Octopus' garden in the Pacific Ocean off Costa Rica
© Current Science written by Rene Ebersole
I'm anxiously waiting beneath warm, blue tropical water for the creature to ooze from its den. My heart pounds as one purplish, sucker-lined arm emerges from under a rock. Then another arm emerges, and another, and another. Then comes a gelatinous head, topped by two beady eyes.
I wait a few more seconds, take a deep breath, and grab the octopus. It squishes and squirms in my hands and shoots a cloud of black ink at me. I can no longer see the eight-armed invertebrate, but I can feel it slipping from my grip. Under the cover of its inky cloud, the octopus retreats deep into its den.
Normally, I don't harass octopuses. This encounter was purely for the sake of science. I recently took an Earthwatch expedition to a remote Costa Rican island off the country's northwest coast to assist a scientist with his octopus research. The Earthwatch Institute is a nonprofit organization that supports the work of scientists by sending volunteers to help collect data in the field.
TREASURE ISLAND
The leader of our expedition was marine biologist John Cigliano. A marine biologist is a scientist who studies life-forms in the sea. Cigliano also teaches at Cedar Crest College, in Allentown, Pa.
Cigliano selected his Costa Rican research site for three reasons. First, the waters that wash the white, sandy beaches of San Jose Island--the largest of Costa Rica's Bat Islands (Islas Murcielagos)--hold a treasure trove of sea life. Second, Cigliano's specialty is octopuses, and little is known about the ones that inhabit that part of the world. Third, the Bat Islands octopuses could be in trouble.
Every year, fishermen harvest thousands of the strange sea creatures from the islands' waters to satisfy a growing global appetite for octopus in salads, sauces, sautes, and sushi. (See page 6, "Is That a Sucker in My Salad?") Cigliano fears that if fishermen harvest too many of Costa Rica's octopuses, some species might vanish.
"Virtually nothing is known about these octopuses," he explained. "Yet they're being fished. We don't know what effect this has on octopus populations and the communities that they inhabit."
OCTOPUS 101
Our team of 11 volunteers was charged with the task of helping Cigliano answer that question by capturing as many octopuses as we could. Once caught, the octopuses would be measured, examined for injuries, identified by species and sex, videotaped in an aquarium by Cigliano and his two research assistants, and then finally set free.
Before we began our work, we learned some octopus basics. "First," said Cigliano, "octopuses do not have tentacles. They have arms--eight of them. Squid have [arms and] tentacles."
Confusing arms and tentacles is a common mistake when it comes to the cephalopods, a group of animals whose limbs are attached directly to their heads. What's the difference between arms and tentacles? Arms are the eight grasping appendanges attached to the head of all cephalopods. Tentacles are two additional extra-long appendages that some cephalopods, such as squid and cuttlefish, use for capturing prey.
Cephalopods belong to a larger group, the mollusks, which also includes snails, clams, and oysters. Mollusks are soft-bodied animals, most of which live in the water and are protected by a hard shell.
Some cephalopods, such as the octopus, lack outer shells. Why? Cigliano explained that the octopus lost its shell as it evolved toward greater speed and agility. But with that loss of a shell, the octopus became more vulnerable to predatory eels and fish, so it had to master the art of hiding.
CHAMELEONS OF THE SEA
Just how well the octopus has mastered that art became apparent each time I donned a wet suit and scuba gear and dived into the waters of the Pacific off the Bat Islands. The bubbles from my regulator made a constant glug, glug, glug as I crawled along the seafloor, overturning shells and rocks and peering into crevices. Like circus contortionists, octopuses can hide in or under anything into which they can squeeze their squishy bodies.
Octopuses are also wizards of disguise. All around me, the water was awash with colorful fish swimming in and out of the gaps between rocks. When I illuminated those gaps with a flashlight, the head of a moray eel often shot out. Finding octopuses was much harder. An octopus can change its skin color to match most backgrounds. The secret of that camouflage, or disguise, is thousands of specialized elastic skin cells, called chromatophores, each of which contains a pigment (coloring agent).
To change its color, an octopus expands and contracts the circular muscles that surround the chromatophores. When a chromatophore expands, the pigment within it spreads out over a large surface area, making the cell look light in color. When the cell contracts, the pigment becomes concentrated in a small area, and the cell appears dark. By manipulating the chromatophores, octopuses can generate a palette of skin colors in a wide variety of patterns to match their surroundings.
ESCAPE ARTISTS
Despite the octopus's clever camouflage and its ability to fit into tight places, our group managed to find a few octopuses almost every time we plunged into the water. But catching an octopus was harder than finding one.
Octopuses are like magicians. They can get out of just about anything. And they produce a smoke screen to cover their escape. When threatened, an octopus releases a cloud of dark ink--a mixture of melanin, seawater, and mucus--from a special sac near its rectum to confuse predators. Melanin is a brownish-black pigment that also exists in human hair and skin. Though dozens of octopuses eluded our team of hunters, we managed to capture almost 20 individuals during our five-day stay on San Jose Island.
Cigliano's research has only just begun, but he may have already discovered a new octopus species. He calls it "Octopus guanacaste," in honor of Area de Conservation Guanacaste (ACG), the conservation area that encompasses the Bat Islands. The name won't be official until Cigliano is absolutely certain that no one has ever scientifically identified the species before. "You have to be really sure before you name a new species," he said, "because if it's not a new species, there will be major egg on your face."
Over the next few years, the information harvested from the animals our team captured will help Cigliano determine whether "Octopus guanacaste" is indeed a new species and whether fishing is a serious threat to the Bat Islands' octopuses.
As for the octopus that shot ink in my face, it eluded me by sealing the opening to its den with pebbles and shells. It left only a crack big enough for it to peek through with one beady eye. "Octopuses are fascinating animals," said Cigliano after my defeat. "When you look at them, they look back at you. You know there's something behind those eyes."
© Current Science written by Rene Ebersole