But who are the colonizers?
I have a friend in Finland, who owns a yacht, a big and costly one. And that means every weekend in the summer he’s got to go sailing and he has little time for anything else. A yacht is not exactly cheap and once you’ve got one you had better use it. Although this limits the choices you have to spend your weekends, there are two further aspects to consider (quite apart from choosing which kind of hull for your boat would be best): firstly, in winter the yacht has to be taken out of the water as the latter will be frozen for several months and secondly you need to make sure that not too many organisms settle on the hull. Paints to discourage the settlers can be applied, but once in a while the hull needs a cleaning.
Nowadays fibreglass boats are the most common around and they have, of course, the advantage over the more traditional wooden hulls that boring organisms have a much harder time to get into the fibreglass than into the wooden hulls. Collectively referred to as the ’infauna’ and exemplified by the feared shipworm (which is not a worm at all, but a kind of clam), the infauna used to be a dreaded problem, but the so-called epifauna (and flora) on the surface of the hull can also make the life of a sailboat owner a bit difficult. Not only will a luxurious growth of seaweeds and the presence of goose and related barnacles, bivalves, snails, sea anemones, sea squirts and a multitude of other organisms slow the vessel down, it is also not exactly cheap to get all these epibionts removed.
To what extent a ship gets colonized by which kinds of organisms depends on many factors: the material of the hull has already been mentioned, but salinity of the water and temperature are also very important. Whether the boat is stationary or moving is another factor and so is the shape of the hull and the ship’s draft. As with the body of a whale, colonized by a variety of epibionts, the success of a colonizer to remain attached to the hull of a yacht also depends where precisely the colonizer will best survive. Some species prefer the ship’s bow, others the stern near the propeller or the ship’s sides. What yacht owners often do not realize is that their unwanted epibiotic settlers can be passively transported by the boat to places where they had not been present before; in other words it is not only the ballast water that is usually held responsible for so many unwanted introductions of species here and there, but alien species can also be carried around on a ship’s hull.
A researcher with the beautiful name of Cristina Maria Rocha Farrapeira and her colleagues in Brazil have examined the hulls of 32 vessels and published their results in 2007. They did not look at the epifauna that would almost certainly have consisted of a variety of seaweeds and other algae with their own microscopic army of microorganisms, but they focused on identifiable and macroscopically visible animal species. Unsurprisingly, of the 60 species they found, 33 were crustaceans and of these 31 belonged to the Cirripedia, i.e. the barnacles and kin. Molluscs were the second most abundant creatures with bivalves (such as oysters and mussels) being responsible for eight species and snails for six species. Relatives of jellyfish and polyps were represented by three species and so-called moss animals (Bryozoa) and sea squirts (Urochordata) had two species each. In between the epibiontic organisms the researchers located flatworms, roundworms and seven species of segmented worms which like barnacles and molluscs attach themselves firmly to the boat’s hull and can only be removed by harsh scrubbing. If I now conclude that rather than owning a yacht myself, I prefer to be invited to take part in an occasional cruise, I think you’ll understand.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021.
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