Chapter 7. Structure of Seaweeds Thallus when flattened, called a blade Holdfast Stipe Lack vascular tissue, roots, stems, leaves and flowers

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1 Chapter 7 Key Concepts Multicellular marine macroalgae, or seaweeds, are mostly benthic organisms that are divided into three major groups according to their photosynthetic pigments. The distribution of seaweeds depends not only on the quantity and quality of light but also on a complex of other ecological factors. Marine algae supply food and shelter for many marine organisms. Flowering plants that have invaded the sea exhibit adaptations for survival in saltwater habitats. Seagrasses are important primary producers and sources of detritus, and they provide habitat for many animal species. Salt marsh plants and mangroves stabilize bottom sediments, filter runoff from the land, provide detritus, and provide habitat for animals. Multicellular Algae Seaweeds - multicellular algae in the oceans Major groups of marine macroalgae: red algae (phylum Rhodophyta) brown algae (phylum Phaeophyta) green algae (phylum Chlorophyta) Seaweeds economically important Provide habitat for other organisms Provide food for other organisms Distribution of Seaweeds Most species are benthic Benthic seaweeds define the inner continental shelf compensation depth Distribution is governed primarily by light and temperature Effects of light on seaweed distribution chromatic adaptation? Distribution dependent on herbivory, competition, pigment concentration, etc. Effects of temperature on seaweed distribution Diversity is greatest in tropical waters Temperature not a limiting factor for algae in tropical/subtropical seas Many colder-water algae are perennials Extreme temperatures can kill algae Structure of Seaweeds Thallus when flattened, called a blade Holdfast Stipe Lack vascular tissue, roots, stems, leaves and flowers

2 Biochemistry of Seaweeds Major distinctions based on photosynthetic 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 Composition of cell walls Primarily cellulose May have calcium carbonate Many secrete slimy mucilage Some have a protective cuticle Reproduction in Seaweeds Fragmentation 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 Sexual reproduction gametes fuse to form a diploid zygote Gametophyte gametangia Alteration of generations Green Algae (Phylum: Chlorophyta) Diverse group containing chlorophyll a & b and carotenoids Structure of green algae Most are unicellular Some have a coenocytic thallus Large diversity of forms Response of green algae to herbivory Tolerance Avoidance Deterrence Red Algae (Phylum: Rhodophyta) Phycoerythrins Structure of red algae multicellular Diversity of forms food for sea urchins, fish, molluscs and crustaceans Response of red algae to herbivory calcium carbonate hard-to-graze forms

3 complex life cycles growing in crevices Ecological relationships of red algae epiphytes Epizoics Human uses of red algae Phycocolloids Irish moss is eaten in a pudding Porphyra are used in oriental cuisines e.g. sushi, soups, seasonings animal feed or fertilizer Brown Algae (Phylum: Phaeophyta) Familiar examples: rockweeds kelps sargassum weed 99.7% of species are marine fucoxanthin Distribution of brown algae more diverse and abundant along the coastlines of high latitudes most are temperate sargassum weeds are tropical Structure of brown algae holdfast, stipe and blade Bladders cellulose alginates trumpet cells Brown algae as habitat kelp forests sargassum weeds Human uses of brown algae thickening agents iodine source used as food cattle feed Marine Flowering Plants vascular plants are distinguished by: phloem xylem 2 types of seed bearing plants: conifers flowering plants all conifers are terrestrial

4 halophytes Seagrasses Hydrophytes Classification and distribution of seagrasses 12 genera in 5 families of 3 clades (groups with a common ancestor): 1 clade = eelgrasses and surf grasses 2 nd clade = paddle grasses (Halophila), turtle grasses, and Enhalus 3 rd clade = paddle grass (Ruppia), manatee grasses, and shoal grasses Seagrasses (Structure) aerenchyme lacunae buoyancy tannins Seagrasses Reproduction in seagrasses fragmentation, drifting and re-rooting inconspicuous flowers hydrophilous pollination viviparity Ecological roles of seagrasses primary producers depositing and stabilizing sediments reduce turbidity habitat human uses of seagrass Salt Marsh Plants Less adapted to marine life 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 Structure of salt marsh plants: smooth cordgrass culm tillers aerenchyme allows diffusion of oxygen flowers are wind pollinated seeds drop to sediment Adaptations of salt marsh plants: facultative halophytes thick cuticle well-developed vascular tissues salt glands succulence

5 Ecological roles of salt marsh plants: contribute to detrital food chains Stabilize sediments habitat for other marine organisms phosphorus cycling remove excess nutrients from runoff Consumed by crabs and terrestrial animals Mangroves Classification and distribution of mangroves: 54 diverse species of trees, shrubs, palms and ferns in 16 families 2 main families: red mangrove black mangrove 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 saline lagoons and tropical/subtropical estuaries mangal Mangroves Structure of mangroves 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 Mangroves (Structure) roots stilt roots prop roots drop roots lenticels anchor roots nutritive roots cable roots pneumatophores Leaves simple, oval, leathery and thick, succulent stomata

6 salt glands concentrating salt in shedding leaves Mangroves Reproduction in mangroves simple flowers pollinated by wind or bees buoyant seeds viviparity propagule Ecological roles of mangroves: stabilize 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