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How can overharvesting cause a trophic cascade in a marine ecosystem?
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commercial fishing
Worker in the Tsukiji fish market, Tokyo.
Overharvesting triggers a trophic cascade by removing top predators, which disrupts the natural balance of an ecosystem and causes reciprocal changes in the populations of predator and prey throughout the food chain.12
When commercially exploited speciesāsuch as cod, haddock, or sea ottersāare removed, the species they once consumed are no longer kept in check. This leads to several ecological consequences:12
- Mesopredator Release: The decline of top carnivores, such as sharks, allows populations of smaller predators to increase, which subsequently depletes the species those mesopredators consume.1
- Loss of Primary Producers: In the case of sea otters, their removal led to an explosion in sea urchin populations, which then overconsumed and decimated kelp forests.12
- Altered Nutrient Cycling: By changing the abundance of herbivores and primary producers, overharvesting can shift biomass and alter the rates at which nutrients are recycled within the marine environment.1
Preserving top predators is essential for maintaining ecosystem structure and the vital services they provide to humanity.1