Octopus (27 page)

Nautiluses use the jet propulsion swimming method like other cephalopods, but it's slower. They take water into the mantle cavity and squeeze it out of the funnel, which is more like a coiled flap. All their activities are done more slowly. In the tropical west Pacific where they live, nautiluses spend much of their lives swimming up or down steep reef faces. They rise at night to feed within 150 ft. (45 m) of the surface, and go down in daytime to around 1800 ft. (550 m) deep, where it is presumably safer for them.

Keeping the flotation balance just right and changing it twice a day must be a metabolic feat. Moving fluid into and out of the inner chambers is part of the process, but nautiluses also actively swim up and down the reef face and swim minimally to maintain their position. If they take out too little fluid, they may sink into the deep, and the excess pressure will implode the shell. If they take out too much fluid, they will float to the surface, bounce around in the waves, and get eaten by predators or washed ashore. Octopuses eat nautiluses; we know because we have found nautiluses' empty shells with drill holes, though it's not clear why octopuses would drill when they could just pull out the animal.

The ability to move down into the deep ocean might account for why nautiluses have survived when so many other early cephalopods are extinct. Their slow metabolism and inactive lifestyle, contrasted with that of the active octopus, fitted them to live in this low-oxygen, colder water. They
can survive on one feeding for over two months, so they'd find an intermittent food supply acceptable. Living deep means that they also avoid most marine predators, and they likely find mates and lay eggs in the deep.

Nautiluses are a complete contrast to the octopuses' “live fast and die young” life history. Unlike other cephalopods, they live after laying eggs—they are iteroparous. They lay a few large 1-in. (2.5-cm) eggs at a time. The eggs take about one year to hatch and there's no planktonic stage—the babies just crawl out, already equipped with two or three shell chambers. Like fish but unlike octopuses, they live a long time—fifteen to thirty years. They truly are a transitional life form between the slow snails and the other, fast cephalopods.

The cephalopod that really does live fast and die young is the Caribbean reef squid. Its body is based on the same eight arms and jet propulsion with the mantle, though it has an additional pair of elastic, elongated tentacles for prey capture. True squid live in groups of hundreds and swim constantly and fast in the surface waters of the open ocean, but the Caribbean reef squid is unusual in that it lives in smaller groups and nearer shore. These squid are big for a cephalopod, 1 ft. (
m) at adulthood. They live about a year or a year and a half, again depending on how cold the water is where they live. The eggs are relatively big (about
in. long, or ⅔ cm), and the tiny, newly hatched squid drift in the open water, eating small crustaceans and fish larvae. As they get older, they take larger prey, more fishes than other groups, swimming close to a school of small fish and shooting the paired tentacles out to catch them.

Because these squid live in a nearshore habitat, we can study their behavior more easily than if they were far out to sea like their relatives. Science has to bend to practicality, which is why open-ocean and deep-sea animals are so poorly known and why much of our knowledge of cephalopods such as the vampire squid is speculative. Martin Moynihan and Arcadio Rodaniche (1982) spent some of several summers watching the Caribbean reef squid at the San Blas Islands, tracing their life history and suggesting that they make a visual language on their skin. Female squid don't usually tend and defend their eggs, and the Caribbean reef squid lay theirs in 100 strings of about three eggs each, hiding them under rocks or dead coral where scavengers won't find them. Young squid probably move into similar habitat as the adults, though scientists have also found them in sea grass beds. They swim together in the daytime and disperse at night to catch small crustaceans and fish. Juvenile squid spend the daytime just
hanging around together doing nothing much. But when they grow up, choice, competition, fighting, and courtship become the focus of their days.

Jennifer has studied these squid for years on the island of Bonaire, a Dutch island in the southern Caribbean and part of the Netherlands Antilles, whose great attraction is that all the shoreline of the island is a protected marine park. The island is informally known as a divers' paradise for its easy access to dive sites and abundant underwater life. There, groups of squid swim together up to 120 ft. (40 m) from shore in crystal-clear water less than 15 ft. (5 m) deep. Jennifer has been exploring chromatophore form and function in squid, and whether squid make a visual language on their skin, which Moyhihan and Rodaniche have suggested. Many octopuses and squid have such a phenomenal range of colors and control of changes in skin texture and pattern that if any cephalopod group has a visual language, it would be squid.

Adult Caribbean reef squid court and fight using visual patterns on the skin. There's the female saddle and the male stripe, exchanged in early courtship to indicate interest, and the highly visible on-and-off male Flicker, showing a drive to mate. But the aggressive zebra display (see plate 35) is possibly the most interesting and definitely the most variable of the displays. It's a pattern of dark diagonal slashes, often on the mantle and sometimes on the arms, made mostly by males.

We have seen squid displays used only for camouflage or courtship. So far, we think squid don't have a language, although they have a fascinating and variable skin display system. Their skin system could make patterns complex enough for a language. Maybe they haven't made a language because of their relatively simple social system. Squid only have a burst of testing, consortship, and competition at the end of their lives. They haven't evolved a language because they don't have enough to say with it.

Like the large reef squid in structure, with its elongated mantle, eight arms, and two tentacles, the tiny pygmy squid (Idiosepius pygmaeus) is quite different in life history. The primary difference is size. Adult pygmy squid grow to about 1 in. (2.5 cm) of mantle length, no more. They are about the same size and shape as little grass shrimp, they live in the same sea grass habitat, and they move with the same short, jerky motions that shrimp accomplish with tail flips. They are so different from the other squid that they have the whole order Idiosepiida for just the one genus. In fact, because of their small size and less linear shape, the pygmy squid were
misplaced for a long time in the Sepiolidae, with the cuttlefish and the stubby squid.

We don't know much about pygmy squid, probably because the group lives in the Indo-East Pacific. Pygmy squid live quite near shore, probably in very large numbers, mostly in shallow beds of sea grass but sometimes near or on floating vegetation. They have a short lifespan of around 100 days. Their young are planktonic, but as adults they move around little. The most interesting thing about their ecology is that the larger adult females (see plate 36) lay egg after egg after egg in rows along the blades of grass. For this large output, they are “minimaximalists,” miniature in size but maximal in egg production. The females spend a lot of time doing this; they will lay a row of eggs, go back to feeding, and then lay another row for up to two weeks, 15 percent of their lifespan. Meanwhile, males display, fight, and court around females, trying to mate. Neither sex makes exclusive pairs with another individual, nor do males guard females, like reef squid do. Females can attract males with a color and posture display, and males can do the same for females. We have seen two or even three males grab onto a female as she laid her eggs, passing spermatophores to stick below her arms as she went on unconcernedly putting down more and more eggs.

We know very little about pygmy squid behavior. They have a fascinating habit of attaching onto grass blades with a sticky glue gland on the upper surface of the mantle, and they can detatch and swim off in an instant if threatened. But we don't know how they get attracted to the grass beds when they are young and drifting in the plankton. About their foraging habits, we know that they eat small crustaceans. For people who want to study these fascinating squid, there's a full bibliography in von Boletzky's 2003 report.

It seems logical that, like pygmy octopuses, pygmy squid would be easy to keep in an aquarium, but this has proved wrong. They are tiny when the eggs hatch, but so are giant Pacific octopuses. They seem to tolerate variations in temperature and salinity that might occur in an aquarium. We don't know what immature pygmy squid would eat; since they live in the plankton, maybe an enterprising squid owner would have to go out with a boat and do plankton tows, very difficult if you don't live near the sea and have access to boats. There are lots of good questions to ask about this cephalopod minimalist, and raising them in the lab would help find answers.

The giant squid is at the other end of the squid size range and is the biggest cephalopod. While it seems like an extreme match, giant squid are relatives of the reef squid and pygmy squid. They are perhaps the best publicized and least known of all the cephalopods. Many people have read about them in adventures such as 20,000 Leagues Under the Sea. Books about this squid have been written, but even the 1998 authoritative volume by Richard Ellis, The Search for the Giant Squid, has only a slim chapter on what is actually known about them.

We know that giant squid get big, and we know sperm whales eat them and are their main predators, but we know little else of their lifestyle. There are no authenticated cases of giant squid ever harming a human. No boats have been pulled under by them. No humans have been eaten by them or even been pulled underwater by their long tentacles. Few have ever seen a live adult giant squid, despite sailors' tales and several well-funded expeditions to find one using manned submersibles, ROVs, and even cameras mounted on sperm whales. Tsunemi Kubodera and Kyoichi Mori (2005) were able to lower a camera into the depths and get video of a giant squid far, far below.

What we know about the giant squid comes from examining their carcasses washed up on beaches, trawled in nets, found floating on the surface, or dissected out of sperm whales' stomachs. The first giant squid was described in 1545 off Scandinavia. It wasn't named until Japetus Steenstrup described its genus in 1857 as Architeuthis, which means chief squid, and named two species. Since then, fifteen other species have been described. But the systematics of the group are hopelessly confused, like for many other cephalopods. Some researchers believe there is only the one species worldwide, A. dux.

How big does the giant squid get? Not as big as legends suggest, since the extended tentacles are added to the length measurement when describing its size. The largest one, measured at 55 ft. (18 m) long, was found off New Zealand in the 1880s. Its body was only 8 ft. (2½ m) long. During the twentieth century, the largest squid found was 47 ft. (15½ m), at Grand Bahamas Bank. A number have been found recently in the New Zealand area; all were about 25 ft. (8 m) and weighed about 500 lb. (227 kg). Most had nothing in their stomachs so they may have been of reproductive age or senescent.

Most scientists today believe that despite its size, the giant squid is not a threatening animal. But this belief is speculation; we have few hard
facts about the behavior of the animal. It has ammonia in its tissues for buoyancy, its mantle is not all muscle, and the ammonia means that it tastes terrible. It has weak muscles in its mantle and small fins so it probably is not a fast swimmer. It may hang in the water with its arms and tentacles dangling down, waiting for a fish to swim into them, which is unlike the octopus's active foraging.

The giant squid has chitinous toothed rings around the outer edge of each sucker on the arms and on the tentacle tips. Other squid also have hooks on the arms and/or suckers but the giant squid does not, which also suggests that it is not the fierce predator that fiction would have us believe. The sucker rings help the animal to grasp prey, and they also leave circular scars on the skin of the sperm whales that eat them. Old-time whalers spoke of squid scars the size of a dinner plate, leading them to speculate there might be huge monster squid lurking in the depths that haven't yet been seen. But no sucker scars larger than 2 in. (5 cm) across have been documented on any whales. For a comparison, a 95-lb. (43 kg) giant Pacific octopus at the Seattle Aquarium had suckers 3 in. (8 cm) across.