Plankton head polewards

Date:
October 15, 2021
Source:
ETH Zurich
Summary:
Ocean warming caused by anthropogenic greenhouse gas emissions will
prompt many species of marine plankton to seek out new habitats,
in some cases as a matter of survival. Researchers expect many
organisms to head to the poles and form new communities -- with
unforeseeable consequences for marine food webs.



FULL STORY ==========================================================================
The ocean is teeming with microscopic plants and animals known
collectively as plankton. Each individual organism is tiny, yet,
taken as a whole, this free- floating community delivers important
ecosystem services. For example, plant- like plankton, or phytoplankton,
use photosynthesis to fix carbon from carbon dioxide, making them a key
driver of the oceanic carbon cycle. Phytoplankton are also a food source
for zooplankton, which, in turn, nourish fish and marine creatures up
to and including the blue whale.


==========================================================================
As the climate heats up and ocean temperatures rise, researchers expect
to see significant changes in plankton distribution. Yet there are
hardly any studies investigating where different species of plankton
might thrive in the future.

Part of this knowledge gap has now been filled by a research team led by
Fabio Benedetti and Meike Vogt, the former a postdoctoral researcher and
the latter a senior scientist in Nicolas Gruber's group at ETH Zurich,
in collaboration with colleagues from the Swiss Federal Institute for
Forest, Snow and Landscape Research (WSL).

The project team put together a new global dataset to create distribution
maps for more than 860 species of phytoplankton and zooplankton based on various statistical algorithms and climate models. They then overlaid
these maps to determine what plankton communities might look like in
the future and where they might occur. The results of their work were
recently published in the journal Nature Communications.

Warming drives diversity Benedetti and his colleagues showed that
the diversity of both phytoplankton and zooplankton can be expected
to increase in the future across many regions, because warmer water
generally tends to promote greater diversity.



========================================================================== However, at very high temperatures -- that is, temperatures above 25
degrees Celsius -- phytoplankton and zooplankton respond differently to warming: phytoplankton diversity continues to increase, while zooplankton diversity decreases. This will lead to a reduction in zooplankton
diversity in the tropics.

Emergence of new communities Plankton species from the tropics and
subtropics will shift polewards and replace species that are adapted to
cooler waters. This will give rise to numerous new communities that have
never existed in these combinations before, a convergence of species that
do not currently occupy the same habitat and whose interrelationships
are not clearly aligned.

Researchers expect the biggest changes to occur in oceans at high and
temperate latitudes -- precisely those regions that are crucial for CO2 fixation and fisheries.

"In some areas of the ocean, we will see a rise in species numbers
that may, on the face of it, seem positive. But this boost in diversity
could actually pose a serious threat to the existence and functioning
of well-established marine ecosystems at higher latitudes," says lead
author Benedetti.



========================================================================== Marine ecosystems at high and mid-latitudes are currently dependent on
species- poor plankton communities. The size distribution of plankton
organisms also has an important influence on the quality of the ecosystem service.

To determine whether these factors change when plankton communities
and thus their size distributions change, the researchers simulated the
effects of climate change on the size structure of two important plankton groups, the diatoms and copepods. Data on the size of individual species
is available for these organisms.

Smaller organisms replace larger ones Using the simulations, the
scientists demonstrated that the quality of the habitat increases for
smaller organisms, while it decreases for the larger ones. Therefore,
plankton communities could change, so too do the relative proportions
of small and large species: smaller organisms become more abundant
and numerous, especially at high and temperate latitudes, while larger organisms decrease in number.

According to the researchers, this will affect the ecosystem services that plankton provide: if changes occur in the plankton's species composition
and size structure, this could have a negative impact on the ecological
pyramid and thus on fish yields.

Plankton also play an important role in oceanic carbon fixation. Some
of the carbon fixed by phytoplankton sinks to the deep ocean and is
effectively removed from exchange with the atmosphere.

For example, the Arctic Ocean is currently home to phytoplankton that are larger than those in tropical seas. Many of these have shells, and their excretions are also larger and heavier. As a result, both dead organisms
and their excrement sink faster and to greater depths before the carbon
they contain is decomposed back to CO2. Dissolved in deeper waters,
this CO2 remains trapped in the depths for long periods of time due to
density stratification and the slower circulation of the deep ocean.

If smaller species replace larger ones, this transfer of carbon to the
deep ocean will decrease.

However, scientists cannot say exactly how significant these effects
will be.

"The only thing we can determine right now is how important certain
areas of the ocean are today in terms of different ecosystem services
and whether this provision of services will change in the future"
Benedetti says.

Distribution shift well underway Scientists have been observing shifts
in plankton distribution since the Researchers have been observing
that the distribution of plankton is shifting for several decades. The
first systematic monitoring programme, the so-called Continuous Plankton Recorder (CPR), began in the North Atlantic in the 1930s.

With the help of the CPR data, other researchers have recently been able
to show that smaller copepods have displaced the larger species in the
North Atlantic since the 1950s due to climate warming. This has also
reduced the sequestration of atmospheric CO2 in the deep sea.

Jellyfish, another type of zooplankton, are also migrating northwards. In
2005, Ireland detected a huge influx of tropical jellyfish, which
devastated salmon farms along the coast. "Events like this show that
shifts in plankton distribution are already well underway," says co-author Meike Vogt.

========================================================================== Story Source: Materials provided by ETH_Zurich. Original written by
Peter Ru"egg. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Fabio Benedetti, Meike Vogt, Urs Hofmann Elizondo, Damiano Righetti,
Niklaus E. Zimmermann, Nicolas Gruber. Major restructuring of marine
plankton assemblages under global warming. Nature Communications,
2021; 12 (1) DOI: 10.1038/s41467-021-25385-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211015184247.htm

--- up 6 weeks, 1 day, 8 hours, 25 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)