Multicellular Algae: Diversity and Ecological Importance

1. Chapter 7Multicellular Primary Producers

2. Primary producers – those organisms that photosynthesize • Previously, we talked about phytoplankton: • Cyanobacteria • We also talked about unicellular protists that are phytoplankton (for example: dinoflagellates, diatoms, etc) • Now we will talk about the macro algae (“seaweeds”) and marine plants

3. Multicellular Algae • Most primary production in marine ecosystems takes place by phytoplankton but seaweed and flowering plants contribute especially in coastal areas • 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)

4. Algae – not “plants” • Red algae • Green algae • Brown algae

5. Multicellular Algae • Scientists who study seaweeds and phytoplankton are called phycologists or algologists • Seaweeds contribute to the economy of coastal seas • Produce 3 dimensional structural habitat for other marine organisms • Consumed by an array of animals, e.g., sea urchins, snails, fish

6. Distribution of Seaweeds • Most species are benthic, attaching and growing on rock, sand, mud, corals and other hard substrata in the marine environment as part of the fouling community • 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 • Distribution is governed primarily by light and temperature

8. 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 • Stipe: a stem-like region between the holdfast and blade of some seaweeds • Seaweeds are not plants • Lack vascular (conductive) tissue, roots, stems, leaves and flowers

12. Biochemistry of Seaweeds • Composition of cell walls • Primarily cellulose, like plants • May be impregnated with calcium carbonate in calcareous algae • Many seaweeds secrete slimy mucilage (polymers of several sugars) as a protective covering • holds moisture, and may prevent desiccation • can be sloughed off to remove organisms • Some have a protective cuticle—a multi-layered protein covering

13. Green Algae • Diverse group of microbes and multicellular organisms that contain some pigments found in vascular land plants • Structure of green algae • Most are unicellular • Unicellular ones are part of the phytoplankton • There is a large diversity of forms among green algae • Multicellular ones are seaweed

15. Red Algae • Primarily marine and mostly benthic • Highest diversity among seaweeds • Red color comes from special protein-pigment complex • Thalli can be many colors, yellow to black • Structure of red algae • Almost all are multicellular • Thallus may be blade-like or composed of branching filaments or heavily calcified (may be hard)

16. Red Algae • Annual red algae are seasonal food for sea urchins, fish, molluscs and crustaceans

17. 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

18. Red Algae • Human uses of red algae • Ice cream • yogurt • 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

19. Brown Algae • Familiar examples: • rockweeds • kelps • sargassum weed • 99.7% of species are marine, mostly benthic (sargassum – not benthic) • Olive-brown color comes form a carotenoid pigment that masks the chlorophylls

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

23. 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

26. Brown Algae • Brown algae as habitat • kelp forests house many marine animals • sargassum weeds of the Sragasso Sea form floating masses that provide a home for unique organisms • There are species of animals that have coevolved with the sargassum and blend in (sargassum fish, sargassum seahorse) • 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

27. Now we will talk about the plants of the marine environments • Most terrestrial plants are not tolerant of the marine environment, not that many plants that grow successfully in the ocean when compared to land

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

29. Marine 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 • Examples are sea grasses, mangroves, dune plants

30. 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

31. Seagrasses • Seagrasses are hydrophytes (generally live and flower beneath the water) • Classification includes: • Eelgrasses • Turtle grass • Manatee grass • Shoal grass

32. Seagrasses • Structure of seagrasses • vegetative growth—growth by extension and branching of horizontal stems (rhizomes) from which vertical stems and leaves arise • 3 basic parts: stems, roots and leaves

33. Seagrasses • Ecological roles of seagrasses • highly productive on local sale • role of seagrasses in depositing and stabilizing sediments • blades act as baffles to reduce water velocity • decay of plant parts contributes organic matter • rhizomes and roots help stabilize the bottom • reduce turbidity—cloudiness of the water

34. Seagrasses (Ecological Roles) • role of seagrasses as habitat • create 3-dimensional space with greatly increased area on which other organisms can settle, hide, graze or crawl • rhizosphere—the system of roots and rhizomes also increases complexity in surrounding sediment • the young of many commercial species of fish and shellfish live in seagrass beds • human uses of seagrass • indirect – fisheries depend on coastal seagrass meadows • direct – extracted material used for food, medicine and industrial application

35. 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

38. 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 • flowers are pollinated by the wind • seeds drop to sediment or are dispersed by water currents

39. 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

40. 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)

41. Mangroves • Classification and distribution of mangroves • red mangrove • black mangrove • white mangroves

43. 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

44. 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) stilt roots of the red mangrove arise high on the trunk (prop roots) or from the underside of branches (drop roots)

47. Mangroves (Structure) • leaves • mangrove leaves are simple, oval, leathery and thick, succulent like marsh plants, never submerged • stomata: openings in the leaves for gas exchange and water loss • salt is eliminated through salt glands (black mangroves) or by concentrating salt in old leaves that shed

48. Mangroves • Ecological roles of mangroves • root systems stabilize sediments • aerial roots aid deposition of particles in sediments • epiphytes live on aerial roots • canopy is a home for insects and birds • mangals are a nursery and refuge • mangrove leaves, fruit and propagules are consumed by animals • contribute to detrital food chains