Warmer the ocean, the more predators it contains

(ORDO NEWS) — To study the possible effect of global warming on marine communities, scientists conducted similar experiments off the coast of the entire New World. They were able to prove a link between rising ocean temperatures and predator activity.

Natural biologists have long noticed that species diversity increases from the polar regions to the equator – this is the so-called Wallace’s rule . Other similar trends are known: increased competition between species and increased activity of predators as you move away from the poles, but much remains unclear in this area.

A new study published by a large team of scientists from around the world in Science helps to better understand this fundamental ecological pattern.

The scale of the work is amazing: the experiments were carried out at 36 sites scattered along the coast of North and South America, including both the Atlantic and the Pacific. It turns out that the study covered an area of ​​almost 15 thousand kilometers in size – from Alaska to Tierra del Fuego.

Three identical experiments were carried out in each of the experimental plots. First, we assessed the activity of predators by the speed with which a standard bait is eaten.

Secondly, we studied the effect of constant predation on the composition and biomass of the benthos community (ie bottom dwellers). Finally, biologists looked at how short-term predation affects an established benthic community.

In the first case, biologists used devices called “squid on a stick” (squid pops). In fact, these are pieces of dried squid, strung on a pin (like a popsicle) and left in the sea for everyone.

Biologists returned to the bait an hour later and counted how many squid were eaten. This value served as the main quantitative indicator of the predatory nature of the ocean.

Warmer the ocean the more predators it contains
Locations of the experiments and the average water temperature in them

The working hypothesis was fully justified: in warm water, local predators ate squid much faster. Moreover, it was the temperature of the water that was decisive, and not the latitude, which is usually mentioned in the relevant laws of biogeography.

What is the “increase in predation” in the sea, along with the temperature, is fraught with for local communities? The answer to this question was helped to find the second and third experiments.

Scientists drew attention to the inhabitants of the bottom, which are usually eaten by predatory fish – mainly bryozoans and tunicates . For three months, identical benthic communities grew side by side: some under protective cages, others left to be eaten.

In the last experiment, the community, initially closed by a cage, was at some point deprived of protection and again watched the predators in action.

The results came out quite clear: in cold waters, protection almost did not change anything – it turns out that predators do not play a significant role in them.

However, there were noticeably fewer surviving benthic invertebrates in warm water. The composition of the communities also changed in them – for example, ascidia, which were more attractive to fish, disappeared first, while bryozoans actively occupied the vacant place.

“As the predator situation changes, some species will win, others will lose,” said Greg Ruiz, co-author of the new paper, of the Smithsonian Center for Environmental Research (USA). Some will be protected, some will be defenseless. But we don’t know for sure how it will all turn out.”

The researchers emphasize that they have yet to figure out what is happening at the equator, in the hottest areas of the oceans.

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