prefer stubby beer bottles to the long-necked variety and brown bottles rather than clear or green ones. Furthermore, they prefer âagedâ bottles that are covered with a growth of barnacles or sea anemones. These characteristics make the containers darker inside, so perhaps the octopus feels safer than in transparent glass.
Dens arenât just places for octopuses to hide. Other animals are attracted to the site of the octopusâs feeding activity, and some animals, such as juvenile parrotfish, arenât found in those sites because of habitat disruption by the digging octopus. Jennifer found that octopus dens in Hawaii attracted scavenging wrasse fish waiting for the scraps after the octopus had finished eating. And the dens also attracted hermit crabs, which need an empty snail shell in which to hide their soft abdomen, and what better place to find one than in the midden of a snail-eating octopus? The dug-up area with a diameter of 3 ft. (1 m) around the den will have less growth of algae, so herbivorous fish wonât bother to hang around in that area. These observations remind us that octopuses are part of a complex web of underwater life. They are attracted to specific den sites because they need to avoid being eaten by some animals. And then when there, they change the area, and therefore have influence on other species.
5
Getting Around
O ctopuses are a remarkable sight when they are out hunting. They seem to flow across the rocks, holding on with some of the eight arms and extending other arms into crevices and under rocks, occasionally lifting off the bottom and gliding about 3 ft. (1 m) or so. Anyone who has taken a long look at an octopus moving this way across the ocean floor or an aquarium tank has likely admired the animalâs fluid movement and flexibility.
There are two kinds of octopus movement: one is about control and coordinationâhow an octopus gets all the arms to do what it wants them to do. The other is locomotionâhow the octopus moves itself around in the environment. Regarding locomotion, the octopus looks as if it has a disadvantage because of its molluscan heritage. Snails and clams just donât move fast, and the molluscan foot, unlike the limbs of vertebrates and arthropods, isnât designed to produce speed of movement. Biologist Richard Mc-Neil Alexander, in his 2003 overview of movement styles among animals, points out that each species makes compromises in balancing the demands for speed and maneuverability with the need to limit energy output. These compromises that octopuses make, based in their phylogenetic history, are intriguing aspects of their means of getting around their environment.
One obvious aspect of locomotion is maximum speed, which varies depending on the medium you are moving through. Cephalopods donât have much speed, comparatively. The cheetah, for example, can manage a top speed of 90 ft. (27 m) per second, which is very fast. Still, the cheetah tires very quickly, and so a prey animal that dodges and runs from it may avoid capture. The pronghorn antelope of the North American prairies specializes in sustained speed and can keep a speed of over 50 ft. (15 m) per second for over ten minutes. Air speed can be faster than land speed since air is not dense, and birds manage sustained speeds near 60 ft. (18 m) per second. A diving peregrine falcon can achieve a gravity-assisted top speed of 170 ft. (50 m) per second, the fastest known. Sea animals are at a disadvantagebecause of the high density of water: dolphins manage 30 ft. (9 m) per second, and pike can accelerate to 12 ft. (4 m) in less than a second. Squid, the fastest cephalopod, can only move 8 ft. (2.4 m) per second, and octopuses 1 ft. (m) per second. Clearly, cephalopods canât always out-swim fish.
Another demand for locomotion is maneuverability or change in direction. This feature is very useful in the short run, for a predator can be dodged if it canât be
Dens arenât just places for octopuses to hide. Other animals are attracted to the site of the octopusâs feeding activity, and some animals, such as juvenile parrotfish, arenât found in those sites because of habitat disruption by the digging octopus. Jennifer found that octopus dens in Hawaii attracted scavenging wrasse fish waiting for the scraps after the octopus had finished eating. And the dens also attracted hermit crabs, which need an empty snail shell in which to hide their soft abdomen, and what better place to find one than in the midden of a snail-eating octopus? The dug-up area with a diameter of 3 ft. (1 m) around the den will have less growth of algae, so herbivorous fish wonât bother to hang around in that area. These observations remind us that octopuses are part of a complex web of underwater life. They are attracted to specific den sites because they need to avoid being eaten by some animals. And then when there, they change the area, and therefore have influence on other species.
5
Getting Around
O ctopuses are a remarkable sight when they are out hunting. They seem to flow across the rocks, holding on with some of the eight arms and extending other arms into crevices and under rocks, occasionally lifting off the bottom and gliding about 3 ft. (1 m) or so. Anyone who has taken a long look at an octopus moving this way across the ocean floor or an aquarium tank has likely admired the animalâs fluid movement and flexibility.
There are two kinds of octopus movement: one is about control and coordinationâhow an octopus gets all the arms to do what it wants them to do. The other is locomotionâhow the octopus moves itself around in the environment. Regarding locomotion, the octopus looks as if it has a disadvantage because of its molluscan heritage. Snails and clams just donât move fast, and the molluscan foot, unlike the limbs of vertebrates and arthropods, isnât designed to produce speed of movement. Biologist Richard Mc-Neil Alexander, in his 2003 overview of movement styles among animals, points out that each species makes compromises in balancing the demands for speed and maneuverability with the need to limit energy output. These compromises that octopuses make, based in their phylogenetic history, are intriguing aspects of their means of getting around their environment.
One obvious aspect of locomotion is maximum speed, which varies depending on the medium you are moving through. Cephalopods donât have much speed, comparatively. The cheetah, for example, can manage a top speed of 90 ft. (27 m) per second, which is very fast. Still, the cheetah tires very quickly, and so a prey animal that dodges and runs from it may avoid capture. The pronghorn antelope of the North American prairies specializes in sustained speed and can keep a speed of over 50 ft. (15 m) per second for over ten minutes. Air speed can be faster than land speed since air is not dense, and birds manage sustained speeds near 60 ft. (18 m) per second. A diving peregrine falcon can achieve a gravity-assisted top speed of 170 ft. (50 m) per second, the fastest known. Sea animals are at a disadvantagebecause of the high density of water: dolphins manage 30 ft. (9 m) per second, and pike can accelerate to 12 ft. (4 m) in less than a second. Squid, the fastest cephalopod, can only move 8 ft. (2.4 m) per second, and octopuses 1 ft. (m) per second. Clearly, cephalopods canât always out-swim fish.
Another demand for locomotion is maneuverability or change in direction. This feature is very useful in the short run, for a predator can be dodged if it canât be
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