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Multicellular Primary Producers Seaweeds or Limu Different from phytoplankton

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Zoology 200 Multicellular Primary Producers – Ch 6 Dr. Bob Moeng

Multicellular Primary Producers

Seaweeds or Limu

  • Different from phytoplankton

  • Multicellular (& macroscopic)

  • Benthic - attached to substrate and thus limited to coastal regions by photic zone

  • Also called macrophytes or macroalgae (some consider them plants)

Seaweeds or Limu (graphic)

More Seaweeds or Limu

  • Domain Eukaryotes

  • Representative Divisions of Kingdom Protista include Phaeophyta and Rhodophyta (marine only) and Chlorophyta (also FW and terrestrial)

  • Major difference based on types of photosynthetic pigments

  • Typically need hardened substrate, particularly in intertidal areas

  • Usually extend down to 30-40 meters

Limu Characteristics (graphic)

Seaweed Structure

  • Most organized as thallus with blade, stipe, and holdfast

  • Blades are frequently flattened with cellular layering

  • Photosynthetic cells near surface

  • No top or bottom of blade

  • No network of “veins”

  • Some have pneumatocysts (gas-filled bulbs) to keep blades near surface

  • Stipes may or may not be present

  • May have photosynthetic cells

  • Usually don’t have conductile tissue

Thallus (graphic)

Pneumatocyst (graphic)

More Seaweed Structure

  • Holdfasts secure the seaweed to substrate

  • Not important for water & nutrients

  • Extent of holdfast determines location seaweed is likely to be found

  • Filamentous and numerous haptera hold in sand or mud

  • Some with calcium cabonate (mostly reds and some greens)

  • Encrusting red algae important to binding coral reefs (in warm waters) together and may create reefs of their own

  • Greens may contribute to sand

Reproductive Cycle

  • Asexual or vegetative reproduction - fragmented pieces continue to grow and reproduce

  • Sexual reproduction typically involves life cycle of two forms - sporophyte and gametophyte

  • Substantial variability among different seaweeds

  • Sporophyte (diploid) creates spores through meiosis

  • Spores germinate forming gametophyte (haploid)

  • Gametophyte produces gametes which fuse (zygote) and germinate to form sporophyte

Sample Reproductive Cycles (graphic)

More Reproductive Cycle

  • In Ulva, both forms appear the same

  • In Codium, the gametophyte stages is absent

  • In Laminaria, the gametophytes are small and sexually separated and dimorphic

  • Green algae spores have 4 flagella, brown - 2, and red - none

  • Growth is by mitotic cell division and differentiation of tissue

  • Along with differentiation is specialization of growth tissue - meristematic tissue

Economic Uses

  • Edible varieties

  • Derivatives - primarily phycocolloids

  • Algin - largely from kelp

  • Used as food additive (stabilizer and emulsifier for dairy products like ice cream, cheese and toppings

  • Used as thickener and emulsifier for variety of other products…shampoo, plastics, pesticides

  • Agar - from certain red algae

  • Used in canning of meats e.g. ham

  • Used in some pharmaceuticals

  • Bacterial growth medium

Phylum Magnoliophyta

  • Marine flowering plants or angiosperms

  • Secondary adaptation (return to marine environment)

  • Have leaves, stems, roots, and conductile tissue, dominant sporophyte phase

  • Typically are seagrasses, 50% of which are found in tropics or subtropics

  • Most have rhizomes - important for anchoring, storage for starch and vegetative reproduction

  • Sexual reproduction (flowering) with formation of current transported pollen, attachment to stigma, and formation of seeds

Rhizomes of Seagrasses (graphic)

More Phylum Magnoliophyta

  • “Meadows” frequently found and result from both sexual and asexual reproduction

  • Not true grasses

  • Hawaii’s forms are marine or estuarine and usually found in soft sediments (silt or sand) - a few found attached directly to rock

  • Mangroves - border terrestrial and marine environments

  • Form thickets or mangals limited to subtropics and tropics

  • Prop roots reach down through intertidal waters with remaining portion of plant above water level

Even More Magnoliophyta

  • Controversy about effect of securing and accumulating sediments

  • Red mangrove (Rhizophora) typical in Hawaii

  • Seeds germinate while still hanging from branches causing bottom to be heavier

  • When dropped, seeds float (distribute) and roots secure in another location

  • Both seagrasses and mangroves form communities of organisms

Mangrove Seed Distribution (graphic)

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