Rising water temperatures could endanger the mating of many fish species


Date:
July 2, 2020
Source:
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine
Research
Summary:
In a new meta-study, experts have published ground-breaking findings
on the effects of climate change for fish stock around the globe.



FULL STORY ========================================================================== Because fish that are ready to mate and their young are especially
sensitive to changes in temperature, in the future up to 60 percent of
all species may be forced to leave their traditional spawning areas.


==========================================================================
In a new meta-study, experts from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have published ground-breaking findings on the effects of climate change for fish stock around the
globe. As they report, the risks for fish are much higher than previously assumed, especially given the fact that in certain developmental stages
they are especially sensitive to rising water temperatures. One critical bottleneck in the lifecycle of fish is their low tolerance for heat
during mating. In other words, the water temperature in their spawning
areas determines to a great extent how successfully they reproduce,
making fish particularly vulnerable to the impacts of climate change --
not only in the ocean, but also in lakes, ponds and rivers. According
to the researchers' analyses, if left unchecked, climate change and
rising water temperatures will negatively affect the reproduction of
up to 60 percent of all fish species. Their study was released today in
the latest issue of the journal Science.

Organisms have to breathe in order for their bodies to produce energy;
this is equally true for human beings and for fish. In addition, we
know that the energy needs of humans and animals alike depend on the temperature: when it's warmer, the need for energy rises exponentially,
and with it, the need for oxygen. On this basis, it follows that
organisms can only adapt to rising temperatures in their immediate
vicinity by providing their bodies with more oxygen. But there are certain species-specific limits on this ability; if those limits are exceeded,
it can lead to cardiovascular collapse.

Armed with this knowledge, in a new meta-study, experts from the Alfred
Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI)
have investigated in which life phases saltwater and freshwater fish
around the world are most sensitive to heat. To do so, the biologists
compiled scientific data on the temperature tolerance of 694 fish species
and analysed the temperature ranges within which fish can survive as
adults ready to mate, as embryos in eggs, as larvae, and as adults
outside the mating season.

Most sensitive during the mating season "Our findings show that, both as embryos in eggs and as adults ready to mate, fish are far more sensitive
to heat than in their larval stage or sexually mature adults outside the
mating season," says first author and AWI marine biologist Dr Flemming
Dahlke. "On the global average, for example, adults outside the mating
season can survive in water that's up to 10 degrees Celsius warmer than
adults ready to mate or fish eggs can." The reason for this variable temperature tolerance lies in the anatomy of fish: fish embryos have no
gills that would allow them to take in more oxygen. In contrast, fish
that are ready to mate produce egg and sperm cells; this additional body
mass also needs to be supplied with oxygen, which is why, even at lower temperatures, their cardiovascular systems are under enormous strain.



========================================================================== Every degree of warming increases the pressure on fish stocks These
findings apply to all fish species, and make it clear why fish are
sensitive to heat, especially during the mating season and in their
embryonic stage. Accordingly, in a second step the team of researchers
analysed to what extent water temperatures in the spawning areas of
the species investigated would likely rise due to climate change. For
this purpose, they employed new climate scenarios (Shared Socioeconomic Pathways -- SSPs), which will also be used in the IPCC's next Assessment Report.

Their conclusions confirm that every degree Celsius of warming spells more trouble for the world's fish stocks. "If we human beings can successfully
limit climate warming to 1.5 degrees Celsius by the year 2100, only
ten percent of the fish species we investigated will be forced to leave
their traditional spawning areas due to rising temperatures," explains
AWI biologist and co- author Prof Hans-Otto Po"rtner. In contrast, if greenhouse-gas emissions remain at a high or very high level (SSP 5 --
8.5), it's likely to produce average warming of 5 degrees Celsius or more, which would endanger up to 60 percent of all fish species.

Limited options for adapting Those species affected would then be forced
to either adapt through biological evolution -- a process that would
most likely take far too long -- or to mate at another time of year
or in some other place. "Some species might successfully manage this
change," says Flemming Dahlke. "But if you consider the fact that fish
have adapted their mating patterns to specific habitats over extremely
long timeframes, and have tailored their mating cycles to specific ocean currents and available food sources, it has to be assumed that being
forced to abandon their normal spawning areas will mean major problems
for them." In addition, fish living in rivers and lakes have the problem
that their habitat is limited by the size and geographic location of the
waters they live in: migrating to deeper waters or to cooler regions is
nearly impossible.

New level of detail for improved projections "Our detailed analyses,
which cover all of the fishes' developmental stages, will help us to
understand how these species are being affected by climate change,
and to what extent the loss of suitable habitats is being driven by the climate-related transformation of ecosystems," says Hans-Otto Po"rtner.

Wherever fish migrate or their reproduction rates decline, there will
be new interactions between species, and in some cases the ecosystems
will experience a drop in productivity. The IPCC published corresponding projections on the future of worldwide fish stocks in its Special Report
on the Ocean and Cryosphere in a Changing Climate. According to Po"rtner:
"Our new detailed assessments will help to improve those projections."

========================================================================== Story Source: Materials provided by Alfred_Wegener_Institute,_Helmholtz_Centre_for_Polar_and
Marine_Research. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Flemming T. Dahlke, Sylke Wohlrab, Martin Butzin & Hans-Otto
Po"rtner.

Thermal bottlenecks in the lifecycle define climate vulnerability
of fish. Science, 2020 DOI: 10.1126/science.aaz3658 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200702144711.htm

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