Using a Dichotomous Key in the Identification of Seagrasses

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1 Title: Using a Dichotomous Key in the Identification of Seagrasses (Classification of Marine Organisms) Grade Level (s): 6-7 Introduction: Biologists identify organisms by physiological and structural characteristics. Thousands of years ago, people formed simple classification systems by grouping living organisms by similar characteristics. The science of classification of organisms into orderly groups by characteristics and evolutionary history is termed taxonomy. In the fourth century B. C., the Greek philosopher Aristotle classified all living things as plants or animals. He grouped animals as either land, water or air dwellers and plants by their stem differences. In the eighteenth century, Swedish scientist Carolus Linnaeus developed a system of classification of living things by similarities in form and structure. Prior to Linnaeus, biologists realized that Aristotle s classification system was inadequate and common terms may not describe species accurately from one locale to another. For example, Portuguese man-of-wars are not specifically found in Portugal, nor are they men. The common term for the jellyfish is not even accurate since they are not fish. Linnaeus is credited for two-part names, or binomial system for identifying organisms. A species is a group of similar offspring that can reproduce living, fertile young, and is named by the genus and species identifier. The genus is capitalized and appears first in the species name and both names are written together in Italics or underlined. For example, humans belong to the genus, Homo, and the species identifier sapiens. The species name for humans is therefore, Homo sapiens. A species name may be descriptive of the organism, as in the amoeba Chaos chaos which is constantly changing its shape. In some instances, names are given to honor a person. For example, Linnaeus s favorite species of northern region flower, Linnaea borealis. Borealis means northern. One method of sorting and identifying organisms in the field is the use of a dichotomous key that uses pairs of descriptions to identify an object. Students will learn that there are many different species of seagrasses, even though the name implies that they are all the same. Seagrasses are a diverse group of marine flowering plants with true roots, leaves and stems. The students will use a dichotomous key to identify the species name of several Florida marine seagrasses. II-A-35

2 Learner Objectives: Students will understand that living things are sorted for convenience and identification Students design and use a dichotomous guide based on structural characteristics of an organism Sunshine State Standards Correlation: Science: SC.G Competency-based Curriculum Correlation: Science: Sci.M/J1 II-A, Sci.M/J II-A, Sci.M/J1 I-A, Sci.M/J2 I-A Materials Field Guide Seagrass Identification Key Seagrass Sketches Scissors Glue/tape Activity Procedures: 1. Ask students to look around the classroom and give suggestions as to how they would group students for a dynamic water snorkeling activity. The end groups, however, will need to be limited to two snorkeling buddy members. (Students may initially start by dividing groups by sex, then hair color, etc.) 2. Explain the importance of using classification systems in science, especially biology. Introduce a dichotomous key as a means of identifying species. 3. Inform students that they are about to embark on a voyage and they have to find the area that is diverse in seagrasses where there will be an abundance of fish to view on their snorkeling trip. 4. Divide class into cooperative learning groups of three or four students. 5. Give groups a copy of the seagrass field guide with identification key. 6. Students are to use the field guides to identify the different types of seagrass they will observe on their adventure. 7. Students should cut and paste the seagrass sketch beside the identified name. 8. Groups should exchange their final products and decide if other groups have accurately identified seagrasses. They should be sure to include feedback if there is disagreement with the other groups final products. II-A-36

3 Assessment: 1. Students create a dichotomous key of marine fish. (Some common Florida marine fish pictures are attached.) 2. Visit a local beach and use the field guide identification key to name the seagrasses observed. Drag a collecting net along a side of the boat to gather and identify marine samplings of floating seagrasses. This can be constructed by using pantyhose and wire hangers. Make a dichotomous key for catches that are not seagrass. Activity Extensions: 1. Seagrasses are important for the maintenance of life in the ocean. They provide food and shelter for a large number of marine organisms. Think about the last time you walked through or saw a bed of seagrass near the ocean shore. Write an essay describing the importance of seagrasses to the existence of marine life. (Language Arts) 2. Describe the impact to the economy if hotel developers were not allowed to build their properties on the beach in order to preserve seagrasses in the water. (Social Studies) Vocabulary: classification, taxonomy, species, dichotomous key, binomial References: Florida Fish and Wildlife Conservation Commission - Bureau of Protected Species. Identification of Florida s Seagrasses. [Online] Available Johnson, G. B. (1995). Evolution and Natural Selection. In K. Harris, L. Jegerlehner, K. Timp, J. Leland (Eds.), The Living World (pp ) Dubuque, Iowa: Wm. C. Brown Publishers Odyssey Expeditions. [Online] Available II-A-37

4 Seagrasses Excerpts from: Florida Fish and Wildlife Conservation Commission - Bureau of Protected Species Reading Passage Seagrasses are the marine flowering plants, and unlike algae, have true roots, stems and leaves. Seagrasses produce flowers and seeds. Although the flowers are often inconspicuous or not very noticeable, this is another contrast to the algae that is usually the dominant marine plant. You will find that in the terrestrial environments the flowering plants often dominate the landscape. In the meadows of seagrasses the species name Thalassia testudinum or Turtlegrass dominates the flat sandy bottoms. These are often referred to as seagrass flats and are an important natural resource. Seagrasses are essential for stabilizing the soil and sandy ocean bottom, just like their terrestrial counterparts do on land. They prevent erosion when storms pass over stirring up the waves. Seagrasses are one of the most productive plant communities on the planet and part of the base of the food chain in Florida s marine environment. They are the food, habitats and nursing grounds for many marine organisms. There are an estimated 2,000,000 acres of seagrass in Florida waters of the Gulf of Mexico and Florida Bay (over 1,000,000 acres in Florida Bay alone). Some 700,000 acres of seagrass exist in the East Coast waters of the state from the middle of Mosquito Lagoon to the lower portion of Biscayne Bay. Florida has an estimated 1,000,000 acres of seasonal seagrass in deeper coastal marine waters as well. Unfortunately tremendous losses of this irreplaceable habitat have occurred along both coasts of Florida mostly due to pollution and the effects of coastal development. II-A-38

5 Seagrasses FCAT Questions Directions: Read the passage, Seagrasses, then answer all the questions below. Answer multiplechoice questions by circling the letter of the answer that you select.write your answer to the Read, Think, and Explain question on the lines provided. 1. According to the article Seagrasses, if the seagrasses in the eastern part of the state of Florida were destroyed, this would account for a loss of what percentage of seagrass? A. 70 percent B. 35 percent C. 50 percent D. 14 percent Answer: B 2. According to the article, Seagrasses, how are seagrasses and many land plants alike? A. They need little or no water to survive. B. They flower once a year. C. They have roots, stems and leaves. D. They are not important to marine life. Answer: C 3. According to the article Seagrasses, how are marine flowering plants different from terrestrial flowering plants? A. Terrestrial plants have different stems and leaves. B. The marine plants occupy more space than terrestrial plants. C. Marine plants are only found on the coast of Florida. D. Marine plants are in water and terrestrial plants are on land. Answer: D 4. If the seagrasses along the east coast of Florida were removed, what would happen to the marine life in that area? II-A-39

6 Field Guide Florida s Seagrasses Dichotomous Identification Key #1a) Plants with flat leaf blades..go to #2 #1b) Plants with round or cylindrical leaf blades.. Syringodium filiforme (syn: Cymodocea filiformis) [Manatee-Grass] Syringodium filiforme #2a) Leaves elliptic, oval or oblong, each associated with 2 scales at the base..go to #3 #2b) Leaves flat or threadlike go to #4 #3a) Leaves in a pseudowhorl, each with 2 scales at the base and two scales halfway up the petioles or leaf stem..halophila engelmannii [Star Grass] Halophila engelmannii #3b) Leaves paired..go to #5 #4a) Leaves threadlike from a branched stem, leaf tip pointed..ruppia_aritime [Widgeon grass] Ruppia _aritime II-A-40

7 #4b) Leaves flat, leaf tip is rounded or truncated..go to #6 #5a) Leaves rounded, generally oval in shape, secondary veins at an angle greater than 45 degrees, leaf margins with minute serrations annuals..halophila decipiens [Paddle grass] Halophila decipiens #5b) Leaves with a pointed tip, secondary veins at an angle of approximately 45 degrees or less, elongated, entire perennials..halophila johnsonii [Johnson s seagrass] Halophila johnsonii #6a) Leaf blades greater than 3 mm in width, generally about 1 cm wide, plants with scaly rhizomes..thalassia testudinum [Turtle grass] Thalassia testudinum #6b) Leaf blades generally less than 3 mm in width, plants without scaly rhizomes..halodule wrightii [Cuban shoal grass] II-A-41

8 Parts of a Fish Diagram Provided By: Odyssey Expeditions Florida Marine Fish Courtesy of: Florida Fish and Wildlife Conservation Commission Pinfish Longbill Spearfish II-A-42

9 Rock Seabass Sandbar Shark Sand Perch Sand Sea Trout II-A-43

10 Common Florida Marine Seagrasses Sketches Courtesy of: Florida Marine Research Institute Halophila johnsonii Syringodium filiforme Halophila decipiens Halodule wrightii II-A-44

11 Halophila engelmanii Thalassia testudinum Ruppia maritima II-A-45