When snails attack

Via a whole bunch of people, and rightly so. A fascinating and disgusting look at the highly complex interplay between different ecologies. Though, "When Sails Attack" would be a much better title for the inevitable Asylum movie... :P
(http://www.theasylum.cc/)

Near to Marcus was Malgas Island—so named for the gannets, a kind of seabird, which nest there (Malgas is old Dutch for “mad geese”)—which looks entirely similar to Marcus Island from the surface. The seabed, however, told Barkai a very different story. Although they’re just a few kilometers apart, the species he saw “were strikingly different,” he said. West Coast Rock Lobsters (Jasus lalandii) or ‘kreef’ as they are known locally were everywhere around Malgas. Several hundred of them per square meter crowded into crevices and under ledges—there was “basically nothing else.” To find anything that wasn’t a lobster, he had to peek under the holdfasts connecting the kelp to the substrate. There, he found mussels and a few Burnupena papyracea—small whelks (a kind of marine snail).

Around Marcus Island, though, “the bottom was covered with anything but lobster,” Barkai said. A dense mat of mussels lined the benthos, and it was decorated with whelks, sea urchins, and sea cucumbers galore, but nary a lobster to be seen.

After consulting with Branch, Barkai decided to conduct an experiment—”a very naive and not really well thought out idea,” as he now describes it. He planned to take about a thousand lobsters from Malgas and move them to Marcus to see how they fared.

Which might seem like a Category One level idea of Maximum Possible Ecological Stupidity, but it's not quite so outrageous :

...Barkai dug into the history of the two islands, and he learned that Marcus actually was a lobster paradise once—just 20 years prior. But that was before the bay was a marine reserve, and Marcus’ connection to land made it a popular lobster fishing ground. He suspects that the lobsters there were overfished, essentially to local extinction.

Which means this would be re-introducing a species that had gone locally extinct thanks to human interference, rather than the thoughtless meddling it might as first appear. Anyway, to return to the experiment :

“Visibility was great that day, and virtually the entire sea bottom started to move,” he said. That movement was countless whelks. They started to climb onto the newcomers, sticking to their legs. “I didn’t know then, but they’d started to suck them alive, basically. It was like a horror movie,” Barkai said. “It actually was a bit frightening to watch.” The lobsters simply didn’t know how to respond. They were outnumbered and overwhelmed. To my horror, in about 30, 40 minutes, all the lobsters were killed.”

Branch and Barkai soon realized they were looking at strong evidence for alternative stable states—the somewhat controversial idea that an ecosystem can exist in very different yet completely stable configurations. “A lot of scientists are skeptical,” said Branch, but further studies on the islands have made a convincing case. Branch (now an emeritus professor at the University of Cape Town) and his colleagues conducted surveys in 2016, and little has changed. “Malgas Island is still dominated by lobsters,” Branch said. “Their numbers are not as great as they were, but nonetheless, there are still large numbers there… And Marcus still has huge numbers of whelks and no lobsters.” So the two very different ecosystems have proven stable for more than 30 years.
http://blogs.discovermagazine.com/science-sushi/2018/08/27/predator-prey-reversal-whelk-lobster-amos-barkai/