Sea: Animal behavior reveals death zones

Behavioral Catalog allows early detection of impending oxygen crises on the seabed

Marine biology "in situ": With the self-developed underwater device EAGU (Experimental Anoxia Generating Unit), a team of researchers is researching seabed inhabitants in oxygen crises. © University of Vienna
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The behavior of seabed inhabitants can predict the emergence of low-oxygen zones of death in the sea. Scientists have found this out by artificially creating zones of death at the bottom of the Adriatic and observing the behavior of the inhabitants. The resulting catalog of behaviors can now greatly facilitate the early detection of impending death zones in the oceans.

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Dangerous oxygen depletion causes in our oceans more and more often for mass extinction on the seabed. In fact, so-called "death zones" have been forming lately, ie zones in which there is too little oxygen in the water. Their emergence is due, among other things, to polluted rivers and global warming. There are already 400 death zones worldwide and their total area is more than 250, 000 square kilometers - the size of Germany. What goes on in detail in such a zone has been virtually unexplored so far.

Now, a research team from the University of Vienna under the direction of Michael Stachowitsch from the Department of Marine Biology has examined this more closely. The study area was the Adriatic seabed at 24 meters depth, two kilometers from Piran, Slovenia. "We explore what happens in detail on the seabed of the Adriatic, when the oxygen is running low, before, during and after, " says the researcher. "We observe how the animal species react to the lack of oxygen exactly."

Oxygen crisis under Plexiglas

To avoid having to wait for oxygen depletion at the bottom of the sea, the research team constructed its own small death zone. But first an underwater device had to be designed and built. EAGU (Experimental Anoxia Generating Unit) is a self-developed plexiglass chamber with high-tech equipment that provides important data. "We first position the 50 x 50 x 50 cm cube in the open state. For 24 hours we observe life in normal-oxygenated water, "explains Bettina Riedel, a marine biologist. "Then the cube is closed. Within a few days, all the oxygen in the EAGU is used up. "Display

Animals flee or become inactive

In relation to the decreasing oxygen content, the behavior changes, including the enclosed mussels, sponges, snails, anemones and sea squirts. "For example, some people try to escape and push themselves up into higher water layers. Others, in turn, reduce their activity or display completely unnatural behavior, "explains Stachowitsch. "The goal of our project is to create a detailed catalog that accurately describes these behaviors and maps them to a specific oxygen content in the water."

Behavioral Catalog helps with early detection

A time-lapse camera delivered images every minute, sensors measure the content of oxygen and hydrogen sulfide in the water, the pH value and the temperature. Thus, the pictorial behavior of the animals could be assigned to the individual oxygen categories. The resulting behavioral catalog allows conclusions about the state of the water without costly and time-consuming measurements.

It thus provides a guideline for the early recognition of death zones. It could thus also make a contribution so that politicians can immediately take the necessary measures in the event of an emergency - for example Cessation of fishing activities in the area concerned, thereby giving the ecosystem the chance of regeneration.

(University of Vienna, July 27, 2010 - NPO)