Balance of nature: ecosystem top predator reversal (Introduction)

by David Turell , Thursday, August 27, 2020, 18:02 (1548 days ago) @ David Turell

Weird. Normally a top predator continues to dominate. not if the local environment changes along shorelines:

https://phys.org/news/2020-08-sticklebacks-dominate-perch.html

"A research project on algal blooms along the Swedish coast, caused by eutrophication, revealed that large predators such as perch and pike are also necessary to restrict these blooms. Ecologist Britas Klemens Eriksson from the University of Groningen and his colleagues from Stockholm University and the Swedish University of Agricultural Sciences, Sweden have now shown that stickleback domination moves like a wave through the island archipelagos, changing the ecosystem from predator-dominated to algae-dominated.

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"This coast consists of countless archipelagos that stretch up to 20 kilometers into the sea, creating a brackish environment. Here, perch and pike are the top predators, feeding on sticklebacks, which themselves eat the small crustaceans that live off algae.

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"'If you just look at the abundances of fish, you find a mixed system in which different species dominate," Eriksson explains. But looking at the changes in these fishery data over time showed an increase in sticklebacks that started in the late 1990s, initially in the outer parts of the archipelagos. "This is presumably caused by a reduction in the number of large predators. The reduction is the combined result of habitat destruction, fishing and increased predation by cormorants and seals." Sticklebacks migrate from the outer archipelagos inwards to reproduce, linking coastal and offshore processes.

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"Reduced predation increases the survival of sticklebacks, while both eutrophication and warming help to increase their numbers even further. As the sticklebacks reduced the number of grazers, algae began to replace seagrass and other vegetation. Furthermore, the sticklebacks also fed on the larvae of perch and pike, thereby further reducing their numbers. "This is a case of predator-prey reversal," explains Eriksson. Instead of top predators eating sticklebacks, the smaller fish strongly reduced the number of perch and pike larvae.

"Over time, the stickleback domination moved inwards like a wave: regional change propagated throughout the entire ecosystem. This has important consequences for ecosystem restoration. "To counter algal blooms, you should not only reduce the eutrophication of the water but also increase the numbers of top predators." It means that those organizations that manage fisheries must start working together with those that manage water quality. "We should not look at isolated species but at the entire food web," says Eriksson. "This is something that the recent EU fishery strategy is slowly starting to implement.'"

Comment: All caused by brackish water and the addition of unwanted extra minerals (eutrophication). All ecosystems are in delicate balance and the sum total of them is the bush of life.