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2- MARINE ORGANISMS the Oceans Are Representing the Largest Living Space on the Planet Today and Throughout Earth's History

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2- MARINE ORGANISMS the Oceans Are Representing the Largest Living Space on the Planet Today and Throughout Earth's History BTEC 4386 IUG 2- MARINE ORGANISMS The oceans are representing the largest living space on the planet today and throughout Earth's history. The creatures that inhabit the wide sea are diverse in both shape and form. The oceans and the coastal seas provide a complex variety of environments for living organisms. At the surface, conditions range from polar to tropical, over depth from light to total and constant darkness and the sea floor may be rock, sand, or rood. Organisms of the marine environment have much in common with the organisms of the land, but they also have very different survival problems and have developed unique solutions to cope with them. Life in the water ranges from microscopic, single celled organisms to the largest fish and the greatest whale. CLASSIFICATIN OF ORGANISMS A wide variety of the organisms inhabit the environment of the ocean. All organisms are classified and placed in groups to promote identification and to increase understanding of the relationships that exists among them. KINGDOMS OF LIFE IN THE SEA The Five-Kingdom System Since the time of Carolus Linnaeus (1707–1778), many new organisms have been discovered, and many classification systems have been proposed. Some of the systems have merit; all try to make sense of the great diversity of life on our planet. However, most scientists now use the classification system that is composed of five kingdoms. (See the Table) TABLE THE FIVE-KINGDOM CLASSIFICATION SYSTEM Monera: This group, commonly called the monerans, includes the bacteria and blue-green bacteria (formerly called blue-green algae). Bacteria are structurally simple microorganisms that are especially significant as decomposers, breaking down organic compounds into nutrients that can be used by other organisms. They are also an important food source and help degrade pollutants. Some species are autotrophic, and account for much of the oceanic primary production. All bacteria are single- celled; all lack a nuclear membrane and thus their nuclear material is dispersed throughout the cell. Scientists call organisms that lack a nuclear membrane prokaryotes. Cyanobacteria are photosynthetic bacteria widely distributed in the marine environment. 6 BTEC 4386 IUG Protista: The kingdom of protists includes mostly single-celled, or unicellular, organisms, although some are composed of many cells or live together in small colonies. All protists have their nuclear material enclosed within a membrane; that is, they have a nucleus. Scientists call organisms with this feature eukaryotes. (All organisms on Earth other than those in the kingdom Monera are eukaryotes.) Tiny protozoa (animal-like organisms) and many kinds of algae (plantlike organisms) make up this group. Diatoms Diatoms (phylum Bacillariophyta) are unicellular, though many species aggregate into chains or star-like groups. These protists usually float and drift near the ocean surface. Diatoms are part of the ocean’s community of plankton (meaning “wanderers” that drift, rather than swim) and are more accurately classified as phytoplankton (“plant wanderers”). Some diatoms (called encrusting diatoms) live attached to solid substrates, while others alternate between attached and free-floating forms. The cell walls of diatoms are made of silica. After their death, they sink to greater depths building up siliceous sediments called the siliceous ooze. Dinoflagellates (dino for “whirling” and flagellum for “whip”) Members of another protist group often found near the ocean’s surface are the dinoflagellates. Three types of dinoflagellates are shown in the next Figure. They are classified in phylum Dinoflagellata or Pyrrophyta, which means “red (or fire) algae.” How do dinoflagellates compare with diatoms? Dinoflagellates have two flagella. Dinoflagellates also possess chloroplasts and, like diatoms, are able to make and store their own food. Many dinoflagellate species have an eyespot that is sensitive to light. They use the eyespot to move toward the light, thus increasing their ability to make food. Unlike diatoms, dinoflagellates are also able to take in food. The cell walls of dinoflagellates and diatoms differ in structure and composition. Dinoflagellate cell walls are made of cellulose like those of plants, not of silica like those of diatoms. A cellulose cell wall is not as transparent as a diatom’s glassy cell wall. 7 BTEC 4386 IUG Seaweeds What do ice cream and toothpaste have in common? It may surprise you to learn that both products contain substances that come originally from seaweed. Seaweeds are multicellular algae that live in the sunlit waters of the ocean. Organisms that are multicellular are made up of more than one cell. More than 500 species of macroscopic algae live in the ocean. These algae are classified according to the color of the pigments in their cells. The three main groups classified in this way are the green algae, brown algae, and red algae. People harvest seaweeds as a useful source of food, food additives, and agricultural fertilizer. The annual harvest of North American kelp weighs some 20,000 tons. Three types of green algae. 8 BTEC 4386 IUG Three types of brown algae. Three types of red algae. PROTOZOANS Thousands of species of protozoans are found living on the surface of marine substrates and in the bottom sediments. These one-celled organisms are classified within the protist kingdom, along with the algae. The protozoa are subdivided into three major groups: the Ciliophora, Zoomastigina, and Sarcodina. The Ciliophora are the largest group of protozoa, composed of thousands of freshwater and marine species, all having cilia. 9 BTEC 4386 IUG The Zoomastigina consist of a group of animal-like protists that move through the water by means of whiplike flagella. Included in this group are the euglena and the dinoflagellates, which take in (as well as make their own) food. The Sarcodina are the protozoan group that includes the forams and radiolarians, as well as the amoebas. They live on the surface of substrates and move by means of cytoplasmic extensions called pseudopods (meaning “false feet”). This kind of movement, typical of the amoeba, is called ameboid movement. Foraminiferan: The foraminiferan (meaning “hole-bearing”), or foram for short, is a unicellular protist. Forams are encased in a shell, or test, made up of calcium carbonate (CaCO3). Parts of a foram’s cytoplasm flow out through holes, or pores, in the shell and form a sticky surface for catching food. Radiolarian. A unicellular zooplankton. It is transparent because its cell wall (like that of a diatom) is composed of silica. Long spines branch out from a radiolarian’s body, like the spokes of a wheel, for added buoyancy and protection. Foraminiferan Radiolarian Fungi: The fungi include both unicellular and multicellular eukaryotic organisms that are not able to make their own food. Fungi absorb their nutrients from dead organic material and live tissues. Like plant cells, fungal cells are enclosed by a rigid cell wall. Unlike plants, fungi do not contain the green pigment chlorophyll. Fungi play an important role in breaking down dead organisms and recycling organic material. Hundreds of species of fungi exist, both on land and in the ocean. Plantae: Plants are multicellular, eukaryotic organisms that are able to make their own food out of simple chemical substances. Sea grasses are the only land plants that have fully adapted to life under the sea. They grow submerged, and their flowers produce pollen grains that drift through the water to reach and pollinate other flowers. They release their seeds underwater, too. Animalia: Animals are multicellular, eukaryotic organisms. Unlike plants, animals are not able to make their own food, but must instead eat plants or other animals to obtain their nutrients. Most animals are capable of movement. We categorize animals in two main groups: those that lack a backbone and skull (the invertebrates) and those that have a backbone and skull (the vertebrates). Both groups are widely represented by animals that live in marine environments. MARINE INVERTEBRATES More than 95 percent of marine animal species do not have backbones; they are invertebrates. They range in size from the miniature fauna living in the seabed sediment and tiny zooplankton drifting in surface waters, to giant squid that reach 18 m long. Marine invertebrates belong to about 30 different groups called phyla (singular phylum), with each phylum-containing species sharing many features in common. 10 BTEC 4386 IUG SPONGES, ROTIFERS, AND BRYOZOANS Each belong to distinct phylum of marine invertebrates. Although each group of species is unique enough to be placed in its own phylum, they do share some characteristics. Rotifers and bryozoans are both microscopic, but sponges can grow quite large. Sponges and bryozoans are both sedentary, but rotifers are capable of movement. However, the animals found in all three groups are multicellular, bottom- dwelling invertebrates. Sponges Sponges (phylum Porifera meaning “pore bearing”) are the simplest multicellular invertebrates. In structure a sponge is little more than a sac with pores. Inside, lining a central cavity, are cells with beating hairlike structures called cilia that create miniature water currents. These draw food particles into the sac through the pores. Sponges show a variety of interesting shapes, sizes, and colors. The bath sponge (Euspongia), which lives in warm tropical waters, may be most familiar to you. The traditional bath sponge which is the skeleton of the sponge is now threatened because of overharvesting. The beautiful Venus’s flower basket (Euplectella), which lives at great depths, is a tubular sponge composed of a delicate network of glassy spicules. The vase sponge (Ircinia), found on sandy bottoms near coral reefs, grows vertically. Some basket sponges, found in tropical waters, grow so large that a person could sit inside of them. Rotifers Meaning “wheel bearer”, dozens of rotifer species live in the moist sands along the shore and in the gravel of aquarium tanks. (Rotifers are also common in freshwater.) Rotifers, which are in their own unique phylum Rotifera, are able to change the shape of their body.
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