Is the collapse of marine food webs threatening?

Researchers warn about the collapse of entire food webs due to climate change

Is there less food for animals like fish due to climate change? © Global Pics / istock
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Mariner collapse: Due to climate change, entire food webs in the oceans could collapse, warn researchers. Because their experiments show that if the water is warmer and more acidic, dominate at the level of producers in certain ecosystems predominantly cyanobacteria. However, these organisms can not be utilized by the animals of the next level of the food web - there is a danger of a lack of energy in the entire system.

Whether on land or in the ocean: every animal and plant organism is in the living community of an ecosystem in mutual relation to other creatures. Often it is about eating and being eaten. The basis of such food chains or nets forms the phytoplankton in the sea with its growth and decay.

As tiny producers, these tiny organisms ensure the feeding of animal micro-organisms, which in turn feed larger animals such as fish. These are an important food for marine carnivores such as seals, which are eventually consumed by even larger predators such as sharks. "Healthy food webs in the sea are important for biodiversity. In addition, they represent a source of human consumption and food, "says Hadayet Ullah of the University of Adelaide in Australia.

Example Australia

The interaction of producers, plant and carnivores works only if it is finely balanced. However, rising temperatures and increasing ocean acidification from climate change could severely disrupt many once-healthy ecosystems.

How such changes affect marine food webs has been studied by Ullah and his colleagues using the example of typical communities in the coastal regions of South Australia. For their study, they stored twelve different types of algae, crabs, sponges, snails and fish in twelve tanks of 1, 600 liters each and simulated possible consequences of climate change by altering either temperature, acidification or both factors simultaneously in the water, display

Worthless food

How would these changes affect the functioning of mini food webs? After six months, the combined effect of the combined increase in temperature and carbon dioxide had a significant effect: "The biomass of the producers increased, which was mainly due to a strong spread of cyanobacteria, " reports Ullah.

The problem: These organisms, also called blue-green algae, are poorly exploitable by next-level animals in the food web and therefore play a minor role as food. By dominance, however, they simultaneously displaced other species of phytoplankton in the experiment. As a result, less energy was available to consumers at the bottom of the food web, which negatively impacted the flow of energy throughout the system.

Shifted balance

The shifted balance changed the food webs so strongly that they even consider a complete collapse long-term possible. Does global warming therefore threaten all marine food webs on our planet? Not really, experts believe.

"The results of the present study quite convincingly show a possible direction of the expected changes in South Australian coastal ecosystems, " says Martin Wahl from the Helmholtz Center for Ocean Research in Kiel. "However, the results certainly can not be transferred to open ocean, deep sea, tropical, or polar regions."

"It always depends on the regional conditions and the prevailing species composition, whether the energy flow through the food web is slowed down or fueled by increases in CO2 and temperature, " adds Harald Asmus from the Alfred Wegener Institute for Polar and marine research on Sylt.

Stabilization possible

In addition, in nature, communities may be able to adapt to slow changes over a longer period of time - or the food web will be rebalanced by the immigration of new species,

"Such processes can not be detected in such experiments. However, they are important for the ecosystem and can lead to stabilization, "emphasizes Inga Hense from the University of Hamburg. (PLOS Biology, 2018; doi: 10.1371 / journal.pbio.2003446)

(PLOS, 10.01.2018 - DAL)