It turns out that not only corals can protect fish from their enemies and fish sometimes help polyps deal with dangerous aggressor. American zoologists found that the representatives of two species of gobies, living near reefs, can eat the poisonous algae destroying corals. And they do it only when polyps will ask them about it.

Although recently coral reefs suffer most from anthropogenic pollution, they are and other enemies. From them the most dangerous are the starfish "crown of thorns" (Acanthaster planci), which is the day can eat up to several thousand individuals coral colonies, and the so-called "turtle grass" - green algae Chlorodesmis fastigiata. In the struggle with polyps uses chemical weapons - toxic substances of class terpenes.

Biologists have long noticed that only the "turtle grass" grow on any area of the colony, as he immediately begins to degrade. Is poisonous algae only to touch the polyp, as he quickly dies of the burns. It is interesting that, apparently, C. fastigiata causes harm the corals are not specially - biologists believe that these algae have created their chemical weapons in the process of evolution as the means of protection of fish. It just happened that they use diterpenes turned out to be toxic to corals. But, you know, the last from this circumstance, unfortunately, not easier.

For quite a long time the scientists of the various countries concerned about the massive loss of corals around the world, tried to think of a way to protect reefs from the activity of this pernicious weed. And recently, the solution seems to be found. The fact that biologists from Georgia Institute of Technology (USA) discovered that the poison of this Alga deters not all fish. Some, on the contrary, happy to include toxic plant in your menu.

The researchers found that living on the coral reefs of the bulls Gobiodon histrio and Paragobiodon echinocephalus not mind sometimes pinch "turtle grass". Moreover, the analysis of stomach contents representatives of these kinds have shown, that G. histrio really eats this poisonous algae, well, P. echinocephalus just obrushivaet it in places where it is in contact with corals, but bitten off pieces do not swallow. Interestingly, both fish have corals invaluable service for three days of observations were received evidence that the emergence of these fish have reduced the population of algae by 70-80%.

However, the most curious of all was the fact that both fish started its work only when the coral received a call for help, of course, in the form of a chemical signal. The researchers found it this way - they are first added to the aquarium to the bulls water taken near healthy colonies, and then - the one that was produced about polyps, which terrorized the seaweed. In the first case, the behavior of the fish did not change, but in the second they immediately rushed to the source of the smell. So, the corals really call Bychkov for help when the algae begin to kill them.

In the control experiment biologists have tried to address coral nylon threads, some of which was soaked with algal diterpenes, and some not. So they found out that the main role here is played exactly the algal toxin and not contact algae and coral - no signal substances in response to simple mechanical contact with the thread polyps were not given, but if it was previously poured poison, then immediately followed the call for help.

Observation in nature, showed that such a relationship between the two kinds of coral Bychkov and polyps Acropora nasuta specific. It was found that no other corals data fish are not defended. However, this attachment is easy to explain - G. histrio and P. echinocephalus not only use the colony here as a permanent shelter, but also feed on mucous discharge of coral, as well as zooplankton and unicellular algae that live here. Therefore we can say that fish protect corals in exchange for the buffet and shelter. This is very similar to the known zoologists relationship between African acacia and ants-tailors (Oecophylla)that in exchange for housing and "thrice ' power to protect plants from pests.

Interestingly, other inhabitants of the same reefs have not expressed a clear desire to help polyps in trouble. So, many people living near pomacentridae fish, hear the alarm in a hurry to get away. However, do not accuse them of cowardice, because, unlike Bychkov, they are not protected from the poisonous diterpenes.

Scientists suggest that, perhaps, covered in scales "rescuers", like G. histrio and P. echinocephalus, there is every species of coral. Just about them is not known. Because, until recently, the idea that the sea may be that the relationship between different types, no one came to mind. So now researchers want to find out what other sea inhabitants are proud name of the fighter of toxic algae (which, besides Chlorodesmis fastigiata, in the ocean enough - for example, red Alga Galaxaura filamentosa) and what type of corals protect these brave create...