Octopus (4 page)

Some species of closely related octopuses are known as sibling species. They appear alike because of their physical features, genetic makeup (or cladistical comparison), and they may even live in the same areas. There are sibling species of zebra-striped octopuses (Octopus chierchiae and O. zonatus) on each side of Panama that were presumably the same species at some time before the isthmus arose. Some of these sibling species have a different place on the r–K line, which also distinguishes them from each other. Sometimes you have to wait until the female lays eggs to know which species of octopus your individual is (see plate 4).

When female octopuses, such as the Caribbean reef octopus (Octopus briareus), put their resources into laying larger eggs, the eggs hatch out larger juveniles that are better prepared to take on the benthic world than their smaller relatives. These larger juveniles are able to crawl, hide, change color, ink, or swim from predators. In other words, they assume a normal subadult octopus life.

We humans use the K strategy. We give birth to just one or a few large offspring, although they are certainly not ready to live by themselves at birth. Anthropocentrically, we may think that having a few large eggs, large offspring, and parental care comprise a good strategy, perhaps the best.
This strategy in octopuses produces juveniles that are well able to live an adult life style on the ocean's bottom. But in octopuses, such a strategy prevents a wide dispersion of the species, because they can't get very far from where they grow up: they must crawl or slowly swim to colonize new areas. So they tend to have small ranges, and a species in a small area can be threatened or even wiped out by ecological disasters, such as storms, El Niño currents, or pollution. Examples of this kind of event are the endemic land snails of Hawaii, which have gone extinct from being eaten by another introduced snail; the many freshwater mussels of the Ohio River that have gone extinct from pollution; and the threatened snails in Banff, Canada, that only live in three hot springs. Because of their lack of dispersion, more freshwater and land mollusks have become extinct than all mammals and birds combined.

The other strategy, producing many small eggs and tiny hatchlings, also has its advantages and disadvantages. A primary disadvantage of the production of small hatchlings is that most of them get eaten, although selection means that the fittest survive. Tiny octopus hatchlings look somewhat like miniature octopuses but have stubby arms, an attached yolk sac, and a few chromatophores. They may or may not have inking ability yet. They swim and drift in the plankton until they are large enough to settle to the bottom and take up a usual octopod benthic existence. These planktonic hatchlings are called paralarvae: they don't go through a true larval stage (looking quite unlike the adult), like caterpillars do before becoming butterflies.

In addition to having few resources when they hatch and needing to eat soon, the planktonic paralarvae are likely to be eaten by larger animals that eat plankton. But since there may be thousands of these hatchlings, the chances are good that a few will survive. And since they are planktonic, they are often carried by currents to new areas of settlement. Generally, the more eggs produced by an octopus species, the larger its range, since the paralarvae can float in currents for several months. Production of many eggs may also be good for the gene pool of the species, because it increases the odds of having a variant that might increase survivability.

As far as we know, all female octopuses that lay eggs guard them. They use several methods of protecting the eggs, depending on the species. The football octopus (Ocythoe tuberculata) is the only known octopus that is ovoviviparous: the fertilized eggs are retained in the extended oviducts until they hatch, and the hatchlings are released directly into the water.
Since the female argonaut is an open-ocean drifter, she can't use rocks for protection. She secretes a thin calcareous coiled shell with the webs of her first arm pair, inside which she attaches her eggs. She then sits in the shell, protects the eggs from overgrowth by algae, and keeps them clean and oxygenated. She lays the smallest known octopus eggs, just less than
in. (2 mm) long.

Some deep-sea octopuses have a bigger problem. On the abyssal plain of the deep ocean, there is a thick layer of mud and few hard things to attach eggs to. This mud results from the sediment, plankton, and feces that drift down through the water's layers. So octopuses on the bottom attach their eggs to anything hard they can find: a rock outcrop, a whalebone, a shell, or a shipwreck. A sheet of plastic trawled from the bottom of the North Atlantic had eleven female deep-sea spoon-arm octopuses guarding a total of more than 100 eggs attached to it.

Octopuses give no care to their hatchlings; the females die about the time their eggs hatch. Once the eggs hatch, the paralarvae, or juveniles, are on their own. But females are wonderful at guarding their eggs. They usually find a den that is protected and has good water conditions—high oxygen, low pollutants, and medium water currents. But even members of the same octopus species have different personalities, so this and chance lead them to establish their maternal dens in different areas, sometimes in places that are not very safe.

While the mother octopus tends her eggs, she stops them from getting fouled by overgrowth of marine algae and settling organisms such as hydroids, barnacles, and tunicates that might grow on the eggs (see plate 5). She does this partly by constantly blowing water through her funnel along and between the eggs or egg strands. The festoons are actively moved and bathed by her water jets, so they must be attached securely in order to take this treatment twenty-four hours a day for the about six months it takes for a giant Pacific octopus egg to hatch. She also manipulates the eggs with her arms, grooming them with her suckers and arm tips, which go snaking through the eggs to remove any fungus or algae growth on eggs that might choke or kill them. The egg strings are made of a chitinous, or fingernail-like, material, to hopefully be tough enough to withstand this constant manipulation.

Because the female octopus usually doesn't eat while she is guarding eggs, she may lose up to 50 percent of her body weight during development of the eggs. Not eating while brooding the eggs has several advantages. First,
she doesn't foul the den with food wastes or feces, which helps ensure good water quality for the eggs. She certainly could leave the den to find food or eliminate body wastes, but that would mean exposing her eggs and herself to danger from predators. Fish of several species follow foraging octopuses, hoping to snatch a bit of food, and being out eating would advertise a female's whereabouts. Second, she won't produce a midden of shells or other food remains in front of her maternal den. Some octopus predators (including humans) target den middens, finding them by sight or chemical cues. Third, not eating eliminates any chemicals arising from her metabolism or in her feces. Moray eels can find octopuses in their dens, but it is not known yet what chemicals from octopuses they sense. It is possible they sense some product of food metabolism that is not present while female octopuses are guarding eggs, rather than the body tissue metabolism females undergo while brooding.

While she is tending her eggs, the female octopus survives by metabolizing muscle tissues (octopuses don't use fat for metabolism as we do, and have very little fatty tissue), so she deteriorates considerably at the end of her life. She turns gray or pale, as though she can't change color any more. She hardly moves. She shrinks to half her size, and actually looks old and wrinkled. She can open her den if she has blocked it up, and may manipulate the eggs somehow to stimulate them to hatch. If she is guarding small eggs, she will blow the paralarvae out of the den, usually at night, giving them a boost into open water.

Sometimes females live after their eggs hatch and go into a state of senescence, but this behavior is more commonly seen in males. Senescent octopuses don't hide in a den, but crawl haphazardly over the sea's bottom, unconcerned about predators or prey. Evolution sets a fine balance between the survival of the female and the survival of the eggs; most females live until after the eggs hatch, since dying sooner would be a disaster for the potential progeny.

The egg laying, guarding, and grooming processes have become well-shown by Olive the Octopus, a giant Pacific octopus who laid her eggs at a popular dive site in Seattle's Puget Sound just offshore from the busy downtown area in 2002 (see plate 6). Olive was first seen guarding eggs in Cove 2 near Armeni Park. Divers guessed she weighed approximately 60 lb. (27 kg), based on the size of her largest suckers. A nearby large male octopus had been named Popeye, after the cartoon character, so she was named Olive, after Popeye's girlfriend Olive Oyl. A group of divers dove at the site every Tuesday night and reported their findings to us at the Seattle Aquarium.

Olive made her den under a cluster of sunken wooden pilings called a dolphin. The dive site is an area of ongoing boating activity, and the dolphin may have been tipped over and sunk by a storm or rammed by a boat. The four pilings are bundled together by steel cables and lie on the bottom in 100 ft. (30 m) of water, parallel to shore. She made her den under this dolphin, midway along it, with two openings, one shoreward and one facing toward deep water. Before laying her eggs, she looked out of the deeper opening through the cool 50°F (10°C) water.

There was little evidence of food remains in front of either den opening at the start of her brooding. We have found that the normally hard shells of red rock crabs, a common prey, become thin and fragile within a few days, and those near her den were hard, so she had either just stopped eating or she was reusing a den recently occupied by another octopus. The cluster of sunken pilings had several dens under it along its length. Unlike most other shallow-water octopuses, she did not wall up the entrance to her den with rocks. Instead, she created a fence of 8-in. (20-cm) rocks in a
semicircle in front of the deeper opening, and she didn't put anything in front of the shoreward one. During her entire brooding period, she was highly visible to hundreds of divers.

Divers first saw her eggs on February 25, 2002. She laid the characteristic strings of eggs on the ceiling of her den, attached to the underside of the wooden pilings. That day, she was observed in an upside-down posture with her suckers facing upward, so it is likely she was still in the process of laying eggs. No one counted the eggs, but giant Pacific octopuses characteristically lay about 70,000 eggs. Larger females lay more eggs and smaller ones lay fewer. Olive was a bit larger than normal, so she may have laid about 100,000 eggs.

On later dives in following weeks, divers saw her right side up, blowing water through the eggs and caressing them with her arm tips. At this time, she was normally a dull gray color, but she turned red-brown in response to divers' bright underwater lights or a gentle touch. During the month after the eggs were seen, she would take a piece of herring offered as food by divers, but later she wouldn't eat, and blew offered food assertively out of the den.

She guarded her eggs through the summer, seemingly unfazed by the hundreds of divers viewing her. She pushed sunflower sea stars away from her brood chamber and fended off other egg predators that hovered nearby. She ignored octopuses that made short-term dens nearby under the dolphin, even when they mated as close as 50 ft. (15 m) away. She probably didn't notice their absence as they moved away, the female to make another maternal den of her own somewhere else and the male going off to die.