How sticklebacks dominate perch
Analysis reveals waves of stickleback domination along the Baltic coast


Date:
August 27, 2020
Source:
University of Groningen
Summary:
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. Ecologists have
now shown that stickleback domination moves like a wave through the
island archipelagos, changing the ecosystem from predator-dominated
to algae-dominated.



FULL STORY ==========================================================================
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. Their study was published on 27
August in the journal Communications Biology.


========================================================================== Eriksson experimented with the effects of nutrients on algal blooms
while working as a postdoctoral researcher in Sweden. When he added
nutrients to exclusion cages in the brackish coastal waters, algae
began to dominate. This was no surprise. However, when he excluded
large predators, he saw similar algal domination. 'Adding nutrients and excluding large predators had a huge effect,' he recalls, 10 years later.

Food web The big question that arose from these results using small
exclusion cages was whether the results would be the same for the real
Swedish coastal ecosystem.

This coast consists of countless archipelagos that stretch up to 20
kilometres 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.

To investigate how this food web developed over the past 40 years,
Eriksson (who had moved to the University of Groningen in the Netherlands) connected with his colleagues at Stockholm University and the Swedish University of Agricultural Sciences to gather data on fish abundances
and to carry out a series of field studies. They were inspired by recent suggestions that regime shifts can occur in closed systems such as lakes
and wondered whether algal blooms in the Baltic sea could also be a
consequence of such a regime change.

Grazers Eriksson and his colleagues sampled 32 locations along a
400-kilometre stretch of coastline. 'We visited these sites in the
spring and autumn of 2014 and sampled all levels of the food web,
from algae to top predators.' These data were subsequently entered
into a food web model, which helped them to find connections between
species. The models showed that the small sticklebacks were important
for the reproduction of the larger predators. And a local increase in sticklebacks means that a lot of the grazers in the ecosystem are eaten,
which drives algal domination.

'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.

Predation 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.' Furthermore, the propagation of local changes throughout a system has
wider implications in ecology, especially in natural ecosystems that
have complex interaction and information pathways. 'And we know this from politics and human behaviour studies. A good example is the Arab Spring,
which started locally and then propagated across the Middle East.'

========================================================================== Story Source: Materials provided by University_of_Groningen. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Johan S. Eklo"f, Go"ran Sundblad, Maarten Erlandsson, Serena Donadi,
Joakim P. Hansen, Britas Klemens Eriksson, Ulf Bergstro"m. A
spatial regime shift from predator to prey dominance in a large
coastal ecosystem. Communications Biology, 2020; 3 (1) DOI:
10.1038/s42003-020- 01180-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200827122108.htm

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