Octopus (6 page)

Second, a huge part of plankton is made up of plants or other organisms that have chlorophyll and produce their own food. As a side effect of this process, the oceans produce 50 percent of the oxygen in the earth's atmosphere, 95 percent of which comes from phytoplankton and 5 percent from bigger algae (kelp and seaweed) or the few marine vascular plants that live near shore. These organisms also provide habitat for marine animals, like mature octopuses and their prey. At the same time, the plankton absorbs carbon dioxide and uses it for metabolism. Because of the large volume and surface area of the oceans, two thirds of the earth, this activity provides an enormous buffer to the oxygen–carbon dioxide budget of the earth's atmosphere. Carbon dioxide is currently increasing in the earth's air despite this buffer, because we humans create huge amounts of it. Plants on land and in the sea can't keep up with our industrial emissions. Plankton may also lessen the atmospheric ozone layer that contributes to global warming and bleaches the coral habitats in which many octopuses live. Clearly, the plankton in the oceans is immeasurably important for our survival.

Third, plankton is important as an energy source. Dead plankton falls to the ocean bottom and collects there slowly, under ½ in. (1 cm) in 1000 years but amounting to thick deposits over millions of years. The rich oil deposits around the Gulf of Mexico are the result of plankton deposits on the floor of an ancient sea there millions of years ago. While it's a harsh environment, some specialized octopuses such as the spoon-arm octopus live there.

Fourth, both live and dead plankton can be ecological indicators. There are some plankton that exist only under specific climatic conditions and some that behave differently at different temperatures. By looking at fossil plankton, scientists can tell what the climate was in the past. For example, some foraminiferans, which are plankton with tiny, coiled shells, shape their shells in one direction in cold water and in the opposite direction in warm water. The percentage of left-to-right coiled fossil forms of these plankton in the ocean's sediments can tell us the sea's temperature at a particular time in the earth's history (see plate 7).

An example of how plankton balance can go wrong occurred in the 1960s. Lake Washington, an urban lake in Seattle, was becoming eutrophic:
it was so rich from fertilizers in runoff and sewage that a blue-green alga bloomed in the freshwater plankton. That alga flourished, taking nutrients away from normal plankton, clogging the gills of fish, and reducing the clarity of the lake, so other organisms in the lake suffered. Swimming areas were closed. The lake was well on the way to becoming a muddy, sterile body of water, much like Long Island Sound is today, with few fish and green growing plants. Based on dire predictions of scientists monitoring the situation, the surrounding community was able to stop the processes leading to eutrophication by diverting sewage and runoff. Lake Washington is now a scientific success story: instead of being a turbid, dead lake, it is clean and clear, and the plankton are back to their normal state.

Fifth, plankton can be lethal, even to some of the organisms that eat it. Or the plankton's poison can be collected by and concentrated in the animals that eat it. One classic example is paralytic shellfish poisoning (PSP), or “red tide.” PSP happens because filter-feeding shellfish we eat, like mussels, clams, and oysters, collect the poisonous plankton. Carnivorous octopuses don't accumulate these poisons and so aren't poisonous to humans. The organisms that cause PSP are one of those pesky groups that seem to be both animal and plant, and they bloom in such huge numbers, they cause the water to be a rust-red color. In 1793, while exploring the North American West Coast, the crew of explorer Captain George Vancouver ate some mussels from the shores of British Columbia. Four of the crew became sick, suffering numbness and tingling of the arms and legs followed by paralysis, and one died. In modern times, few people are affected by PSP, since commercial shellfish harvests come from safe water and at safe times, and the public is notified of red tide blooms. Red tides usually occur in the summer: there's an old, usually reliable adage that says to only eat oysters in months with an R in them. Red tide can kill marine animals too; a red tide bloom off the coast of Florida recently eliminated a local population of pygmy octopuses that ate infected shellfish.

While dead plankton and its waste products are constantly falling down through the ocean to the bottom, continually adding to the sediment, living plankton must remain in the rich, well-lighted surface layers. This is particularly important for a plant or an animal with chlorophyll, which needs the energy of sunlight to drive photosynthesis. Light is absorbed in the upper 1000 feet (300 m) of the ocean, and the lower depths are essentially black.

Although plants and animals of the plankton, including cephalopods,
use several methods to stay near the surface, many members of the plankton have no special adaptations for staying afloat. They slowly sink down through the ocean's surface layers and die when they get too deep to photosynthesize or find food. But they are fast and prolific spawners, and they reproduce before they sink too deep. Their eggs and sperm are buoyant, so they float to the surface, where fertilization takes place and the whole life cycle begins anew. Organisms that go through this cycle (such as diatoms) are usually small.

Other planktonic organisms are adapted in some way to making themselves buoyant or to hover, maintaining their position. These adaptations can either be active or passive. One common passive method is to increase the ratio of the area of the outer surface to the volume, thus making the animal or plant more buoyant or likely to sink more slowly: for example, some organisms have spines or other projections on the outer surface that provide resistance to falling through the water. Octopus paralarvae have bundles of bristles, Kölliker's organs, sticking out of the skin that may do this. And, paralarval Atlantic long-arm octopuses (Octopus defilippi), which have a specialized, long, third arm pair, can extend these arms and drift in the surface waters. Planktonic octopus paralarvae with these adaptations look a bit different from the adults, but they are still recognizable as octopuses.

Another way members of the plankton increase buoyancy is to produce a substance that is lighter than water and retain it in their tissues. Many animals and plants of the plankton do this by secreting a type of oil, and oil is lighter than water. This oil eventually winds up as the hydrocarbons of petroleum deposits. The oil-rich blubber of whales helps offset the sinking of the whales' heavy bodies and also keeps them insulated from the cold. Many planktonic organisms have oil globules in their cells, which are visible when they are examined under a microscope.

Another substance used to keep plankton buoyant is ammonia, again lighter than water. Ammonia is primarily used by the large squid species, including the giant squid (Architeuthis dux), in their tissues, although the glass squid (Cranchia scabra) concentrates ammonia inside a special organ. The ammonia in the tissues of these squid makes the living or dead animals smell pungent. Dead or dying giant squid floating on the ocean's surface smell particularly foul. The ammonia in these giant squid also makes them inedible—there will be no giant squid calamari. Clyde Roper (1984),
expert on the giant squid, once sampled a cooked piece of this monster and remarked that it was really terrible tasting stuff.

Other sea creatures use jelly and air as flotation substances. The mesoglea, or jelly layer, of jellyfish helps them maintain their buoyancy. We have been recently finding many new deep-water species of jellyfish, which, even though they are light, have to swim to keep from sinking to the bottom. Some jellyfish use air for flotation, such as the Portuguese men-of-war, as do some cephalopods (such as cuttlefish and nautiluses), fish, and marine mammals. Cuttlefish have an internal shell of porous air-retaining calcium, a cuttlebone, and nautiluses have a coiled shell with air-filled chambers.

Another trick to increase buoyancy is to decrease the density of one's tissues. The few mid-water cephalopods, those that live just above the deep bottom, are usually gelatinous, with tissues close to the density of the deep water they live in. The flapjack devilfish (Opisthoteuthis californiana) and other octopuses like it are sometimes called jellyfish octopuses, because their flabby, gelatinous bodies remind researchers of jellyfish.

Many of the planktonic animals, including young octopuses, swim to maintain their level in the ocean. The methods of swimming are as diverse as the planktonic organisms themselves. Some general methods include beating of the hairlike cilia, thrashing with one or several whiplike flagella, paddling with fins or feet, pulsing, oscillation or undulations of the whole body, or the jet propulsion used by paralarval octopuses. Hatchling octopuses, like squid, may use jet propulsion to raise them in the water column, and then take a long glide to rest before pumping again.

It is hard for us to be able to imagine a baby octopus living in the plankton, constantly avoiding sinking into the abyss, watching for gigantic predators that would scoop it up, and deciding which way to swim. We humans are used to living in two dimensions, not looking overhead much, looking forward from our head, and pivoting to see behind us. Our eyes are binocular—both eyes are directed forward with the fields overlapping. Many predators have this arrangement, because it is the best method for tracking mobile prey by sight. But living in the plankton is a three-dimensional experience. Animals in the plankton in open water, such as octopus paralarvae, need to look up and down, left and right, forward and backward to avoid getting eaten by hungry predators. So these animals have big, wide-angle eyes that are adapted to seeing in all directions.

For the most part, living in the plankton means living in a miniature world. Most planktonic organisms are tiny: a hatchling common octopus is just over 0.1 in. (3 mm) long. Within a drop of ocean water, there is a tiny world, with plants, grazers, and predators. Young octopuses have good vision and some swimming ability, so they can jet after tiny crustacean larvae and capture them with their stubby arms. They also try to avoid getting eaten by sinking quickly when a predator looms. Many do get eaten, but the species usually is not extinguished because there are so many hatchlings. Many of the predators are tiny themselves.

Since living in plankton means being carried by the ocean's currents, paralarval octopuses go wherever the currents carry them, and such dispersal is good because it can lead to a wide species range. Yet, paralarvae from octopuses in shallow waters carried by currents out into the mid ocean will probably die. The mid-oceanic islands of Hawaii and Bermuda provide interesting parallels and contrasts for planktonic dispersal of octopuses. Bermuda sits in the mid Atlantic, but it is swept by an arm of the Gulf Stream, the largest river on earth. Although Bermuda is at the same latitude as South Carolina, it is kept subtropical by warm currents that sweep by equatorial South America and through the Caribbean before hitting it. After flowing past Bermuda, the Gulf Stream flows to the cold North Atlantic.

Bermuda is colonized by planktonic paralarvae and juveniles carried to it by the Gulf Stream, including those of common octopuses. So the octopuses there are the same species as in the Caribbean, though fewer. Also, the planktonic offspring from marine animals living in Bermuda are carried northward, often dying in the colder waters or unable to find a place to settle. Some live because they are caught in local currents and stay in the warm bays of the islands themselves. They have to land on an island or a continent to live.