12 Seaweeds, Seagrasses, and Benthic Microorganisms Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton Seaweeds • General morphology: colonial members of the kingdom Protista • Usually connect to a substratum • Take up nutrients from the surrounding water; do not have the extensive support structures or other adaptations needed for life in air • Morphological differentiation: holdfast, stipe, frond, reproductive structures, flotation structures (pneumatocyst) in some species Seaweeds - Main Morphological Features The brown seaweed Durvillaea antarctica on the coast of Chile, showing holdfast, stipe, and a frond. Seaweeds The intertidal brown seaweed Fucus gardneri, intertidal of British Columbia, Canada Seaweeds Floating pneumatocysts of a number of individuals of the kelp Nereocystis leutkeana, near Bamfield, British Columbia. Seaweeds • Classification based on pigments used in gathering light for photosynthesis, storage products, cell wall characteristics Seaweeds • Life histories - based on alternation of life history stages, vary in whether forms are identical, haploid or diploid Variation in the life histories of seaweeds. Diploid (2N) or haploid (N) status is indicated. G = gametophyte; S = sporophyte; M = meiospore Seaweeds (a) the green seaweed Ulva (ca. 25 cm high), (b) the green seaweed Codium fragile (ca. 30 cm high), (c) the red coralline alga Corallina (ca. 1 cm tall), (d) the red seaweed Polysiphonia (ca. 25 cm high), and (e) the brown seaweed Laminaria (ca. 2 m long) Seaweeds • Green seaweeds - Chlorophyta: photosynthetic pigments similar to higher plants, store starch, wide variety of morphologies • Examples, Ulva, Codium Seaweeds • Brown Seaweeds - Phaeophyta: dominate low intertidal, shallow subtidal, include largest seaweeds (kelps), usually more morphologically differentiated than green seaweeds • Example, Laminaria Seaweeds • Red seaweeds - Rhodophyta: appear red because of photosynthetic pigment phycoerythrin, most diverse group, including diverse soft forms and calcareous coralline algae • Example, Corallina Seaweeds Red coralline algae on a rocky shore with chitons Seagrasses • Worldwide, higher plants, in very shallow water, light limited, very simple flowers, pollen spreads floating on water • Basic structure: rhizome system often with symbiotic nitrogen-fixing bacteria within the sediment (allows asexual growth and lateral spread), with shoots coming out of the sediment, spreading toward surface Seagrasses Surfgrass Phyllospadix sp., west coast of U.S. Turtle grass, Thalassia testudinum, Florida Benthic Microorganisms • Diatoms: grow as cells, chains of cells, cell wall impregnated with silica, abundant on soft sediments and rocks, readily grazed by many benthic animals • Bacteria: abundant in sediments and on surfaces, most heterotrophic (saprophytic - breakdown organic matter), some autotrophic, some chemolithotrophic and capable of gaining energy by oxidizing or reducing a number of substances Benthic Microorganisms • Cyanobacteria: occur in single cells and chains (rows of cells known as trichomes), nitrogen-fixing, often grow in mats where sediment is anoxic • Fungi: eukaryotic, often occur in filaments, single cells or chains, saprophytic organisms, may be important disease organisms in sea grasses Benthic Microorganisms The benthic cyanobacterium Lyngbya The End
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