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A stranger in the glaciers of the south

Crab from the Arctic is the first invading marine species found in Antarctica


On its return from a journey to Antarctica in 1986, the oceanographic ship Prof. W. Besnard, of the University of São Paulo (USP), brought samples of a kind of crustacean that it had collected in the course of its journey of exploration. They were two small crabs: one male, whose carapace measured 4.1 centimeters in length by 2.8 in width, and a female whose dimensions were 20% larger. Caught in waters neighboring the Antarctic peninsula, to the northwest of the white continent, the specimens did not at first attract much attention. Like so many other specimens netted by the Besnard in the Austral Ocean, the icy sea that surrounds Antarctica, they were forwarded to USP’s Zoology Museum.

In May 1987, soaked in an alcohol-based solution and sharing the same glass jar, the crabs joined the collection of this institution from São Paulo. The flask that held the pair of marine animals was given the name of batch MZUSP 8878 and went on to occupy its due place on a shelf. At the moment of cataloging them, researcher Gustavo Augusto Schmidt de Melo, then curator of the carcinology (crustacean) section, found the crabs interesting, perhaps they could even be a new species, as yet unknown to science. Without a doubt, this kind of animal was not to be found in Brazil. That is why he left a note that it was worth the while to study them one day – as soon as more pressing tasks were tackled and there were people to get their hands on the work.

Sixteen years went by, and this day finally arrived. At the beginning of 2003, Marcos Tavares, a specialist in crustaceans from Rio, moved to São Paulo and took up the post of curator of the carcinology section of the Zoology Museum, precisely in the place of Melo, who had just retired. Talking about work with his predecessor in the job, Tavares came to know about the strange crab samples obtained by the Besnard.

They thought it was time to research in detail those crustacean specimens. The interest for the sample grew even more when they found in the scientific literature that there were no live species of crab native to Antarctica, but only extinct fossil species. This motivated them to study really deeply the samples that had come in from the cold. And the result of the research came rapidly: in a few months, the researchers concluded that the crabs caught by the Brazilian ship represent the first evidence of an introduction, probably mediated by man, of invading marine species originating from other parts of the globe into the Austral Ocean.

Instead of being a new form of life, the little creatures picked up in the Besnard’s nets in 1986 belong to an old and well-known variety of crustacean. Described in scientific literature for almost 250 years now, the Hyas araneus species is given, amongst fishermen, the common name of great spider crab or toad crab. Fishermen from the North Sea and the Arctic Ocean, let it be understood. Native to these regions, very cold, like the Antarctic peninsula, the great spider crab had only been found, up until then, in stretches of the sea above 41 degrees latitude North.

Never in the Austral Ocean, on the other side of the globe, at 61 degrees latitude South. Accordingly, the species in itself is far from being a new one. New is its presence on the fringes of Antarctica, the most inhospitable, least polluted, and most difficult to access continent.

“The endemic fauna of the Austral Ocean has been isolated from the others for at least 25 million years, and is now being exposed to contact with exotic species”, Tavares says. Before the H. araneus, larvae from subantarctic species, originating from the far south of South America, had already been located in the environs of the Antarctic peninsula, but their presence in this region was due (and still is due) to the natural dynamics of the ocean currents, without the influence of man. They were occurrences of a different nature from those that led the great spider crabs to the coast of Antarctica.

Drawing close again
In biologists’ jargon, the expression exotic species denotes any form of life, animal or vegetable, introduced into a habitat different from its place of origin. It is a definition of relative value. Endemic and native to the Arctic and the North Sea, H. araneus is regarded as exotic and an invader in Antarctica (and in any other part of the world). The discovery that, after at least 25 million years of isolation, the fauna of the Austral Ocean is no longer to be found completely separated from the marine species of other seas resulted in a scientific article.

Signed by Tavares and Melo, the text will be published in the issue of June this year of the British magazine Antarctic Science, which is specialized in subjects of the white continent. In a preliminary way, the discovery of the great spider crab in the Austral Ocean was presented last October at a congress about Antarctic research held in Ushuaia, in the Argentinean portion of Patagonia. Tavares, who is not a specialist in Antarctica, where, by the way, he has never been, was invited to address the subject, as soon as he told the story informally to some researchers from abroad.

The presence of the two specimens of H. araneus in the Antarctic peninsula does not necessarily mean that the great spider crabs have established colonies there. There is no record of the species having been collected again in the region. “But we need more data to find out if the introduction of the crabs into the Austral Ocean has really not prospered, or if perhaps it has been a success and has gone unnoticed”, Tavares ponders. It is possible that its presence in waters so distant from its place of origin may have, for the while, a more symbolic than practical effect.

It may mean that it is becoming easier to arrive in those whereabouts. The greater presence of man in Antarctica and the increase in the average temperature of the planet – including the very cold waters of the Austral Ocean, which normally work as a natural barrier to the arrival of marine beings from other ecosystems – may be factors that induce the entry of marine species that are exotic to the southernmost region of the Earth. On Antarctic soil, the coming and going of researchers and tourists has already brought many alien beings, with terrestrial habits, to the continent.

One notorious case was the one of the dogs, who arrived there to pull sleds over the snow until the beginning of last decade, when their presence in Antarctica was prohibited. If the introduction of alien species has already happened in the lands of Antarctica, the same now seems to be taking place on the coast of the continent. That is why it is important to discover in what way the pair of great spider crabs changed hemisphere and ended up on the other side of the world, in the Austral Ocean.

How is it that these creatures from the Arctic, used to living on seabeds made up of rocks, sand and mud, at a maximum depth of 550 meters, managed to leave the environs of the North Pole, cross unharmed the high temperatures of the equator, and disembark in the neighborhood of the South Pole? Disembark seems to be the right word to describe the means of transport used by the great spider crabs to reach Antarctica. “We suspect that the crustaceans may have entered the Antarctic peninsula encrusted on the hulls of ships or in the midst of their ballast water”, Melo comments. For the researchers, due to the proportions of the crustaceans, a little too big for them to be lodged on the outer walls of the ships, the second hypothesis is the more probable.

“The traffic of ships in the Austral Ocean has increased a lot in the last few decades because of the rise in the activities of research, fishing and tourism”, Melo explains. It is estimated that there are 4,000 researchers living in Antarctica during the summer months. In the winter, this figure is reduced to a thousand scientists. The quantity of tourists that visit the glaciers and the penguins in the white continent is reaching the 10,000, sometimes 15,000, mark. Imagine the boats needed to transport all these people. This is without mentioning the fishing boats, usually in search of the abundant krill, a kind of crustacean similar to shrimps.

Holds with water
There is no concrete evidence that ballast water was actually responsible for the introduction of the H. araneus into the Austral Ocean. By excluding the other alternatives, it is the one left over to be investigated. This is because the other ways of introducing exotic marine species, like the commercial cultivation of fish and crustaceans or the construction of navigational channels, are no part of the reality of the white continent. These hypotheses make sense in other points of the globe, but not in Antarctica.

Stored in the ships’ holds, in sealed compartments, ballast water is essential for guaranteeing good navigability and structural integrity, above all in cargo vessels. “Ships are designed to travel with their holds full of merchandise”, says Tavares. By virtue of these characteristics, when there is no cargo to be taken from one place to another, the ships move around with their holds full of water – the so-called ballast water, rich in samples of the local fauna and flora ? to guarantee their balance. When they reach their destination, where they are going to be stocked up with products or fish, they pour out the ballast water taken on board at the port of origin, to avoid excess weight.

The International Maritime Organization (IMO), an agency of the United Nations that monitors the safety of naval transport, estimates that about 7,000 marine species, often in the form of larvae, travel in the tanks with the ballast water of the international naval fleet, thus invading habitats distant from their natural environment. This is not to count microorganisms and bacteria, like the cholera vibrio, which can also be transported in this way.

The involuntary introduction of exotic species brought about by the ships that carry about 80% of the merchandise traded in the globalized world has resulted in significant alterations in ecosystems in some parts of the world, with implications of an environmental, sanitary, and often economic nature. In the United States, a species freshwater mollusk of European origin, the zebra mussel (Dreissena polymorpha), reached, via ballast water, probably at the beginning of the 1980’s, the Great Lakes, and has spread over 40% of the country’s navigable rivers. Between 1989 and 2000, the costs for controlling this pest, whose shell sticks to anything solid, were estimated at US$ 750 million at the least.

There is no lack of stories similar to the zebra mussel’s in other parts of the planet, including in Brazil. Native to the Pacific Ocean, the Charybdis hellerii crab, after colonizing the eastern Mediterranean, migrated to the Atlantic in the 1980’s, possibly on board the ballast water compartments of vessels that called on ports in Israel. Also in that decade, specimens of this marine species were found in Cuba, in Venezuela, and in the Colombian Caribbean.

In 1995, its presence was spotted in Florida and in Rio de Janeiro. Today, the C. hellerii, which may become a competitor for the habitat normally occupied by commercially important crustaceans, is to be found in seven Brazilian coastal states, at the least. Another famous case of the accidental introduction of an exotic species into the Brazilian territory is the story of the golden mussel (Limnoperna fortunei), of Asian origin.

Transported in ships’ ballast water, the mollusk appeared firstly in the River Plate, in Argentina, in the 1990’s. Nowadays, it is present in some rivers in the south of Brazil. Like the zebra mussel in the United States, the shell of the L. fortunei is very sticky. One of its side effects is sticking to the turbines of the Itaipu power station, in Foz do Iguaçu, north of Paraná, and increasing the trouble and expense with cleaning the hydroelectric machinery.

One cannot, however, generalize and debit the arrival of all the invasive marine species as a liability of the ballast water. The Pacific white shrimp, Litopenaeus vannamei, was introduced into Rio Grande do Norte in 1981 for commercial cultivation in hatcheries, usually on land by the seaside, which makes it easier to get seawater for the crustaceans. This species, of Asiatic origin, is today the kind of shrimp most cultivated in Brazil, generating millions of dollars for the export trade.

Some biologists are afraid that the white shrimp, very susceptible to viral diseases, may be attacked by the TSV virus, which attacked in the American states of Texas and South Carolina in the middle of the last decade, and transmit this exotic pathogen to native species of shrimps. There is a similar concern with the Procambarus clarkii crayfish, native to the south of the United States. Brought to Brazil by breeders and much appreciated by aquarium owners, the species carries a fungus, Aphanomices astaci, to which it is insensitive, but which can be harmful to other marine beings.

“The introduction of exotic species is environmental roulette”, Tavares says. “Its consequences are unforeseeable.” The problem is that, as the discovery of the pair of giant spider crabs from the Arctic right in the middle of the Austral Ocean demonstrates, no stretch of the sea is free of this game of chance. Not even around the Antarctic, where the wheel has started to do its first few spins.