Friday, June 1, 2012

Giant Pacific Octopuses - No Mother Could Give More!

No matter how many Talk and Walk presentations I attend, I am constantly amazed at the breadth and depth of knowledge that people freely and generously give.
April was a case in point when Jim Cosgrove, former head of Natural History Collections at RBCM, agreed to come out to Metchosin to give a talk on octopuses.
His enthusiasm and fondness for these sea creatures was evident throughout the evening as he informed and amused with his twenty plus years of research and experiences with these mollusks.
And it is octopuses, not octopi (which is a pie of eight servings...).
These amazing and intelligent creatures are cephalopods, in the same phylum, Mollusca, as squid and cuttlefish and their terrestrial relatives of which we are more familiar, slugs and snails.
Two of the world's 300 plus octopus species are generally found off BC's shores. The Ruby octopus (Octopus rubescens) only weights 100 to 400 grams, with arms that reach thirty to forty cm. The Giant Pacific Octopus (O. dofleini), with a range from California to Korea, is considered the largest of all octopuses. Jim once found a specimen that measured almost seven metres across (twenty-two feet) and weighed over seventy kilograms (156 lbs). Wikipedia reports the largest ever found weighed 600 lbs and had an arm spread of thirty feet (that’s 272 kilograms and over nine meters)! Generally they mature at thirty-five lbs, about sixteen kg, with an arm span of fourteen feet, a little over four metres.
Octopuses do not have tentacles, they have eight arms, covered with 200 very sensitive suckers per arm. Fifty percent of their nerves are located in their arms, which have enormous strength, one sucker (3.5 to 4 inches across) can lift thirty-five lbs (sixteen kg), times 200 suckers, well...that is brute strength can't pull them from their dens. The suckers are used to explore their world, tasting whatever they touch.
Besides humans - harbour seals, sea lions, some beaked whales, ling cod and halibut are their usual predators - creatures that use their visual sense to hunt. Octopuses have developed a range of strategies in order to evade capture. Specialised cells in their skin, called chromatophores, which can change colour and texture in a fraction of a second, are an effective, primary means of avoiding predation, when they appear to disappear. Hiding in rocks, shells and crevices, fleeing at great speed, and of course, shooting jets of "ink" are all in their arsenal of survival techniques. Their eyes are not restricted by any bone structure, so they can move anywhere in their head, giving them a further advantage in eluding predators.
They generally propel themselves by pushing their arms back or through "jet propulsion", where they take in water and forcefully release it through a siphon.
As predators, octopuses gather their prey into the upper part of their arms, the interbrachial web, which can form a large sac. An anesthetic is injected into this area, immobilising their prey. They can then either use their rasp-like tongue to drill into a shell, or their powerful beak to break it apart; their salivary glands reduce the meat into a fluid they can ingest. At dawn and dusk, Giant Pacific adult octopuses hunt crabs and clams, but will also hunt and consume larger species such as dogfish. Recently, a story and photos of an octopus catching a gull off the rocks at Ogden Point in Victoria has garnered international attention.
An octopus has a short life span, often only two or three years, although the Giant Pacific Octopus can live up to five years, which is remarkable when you consider their amazing intelligence and the fact they do not receive any knowledge directly from their parents. They learn through trial and error, although octopuses in neighboring tanks have learned from observing each other.
There are many documented instances of a captive octopus leaving it's supposedly secure tank, slithering across aquarium and lab floors, entering other fish tanks and consuming the fish, then returning to their own tanks. Staff would be scratching their heads, wondering how all the fish had disappeared without a trace with no intruder alarms sounding. It wasn't until videos were installed to watch the suspicious night-time activities that the true culprit was identified.
In another show of their intelligence, an octopus was placed in a tank with a jar, which it was left to explore for several days. Eventually the scientists placed a crab in the jar, and within a short period of time, the octopus was able to remove the crab. Then they put a cork on the jar and within a few minutes, the octopus was able to pop the cork and again remove the crab. They continued to make it harder and harder for the octopus to get at the crab in the jar and each time the octopus was able to open the jar and remove the crab. It could remember this even after months had gone by. I only wish my own memory was half as good! With another octopus test subject, the octopus was one step ahead of the scientists and as soon as it saw them enter the room, it would enter the jar and wait for the crab!
I think all parents have considered at one time or another that they have made great sacrifices for their children, I'm convinced that the worry of my children's teenage misadventures has probably reduced my life expectancy by a number of years....
We hold no candle to a mother octopus though! When a female Giant Pacific Octopus  is ready to reproduce, at three to four years, she gives off a pheromone to attract a mate. The male will transfer a sperm sac which she will store for about a month as she searches for the perfect den, usually under an overhanging boulder. She will then amass a large pile of rocks and eventually seal herself into the den.
She individually fertilizes each one of her 55,000 to 75,000 eggs and glues them onto strings holding about 175 eggs each, which she attaches to the ceiling. When this has been accomplished, over approximately one month, she devotes her attention to keeping them groomed and clean of algae and bacteria, or anything else that might hinder their development. She continually blows air around the eggs, to provide a constant supply of oxygen. The minute (.028 gram) babies, called paralarvae, only the size of a grain of rice, hatch in 240-270 days. Again the mother works tirelessly to help her babies by blowing water and thrashing the eggs, which aids them in their escape from their embryonic sacs. Without this motherly intervention, most babies would not be able to hatch. During this entire time the mother has not left her nest, or eaten - losing half to three quarters of her weight.  She dies 220 to 270 days after reproduction, which can mean that some mothers might die before their young have fully developed and hatched. Even with a successful brood, it's estimated that only two, of her 75,000 octopus babies, will survive to adulthood.
Males are sexually mature at three and a half years, after mating they will live only a short period, becoming senescent and displaying inappropriate behaviour....sometimes crawling onto land and following people.
Octopuses are fascinating creatures, living in a marine world that is alien to most of us. Their adaptable minds and bodies have evolved survival mechanisms far outside of our terrestrial adaptations. But no amount of evolutionary success will enable them to withstand the effects of shipping accidents and oil spills and the over-harvesting of our oceans.

picture from:

No comments: