Ocean and Deep Sea Terms

Fissures on the floor of a sea out of which flows water that has been heated by underlying magma.

The water can be as hot as 400°C (752°F) and usually contains dissolved minerals that precipitate out of them upon contact with the colder seawater, building stacks of minerals, or chimneys.

Hydrothermal vents form an ecosystem for microbes and animals; such as, tubeworms, giant clams, and blind shrimp, that can withstand the hostile environment.

The hottest hydrothermal vents are called black smokers because they spew iron and sulfide which combine to form iron monosulfide, a black compound.

For decades, oceanographers, biologists, and geologists have insisted that the only food for creatures in the deep seafloor primarily came from food particles drifting down from the surface

Until the discovery of a profusion of life at a depth of 2,500 meters (8,202 feet) in February of 1977, scientists were convinced that the deep seafloor, where darkness and cold reign, there was the earth's largest, and least known, ecosystem.

Although there were expeditions with special zoological interests up to the end of the nineteenth century, it was long considered to be a deserted environment.

Oceanographic expeditions sure that in the absence of photosynthetic production, the only food resources available in the lowest levels of the seas were those from the surface, primarily in the form of rains of particles.

So it was assumed that the abyssal plains were populated by animals that were very unusual, few in number, and normally very small.

Such concepts existed until the American submersible named Alvin dived over the Galapagos Ridge and researchers were amazed to find a profusion of life; communities of strange organisms of spectacular sizes and astonishing shapes clustered around warm springs of about ten degrees above the surrounding temperatures at the bottom of the sea.

The very first discovery of the hydrothermal vents in 1977 and the new species of organisms that the researchers found there were named in terms of what they seemed to resemble: the "giant tube worm" the "dandelion", the "spaghetti worm: and the "giant clam".

The discovery of hydrothermal vents raised the curiosity of scientists and how it was possible that a dense group of fauna can prosper in an environment characterized by toxicity, crushing pressures, and a total absence of light.

The explanation for the existence of such life was found to be based on bacteria using the chemical substances belched forth by the chimneys of the vents to synthesize organic matter, and this serves as the basis for the entire hydrothermal food chain.

Further research indicated that bacteria substitute for green plants in that dark world, and chemistry replaces solar energy. The process of primary production is called chemosynthesis, a term that parallels photosynthesis.

Pertaining to the shore areas that alternate between submergence and nonsubmergence due to tidal oscillation.

The life span of this tubeworm is among the longest in the animal kingdom; 250 years!

Like its close hydrothermal cousins, it "eats" hydrogen sulfide via the bacteria it cohabits with. Unlike its relatives, the cold seep tubeworm has roots that it drives into the substrate, seeking essential resources.

It is also possible that it uses the roots to inject its sulfate excrements back into the sediment. This method would permit it to stimulate beneath it very "feet" the hydrogen sulfide production that nourishes it and so explain the creature's exceptional longevity.

This cold seep tubeworm lives in the area of hydrocarbon seeps, which are thought to be much more stable habitats in the long run than hydrothermal vents.

Gelatinous filter feeders, at times important phytoplankton grazers.

The spin a transparent mucilaginous "house", in which they live. Their body consists of a trunk and an elongated tail, which they beat to set up a current that draws water into the house and through a fine filter, on which phytoplankton is collected.

Larvacean, along with salps (tiny free-swimming organisms that has a transparent barrel-shaped body), belong to the invertebrate protochordate subphylum of the phylum Chordata (which is mostly made up of vertebrates).

Pelagic fauna between 200 microns and two millimeters.

In the shallow benthos, refers to organisms retained on a one millimeter mesh but too small to be trawled or observed in photographs (about 1-2 centimeters).

In the deep sea, where much of the benthic fauna is reduced in size, the term refers to the same taxa, or classifying plants and animals according to their presumed natural relationships; such as, polychaete worms, small crustaceans, and mollusks that are retained on a 0.3-0.5 millimeter mesh.

Those pelagic species large enough to be readily trawled or, in the benthos, observed in photographs or from submersibles.

The benthic fauna consisting mostly of nematodes, larger protists; such as, forams, and small benthic copepods (harpacticoids) that are retained on the finest meshes (about 62 micrometers) and are generally smaller than the macrofauna.

The layer of the water column between about 200 meters (the lower limit of the epipelagic layer) and 1,000 meters (the lower detection limit of sunlight, and the approximate lower limit for the vertical migration of fishes that feed in near-surface waters).

The spatial scale in the ocean on the order of tens to hundreds of kilometers.

The ecological era, often referred to as the Age of Dinosaurs, extending from the end of the Permian Period 245 million years ago to the end of the Cretaceous 65 million years ago.

The era comprises three periods, the Triassic, Jurassic, and Cretaceous.

Methane which is formed within the seafloor and that can be squeezed upward by the subduction of oceanic plates under the continental margins.

That's why these new ecosystems were named methane seeps when they were first discovered. Since then, scientists have learned that methane does not always "seep" out of the seafloor because it can also be exposed by earthquake-induced landslides.

Seep communities can also occur in other settings, in association with hydrocarbons; such as, petroleum oil, tar, or asphalt.

When deep-buried methane moves upwards towards the seafloor, it is consumed by microbes that interact with other bacteria to produce sulfide. Although sulfide, which smells like rotten eggs, is usually highly toxic, it supports a group of animals that are specialized in dealing with chemical environments known as chemosynthetic animals, similar in thier body organizations to the animals found at hydrothermal vents.

The fauna attracted to the methane seepage form what is known as "true animal bases" on a landscape of otherwise relatively featureless, homogeneous sediment in the deep sea.

First, bacteria graze on the chemical fluids (methane and sulfide) that seep out of the seafloor. Then, special clams and mussels arrive that house symbiotic bacteria that can harvest the chemicals to produce energy for their hosts.

Also present at seeps are tubeworms with sulfide-consuming bacteria; some of which have very long roots that can reach a meter down under the seafloor to look for sulfide.

The pelagic food web (consisting of small phytoplankton, microzooplankton, and microbes) which efficiently grows, grazes, and recycles nutrients.

The larger crustaceans; such as, pelagic shrimps, and small fish and squids within the water column.

The upper layer of the ocean that is reasonably well mixed due to the action of the wind, tides, or winter convective cooling.

This layer is reasonably homogenous in terms of its temperature, salinity, and nutrient concentrations; this is also the layer where most primary production occurs.

Small planktonic crustaceans, sometimes known as opossum shrimp, on the order of a centimeter in size.