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 -
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) Most organized as thallus with blade, stipe, and holdfast Blades are frequently flattened with cellular layering -
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 -
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 -
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 -
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 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 -
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 -
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 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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