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Entering the Twilight Zone Gulf of Mexico Exploration Entering the Twilight Zone FOCUS Polychaete worm Deep-sea habitats Bacteria Symbiotic GRADE LEVEL Trophosome 5-6 Life Science Hemoglobin Organic FOCUS QUESTION Inferences What organisms are typical of major deep-sea habitats, and how do they interact? The key words are integral to the unit but will be very difficult to introduce prior to the activity. They are LEARNING OBJECTIVES really the material of the lesson. There are no formal Students will be able to describe major features of signs in American Sign Language for any of these cold seep communities, and list at least five organ- words and many are difficult to lipread. Having the isms typical of these communities. vocabulary list on the board as a reference during the lesson will be extremely helpful. Also give the list as a Students will be able to infer probable trophic handout to the students to refer to after the lesson. relationships within and between major deep-sea habitats. If these topics have not already been covered in your class you will need to add an additional class Students will be able to describe the process of period to cover all the material. Additionally, you chemosynthesis in general terms, and will be able may want to make stations for each ocean habitat to contrast chemosynthesis and photosynthesis. zone. Take the information listed in the Background Information and enlarge it to put on posters. Students will be able to describe major deep-sea Include pictures. Use these as the starting point for habitats and list at least three organisms typical of your discussions. Also have copies of the informa- each habitat. tion available as handouts. ADDITIONAL INFORMATION FOR TEACHERS OF DEAF STUDENTS Pick two or three of the ocean habitats and gather In addition to the words listed as key words, the some reference materials ahead of time and place following words should be part of the list. them at established stations. Since there is a great Photosynthesis deal of information to be covered in the second Symbiosis step in the procedure, especially with a small group Hydrothermal vent of students, so instead of dividing the students into Hydrocarbon groups consider having them work as one or two Sediment teams. The students can then pick a habitat from 1 Gulf of Mexico Exploration - Grades 5-6 (Life Science) Gulf of Mexico Exploration - Grades 5-6 (Life Science) Focus: Deep-sea hobitats oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: Deep-sea habitats the two or three that you have already gathered years is the presence of extensive deep sea com- materials for. To allow for less frustration and com- munities that do not depend upon sunlight as their pletion in a reasonable timeframe, have students primary source of energy. Instead, these communities identify four rather than six organisms. derive their energy from chemicals through a process called chemosynthesis (in contrast to photosynthesis MATERIALS in which sunlight is the basic energy source). Some 5 x 7 index cards chemosynthetic communities have been found near Drawing materials underwater volcanic hot springs called hydrothermal Corkboard, flip chart, or large poster board vents, which usually occur along ridges separating “Generalized Ocean Habitats” diagram the Earth’s tectonic plates. Hydrogen sulfide is abun- dant in the water erupting from hydrothermal vents, and is used by chemosynthetic bacteria that are the AUDIO/VISUAL MATERIALS None base of the vent community food chain. These bac- teria obtain energy by oxidizing hydrogen sulfide to sulfur: TEACHING TIME CO + 4H S + O > CH O + 4S +3H O Two 45-minute class periods, plus time for indi- 2 2 2 2 2 vidual group research (carbon dioxide plus sulfur dioxide plus oxygen yields organic matter, sulfur, and water). Visit http://www.pmel.noaa.gov/vents/home.html for more informa- SEATING ARRANGEMENT Groups of four students tion and activities on hydrothermal vent communities. Other deep-sea chemosynthetic communities are MAXIMUM NUMBER OF STUDENTS 32 found in areas where hydrocarbon gases (often methane and hydrogen sulfide) and oil seep out of sediments. These areas, known as cold seeps, are KEY WORDS Cold seeps commonly found along continental margins, and (like Methane hydrate ice hydrothermal vents) are home to many species of Chemosynthesis organisms that have not been found anywhere else Brine pool on Earth. Typical features of communities that have Trophic level been studied so far include mounds of frozen crystals Pelagic zone of methane and water, called methane hydrate ice, Epipelagic zone that is home to polychaete worms. Brine pools, con- Mesopelagic zone taining water four times saltier than normal seawater, Bathypelagic zone have also been found. Researchers often find dead Hadopelagic zone fish floating in the brine pool, apparently killed by Benthic zone the high salinity. Intertidal zone Subtidal zone As is the case with hydrothermal vents, chemosyn- Bathyal zone thetic bacteria are also the base of the food web in Abyssal zone cold seep communities. Bacteria may form thick bac- Hadal zone terial mats, or may live in close association with other Hydrothermal vent organisms. One of the most conspicuous associations exists between chemosynthetic bacteria and large tubeworms that belong to the group Vestimentifera BACKGROUND INFORMATION One of the major scientific discoveries of the last 100 (formerly classified within the phylum Pogonophora; 2 3 Gulf of Mexico Exploration - Grades 5-6 (Life Science) Gulf of Mexico Exploration - Grades 5-6 (Life Science) Focus: Deep-sea hobitats oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: Deep-sea habitats recently Pogonophora and Vestimentifera have been the dominant primary producers in this zone. included in the phylum Annelida). Pogonophora B. The mesopelagic zone (about 200 m-1,000 m) is means “beard bearing,” and refers to the fact that the twilight zone. Because there is not enough many species in this phylum have one or more ten- light for photosynthesis, much less energy is tacles at their anterior end. Tentacles of vestimentifer- available to support animal life. Bacteria and ans are bright red because they contain hemoglobin detritus (pieces of dead plants and animals (like our own red blood cells). Vestimentiferans can that slowly settle to the bottom) are the prima- grow to more than 10 feet long, sometimes in clus- ry sources of food for animals like jellyfishes ters of millions of individuals, and are believed to that are confined to this zone. Other animals, live for more than 100 years. They do not have a including squids, fishes, and shrimps can mouth, stomach, or gut. Instead, they have a large move up and down through the water column, organ called a trophosome, that contains chemosyn- and have a wider range of food available to thetic bacteria. Hemoglobin in the tubeworm’s blood them. absorbs hydrogen sulfide and oxygen from the water C. The bathypelagic zone (sometimes divided further around the tentacles, and then transports these raw into an additional abyssopelagic zone) has no materials to bacteria living in the trophosome. The light at all. Deep-sea organisms are depen- bacteria produce organic molecules that provide dent upon production in other zones. The nutrition to the tubeworm. Similar relationships are base of bathypelagic food webs may be pri- found in clams and mussels that have chemosynthetic mary production in shallower water (obtained bacteria living in their gills. A variety of other organ- by feeding on detritus or on other animals isms are also found in cold seep communities, and feeding in shallower water) or chemosynthetic probably use tubeworms, mussels, and bacterial communities like hydrothermal vents or cold- mats as sources of food. These include snails, eels, seeps. sea stars, crabs, isopods, sea cucumbers, and fishes. D. The hadopelagic zone is sometimes used to Specific relationships between these organisms have include the water column in the deepest ocean not been well-studied. trenches (about 11,000 m). Cold-seep communities are surrounded by a much II. Benthic zones are areas on or in the ocean larger ocean environment. Very little is known bottom. Animals that swim near the bottom are about interactions between cold-seep communities called “benthopelagic.” and organisms in other ocean habitats. This activity A. The intertidal zone is on the shore between the focuses on major ocean habitats, organisms typi- level of high and low tide. cally found in these habitats, and the interactions B. The subtidal zone includes the ocean bottom on that take place within and among these habitats. continental shelves down to about 300 m. Green plants are the base of food webs in Ocean habitats are usually categorized into zones: shallower waters, but bacteria and detritus I. Pelagic zones are found in the water column are the primary energy source below about above the bottom. Organisms that inhabit pelagic 200 m. zones are divided into plankton that drift with the C. The bathyal zone includes the rest of the conti- ocean currents and nekton that can swim and nental shelf (between about 300 m and 3,000 control their motion in the water (at least to some m). extent). D. The abyssal zone is the ocean bottom between A. The epipelagic zone includes surface waters 3,000 m and 6,000 m. The bottom is primar- where light is adequate for photosynthesis ily muddy and flat in most places (hence the (about 200 m, maximum). Phytoplankton are common term “abyssal plain”). This is the larg- 2 3 Gulf of Mexico Exploration - Grades 5-6 (Life Science) Gulf of Mexico Exploration - Grades 5-6 (Life Science) Focus: Deep-sea hobitats oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: Deep-sea habitats est benthic zone and covers about half of the lowing deep ocean habitats to research: Earth’s surface.
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