Tipping point in Humboldt Current off Peru leads to species shift

Date:
January 7, 2022
Source:
Kiel University
Summary:
Fundamental changes in the ocean, such as warming, acidification
or oxygen depletion, may have significant consequences for
the composition of fish stocks, including the displacement of
individual species.

Researchers have reconstructed environmental conditions of the
warm period 125,000 years ago (Eemian interglacial) using sediment
samples from the Humboldt Current System off Peru. They were able
to show that, at warmer temperatures, mainly smaller, goby-like
fish species became dominant and pushed back important food fish
such as the anchovy (Engraulis ringens). The trend is independent
of fishing pressure and fisheries management.



FULL STORY ========================================================================== Fundamental changes in the ocean, such as warming, acidification or oxygen depletion, may have significant consequences for the composition of fish stocks, including the displacement of individual species. Researchers at
Kiel University (CAU), together with colleagues from Germany, Canada,
the USA, and France, have reconstructed environmental conditions of
the warm period 125,000 years ago (Eemian interglacial) using sediment
samples from the Humboldt Current System off Peru. They were able
to show that, at warmer temperatures, mainly smaller, goby-like fish
species became dominant and pushed back important food fish such as
the anchovy (Engraulis ringens). The trend is independent of fishing
pressure and fisheries management. According to the study, the greater
warming of the Humboldt Current System as result of climate change has
more far-reaching implications for the ecosystem and the global fishing industry than previously thought. The findings appeared in the journal
Science, January 7.


==========================================================================
The sea off the west coast of South America is one of the most vital and productive fishing grounds on earth. Around eight percent of the global
catch of marine species comes from the areas off the coasts of Peru,
where the near- surface Humboldt Current provides a high nutrient supply
and thus sufficient food for commercially exploited fish species such
as the anchovy. Ten percent of the total global catch of anchovies alone
comes from the region. Much of it is processed into fish meal and oil and
used primarily for aquacultures in China and Norway. However, catches of anchovy in the Humboldt upwelling system are currently declining. The
causes of species shifts are mainly due to climate change according to
the results of the new study.

Researchers from the Institute of Geosciences at Kiel University,
together with colleagues from GEOMAR Helmholtz Centre for Ocean Research
and international partners, have for the first time investigated the relationships between temperature, oxygen, nutrient supply and the
occurrence of individual fish species using paleo-oceanographic data
from the Humboldt Current region. The scientists focused on the warm
period about 125,000 years ago (Eemian interglacial). During this time, conditions were similar to those predicted by climate projections (e.g.,
the IPCC report) for the end of the 21st century at the latest: comparable primary production but water temperatures two degrees Celsius higher
than today and increased oxygen deficiency in mid-depth water masses.

For their paleo-oceanographic studies, the researchers at Kiel University primarily analyzed small fish vertebrae that they were able to isolate
from the sediment cores. According to the results, smaller, goby-like
fish predominated in coastal waters during the ancient warm period,
while anchovies made up only a small proportion. Fish with smaller body
sizes can adapt better to warmer temperatures. They retain their high
activity even in less oxygenated waters thanks to their larger gill
surface area relative to their body volume.

"The conditions of this past warm period that we were able to reconstruct
from our samples can definitely be compared to the current development
and put in context with future scenarios," says first author of
the study, Dr. Renato Salvatteci, who is currently working at the
Center for Ocean and Society of the Kiel Marine Science (KMS) priority
research area at Kiel University and in the BMBF-funded Humboldt-Tipping project. "According to this, there is a clear regime shift towards smaller
fish that feel more comfortable in the warm, lower-oxygen conditions. We conclude from our results that the effects of human-induced climate change
may have a stronger influence on the evolution of stocks in the region
than previously thought," Salvatteci added. Smaller fish are harder to
catch and less palatable. According to the report, the impact on the
Peru region, local fisheries income and global trade in anchovies could
be far-reaching -- potentially affecting global food security.

"Our studies using sediment cores can give us fairly accurate information
about the changes and their dynamics in highly productive coastal
waters around the world that have occurred in the wake of different
climate states and over different time scales," explains Professor Ralph Schneider, a paleoclimate researcher at the Institute of Geosciences at
Kiel University and co-author of the study.

The results indicate that due to increasing warming in the Humboldt
Current upwelling area, the ecosystem is heading towards a tipping
point beyond which anchovy will begin to retreat and not continue to
dominate nearshore fishing grounds. "Despite a flexible, sustainable
and adaptive management strategy, anchovy biomass and landings have
declined, suggesting that we are closer to the ecological tipping point
than suspected," summarizes lead author Renato Salvatteci.

The results of the study help to better assess the extent to which a
warming ocean can provide sufficient food for the world's population
and what changes should be expected for the development of important
fish species such as the anchovy.

The study was funded by the Collaborative Research Center (SFB)
754 "Climate- Biogeochemical Interactions in the Tropical Ocean,"
a collaborative project of Kiel University (CAU) and GEOMAR Helmholtz
Centre for Ocean Research Kiel.

Additional support came from the BMBF project Humboldt-Tipping,
coordinated at the Center for Ocean and Society, as well as funding
from the Emmy-Noether Junior Research Group ICONOX at GEOMAR. First
author Renato Salvatteci was further supported by a fellowship from the Alexander von Humboldt Foundation.

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


========================================================================== Related Multimedia:
* Research_near_the_Humboldt_upwelling_system ========================================================================== Journal Reference:
1. Renato Salvatteci, Ralph R. Schneider, Eric Galbraith, David Field,
Thomas Blanz, Thorsten Bauersachs, Xavier Crosta, Philippe Martinez,
Vincent Echevin, Florian Scholz, Arnaud Bertrand. Smaller fish
species in a warm and oxygen-poor Humboldt Current system. Science,
2022; 375 (6576): 101 DOI: 10.1126/science.abj0270 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220107121449.htm
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