980) or by altering their behavior (Abrams 1995;Preisser et al 2005;Trussell et al 2002). Although trophic cascades require that top predators be present, predator presence-alone-may not always be suYcient (Schmitz et al 2004;Werner and Peacor 2003).…”

Trophic cascades in the western Ross Sea, Antarctica: revisited

“…Myers et al 2007, Estes 2014. As the capacity for top-down forcing declines due to upper-level predator removal (e.g.…”

Effects of Altered Offshore Food Webs on Coastal Ecosystems Emphasize the Need for Cross-Ecosystem Management

“…In particular, decreased stocks of predatory fish have generated strong increases in their prey, medium-sized or ''meso-'' predators (i.e., ''mesopredator release''), changing the interactions between higher trophic levels considerably (e.g., Myers et al 2007;Baum and Worm 2009). In some instances, there are documented cascading effects from such mesopredator increases on lower levels in the pelagic food web, including communitywide decreases of zooplankton, and increases in jellyfish and phytoplankton (e.g., Frank et al 2005;Daskalov et al 2007;Casini et al 2008).…”