Crustaceans are not fault
Russian scientists have disproved the hypothesis on the bacterial origin of «tumor» on corals transmitted by copepod crustaceans
Previously, there were found some evidence on the fact that some small crustaceans could transmit bacteria causing the appearance of pathogenic growths, galls, on corals. «Such growths are similar to the tumor but not cancer one. They are more likely should be compared to abscesses appearing due to parasites,» - a coauthor of the study, Mikhail Nikitin commented. — "The role of galls and risks connected with them are not clarified up to now, although we have observed some galls on the corals which look quite healthy."
Contrary to the common mistake, the corals are not plants. These immobile formations are composed in very deed by skeletons of invertebrate animals of class Anthozoa, coral polyps. A distinct polyp is small, but their colonies may form giant systems up to Great Barrier Reef which occupies an area of about 350 thousand square kilometers and spreads over two and a half thousand kilometers over Australian shore. In coral reefs, up to one-quarter of all known sea animals reside. However, now they are in danger due to increasing temperature and content of carbon dioxide in water.
The death of coral may have extremely unpleasant consequences ranging from threat for fishing to the destruction of reefs which protect shorelands.
An intensive study of coral will allow for finding approaches to rescue coral reefs from global warming. Previously, Mikhail Nikitin has told that up to 2050, most of the corals might die while traditional ways of protecting rare species are powerless in such case. Even if one denies the human access to all reefs completely and ceases the pollutions of carbon dioxide completely entirely, the polyps are doomed to disappear. To restore their population, one need to populate endangered reefs by new species actively. These new inhabitants must be not common species but specially adapted with different techniques including gen engineering.
In order to prevent a disaster, the biologists are carrying out intensive studies of these ecosystems and trying to understand the connections between composing organisms. The copepod crustaceans measuring about one millimeter, bacteria, and corals themselves actively interact with each other. However, the details of their mutual influence are not clear so far. Moreover, according to the new publication (https://www.nature.com/articles/s41598−018−29 953-y) in the Scientific Reports journal, the coral species Gorgonia ventalina and Stylophora pistillata should be considered not stand-alone but in connection with crustaceans Sphaerippe and Spaniomolgus which was not the case before. Previously, scientists have supposed that these animals transmit microorganisms causing the formation of growths on corals. Inside galls, copepods have higher chances to find food and home. Consequently, such an alliance «copepods + agent gall» should ingrain due to natural selection principle.
To verify this hypothesis and also to broaden the knowledge of coral ecosystems in general, the researchers from the M.V. Lomonosov Moscow State University (MSU), Vavilov Institute of General Genetics at Russian Academy of Sciences (RAS), A.A. Kharkevich Institute for Information Transmission Problems RAS, Skolkovo Institute of Science and Technology, Higher School of Economics, Red Sea Research Center at King Abdullah University of Science and Technology (Saudi Arabia) and Naturalis Biodiversity Center (Leiden) have carried out a metagenomic sequencing of corals and copepods and analyzed the bacterial RNA from collected samples.
As a result, a detailed census of all bacteria in healthy systems «coral + copepods» as well as in systems «copepods and coral galls» has been accomplished. Contrary to expectations, in all samples, microbiomes of halls are analogous to microbiomes of healthy corals although with somewhat different structure. Based on this study, the researchers have concluded that it is not correct to assert that halls on corals grow due to infection by crustaceans.
«In my opinion, the results of the study have shown the timeliness of further investigations of microbe composition of other symbiotic complexes of invertebrates including massive microscopic crustaceans, the majority of those are surprisingly new species. It will be interesting to take a closer look at microbe composition of symbiotic complexes of various invertebrates which can show different character and strength of symbiotic relations. The expertise acquired by us will be useful in planning further research activities,» - Vyacheslav Ivanov, the leading research assistant at the Laboratory of Morphology, Ecology, and Systematic of Invertebrates at Faculty of Biology MSU said.
Nikitin has also drawn the attention that some inoffensive bacteria are transmitted into a coral by copepods. «This fact proves the principal ability of transmission of bacteria into coral reefs, which is of high importance for understanding how various diseases of polyps may spread,» - the researcher said.