As a result, populations of large-bodied herbivorous zooplankton, which are consumed by small pelagic fishes, decreased, which in turn led to an increase in the phytoplankton. For example, overfishing of cod ( Gadus morhua) and other commercially exploited fishes such as haddock ( Melanogrammus) and hake ( Urophycis, Raniceps, and Phycis) in the North Atlantic Ocean led to an increase in small pelagic (open ocean) fish consumed by cod, snow crab ( Chionoecetes opilio), and shrimp. Research in a wide variety of terrestrial and aquatic environments has shown that trophic cascades control species composition, biomass, and production of herbivores and plants. Because trophic cascades affected the rates of primary production and respiration by the lake as a whole, they affected rates of exchange of carbon dioxide and oxygen between the lake and the atmosphere. Those experiments showed that trophic cascades controlled biomass and production of phytoplankton, recycling rates of nutrients, the ratio of nitrogen to phosphorus available to phytoplankton, activity of bacteria, and sedimentation rates.
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Effects on aquatic and terrestrial ecosystemsĭuring the 1980s and ’90s a series of experiments demonstrated trophic cascades by adding or removing top carnivores, such as bass ( Micropterus) and yellow perch ( Perca flavescens), to or from freshwater lakes. In the 1980s others used the term to describe changes in aquatic ecosystems arising from factors such as sudden increases in predatory fish populations from stocking or dramatic declines in predatory fishes caused by overfishing. American zoologist Robert Paine coined the term trophic cascade in 1980 to describe reciprocal changes in food webs caused by experimental manipulations of top predators. For example, in eastern North America the removal of wolves ( Canis lupus) has been associated with an increase in white-tailed deer ( Odocoileus virginianus) and a decline in plants eaten by the deer. In a three-level food chain, an increase (or decrease) in carnivores causes a decrease (or increase) in herbivores and an increase (or decrease) in primary producers such as plants and phytoplankton.
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