Coral

Coral, small, sedentary marine animal, related to the sea anemone but characterized by a skeleton of horny or calcareous material. The skeleton itself is also called coral. Although most corals form colonies by budding, there are some solitary corals; in both types the individual animals, called polyps, resemble the sea anemone in form.

Corals grow in warm and temperate climates and in the cold water found at greater depths, but they are most abundant in warm, shallow water; over 200 coral species are found in the Great Barrier Reef of Australia. In many shallow-water species the polyps contain unicellular plants, which may provide the high oxygen concentration required by such corals.

Stony Corals 

In the large group known as stony corals, or true corals (Madreporaria), each polyp secretes a cup-shaped skeleton, the theca, around itself. Some solitary corals of that group may reach a diameter of 10 in. (25 cm); in the colonial forms the individual polyps are usually under 1-8 in. (3 mm) long, but the colonies may be enormous. The body of each polyp is saclike, consisting of a wall of jellylike material surrounding a digestive cavity, with a single opening, the mouth, at the unattached end. The mouth is surrounded by tentacles used to capture small prey and is invaginated to form a pharynx leading into the body cavity. Thin sheets of tissue (mesentaries) extend radially from the wall to the pharynx, dividing the cavity. A second set of radial divisions is created by folds (septa) of the outer skeleton and body wall, which extend upward from the floor of the body cavity. Reproduction occurs both sexually and by budding. Sexual reproduction is by means of eggs and sperm, which are produced in the mesentaries and shed into the water. Fertilization results in a free-swimming larva, which attaches to a surface and secretes a skeleton, becoming (in colonial forms) the parent of a new colony. 

As new polyps are produced by budding they remain attached to each other by thin sheets of living tissue as well as by newly secreted skeletal material. The great variety in the form of various colonial corals, which may be treelike and branching, or rounded and compact, depends chiefly on the method of budding of the particular species. In the brain corals, for example, each theca merges with the one next to it on either side, forming long rows of polyps separated by deep channels. In some of the branching corals the polyps occupy small, discrete pits on the surface of the skeleton. As a colonial coral produces more polyps the lower members die and new layers are built up on the old skeleton, forming a large mass. In tropical and subtropical regions these massive corals, along with other plants and animals, may form a coral reef. Most of the reef-forming corals belong to the stony coral group. 

Soft Corals 

The soft corals (Alcyonaria) are a group of soft, often feathery forms, with skeletons composed of calcareous or horny particles imbedded in the body wall. Each polyp of a soft coral has eight tentacles. Among the well-known soft corals are the sea pen, sea pansy, whip coral, and organpipe coral. The precious red coral (Corallium) of the Mediterranean Sea, used for jewelry, also belongs to that group. The spicules of its skeleton are fused together. 

Classification: Stony and soft corals are classified in the phylum Cnidaria, class Anthozoa.

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Common Species of Seaweed and Their Uses

The largest of the green algae, Ulva (sea lettuce), grows to a ribbon or sheet 3 ft (91 cm) long. It provides food for many sea creatures, and its broad surface releases a large amount of oxygen. Fucus, called rockweed or bladderwrack, is a tough, leathery brown alga (though it often looks olive-green) that clings to rocks and has flattened, branched fronds buoyed by air bladders at the tips.

Seaweeds, especially species of the red algae Porphyra (nori) and Chondrus, form an important part of the diet and are farmed for food in China and Japan; other species (often called laver) are eaten in the British Isles and Iceland. Commercial agar (vegetable gelatin) is obtained from species of red algae and is the most valuable seaweed product. Irish moss or carrageen (Chondrus crispus), a red alga, is one of the few seaweeds used commercially in the United States. After being bleached in the sun the fronds contain a high proportion of gelatin, which is used for cooking, textile sizing, making cosmetics, and other purposes. In Japan it is made into a shampoo to impart gloss to the hair.

The kelps generally include the many large brown seaweeds and are among the most familiar forms found on North American coasts. Some have fronds up to 200 ft (61 m) long, e.g., the Pacific coast Nereocystis and Macrocystis, found also off the Cape of Good Hope. Common Atlantic species include Laminaria and Agarum (devil's apron). The kelps are a source of salts of iodine and potassium and, to a lesser extent, other minerals. When the seaweed is burned, the soluble mineral compounds are removed from the ashes (also called kelp) by washing. They are used chiefly as chemical reagents and for dietary deficiencies in people and in livestock. Kelp is also a commercial source of potash, fertilizer, and medicines made from its vitamin and mineral content. Kelps are especially abundant in Japan, and various foods known as kombu are made from them.

The brown algae of the genus Sargassum are called gulfweed. They inhabit warm ocean regions and are commonly found floating in large patches in the Sargasso Sea and in the Gulf Stream. Gulfweed was observed by Columbus. Although it was formerly thought to cover the whole Sargasso Sea, making navigation impossible, it has since been found to occur only in drifts. Numerous berrylike air sacs keep the branching plant afloat. The thick masses of gulfweed provide the environment for a distinctive and specialized group of marine forms, many of which are not found elsewhere.

Seaweed

Seaweed, name commonly used for the multicellular marine algae. Simpler forms, consisting of one cell (e.g., the diatom) or of a few cells, are not generally called seaweeds; these tiny plants help to make up plankton. The more highly developed types of seaweed usually have a basal disk, called a holdfast, and a frond of varying length and shape, which often resembles a plant in having stemlike and leaflike parts.

Types of Seaweed

The simplest of the seaweeds are among the cyanobacteria, formerly called the blue-green algae, and green algae (division Chlorophyta), found nearest the shore in shallow waters and usually growing as threadlike filaments, irregular sheets, or branching fronds. The brown algae (division Phaeophyta), in which brown pigment masks the green of the chlorophyll, are the most numerous of the seaweeds of temperate and polar regions. They grow at depths of 50 to 75 ft (15–23 m). The red seaweeds (division Rhodophyta), many of them delicate and fernlike, are found at the greatest depths (up to 879 ft/268 m); their red pigment enables them to absorb the blue and violet light present at those depths.

Reproduction in Seaweeds

Seaweeds reproduce in a variety of ways. Lower types reproduce asexually. More advanced kinds produce motile zoospores that swim off, anchor themselves, and grow into new individuals, or they reproduce sexually by forming sex cells (gametes) that, after fusing, follow the same pattern. Sometimes pieces of a seaweed break off and form new plants; in a few species there is a cycle of asexual and sexual reproduction foreshadowing the alternation of generations characteristic of plants.

See: Common Species of Seaweed and Their Uses

Symbiosis

Symbiosis, the habitual living together of organisms of different species. The term is usually restricted to a dependent relationship that is beneficial to both participants (also called mutualism) but may be extended to include parasitism, in which the parasite depends upon and is injurious to its host; commensalism, an independent and mutually beneficial relationship; and helotism, a master-slave relationship found among social animals (e.g., the ant and the aphid). True symbiosis is illustrated by the relationship of herbivorous animals (e.g., cockroaches, termites, cows, and rabbits) to the cellulose-digesting protozoans or bacteria that live in their intestines; neither organism could survive without the other. Other symbiotic relationships include the interdependence of the alga and the fungus that form a lichen and the relationship between leguminous plants and the nitrogen-fixing bacteria, which is important in agriculture. Two obvious examples of a plant-to-animal relationship are yucca and yucca moth, fig and fig wasp; in both cases the insect fertilizes the plant, and the plant supplies food for the larvae of the insect.

Peat Moss

Peat Moss, also called sphagnum moss and bog moss, common name for about 300 species of moss plants that grow in swamps and bogs throughout the world. Peat moss may grow to 30 cm (12 in) or more in height. The plants have many branches covered with small, light green leaves. The leaves and stems have special cells that absorb and hold much water.

Peat moss is one of the most common plants from which peat, a fuel, is produced. When the plants die, the dead organic matter is preserved more or less intact because the moss is acidic, so bacterial and fungal decay occurs slowly. The dead peat moss and other plants are compressed by the weight of the living plants growing above them. This compressed matter eventually forms the peat. The peat can be cut into blocks and removed for use as fuel. Peat moss is also useful in gardening. It combats excessive alkalinity in the soil and produces the acid environment that certain plants need to grow, including such ornamental shrubs as rhododendrons. Its absorptive characteristics make peat moss useful as a packing material for shipping plants.

Scientific classification: Peat mosses are members of the family Sphagnaceae. They belong to the genus Sphagnum.

Moss Growing on a Tree Trunk
There are over 14,000 species of primitive plants called mosses belonging to the phylum Bryophyta. Most species are terrestrial and, although requiring abundant moisture, are highly adaptable, living on rocks, tree trunks, stumps, wooden buildings, and asphalt roofing shingles. Several species are adapted for life in bogs, swamps, and streams.


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