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Entering the Twilight Zone [Adapted from the 2002 Gulf of Mexico Expedition]

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Entering the Twilight Zone [Adapted from the 2002 Gulf of Mexico Expedition] Expedition to the Deep Slope 2007 Entering the Twilight Zone [adapted from the 2002 Gulf of Mexico Expedition] FOCUS TEACHING TIME Deep-sea habitats Two 45-minute class periods, plus time for indi- vidual group research GRADE LEVEL 5-6 (Life Science) SEATING ARRANGEMENT Groups of 4 students FOCUS QUESTION What organisms are typical of major deep-sea MAXIMUM NUMBER OF STUDENTS habitats, and how do they interact? 32 LEARNING OBJECTIVES KEY WORDS Students will be able to describe major features Cold seeps of cold-seep communities, and list at least five Methane hydrate ice organisms typical of these communities. Chemosynthesis Brine pool Students will be able to infer probable trophic Trophic level relationships within and between major deep-sea Pelagic zone habitats. Epipelagic zone Mesopelagic zone Students will be able to describe the process of Bathypelagic zone chemosynthesis in general terms, and will be able Hadopelagic zone to contrast chemosynthesis and photosynthesis. Benthic zone Intertidal zone Students will be able to describe major deep-sea Subtidal zone habitats and list at least three organisms typical Bathyal zone of each habitat. Abyssal zone Hadal zone MATERIALS Hydrothermal vent 5 x 7 index cards Drawing materials BACKGROUND INFORMATION Corkboard, flip chart, or large poster board Cold seeps are areas of the ocean floor where “Generalized Ocean Habitats” diagram gases (such as methane and hydrogen sulfide) and oil seep out of sediments. These areas are AUDIO/VISUAL MATERIALS commonly found along continental margins, and None are home to many species of organisms that 1 Expedition to the Deep Slope 2007 – Grades 5-6 (Life Science) Focus: Deep-sea habitats oceanexplorer.noaa.gov have not been found anywhere else on Earth. and organisms in other ocean habitats. This activ- Recently, increasing attention has been focused ity focuses on major ocean habitats, organisms on cold seeps in the Gulf of Mexico, an area that typically found in these habitats, and the interac- produces more petroleum than any other region tions that take place within and between these in the United States. Responsibility for managing habitats. exploration and development of mineral resources on the Nation’s outer continental shelf is a central Ocean habitats are usually categorized into mission of the U.S. Department of the Interior’s zones: Minerals Management Service (MMS). In addi- I. Pelagic zones are found in the water column tion to managing the revenues from mineral above the bottom. Organisms that inhabit resources, an integral part of this mission is to pelagic zones are divided into plankton that protect unique and sensitive environments where drift with the ocean currents and nekton that these resources are found. MMS scientists are can swim and control their motion in the particularly interested in finding deep-sea che- water (at least to some extent). mosynthetic communities in the Gulf of Mexico, A. The Epipelagic zone includes surface because these are unique communities that often waters where light is adequate for pho- include species that are new to science and tosynthesis (about 200m, maximum). whose potential importance is presently unknown. Phytoplankton are the dominant primary In addition, the presence of these communities producers in this zone. often indicates the presence of hydrocarbons at the surface of the seafloor. B. The Mesopelagic zone (about 200m- 1000m) is the twilight zone. Because The 2006 Expedition to the Deep Slope was there is not enough light for photosyn- focussed on discovering and studying the sea thesis, much less energy is available to floor communities found near seeping hydrocar- support animal life. Bacteria and detritus bons on hard bottom in the deep Gulf of Mexico. (pieces of dead plants and animals that The sites visited by the Expedition were in areas slowly settle to the bottom) are the pri- where energy companies will soon begin to drill mary sources of food for animals like for oil and gas. A key objective was to provide jellyfishes that are confined to this zone. information on the ecology and biodiversity of Other animals, including squids, fishes, these communities to regulatory agencies and and shrimps can move up and down energy companies. Dives by scientists aboard through the water column, and have a the research submersible ALVIN revealed that wider range of food available to them. hydrocarbons seepage and chemosynthetic com- munities were present at all ten sites visited by the C. The Bathypelagic zone (sometimes Expedition. The most abundant chemosynthetic divided further into an additional organisms seen were mussels and vestimentiferan Abyssopelagic Zone) has no light at tubeworms. Expedition to the Deep Slope 2007 all, with the exception of light produced is focused on detailed sampling and mapping of by bioluminescent organisms. Deep-sea four key sites visited in 2006, as well as explor- organisms are dependent upon produc- ing new sites identified from seismic survey data. tion in other zones. The base of bathype- lagic food chains may be primary pro- Cold-seep communities are surrounded by a much duction in shallower water (obtained by larger ocean environment. Very little is known feeding on detritus or on other animals about interactions between cold-seep communities feeding in shallower water) or chemosyn- 2 Expedition to the Deep Slope 2007 – Grades 5-6 (Life Science) oceanexplorer.noaa.gov Focus: Deep-sea habitats thetic communities like hydrothermal vents LEARNING PROCEDURE or cold-seeps. 1. To prepare for this lesson, visit http://oceanexplorer. D. The Hadopelagic zone is sometimes used noaa.gov/explorations/07mexico/welcome.html for informa- to include the water column in deepest tion about Expedition to the Deep Slope 2007. ocean trenches (about 11,000 m). You may want to visit http://www.bio.psu.edu/cold_seeps for a virtual tour of a cold seep community, and II. Benthic zones are areas on or in the ocean http://www.bio.psu.edu/hotvents for a virtual tour of a bottom. Animals that swim near the bottom hydrothermal vent community. and called “benthopelagic.” A. The Intertidal zone is on the shore 2. Lead a discussion of the major categories of between the level of high and low tide. ocean habitat. Introduce the recently-discovered deep-sea chemosynthetic communities (hydro- B. The Subtidal zone includes the ocean bot- thermal vents and cold seeps). Emphasize the tom on continental shelves down to about contrast between communities that depend 300 m. Green plants are the base of upon chemosynthesis with those dependent food chains in shallower waters, but bac- upon photosynthesis. You may want to point teria and detritus are the primary energy out that through both processes, organisms source below about 200 m. build sugars from carbon dioxide and water. This process requires energy; photosynthesizers C. The Bathyal zone includes the rest of the obtain this energy from the sun, while chemo- continental shelf (between about 300 m synthesizers obtain energy from chemical reac- and 3,000 m). tions. Review the concepts of food chains and food webs, including the concept of trophic D. The Abyssal zone is the ocean bottom levels (primary producer, primary consumer, between 3,000 m and 6,000 m. The bot- secondary consumer, and tertiary consumer). tom is primarily muddy and flat in most Be sure students understand that food chains places (hence the common term “abyssal in most of the habitats are largely based upon plain”). This is the largest benthic zone photosynthetic production, either directly (prima- and covers about half of the Earth’s sur- ry consumers obtain energy from photosynthetic face. plants) or indirectly (primary consumers obtain energy from detritus). This situation is fundamen- E. The Hadal zone is sometimes used to tally different in deep-sea chemosynthetic com- describe the very deep ocean bottom munities, which may also provide an alternative between 6,000 m and 11,000 m basis for food chains in adjacent habitats. F. Vents and seeps are unusual deep-water 3. Assign each student group one or more of the habitats that support communities of liv- following deep ocean habitats to research: ing organisms whose food chains are • Mesopelagic zone based on chemosynthetic bacteria, rather • Bathypelagic zone than photosynthetic activity near the sur- • Hadopelagic zone face. Vent and seep communities may, • Bathyal zone in turn, be a significant energy (food) • Abyssal zone source for organisms living in other ben- • Hadal zone thic habitats nearby. • Hydrothermal vents • Cold seeps 3 Expedition to the Deep Slope 2007 – Grades 5-6 (Life Science) Focus: Deep-sea habitats oceanexplorer.noaa.gov In addition to written reference materials (ency- students infer about the relative abundance clopedia, periodicals, and books on the deep- of each trophic level? In the simplest analysis, sea), the following Web sites contain useful organisms at lower trophic levels (primary pro- information: ducers and primary consumers) must be more http://www.bio.psu.edu/cold_seeps abundant than those on higher trophic levels. If http://people.whitman.edu/~yancey/deepsea.html this does not appear to be true, then there must http://oceanlink.island.net/ be additional energy sources for the higher http://www.pbs.org/wgbh/nova.abyss/life.bestiary.html trophic levels (for example, some secondary http://www.pbs.org/wgbh/nova/abyss/life/bestiary.html or tertiary predators may feed in more than http://biodidac.bio.uottawa.ca/ one habitat. Considering that the abyssal plain http://www.fishbase.org/search.cfm covers about half of the Earth’s surface, and is largely unexplored, how might the students’ Each student group should identify six organ- ocean food web change with further explora- isms typical of their assigned habitat, and tion? determine the energy (food) source(s) of each of these organisms. It may not be possible to THE BRIDGE CONNECTION precisely determine specific foods in all cases, www.vims.edu/bridge/ – Click on “Biology” in the but students should be able to draw reason- navigation menu to the left, then “Plankton,” then able inferences from information about related “Phytoplankton” for resources on ocean food organisms and anatomical features that may webs.
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