7 _________________________________________________________ MULTICELLULAR PRIMARY PRODUCERS Chapter Outline MULTICELLULAR ALGAE Distribution of Seaweeds Effects of Light on Seaweed Distribution Effects of Temperature on Seaweed Distribution Structure of Seaweeds Biochemistry of Seaweeds Photosynthetic Pigments Composition of Cell Walls Nature of Food Reserves Reproduction in Seaweeds Green Algae Structure of Green Algae Response of Green Algae to Herbivory Reproduction in Green Algae Human Uses of Green Algae Red Algae Structure of Red Algae Response of Red Algae to Herbivory Reproduction in Red Algae Ecological Relationships of Red Algae Human Uses of Red Algae Brown Algae Distribution of Brown Algae Structure of Brown Algae Reproduction in Brown Algae Brown Algae as Habitat Human Uses of Brown Algae MARINE FLOWERING PLANTS General Characteristics of Flowering Plants Invasion of the Sea by Plants Sea Grasses Classification and Distribution of Seagrasses Structure of Seagrasses Reproduction of Seagrasses Ecological Roles of Seagrasses Human Uses of Seagrasses Salt Marsh Plants Classification and Distribution of Salt Marsh Plants Structure of Salt Marsh Plants Adaptation of Salt Marsh Plants to a Saline Environment Ecological Roles of Salt Marsh Plants Human Uses of Salt Marsh Plants Mangroves Classification and Distribution of Mangroves Structure of Mangroves Reproduction in Mangroves Human Uses of Mangroves Chapter Objectives •
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Describe the structure and characteristics of multicellular algae. Interpret a phylogenetic tree of marine algae. Identify the three different groups of marine algae. Describe the structure and characteristics of brown algae, green algae, red algae, sea grasses, salt marsh plants, and mangroves. Chapter 7 72 •
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Explain the adaptations of brown algae, green algae, red algae, sea grasses, salt marsh plants, and mangroves. Describe the ecological niche and distribution of brown algae, green algae, red algae, sea grasses, salt marsh plants, and mangroves. Recognize the symbiotic relationships that algae and marine flowering plants have with other marine organisms. Describe the reproduction of brown algae, green algae, red algae, sea grasses, salt marsh plants, and mangroves. Explain the various uses of algae and marine flowering plants by humans. Key Terms seaweeds macroalga phycologist algologist fouling community compensation depth chromatic adaptation perennial thallus vascular tissue frond blade holdfast stipe cuticle fragmentation drift algae sporangium sporophyte gametophyte gametangium alternation of generations green algae coenocytic tolerance avoidance deterrence red algae nori algal turf carposporophyte carpospores tetrasporophyte tetraspores epiphyte epizoic coralline algae phycocolloids agar carrageenan brown algae fucoxanthin bladders alginates trumpet cells mannitol receptacles conceptacle rhizoids stonewort phloem xylem seed flowering plants fruits halophytes sea grasses hydrophyte vegetative growth rhizomes internode nodes root hairs scale leaves foliage leaves sheath blade epidermis senescence aerenchyma lacunae tannins bioturbation pollen stigma hydrophilous pollination viviparity turbidity rhizosphere culm tillers facultative halophyte salt glands succulent mangrove mangal aerial root stilt root prop root drop root lenticels anchor roots nutritive roots cable root pneumatophores stomata propagule hypocotyl
Chapter 7 73 Chapter Summary 1. Multicellular marine algae are divided into three major groups based on the accessory pigments they contain. Algal cells have cell walls in addition to their membranes, and their pigments are located within organelles called chloroplasts. Algal life cycles tend to be complex. Algae are a food source for many organisms, including humans, and they provide a habitat for many species. They are also a source of many commercial products. 2. Green algae are found in shallow coastal waters. Many marine species of green algae exhibit a coenocytic body plan. Red algae are most widespread in the tropics. Their red color is due to the presence of the pigment phycoerythrin. Brown algae are almost exclusively marine organisms. With the notable exception of Sargassum weed, most brown algae can be found along continental shorelines. Many brown algae have flexible bodies, an advantage for avoiding wave shock. 3. The plants living in marine environments are vascular plants that produce seeds. All marine plants exhibit adaptations that allow them to survive in salt water. Marine plant communities play many important ecological roles in the environment. Marine plants are primary producers, and they contribute to marine food webs by way of detrital pathways both locally and offshore. They also provide habitats for many organisms, especially nursery grounds for many species in the commercial and sport fishing industries. 4. Sea grasses are mainly found in shallow waters of temperate and tropical oceans. Temperate salt marsh plants generally grow in the middle to upper intertidal zones, where they are protected from wave action. Mangroves are tropical trees and shrubs that grow in sandy and muddy coastal areas that are protected from wave action and have high sedimentation rates. Chapter Outline I.
Multicellular Algae A. Three major groups of seaweeds: red, brown, and green. B. Provide habitat for fishes, invertebrates, and other algae. C. Distribution of seaweeds. 1. Fouling communities. 2. Compensation depth. 3. Chromatic adaptation. 4. Perennial. D. Structure of seaweeds. 1. Lack vascular tissue that characterizes higher plants. 2. Thallus. 3. Blade. 4. Holdfast. 5. Stipe. Chapter 7 74 6. Marine biology and the human connection: seaweeds and their medicine. E. Biochemistry of seaweeds. 1. Photosynthetic pigments. a. Chlorophyll a present in all macroalgae. b. Chlorophyll b present in green algae. c. Chlorophyll c present in brown algae. d. Chlorophyll d present in red algae. e. Accessory pigments vary: carotenes, xanthophylls, and phycobilins. 2. Cell wall composition varies by taxonomic group. 3. Calcareous algae also have calcium carbonate embedded in their cell walls. F. Seaweed reproduction. 1. Fragmentation. 2. Drift algae. 3. Sporophyte. 4. Gametophyte. 5. Alternation of generations. G. Green algae. 1. Varied thallus forms: tubes, sheets, and filaments. 2. Coenocytic. 3. Herbivory responses. a. Calcium carbonate in cell walls discourages predation. b. Small size and short life cycles prevent herbivores from decimating the algal species. c. Production of toxic anti-­‐‑herbivory compounds. 4. Green algae exhibit alternation of generations. H. Red algae. 1. Largely marine (98%) with few freshwater species. Great tropical diversity. 2. Benthic species; can be distributed to depths of 200 m in clear water. 3. Smaller than 1 m, thallus can be bladelike or filamentous and branching. 4. Used for food in Asian cultures. 5. Herbivory responses. a. Calcium carbonate embedded in cell walls deters herbivory and lowers nutrition value; tropical red coralline algae important source of calcium in reef communities. b. Evolve complex life cycles with short phases that discourage herbivory. c. Growth forms that discourage herbivory (turf algae in algal mats) that are difficult to eat. 6. Reproduction. a. Complex life cycles with two sporophyte phases and one gametophyte phase. b. Sexual cells lack flagella. c. Dioecious gametophytes: male and female thalli. 7. Ecology of red algae. a. Epiphytes. b. Epizoics. 8. Commercial uses of red algae. I. Brown algae. 1. Virtually entirely marine (99.7% of 1500 species are marine), predominantly benthic. 2. More abundant and diverse in higher latitude, cooler waters than in tropics. 3. Morphology of brown algae. a. Well developed thallus with blade, stipe, and holdfast. Chapter 7 75 b.
Larger blades have air bladders that keep the thallus suspended in the water column, maximizing photosynthetic surface area. 4. Cell walls of cellulose and alginates (similar to agar and carrageen) produce a flexible yet sturdy thallus that can withstand wave shock. 5. Specialized conductive cells (trumpet cells) that conduct photosynthetic byproducts (mannitol) from the blade to the rest of the thallus. 6. Reproduction. a. Alternation of a perennial sporophyte with annual gametophyte. b. Haploid heterokont spores. c. Conceptacles: haploid gamete-­‐‑producing chambers in macrophytic brown algae. d. Rhizoids: rootlike structures produced by the zygote to anchor it to the substrate. 7. Ecology of brown algae. a. Kelp forests provide essential habitat for sea otters, fish, sea lions, sea urchins, molluscs, and crustaceans—including many commercially important species. b. Sargassum provides floating habitat for many small organisms in the open ocean. 8. Commercial uses of brown algae. II. Marine Flowering Plants A. Vascular tissue present: phloem and xylem. B. Structures with vascular tissue: roots, stems, leaves. C. Halophytes: salt-­‐‑tolerant flowering plants. D. Sea grasses. 1. Hydrophytes; subtidal (submerged) plants. 2. Types of sea grasses: eelgrasses, surf grasses, manatee grasses, shoal grasses, paddle grasses, and turtle grasses. 3. Sea grass morphology. a. Rhizomes: horizontal underground stems anchored in the sediment. b. Blades arise from the sheath on the vertical stem. c. Roots come off the rhizome. d. Flowers come off vertical stem at leaf base. 4. Sea grasses are generally found in subtidal low-­‐‑wave energy environments that have soft substrates (mud or sand) with relatively low nutrients and high light. 5. Leaves age (senescence) and break off; replaced by a new blade over time. 6. Aerenchyma. 7. Lacunae. 8. Reproduction identical to terrestrial flowering plants—hydrophilous pollination. 9. Ecology of sea grasses. a. Require high light (except for paddle grasses, Halophila). b. Few animal species graze sea grasses because of high cellulose content. c. Stabilize coastal sediments. d. Algal blooms increase turbidity, reducing light and killing sea grasses. e. Sea grasses provide critical habitat for larval fishes and invertebrates. 10. Commercial uses of sea grass. E. Salt marsh plants. 1. Temperate intertidal communities found in areas of low water velocity with muddy or silty substrates. 2. Salt marsh plants. a. Cord grasses: Spartina. b. Needle rushes: Juncus. Chapter 7 76 F.
c. Saltworts. d. Glassworts. 3. Spartina growth form. a. Culm: vertical cord grass stems. b. Tillers: small additional stems produced around the base of the culm. c. Rhizomes anchor plants to substrate. d. Roots branch off rhizomes. e. Wind pollinated. f. Height of plant inversely proportional to the distance to the low tide water level. 4. Adaptations to saline environment. a. Facultative halophyte. b. Unlike sea grasses, salt marsh plants can adapt to widely varying salinities. c. Spartina: salt glands on leaves excrete excess salt. d. Succulent growth form (as in saltworts and glassworts), conserve water. 5. Ecology of salt marsh plants. a. Accumulate and stabilize sediments in coastal areas. b. Nursery area for juvenile fishes and invertebrates. c. Recycle excess nutrients from coastal runoff, especially phosphorus. d. Salt marsh detrital food chain critical to coastal fisheries. 6. Commercial significance. Mangroves. 1. Tropical intertidal plants found in areas of low water velocity and sandy or muddy substrates. 2. Mangrove morphology. a. Prop roots. b. Lenticels. c. Pneumatophores. d. Thick highly lignified leaves prevent water loss; stomata on leaf underside. e. Some mangroves deposit excess salt in bark. f. Concentrate salt in xylem fluid where it is sequestered from living tissue. 3. Mangrove reproduction. a. Wind-­‐‑ or bird-­‐‑pollinated flowers. b. Buoyant seeds that can float to suitable habitat. c. Propagule. 4. Mangrove ecology. a. Roots trap and stabilize coastal sediments, preventing sediments from washing out into sea grass beds and coral reef areas. b. Roots provide a nursery area for fishes and invertebrates. c. Rookeries for birds. 5. Human uses of mangroves. Chapter 7 77