Transcript Chapter 7
Who, What, When, Where, Why, and How of Primary Producers • What is a primary producer? • Where are primary producers found in the marine ecosystem? • When are primary producers a problem? • Why are primary producers important? • How do algae differ from plants? Chapter 7 Multicellular Primary Producers Karleskint Turner Small • 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 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) Algae • Red algae • Green algae • Brown algae 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 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 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 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 Green Algae (Phylum: Chlorophyta) • Diverse group of microbes and multicellular organisms that contain some pigments found in vasculaar plants • Structure of green algae – Most are unicellular or small multicellular filaments, tubes or sheets – There is a large diversity of forms among green algae Green Algae • Response of green algae to getting eaten by herbivore animals – Tolerance: rapid growth and release of huge numbers of spores and zygotes – Avoidance: small size allows them to occupy out-of-reach crevices – Deterrence: • calcium carbonate deposits require herbivores with strong jaws and fill stomachs with non-nutrient minerals • many produce repulsive toxins Red Algae (Phylum: Rhodophyta) • 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) • algal turfs: low, dense groups of filamentous red (along with greens, browns) and branched thalli that carpet the seafloor over hard rock or loose sediment Red Algae • Annual red algae are seasonal food for sea urchins, fish, molluscs and crustaceans • Response of red algae to not getting eaten by herbivores – making their thalli less edible by incorporating calcium carbonate – changing growth patterns to produce hard-tograze forms like algal turfs – evolving complex life cycles which allow them to rapidly replace grazed biomass – avoiding herbivores by growing in crevices 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 Red Algae • Human uses of red algae – phycocolloids (polysaccharides) from cell walls are valued for gelling or stiffening properties • e.g. agar, carrageenan (used in ice cream, yogurt, etc) – 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 Brown Algae (Phylum: Phaeophyta) • Familiar examples: – rockweeds – kelps – sargassum weed • 99.7% of species are marine, mostly benthic (sargassum – not benthic) • Olive-brown color comes form the carotenoid pigment fucoxanthin, masks green pigment of chlorophylls a & c Brown Algae • Distribution of brown algae – more diverse and abundant along the coastlines of high latitudes – most are temperate – sargassum weeds are tropical 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 – cell walls are made up of cellulose and alginates (phycocolloids) that lend strength and flexibility 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 • 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 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 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 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 • Their bodies are composed of polymers like cellulose and lignin that are indigestible to most marine organisms Seagrasses • Seagrasses are hydrophytes (generally live and flower beneath the water) • Classification includes: • • • • Eelgrasses Turtle grass Manatee grass Shoal grass 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 Seagrasses • Ecological roles of seagrasses – highly productive on local sale – role of seagrasses as primary producers • less available and less digestible than seaweeds • contribute to food webs through fragmentation and loss of leaves – sources of detritus – 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 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 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 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 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 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) Mangroves • Classification and distribution of mangroves • red mangrove • black mangrove • white mangroves 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 – mangal: a mangrove swamp community 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) 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 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 Chapter 7 Concepts • What is the difference between algae and plants? What makes a plant a plant? • What differentiates the types of algae? • Table 7 • Are plants and algae in the same domain?