This is an environmental issue that emerged in the 1990s, though the reasons for it go back much further. For example, the building of the Suez Canal has resulted in the movement of many species from the Red Sea into the eastern Mediterranean, some of which, like large sharks, are not popular newcomers. Another route is the expansion of shellfish culture, especially of oysters, in which the local stocks have been ‘improved’ by the introduction of larger, faster-growing species from far afield, often bringing with them pests and diseases that have subsequently run rampant. The growing popularity of keeping marine species in aquaria has also resulted in the importation of undesirable new species, the most notorious of these being the appearance of a vigorous spore of a highly invasive green seaweed, Caulerpa, beneath the windows of the marine aquarium in Monaco. This male spore can only reproduce by fragments of it being carried around by ships. However, once established it overgrows the local seaweed communities, drastically reducing the diversity, and destroying local fisheries. Not being able to breed sexually has been no bar to its dispersal; in two decades it has become established all round the western Mediterranean and is now in the eastern Mediterranean, most probably carried on the anchors of pleasure craft. Even more surprising has been its recent appearance in the seas off Japan, Australia, and California, in each case probably as a result of establishing marine aquaria.
