Authors: Roland C. Anderson
Octopus (2 page)
Octopuses will eat almost any animal that can't get away from them. Their menu depends on size. Tiny pygmy octopuses eat small hermit crabs, and adult giant Pacific octopuses favor big Dungeness crabs and geoduck clams. They have lots of ways of getting into shelled preyâscraping with their teeth, or radula, grasping with their parrotlike beak, even drilling a
hole in the shell of a clam and injecting venom to weaken the muscles so the shell gapes open. The octopus's toxic venom also contains enzymes that start digesting the food. We found that the common octopuses we studied in Bonaire ate seventy-five different animal species. Sifting through the shells of their prey in the midden, or garbage heap, outside their sheltering homes, we discovered that their food ranged from immature conch snails and pen shell clams to shore crabs and shrimp. Some octopuses seem to specialize in one or a few species: the spoon-arm octopus eats brittle stars, one of the few animals common in the deep. Some octopuses have favorite species: the Hawaiian day octopus eats crabs almost exclusively, while the night-active white-striped octopus (Octopus ornatus) in the same islands eats cowry sea snails. All common octopuses adapt, as studies across their huge range have shown, to eating whatever is most easily available where they live.
Surfing the Web for Science
In 2008, Roland completed the data analysis for our study of whether octopuses can remember and recognize individual humans (yes, they can). One measure that distinguished octopuses' reactions to a person who fed them from their reactions to a person who hassled them by touching them with a piece of Astroturf-covered plastic pipe was a specific skin display, the eyebar. The eyebar extends the horizontal line of the octopus's horizontal pupil slit onto the skin on either side of the eye, presumably making the eye look less like an eye. An eye is a dead giveaway that you're facing an animal and not just a piece of the landscape. Many animals manipulate the appearance of the eyes, disguising their real ones or adding fake eyes as displays on the skin, to startle or confuse predators.
All we knew about the eyebar display at that point was that we had seen it when the octopus was annoyed. So I promised Roland that I would look into the structure of the display and its occurrence in different octopus species. How to begin? One situation that qualifies as annoyance to an octopus is being stalked by an underwater photographer, who appears literally in the animal's face, with lots of equipment and trailing streams of bubbles, letting off flash after flash in the octopus's eyes. It's not surprising that when I looked at pictures of octopuses, I saw a large proportion with eyebars.
I gathered photographs of octopuses from colleagues, especially Roland, James, and former graduate student Tatiana Leite, primarily of the common octopus and the giant Pacific octopus. But wanting more, I went to the Web. Finding countless pictures of live octopuses, I selected ones with eyebar displays to enter into my database. I chose the common octopus, the giant Pacific octopus, and the Hawaiian day octopusâspecies that live in different areas of the world, so that even if the Internet photo description didn't identify the species, I could figure it out from the location where the photo was taken.
After Tatiana ran the photos through a sophisticated data analysis, we found some intriguing things about the display. It's nearly always symmetricalâthe line extends on the skin both forward and backward from the eyeâand it's painted on the same mottled, pale or red background around the eye. The display is also different among the three species, dark and pencil thin for common octopuses, and wider, delineated by thin white stripes in the other two species. We don't yet know what situations cause octopuses to put the eyebar on their skin, but we do know what it looks like, which is a first step.
This was the first (and probably only) time I've done a research study without leaving my desk.
âJennifer A. Mather
Even if they get very big, like the giant Pacific octopus, all the group live short lives. The longest octopus lifespan is three to four years, and most of the smaller octopuses die after about six months to a year. Most species start off very tiny, floating in and eating the tiny organisms of the plankton of the upper open ocean, and then they settle to the sea bottom as they get bigger. Young octopuses have only two things on their mind, eating and not getting eaten. They convert food to body muscle and fat very efficiently, partly because they are poikilothermsâthey don't spend energy keeping their body warm. At the end of their life cycle, after being solitary animals, octopuses get interested in sex and find each other for mating. After mating, males become senescent and soon die. The female lays from fifty to tens of thousands of eggs, and tends them faithfully, keeping them well oxygenated, clean, and protected from predators. After the eggs hatch, the female dies.
Many octopus babies travel a long distance between the time they hatch and the time they settle to the bottom. Eggs of the smaller octopuses are only about
in. (3 mm) long. When they hatch, the babies rise to the surface of the water and are washed out to sea or along the shore, floating great distances on marine currents. If they survive, young octopuses eventually get heavy enough that they settle to the bottom, find a likely rocky ledge, muddy bottom, or boulder field, and make a home there. But this isn't true for all octopuses. In California, there are two species of two-spot octopus that look very much alike. One species, Verrill's two-spot octopus (Octopus bimaculatus), lays 20,000 tiny eggs that hatch into planktonic (open-ocean surface) young. But the second species, the Californian two-spot octopus (O. bimaculoides), lays 800 eggs that are five times as long as those of the other species, and when the babies hatch, they are benthic youngâthey just crawl out and start their life on the bottom of the ocean right away.
Divers and aquarium visitors are fascinated by the octopus's appearance. Octopuses can change what they look like in less than 30 milliseconds by expanding tiny pigment sacs in the skin, chromatophores. They can go from dark to pale, plain to patterned, rough to smooth, and a clumped shape to an elongated form. They change their appearance mostly to hide from predators, camouflaging to match the colors and the patterns of their background. Over brown algae, they will go blotchy brown, on sand they can change to tiny dappled grays and blacks, and under the shade of a rock they can become plum-purple. They can make half of the body pale and the other half dark (see plate 2). And when an octopus is finished matching its background and lifts off to swim away, it can put on a striped pattern, making it harder for a predator to track it. If all else fails, an octopus can squirt out a cloud of ink so the predator loses sight of it.
Although the octopus hides as much as possible to avoid trouble, there is another side to these animals: they can be deadly predators. They can bite into prey with their beak and inject venom from the salivary gland. A small Caribbean pygmy octopus (Octopus joubini/mercatoris) can catch a crab its own weight, and after one quick bite the crab stops moving and in thirty seconds it is dead. One of the most deadly marine animals is the blue-ringed octopus (Hapalochlaena maculosa) of Australia; its venom can be fatal to humans (see plate 3).
What's in a Name
?
Throughout this book and in scientific publications, animals are referred to by their scientific namesâby genus and speciesâthough we also use common names when they exist. Why not just use common names? The answer is that they are not common, but vary with the location. Think of the robin, quite a different bird in England than in North America, but known by the same common name. In the early eighteenth century, Swedish scientist Carl Linnaeus developed the system of nomenclature for animals and plants, using ancient Latin and Greek linguistics to form binomial scientific names, and it has proved a great blessing for sorting out the diversity of animals and plants. For instance, wherever it occurs,
Octopus vulgaris
is an animal name everyone can understand. And the sorting also tells us about relatedness: every species in the genus
Octopus
is related to others in that genus, and is a bit more distantly related to those in the genus
Enteroctopus
, like
Enteroctopus dofleini
.
How do animals get their scientific names? The scientist who reports a species as a new one has the privilege of naming it or of having it eventually named after him or her. Sometimes an animal is named for a particular feature, like the two-spot octopus,
Octopus bimaculoides
. Sometimes the name refers to where the animal lives; a good example is
Vulcanoctopus infernalis
, which lives around deep-sea volcanic vents. Sometimes the name honors a previous researcher, so
Octopus joubini
is named after French naturalist Louis Joubin, who studied cephalopods in the nineteenth century (
O. joubini
was split into
joubini
and
mercatoris
). Sometimes the name is more whimsical, like
Wunderpus photogenicus
, which was known to divers as very photogenic years before it was described by scientists.
Just because scientific names are useful and commonly used doesn't mean they are fixed in stone; in fact they are fairly changeable. A species is an interbreeding group of animals that doesn't interbreed with other groups, and this can change. Sometimes these taxonomic decisions are challenging for those who are just studying behavior, since it makes us question what species we are working with. I've studied six octopuses over thirty years, and during that time, taxonomists have changed the species name of one of the animals I studied, the genus of another, and we are still not sure of the taxonomic relationships of
Octopus vulgaris
.
âJennifer A. Mather
A Guide to the Mollusks in the Book
Here are genus and species names for the mollusks discussed in this book, alphabetically within each group, with common names when they exist, based on Mark Norman 2000.
Genus
Octopus
| Octopus abaculus | âââ |
| Octopus alpheus | Capricorn night octopus |
| Octopus bimaculatus | Verrill's two-spot octopus |
| Octopus bimaculoides | Californian two-spot octopus |
| Octopus briareus | Caribbean reef octopus |
| Octopus chierchiae | âââ |
| Octopus cyanea | Hawaiian day octopus |
| Octopus defilippi | Atlantic long-arm octopus |
| Octopus dierythraeus | red-spot night octopus |
| Octopus digueti | Diguet's pygmy octopus |
| Octopus insularis | âââ |
| Octopus joubini/mercatoris | Caribbean pygmy octopus |
| Octopus macropus | white-spotted night octopus |
| Octopus mimus | âââ |
| Octopus ornatus | white-striped octopus |
| Octopus rubescens | red octopus |
| Octopus vulgaris | common octopus |
| Octopus wolfi | star-sucker pygmy octopus |
| Octopus zonatus | âââ |
Other Members of the Order Octopoda
| Abdopus aculeatus | âââ |
| Ameloctopus litoralis | banded string-arm octopus |
| Argonauta argo | argonaut |
| Bathypolypus arcticus | spoon-arm octopus |
| Cirrothauma murrayi | blind cirrate octopus |
| Enteroctopus (Octopus) dofleini | giant Pacific octopus |
| Grimpella thaumastocheir | velvet octopus |
| Hapalochlaena maculosa | blue-ringed octopus |
| Ocythoe tuberculata | football octopus |
| Opisthoteuthis californiana | flapjack devilfish |
| Thaumoctopus mimicus | mimic octopus |
| Vitreledonella richardi | glass octopus |
| Vulcanoctopus hydrothermalis | deep-sea vent octopus |
| Wunderpus photogenicus | wunderpus |
Other Members of the Class Cephalopoda
| Architeuthis dux | giant squid |
| Cranchia scabra | glass squid |
| Dosidicus gigas | Humboldt squid |
| Euprymna scolopes | Hawaiian bobtail squid |
| Euprymna tasmanica | southern bobtail squid |
| Heteroteuthis dispar | âââ |
| Idiosepius pygmaeus | pygmy squid |
| Metasepia pfefferi | flamboyant cuttlefish |
| Nautilus spp. | nautilus |
| Rossia pacifica | stubby squid |
| Sepia apama | giant cuttlefish |
| Sepia latimanus | broadclub cuttlefish |
| Sepia officinalis | common cuttlefish |
| Sepioteuthis sepioidea | Caribbean reef squid |
| Vampyroteuthis infernalis | vampire squid |
Other Members of the Phylum Mollusca
| Aplysia californica | sea hare |
| Arca zebra | zebra mussel |
| Archidoris montereyensis | sea lemon nudibranch |
| Clione limacina | sea angel |
| Crepidula fornicata | slipper limpet |
| Ctenoides spp. | file clam |
| Humilaria kennerleyi | Kennerley's venus clam |
| Janthina janthina | janthina |
| Lima spp. | file clam |
| Melibe leonina | lion nudibranch |
| Pinna carnea | pen shell clam |
| Protothaca staminea | Pacific littleneck clam |
| Strombus gigas | queen conch |
| Tegula funebralis | top snail |
| Venerupis philippinarum | Manila clam |