ALL AT SEA - The New Wild: Why Invasive Species will be Natures Salvation - page 28

pollution—from sewage outfalls and so on,” he told me. The sea grasses that Meinesz said had been
killed off by Caulerpa were already in a bad state before the alien weed came down the pipe from the
museum. The weed was not a killer but an opportunist. Its spread was “the long-term effect of pollution
over two or three decades in the Cote d'Azur.” If the pollution receded, so, in all probability, would the
infestation.
I must admit that at the time I didn't entirely believe him. But it turned out Chisholm was right.
Tim Glasby of the Port Stephens Fisheries Institute in New South Wales, who had seen a similar boom
and bust with Caulerpa in Australia, says that its arrival could be seen as the first stage of ecological
recovery along the Riviera, rather than decline. The new arrival had not pushed out rich sea meadows
but colonized bare rock and sediment that the meadows had vacated. It was savior rather than villain. It
has turned out that many Caulerpa beds in the Mediterranean had more marine life, and more species,
than the former sea meadows. Clams did especially well, and cockles hid from predators in its green em-
brace. The weed from the Indian Ocean liked sewage pollution so much that it was an effective means
of treating the stuff. It might, theoretically at least, eventually help the return of sea grasses. It began to
look like Jacques Cousteau's poor aquarium hygiene three decades ago had done the Mediterranean a
good turn. And that the “killer” algae's recent decline might be a bigger problem for marine life than its
arrival.
To me this was a fascinating story, at least as interesting as the original upsurge in the weed—and
arguably much more revealing. Yet marine biologists seemed much less eager to report and analyze the
retreat of Caulerpa than its spectacular arrival. Published papers were rare, and the entry for Caulerpa
in the supposedly authoritative Global Invasive Species Database of the IUCN had not been updated for
almost a decade. In late 2013, it said nothing about the weed's demise. It claimed the weed still covered
more than thirty thousand acres along the Riviera, something that had not been true for many years. And
it continued to insist that Caulerpa “excludes almost all marine life,” which is demonstrably untrue. 13
The stories of Caulerpa , Mnemiopsis , and many others show how we instinctively blame aliens for
ecological problems that may have a lot more to do with our own treatment of nature. Like ranting xeno-
phobes in human affairs, conservationists too often think the worst of the aliens. But if we must think in
terms of good and bad, then aliens can be good too. Successful aliens are usually just taking advantage
of what they find. Indeed, on occasions, they are, if we give them a chance, part of the solution rather
than the problem. Caulerpa moved onto bare rocks after sea meadows had been vanquished by pollu-
tion, creating not an ecological desert but a rich nursery for marine life.
The oceans are a good medium for species to travel the world. These organisms don't need a ballast tank,
though that clearly makes it easier. Anything capable of staying afloat and capturing food can travel
anywhere the currents will take it. But equally, in the oceans it is hard to say what is alien and what is
not. Indeed, the very idea of species having a unique home to which they are uniquely adapted makes
even less sense than it does on land. Many marine organisms cross the oceans as part of their natural life
cycles. And these migrants often take many more unsuspecting species along for the ride. The oceans
are alive with tree branches, animal carcasses, and other organic detritus washed down rivers. The larger
items will often be inhabited by other species that either live on their floating home or join en route.
These days, it is true that there is more junk in the oceans to provide lifts for would-be migrants.
Human activity on land, like cutting down forests, creates potential seafarers, and we also provide con-
tainers. The oceans are full of plastic: beverage bottles, abandoned fishing nets, six-pack rings, and