Octopuses multiply while fisheries collapse, and coral reefs bleach

As many coral reefs are withering causing a loss of habitat for many fish, and as some fisheries virtually collapse, octopuses and other cephalopods are thriving.

There are about 800 living species of cephalopods including squids, octopuses, and cuttlefish. All live in salt water. Some fishermen call them "inkfish" as most of them can eject what looks like ink as a means to hide themselves. An analysis just published in Current Biology shows that numerous cephalopod species have increased their numbers since 1950.

The study was carried out by researchers at the University of Adelaide in Australia. Zoe Doubleday, the lead author said: “The consistency was the biggest surprise. Cephalopods are notoriously variable, and population abundance can fluctuate wildly, both within and among species. Cephalopods tend to boom and bust—they’re called the weeds of the sea.”Ironically the Australian study was begun after researchers were investigating a sudden crash in the population of the giant Australian cuttlefish.

The researchers are not certain exactly why many cephalopod species are doing so well but they can point to a number of factors that could contribute to the increase. They note that when environmental conditions are favorable, the cehalopod numbers can increase very rapidly. One of the main controls on cephalopods are predatory fish many of which are being eaten by humans. Global warming may also be a factor. Doubleday said that she did not think that there was just one single factor causing the increase in cephalopod numbers. The Adelaide study showed evidence of an increase in cephalopod numbers both in scientific data, and also fisheries records. Most species live only a year or two, dying after they give birth. They grow very quickly. They are also voracious eaters with some species eating 30 per cent of their body weight each day as adults.

Paul Rodhouse, a biological oceanographer with the British Antarcic Survey in Cambridge UK said:“This is not a sensational ‘cephalopods are taking over the world’s oceans’ story.” Further climate change could have unpredictable effects, squeezing generation times to less than a year and throwing off some species’ annual mating gatherings in the process.There is evidence that there is increasing acidification of oceans. This could impair development of some cephalopods. As many species of fish become less available for eating, humans may come to eat more squid and octopuses. If cephalopods increase too much in an area they simply may run out of food. They are also cannibalistic which also helps areas becoming too overcrowded with them. As Doubleday puts it: “There’s always competition stabilizing things. I don’t know whether we’ll eat them first or they’ll start eating each other.”