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Home , Abyssal zone, Aphotic zone, Benthic zone, Continental shelf, Largest organisms, Marine life

Section 15.2 15.2 The Diversity of

1 FOCUS

Section Objectives 15.5 Recognize how marine Key Concepts Vocabulary Reading Strategy can be classified. How can marine ◆ Building Vocabulary Copy the below. organisms be classified? ◆ As you read, add definitions and examples to 15.6 Differentiate between complete the table. plankton and . What is the difference ◆ between plankton and ◆ nekton 15.7 Describe the area of the ocean Definitions Examples nekton? ◆ Plankton: organisms that drift with in which most benthic In which area of the ◆ ocean currents organisms live. ocean can most benthos ◆ organisms be found Phytoplankton: a. ? b. ? 15.8 List the factors used to divide ◆ living? the ocean into marine zones. ◆ Zooplankton: c. ? d. ? What factors are used to ◆ divide the ocean into Nekton: e. ? f. ? ◆ zones? Benthos: g. ? h. ? ◆ Reading Focus

Build Vocabulary L2 Concept Map Have students make a concept map using the term marine life A wide variety of organisms inhabit the marine environment. These zones as the starting point that connects organisms range in size from microscopic bacteria and to the to the following three terms: availability alive today—blue , which are as long as three of , distance from , and depth. Figure 7 Plankton are organisms buses lined up end to end. Marine biologists have identified over Students should use the following terms that drift with ocean currents. 250,000 marine . This number is constantly increasing as new A This photo shows a variety of organisms are discovered. to complete their concept map: pelagic phytoplankton from the Atlantic zone, photic zone, oceanic zone, benthic Ocean. B The zooplankton shown Most marine organisms live within the sunlit surface . Strong zone, abyssal zone, intertidal zone, and here include and the sunlight supports by marine algae. Algae either directly larval stages of other common or indirectly provide food for the majority of organisms. All marine neritic zone. marine organisms. algae live near the surface because they need sunlight to survive. Most L2 marine also live near the surface because this is where they Reading Strategy A a. plankton capable of photosynthesis can find food. b. microscopic algae c. plankton Classification of Marine Organisms d. larval Marine organisms can be classified according to where they live e. organisms capable of moving and how they move. They can be classified as either plankton (floaters) independently of ocean currents or nekton (swimmers). All other organisms are benthos, or bottom f. fish B dwellers. g. organisms living on or near the ϭ ocean bottom Plankton Plankton (planktos wandering) include all - h. marine isms—algae, animals, and bacteria—that drift with ocean currents. Just because plankton drift does not mean they are unable to swim. 2 INSTRUCT Many plankton can swim but either move very weakly or move only vertically. Classification of Marine Animals 428 Chapter 15 Build Reading Literacy L2 Refer to p. 362D in Chapter 13, which provides the guidelines for this reading strategy. Use Prior Knowledge Have students write the names of several ocean organisms they know about or have heard about. Next to each name, have students write a description of the , where it , and how it obtains food. After students have read the section, have them review their lists and make corrections, if necessary. Logical

428 Chapter 15 L1 Among plankton, the algae that undergo photosynthesis are called Figure 8 Nekton includes all Use Visuals animals capable of moving Figure 7 Have students examine the phytoplankton. Most phytoplankton, such as , are micro- independently of ocean currents. scopic. Animal plankton, are called zooplankton. Zooplankton include A This can use propulsion to two photographs. Explain that the the larval stages of many marine organisms such as fish, stars, , move through the . B This phytoplankton organisms shown in school of grunts swims through photograph A include and . Figure 7 shows members of each group. the water with ease. Inferring Why do you think and diatoms. Explain that long narrow Nekton Nekton (nektos ϭ swimming) include all animals some organisms, such as fish, projections and other distinctive shapes capable of moving independently of the ocean currents, by swim- are classified as plankton during contribute to the ability of these some stages of their lives and ming or other means of propulsion. Nekton are able to determine nekton during other stages? organisms to stay afloat. Remind their position within the ocean and in many cases complete long students that diatoms have shell-like migrations. Nekton include most adult fish and squid, marine mam- A tests. Ask: What may happen to these mals, and marine . Figure 8 shows examples of nekton. hard parts after these organisms die? Fish may appear to exist everywhere in the , but they are (decay, or fall to the bottom and contribute more abundant near and and in colder waters. Some to the layer) Explain that the fish, such as , swim upstream in to . zooplankton shown in photograph B Many do just the reverse, growing to maturity in fresh water and are larval and adult copepods. Inform then swimming out of the to breed in the depths of the ocean. students that copepods are small B (related to and ) Benthos The term benthos (benthos = bottom) describes on which many larger organisms depend organisms living on or in the ocean bottom. Figure 9 shows some for food. Ask: What are the likely examples of benthos organisms. The shallow coastal ocean floor con- functions of the on tains a wide variety of physical conditions and levels. Most the larger specimens shown in the benthos organisms can be found living in this area. Shallow coastal photograph? (feeding and swimming) areas are the only locations where large marine algae, often called sea- Visual, Logical weeds, are found attached to the bottom. These are the only areas of L2 the seafloor that receive enough sunlight for the algae to survive. Build Science Skills Throughout most of the deeper parts of the seafloor, animals live Classifying Show students photographs in perpetual darkness, where photosynthesis cannot occur. They must or dried or preserved specimens of feed on each other or on whatever fall from the productive organisms to classify as plankton, surface waters. The deep-sea bottom is an environment of coldness, nekton, or benthos. Ask students to stillness, and darkness. Under these conditions, life progresses slowly. Figure 9 Benthos describes explain the reasoning behind their organisms living on or in the classification decisions. (Possible answers: Organisms that live in the usually are widely distributed ocean bottom. A Sea star because physical conditions vary little on the deep-ocean floor. B crab Plankton are microscopic or very small. Phytoplankton have green pigment and show the ability to photosynthesize. Zooplankton have small swimming A B appendages; examples include diatoms, dinoflagellates, copepods, , larval fish. Nekton have swimming appendages, are large and strong enough to swim against ocean currents; examples include adult fish, , whales, squid. Benthos live on the ocean bottom; examples include sea stars, most crabs, sea anemones, sea , , .) Visual, Logical

Ocean Water and Ocean Life 429

Customize for Inclusion Students

Behaviorally Disordered Have students board or butcher paper. Have students add work together to create a two-dimensional labeled organisms to appropriate areas of their model of ocean life zones on the classroom model. Students can make their own drawings bulletin board. Students can use Figure 10 as of organisms, cut out photographs from old a starting point. Challenge students to draw or magazines, or photocopy illustrations from Answer to . . . paint and label , continental books. slope, ocean basin, photic zone, , Figure 8 As larvae, fish are not able and benthic zone on a large piece of poster to move against ocean currents, they drift with the . As adults, fish are able to swim and move independ- ently of ocean currents.

Ocean Water and Ocean Life 429 Section 15.2 (continued) Marine Life Zones The distribution of marine organisms is affected by the chemistry, Marine Life Zones physics, and geology of the oceans. Marine organisms are influenced Use Community by a variety of physical factors. Three factors are used to divide the L2 For: Links on marine Resources Visit: www.SciLinks.org ocean into distinct marine life zones: the availability of sunlight, the Aquarium Field Trip Take students Web Code: cjn-5152 distance from shore, and the water depth. Figure 10 shows the dif- on a field trip to a local public aquarium ferent zones in which marine life can be found. or museum with ocean life exhibits. Alternatively, students could visit a Availability of Sunlight The upper part of the ocean into ϭ pet store that specializes in saltwater which sunlight penetrates is called the photic zone (photos light). aquariums. Have students select one or The clarity of is affected by many factors, such as the amount more organisms they observe during of plankton, suspended sediment, and decaying organic particles in their visit and write a short paper the water. In addition, the amount of sunlight varies with atmospheric describing it. Encourage students to conditions, time of day, season of the , and latitude. classify each of their organisms as The euphotic zone is the portion of the photic zone near the sur- belonging to plankton, nekton, or face where light is strong enough for photosynthesis to occur. In the benthos; to identify the ocean zone in open ocean, this zone can reach a depth of 100 meters, but the zone which the organism lives; and to explain will be much shallower close to shore where water clarity is typically how the organism obtains food. reduced. In the euphotic zone, phytoplankton use sunlight to produce Kinesthetic, Logical food and become the basis of most oceanic food webs. Although photosynthesis cannot occur much below 100 meters, Use Visuals L1 there is enough light in the lower photic zone for marine animals to avoid predators, find food, recognize their species, and locate mates. Figure 10 Have students examine the drawing of the ocean basin. Ask: Below this zone is the aphotic zone, where there is no sunlight. What marine life zones are found What is the difference between the photic zone on or above the continental shelf? and the aphotic zone? (intertidal, neritic, photic) Where does Figure 10 Marine Life Zones photosynthesis take place? (euphotic The ocean is divided into marine life zones, based on Intertidal Sunlight zone) zone Visual, Logical availability of light, distance High Low from shore, and water depth. tide Interpreting Diagrams Why Neritic Build Science Skills L2 are phytoplankton and larger zone Phytoplankton Zooplankton algae found only in Oceanic Inferring After students have examined surface waters? zone Limit of Figure 10, ask: Should all intertidal light penetration and neritic organisms be classified Euphotic zone as benthos? Why? (No. Not all of the Continental Photic zone organisms in these zones live on the shelf ocean bottom. Some of these organisms, including many fish species, jellyfish, and Continental slope Pelagic plankton, live above bottom in the water Benthic Aphotic zone column.) zone zone Logical, Verbal

Abyssal zone

430 Chapter 15

Download a worksheet on marine ecosystems for students to complete, and find additional Facts and Figures teacher support from NSTA SciLinks. Of the more than 300 species, about shark (Carcharodon carcharias) is a predator 80 percent are unable to harm people or rarely that feeds preferentially on (seals encounter people. The largest shark—also the and sea lions) and has attacked largest fish in the world—is the shark swimming or in areas. (Rhincodon typus). It reaches lengths of up to A great white can grow to 7 m long and 15 m but eats only plankton and is therefore weigh up to 2250 kg. are classified as not considered dangerous. The great white nekton.

430 Chapter 15 Build Science Skills L2 Distance from Shore Marine life zones can also be subdivided based on distance from shore. The area where the land and ocean meet Classifying After students have finished and overlap is the intertidal zone. This narrow strip of land between reading about marine life zones, have them create a table with two columns. high and low is alternately covered and uncovered by seawater Q Do any deep-sea organisms with each tidal change. It appears to be a harsh place to live with crash- produce light themselves? Have students label the left column Photic Zone and the right column ing waves, periodic drying out, and rapid changes in , A Over half of deep-sea salinity, and concentrations. However, the species that live here organisms—including fish, Aphotic Zone. Ask students to place are well adapted to the constant environmental changes. jellies, crustaceans, and deep- each of the following marine life zones sea squid—can bioluminesce, Seaward from the low-tide line is the neritic zone. This zone covers in the correct column: intertidal, neritic, which means they can produce oceanic, benthic, abyssal. If necessary, the gently sloping continental shelf. The neritic zone can be very light organically. These organ- offer students the hint that some marine narrow or may extend hundreds of kilometers from shore. It is often isms produce light through a life zones may exist in both photic and shallow enough for sunlight to reach all the way to the ocean floor, chemical reaction in specially designed structures or cells aphotic zones. Photic: intertidal, neritic, putting it entirely within the photic zone. called . Some of oceanic (partly), pelagic (partly) benthic Although the neritic zone covers only about 5 percent of the world these cells contain luminescent (partly); Aphotic: benthic (partly), oceanic ocean, it is rich in both and number of species. Many organ- bacteria that live symbiotically (partly), pelagic (partly), abyssal isms find the conditions here ideal because photosynthesis occurs within the organism. In a world of darkness, the ability to Logical readily, nutrients wash in from the land, and the bottom provides shel- produce light can be used to ter and habitat. This zone is so rich that it supports 90 percent of the attract prey, define territory, world’s commercial fisheries. communicate with others, or Beyond the continental shelf is the oceanic zone. The open ocean avoid predators. reaches great depths. As a result, surface waters typically have lower nutrient concentrations because nutrients tend to sink out of the photic zone to the deep-ocean floor. This low nutrient concentration usually results in smaller populations than the more productive neritic zone.

Water Depth A third method of classifying marine is based on water depth. Open ocean of any depth is called the pelagic zone. Animals in this zone swim or float freely. The photic part of the pelagic zone is home to phytoplankton, zooplankton, and nekton, such as , sea , and dolphins. The aphotic part of this zone has and other species that are adapted to life in deep water. Benthos organisms such as giant , , crabs, sea anemones, sea stars, and marine worms that attach to, crawl upon, or into the seafloor occupy parts of the benthic zone. The benthic zone includes any sea-bottom surface regardless of its distance from shore and is mostly inhabited by benthos organisms. The abyssal zone is a subdivision of the benthic zone. The abyssal zone includes the deep-ocean floor, such as abyssal plains. This zone is characterized by extremely high water pressure, consistently low tem- perature, no sunlight, and sparse life. Food sources at abyssal depths typically come from the surface. Some food is in the form of tiny decaying particles that steadily “rain” down from the surface. These particles provide food for filter-feeders, brittle stars, and burrowing worms. Other food arrives as large fragments or entire carcasses of organisms that sink from the surface. These pieces supply meals for actively searching fish, such as the grenadier, tripodfish, and hagfish.

Ocean Water and Ocean Life 431

Customize for Inclusion Students

Gifted Invite interested students to create students could put together a labeled photo classroom exhibits describing an collage of intertidal benthos organisms or from one of the marine life zones. For example, a poster depicting a pelagic . Answer to . . . Figure 10 Both types of organisms need sunlight for photosynthesis. Sunlight penetrates the photic zone; no sunlight reaches the aphotic zone.

Ocean Water and Ocean Life 431 Section 15.2 (continued) Hydrothermal Vents Among the most unusual seafloor discoveries of the past Hydrothermal Vents 30 have been the hydrothermal vents along the L2 Integrate Biology oceanic ridge. Here seawater seeps into the ocean floor Explain to students that the giant through cracks in the . tubeworms living in The water becomes super-heated and saturated with communities do not have digestive minerals. Eventually the heated water escapes back into systems. Even so, they can grow up the ocean. When the hot water comes in contact with the to 3 m long. When scientists first Figure 11 When super-heated surrounding cold water, the minerals precipitate out, discovered these organisms, they were water meets cold seawater, giving the water the appearance of black smoke. These geysers of hot minerals and metals precipitate baffled as to how they could grow so out of the water to form this water are referred to as black smokers, like the one shown in Figure 11. large with no obvious means of black smoker. At some vents water of 100°C or higher support obtaining . Eventually, scientists communities of organisms found nowhere else in the world. In fact, learned that the worms get all the hundreds of new species have been discovered surrounding these deep- nutrition they need from bacteria sea habitats since scientists found some vents along the Galápagos Rift growing inside their body cavities. in 1977. Chemicals from the vents become food for bacteria. The bac- Encourage students to look up more teria produce sugars and other foods that enable them and many other information about hydrothermal vents organisms to live in this very unusual and extreme environment. Look and the biological communities they at Figure 12 for another example of organisms found along hydrother- support. mal vents. Verbal, Logical

3 ASSESS Evaluate Figure 12 Tube worms up to 3 meters L2 in length are among the organisms found Understanding along hydrothermal vents. To assess students’ understanding of section content, present a profile of the ocean floor and have them label the locations of the following marine life Section 15.2 Assessment zones: intertidal, neritic, oceanic, benthic, abyssal, photic, aphotic, and euphotic. Reviewing Concepts 7. Inferring Organisms that live in the intertidal 1. How can marine organisms be classified? zone must deal with harsh and changing Reteach L1 conditions. What types of would 2. What is the difference between plankton benefit organisms living in this zone? Help students review the marine life and nekton? zones by asking them to identify 3. In which area of the ocean do most similarities and differences in pairs of benthos organisms live? terms, such as intertidal zone and neritic 4. What factors are used to divide the ocean zone (both in photic zone, continental into marine life zones? Making Tables Make a table to organize shelf region, include benthos, nekton, and 5. Why is the neritic zone rich in life? the information about marine life zones plankton; interidal is between tides, neritic presented in this section. Include the basis is below tides); phytoplankton and Critical Thinking by which the zone is classified, any subdivi- zooplankton (float with ocean currents, 6. Inferring Why do many fish in the abyssal sions of the zone, and the characteristics of zone locate food through chemical sensing? each zone within the table. found in oceanic and intertidal zones, phytoplankton photosynthesize, zooplankton do not); benthic zone and abyssal zone (both involve ocean bottom, abyssal is deep ocean bottom only) 432 Chapter 15

Student tables should reflect the Section 15.2 Assessment 6. The abyssal zone is vast and there is no material presented in this section. light, so fish cannot depend on being able to 1. by where they live and how they move find food by sight. 2. Nekton are able to move independently of 7. Students’ answers will vary but should ocean currents. Plankton are not. show that they understand the factors an 3. on the shallow coastal ocean floor organism living in the intertidal zone has to 4. availability of sunlight, distance from shore, deal with. Answers may include having a shell water depth that can be sealed to prevent drying out, hav- 5. Conditions are ideal for photosynthesis ing a way to attach firmly to rocks, having a because there is light and nutrients from runoff; shell to protect against wave action, being the bottom provides shelter and habitat. able to live in an area with a wide tempera- ture and salinity range.

432 Chapter 15