Chapter 7 Multicellular Primary Producers

1. Chapter 7 Multicellular Primary Producers

2. Multicellular Algae • Seaweeds are multicellular algae that inhabit the oceans • Major groups of marine macroalgae: • red algae (phylum Rhodophyta) • brown algae (phylum Phaeophyta) • green algae (phylum Chlorophyta)

3. Multicellular Algae • Scientists who study seaweeds and phytoplankton are called phycologists or algologists. • Algae are divided taxonomically into different groups based on differences in accessory pigments.

4. Distribution of Seaweeds • Benthic seaweeds define the inner continental shelf, where they provide food and shelter to the community • compensation depth: the depth at which the daily or seasonal amount of light is sufficient for photosynthesis to supply algal metabolic needs without growth

5. Distribution of Seaweeds • Distribution is governed primarily by light and temperature • Effects of temperature on seaweed distribution • diversity of seaweeds is greatest in tropical waters, less in colder latitudes • In colder regions, some algae die off in winter, but others termed perennials live for at least 2 years.

6. Structure of Seaweeds • Thallus: the seaweed body, usually composed of photosynthetic cells • when flattened, called a frond or blade • Holdfast: the structure attaching the thallus to a surface

7. Structure of Seaweeds Stipe: a stem-like region between the holdfast and blade of some seaweeds Lack vascular (conductive) tissue, roots, stems, leaves and flowers

8. Biochemistry of Seaweeds • Photosynthetic pigments • Color of thallus due to wavelengths of light not absorbed by the seaweed’s pigments • All have chlorophyll a plus: • chlorophyll b in green algae • chlorophyll c in brown algae • chlorophyll d in red algae • Accessory pigments absorb various colors • e.g. carotenes, xanthophylls, phycobilins pass energy to chlorophylls for photosynthesis

9. Biochemistry of Seaweeds • Composition of cell walls • Primarily cellulose • Many seaweeds secrete slimy mucilage (polymers of several sugars) as a protective covering • holds moisture, and may prevent desiccation • Some have a protective cuticle—a multi-layered protein covering

10. Biochemistry of Seaweeds • Nature of food reserves • Excess sugars are converted into polymers • Stored in cells as starches • Chemistry of starches differs among groups of macrogae • Unique sugars and alcohols may be used as antifreeze substances by intertidal seaweeds during cold weather

11. Reproduction in Seaweeds • Fragmentation: asexual reproduction in which the thallus breaks up into pieces, which grow into new algae • drift algae: huge accumulations of seaweeds formed by fragmentation, e.g., some sargassum weeds

12. Reproduction in Seaweeds • Asexual reproduction through spore formation • haploid spores formed within an area of the thallus (sporangium) through meiosis • sporophyte (diploid): stage of the life cycle that produces spores, which is diploid

13. Reproduction in Seaweeds • Sexual reproduction • gametes fuse to form a diploid zygote • Gametophyte (usually haploid): stage of the life cycle that produces gametes • Alteration of generations: the possession of 2 or more separate multicellular stages (asexual sporophtye, sexual gametophyte) in succession

14. Green Algae (Phylum: Chlorophyta) • Structure of green algae • Most are unicellular or small multicellular filaments, tubes or sheets • Some tropical green algae have a coenocytic thallus consisting of a single giant cell or a few large cells containing more than 1 nucleus and surrounding a single vacuole

15. Green Algae • Response of green algae to herbivory • Tolerance: rapid growth and release of huge numbers of spores and zygotes • Deterrence: • calcium carbonate deposits require herbivores with strong jaws and fill stomachs with non-nutrient minerals • many produce repulsive toxins

16. Green Algae • Reproduction in green algae • the common sea lettuce, Ulva, has a life cycle that is representative of green algae

17. Red Algae (Phylum: Rhodophyta) • Primarily marine and mostly benthic • Highest diversity among seaweeds • Red color comes from phycoerythrins • Thalli can be many colors, yellow to black

18. Structure of red algae • Almost all are multicellular • Thallus may be blade-like or composed of branching filaments or heavily calcified • algal turfs: low, dense groups of filamentous red (along with greens, browns) and branched thalli that carpet the seafloor over hard rock or loose sediment

19. Red Algae • Annual red algae are seasonal food for sea urchins, fish, molluscs and crustaceans • Response of red algae to herbivory • making their thalli less edible by incorporating calcium carbonate

20. Red Algae • Reproduction in red algae • 2 unique features of their variety of life cycles: • absence of flagella • occurrence of 3 multicellular stages: • 2 sporophytes in succession and one gametophyte

21. Red Algae • Ecological relationships of red algae • a few smaller species are: • epiphytes—organisms that grow on algae or plants • epizoics—organisms that grow on animals • red coralline algae precipitate calcium carbonate from water and aid in consolidation of coral reefs Corraline red algae

22. Red Algae • Human uses of red algae • phycocolloids (polysaccharides) from cell walls are valued for gelling or stiffening properties • e.g. agar, carrageenan

23. Red Algae • Irish moss is eaten in a pudding • Porphyra are used in oriental cuisines • e.g. sushi, soups, seasonings • cultivated for animal feed or fertilizer in parts of Asia

24. Brown Algae (Phylum: Phaeophyta) • Familiar examples: • rockweeds • kelps • sargassum weed

25. Brown Algae • Distribution of brown algae • more diverse and abundant along the coastlines of high latitudes • most are temperate • sargassum weeds are tropical

26. 99.7% of species are marine, mostly benthic (sargassum – not benthic) • Olive-brown color comes form the carotenoid pigment fucoxanthin, masks green pigment of chlorophylls a & c • Brown algae can reach up to 100 meters in length.

27. Brown Algae • Structure of brown algae • most species have thalli that are well differentiated into holdfast, stipe and blade • bladders—gas-filled structures found on larger blades of brown algae, and used to help buoy the blade and maximize light

28. Brown Algae • Reproduction in brown algae • usual life cycle, i.e., alternation of generations between a sporophyte (often perennial) and a gametophyte (usually an annual) • rockweed (Fucus) eliminates gametophyte stage;

29. Brown Algae • Brown algae as habitat • kelp forests house many marine animals • sargassum weeds of the Sargasso Sea form floating masses that provide a home for unique organisms

30. Brown Algae • Human uses of brown algae • thickening agents are made from alginates • once used as an iodine source • used as food (especially in Asia) • used as cattle feed in some coastal countries

31. Marine Flowering Plants • Seagrasses, Marsh Plants, Mangroves

32. Marine Flowering Plants • General characteristics of marine flowering plants • vascular plants are distinguished by: • phloem: vessels that carry water, minerals, and nutrients • xylem: vessels that give structural support • seed plants reproduce using seeds, structures containing dormant embryos and nutrients surrounded by a protective outer layer

33. Marine Flowering Plants • 2 types of seed bearing plants: • conifers (bear seeds in cones) • flowering plants (bear seeds in fruits) • all conifers are terrestrial • marine flowering plants are called halophytes, meaning they are salt-tolerant

34. Marine Flowering Plants • Seagrasses, Marsh Plants, Mangroves

35. Invasion of the Sea by Plants • Flowering plants evolved on land and then adapted to estuarine and marine environments • Flowering plants compete with seaweeds for light and with other benthic organisms for space • Their bodies are composed of polymers like cellulose and lignin that are indigestible to most marine organisms • Have few competitors and often form extensive single-species stands on which other members of the community depend

36. Marine Flowering Plants • Seagrasses, Marsh Plants, Mangroves

37. Salt Marsh Plants • Much less adapted to marine life than seagrasses; must be exposed to air by ebbing tide • Classification and distribution of salt marsh plants • salt marshes are well developed along the low slopes of river deltas and shores of lagoons and bays in temperate regions • salt marsh plants include: • cordgrasses (true grasses) • needlerushes • various shrubs and herbs, e.g., saltwort, glassworts

40. Salt Marsh Plants • Structure of salt marsh plants • smooth cordgrass, initiates salt marsh formation, grows in tufts of vertical stems connected by rhizomes, dominates lower marsh • culm: vertical stem • tillers: additional stems produced by a culm at its base, gives a tufted appearance • aerenchyme allows diffusion of oxygen from blades to rhizomes and roots • flowers are pollinated by the wind • seeds drop to sediment or are dispersed by water currents

42. Salt Marsh Plants • Adaptations of salt marsh plants to a saline environment • facultative halophytes—tolerate salty as well as fresh water • leaves covered by a thick cuticle to retard water loss • well-developed vascular tissues for efficient water transport • Spartina alterniflora have salt glands, secrete salt to outside • shrubs and herbs have succulent parts

43. Salt Marsh Plants • Ecological roles of salt marsh plants • contribute heavily to detrital food chains • stabilize coastal sediments and prevent shoreline erosion • serve as refuge, feeding ground and nursery for other marine organisms • rhizomes of cordgrass help recycle phosphorus through transport from bottom sediments to leaves • remove excess nutrients from runoff • are consumed by (at least in part) by crabs and terrestrial animals (e.g. insects)

44. Mangroves • Classification and distribution of mangroves • mangroves include 54 diverse species of trees, shrubs, palms and ferns in 16 families • ½ of these belong to 2 families: • red mangrove (Rhizophora mangle) • black mangrove (Avicennia germinans) • others are white mangroves, buttonwood, and Pelliciera rhizophoreae

46. Mangroves (Distribution) • thrive along tropical shores with limited wave action, low slope, high rates of sedimentation, and soils that are waterlogged, anoxic, and high in salts • low latitudes of the Caribbean Sea, Atlantic Ocean, Indian Ocean, and western and eastern Pacific Ocean • associated with saline lagoons and tropical/subtropical estuaries • mangal: a mangrove swamp community

47. Mangroves • Structure of mangroves • trees with simple leaves, complex root systems • plant parts help tree conserve water, supply oxygen to roots and stabilize tree in shallow, soft sediment • roots: many are aerial (above ground) and contain aerenchyme • stilt roots of the red mangrove arise high on the trunk (prop roots) or from the underside of branches (drop roots) • lenticels: scarlike openings on the stilt root surface connecting aerenchyme with the atmosphere

48. Mangroves (Structure) • anchor roots: branchings from the stilt root beneath the mud • nutritive roots: smaller below-ground branchings from anchor roots which absorb mineral nutrients from mud • black mangroves have cable roots which arise below ground and spread from the base of the trunk • anchor roots penetrate below the cable root • pneumatophores: aerial roots which arise from the upper side of cable roots, growing out of sediments and into water or air • lenticels and aerenchyme of pneumatophores act as ventilation system for black mangrove