Research reveals fishing pressures affect tropical and temperate reefs differently

Date:
June 30, 2020
Source:
University of Hawaii at Manoa
Summary:
An international team of researchers focused on what can happen to
ocean ecosystems when fishing pressure increases or decreases,
and how this differs between tropical to temperate marine
ecosystems. The team found ecosystems do not respond universally
to fishing.



FULL STORY ==========================================================================
In a study published recently in Ecology and Evolution, an international
team of researchers focused on what can happen to ocean ecosystems
when fishing pressure increases or decreases, and how this differs
between tropical to temperate marine ecosystems. The team, led by
Elizabeth Madin, researcher at the Hawai'i Institute of Marine Biology
(HIMB) in the University of Hawai'i (UH) at M?noa School of Ocean and
Earth Science and Technology (SOEST), found ecosystems do not respond universally to fishing.


========================================================================== There has been much debate about the degree to which ocean ecosystems
are impacted by fishing, also termed "top-down forcing" because such
changes occur when predators at the top of the food web are removed,
versus the availability of nutrients and other resources in an ecosystem, termed "bottom-up forcing." "Examples from a variety of marine systems
of exploitation-induced, top-down forcing have led to a general view
that human-induced predator perturbations can disrupt entire marine
food webs, yet other studies that have found no such evidence provide
a counterpoint," said Madin.

Madin worked with an amazing team of marine ecologists from all over the
world, particularly those from the Australian Institute of Marine Science (AIMS) and the University of Tasmania (UTas). Using time?series data
for 104 reef communities spanning tropical to temperate Australia from
1992 to 2013, they aimed to quantify relationships among populations
of predators, prey, and algae at the base of the food web; latitude;
and exploitation status over a continental scale.

As expected, no-take marine reserves -- where fishing is prohibited --
led to long-term increases in predator population sizes.

"This is good news for fishers, because as populations increase, the
fish don't recognize the reserve boundaries and are likely to 'spill
over' into adjacent areas where fishing is allowed, creating a kind of insurance policy whereby marine reserves ensure the ability of fishers
to catch fish into the future," said Madin.



========================================================================== Surprisingly though, the team found that in the tropics, the system
tends to be driven predominantly by bottom-up forcing, whereas colder, temperate ecosystems are more driven by top-down forcing.

"I assumed at the start of the project that in places where fishing
pressure was high and predators were depleted, we would see consequent increases in the population sizes of the predators' prey species, and
the decreases in the prey's prey species," explained Madin. "However, in
the tropical part of our study system, that is, Australia's Great Barrier
Reef, this simply wasn't the case. This result had me scratching my head
for quite some time, until I realized that this type of domino effect,
called a trophic cascade, is simply a real, but rare, phenomenon in
the tropics." These kinds of continent-scale analyses are only possible
with large, long-term datasets.

This study relied on data from the AIMS long-term coral reef monitoring
program and the UTas Australian Temperate Reef Collaboration -- creating
one enormous, continental-scale reef dataset.

"Only by looking at the very big picture, it turned out, were we able
to find these trends," said Madin.

Predator loss is now a globally pervasive phenomenon that touches nearly
every marine ecosystem on the planet. Ecosystem destabilization is a widely-assumed consequence of predator loss. However, the extent to
which top-down versus bottom-up forcing predominates in different types
of marine systems is not definitively understood.

"Understanding how our fisheries are likely to impact other parts of the
food web is important in making the best possible decisions in terms of
how we manage our fisheries," said Madin. "By understanding how coral
reef food webs are likely to respond to fishing pressure, or conversely
to marine reserves, we can make more informed decisions about how much
fishing our reefs can safely handle. Likewise, this knowledge gives us a
better idea of what will happen when we create marine reserves designed
to serve as an insurance policy so communities can continue to catch
fish long into the future."

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


========================================================================== Journal Reference:
1. Elizabeth M. P. Madin, Joshua S. Madin, Aaron M. T. Harmer,
Neville S.

Barrett, David J. Booth, M. Julian Caley, Alistair J. Cheal,
Graham J.

Edgar, Michael J. Emslie, Steven D. Gaines, Hugh
P. A. Sweatman. Latitude and protection affect decadal trends
in reef trophic structure over a continental scale. Ecology and
Evolution, 2020; DOI: 10.1002/ece3.6347 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200630092209.htm

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