Chapter 6 Multicellular Primary Producers: Seaweeds and Plants

Seaweeds -multicellular (a few exceptions), eukaryotes -important source of food, habitat -producers of oxygen for organisms on land and in oceans -economic importance -also called MACROPHYTES or MACROALGAE -NOT PLANTS (Kingdom Protista) -Lack true roots, stems, leaves

General Structure: -thallus: complete body -blade: leaflike flattened portion -pneumatocysts: gas-filled bladders -stipe: stem-like structure -holdfast: rootlike portion that attaches thallus to bottom

General Structure

Holdfast

3 Major Divisions (Phyla): -Green algae (PHYLUM CHLOROPHYTA) -Brown algae (PHYLUM PHAEOPHYTA) -Red algae (PHYLUM RHODOPHYTA)

Green Algae CHLOROPHYTA

Green Algae Mostly freshwater and terrestrial environments Also bays estuaries, rocky tide pools Simpler thallus than red or brown algae Pigments and food reserve (starch) same as land plants Land plants evolved from green algae Typically bright green (chlorophyll not masked by other pigments)

Genera of Green Algae Enteromorpha Ulva Valonia Caulerpa Codium Halimeda

Enteromorpha Filamentous Thin thallus in the form of a hollow tube

Enteromorpha

Ulva Also called sea lettuce Paper-thin sheets Shape varies according to environmental factors Polar to tropical

Ulva

Valonia Large spheres or clusters of spheres Tropical and subtropical

Valonia

Caulerpa Tropical and subtropical Great variety of shapes Thin filaments or tubes (siphons) formed by a single giant cell with many nuclei

Caulerpa

Codium “Dead man’s fingers” Multinucleated filaments woven into a branching thallus Tropical to temperate Both coasts of North America

Codium

Halimeda Calcareous green alga Numerous segments with deposits of CaCO3 Accumulation of dead, calcified segments plays an important role in the formation of coral reefs

Halimeda

Coral Reef Seaweeds- 3 major groups Turf algae-small, filamentous, colonize vacant surfaces that cover non-living hard surfaces on the reef Coralline algae-red algae; produce hard calcareous skeleton; hold reefs together Macroalgae (larger in size)-together with coralline algae plays role in CaCO3 deposition

Coral Reef Seaweeds Seaweeds not often regarded as components of healthy coral reefs Reefs impacted by pollution are often overrun with seaweeds Coral Reef Ecosystem Divison (CRED) of NOAA found that in central Pacific Ocean (subtropical northwestern Hawaiian islands), some healthy coral reefs are dominated by seaweeds rather than corals

Brown Algae PHAEOPHYTA

Brown Algae Varies from olive green to dark brown Contains yellow-brown pigments: FUCOXANTHIN (versus chlorophyll) Usually temperate and rocky polar coasts Largest & most complex seaweeds

Genera of Brown Algae Ectocarpus Dictyota Padina Desmarestia Fucus Ascophyllum Sargassum Kelps (several genera: Laminaria, Agarum, Alaria, Postelsia, Egregia, Eisenia, Nereocystis, Pelagophycus, Macrocystis)

Ectocarpus Simplest brown algae Finely filamentous thallus

Ectocarpus

Dictyota Flat, branched thallus Tropical and subtropical

Dictyota

Padina Lightly calcified Fan-shaped Tropical and subtropical

Padina

Desmarestia Typically Antarctic, some species in temperate areas

Desmarestia

Ascophyllum Knotted seaweed Temperate Atlantic coasts

Ascophyllum

Fucus Rockweed, wracks Atlantic and Pacific Coasts North American and other temperate shores

Fucus

Sargassum Warm waters, including Gulf of Mexico and CA Sargasso Sea (in the Atlantic, north of West Indies) Most species grow on rocks 2 species float offshore in huge masses

Sargassum

Sargasso Sea

Laminaria Agarum Alaria Postelsia Nereocystis Pelagophycus Macrocystis Kelps Laminaria Agarum Alaria Postelsia Nereocystis Pelagophycus Macrocystis

Laminaria Single large blade, up to 3 m in length Blades harvested for food May have a split or branched blade

Laminaria

Agarum Conspicuous rib runs along the middle of a single blade

Agarum

Alaria Like Agarum, with a conspicuous rib running down the middle of a single blade Blades can be as long as 25 m

Alaria

Postelsia Known as sea palm because of its appearance Grows on intertidal rocks with heavy wave action Thick clusters from central California to British Columbia

Postelsia

Nereocystis Bull kelp Whip-like stipe up to 30 m Large, spherical pneumatocyst at upper end

Nereocystis

Pelagophycus Similar to the bull kelp in size Antler-like branches

Pelagophycus

Macrocystis ***Largest of the kelps*** Massive holdfast attached to hard bottoms Individuals as long as 100 m Can grow 50 cm or more per day Forms kelp beds or forest in the colder waters of the North and South Pacific Forms some of the richest, most productive marine environments (research kelp communities)

Macrocystis

Red Algae RHODOPHYTA

Red Algae Largest group of seaweeds (more spp. than green and brown combined) Simple structure, some are completely heterotrophic (parasites) Most appear red; depends on exposure to light phycobilins: red pigments

Gelidium, Gracilaria Found worldwide Dense clumps common on upper levels of rocky shores exposed at low tide Longer and flatter branches in areas less exposed to air and in deeper water

Gelidium

Gracilaria

Endocladia Wiry clumps on rocky shores from Alaska to Southern California

Endocladia

Gigartina Among the most massive red algae with blades as long as 2 m

Gigartina

Porphyra Common on rocky shores above the lowest tide marks from polar to tropical coasts Thallus with thin, large blades

Porphyra

Rhodymenia Common in the North Atlantic Blades may reach 1 m in length

Rhodymenia

Chondrus Irish moss Common in the North Atlantic Tolerates wide range of temperatures, salinity, and light Shapes vary in response to above factors

Chondrus

Coralline Algae Red algae that deposit CaCO3 within their cell walls Calcified thallus takes a variety of shapes Color of live coralline algae is reddish-pink Dead coralline algae is white Warm-water coralline algae involved in formation and development of coral reefs Some in temperate and polar waters

Coralline Algae

Life History in Seaweeds Is both asexual (a.k.a. vegetative) and sexual Asexual: a piece of thallus can grow into a new individual (e.g. Sargassum) Alternation of generations: sexual stage alternates with an asexual one gametophyte alternates with a sporophyte

Types of cell division: Mitosis: resulting cells are identical to original chromosomes in pairs (diploid or 2n) e.g. somatic cells Meiosis: resulting cells are haploid (n) gametes contain half the number of parent’s chromosomes

Four types of reproduction Type 1 (sea lettuces and kelps) Type 2 (many red algae) Type 3 (rockweeds) Type 4 (some green algae)

Reproduction in sea lettuce (Type 1) ***Most common*** Involves 2 types of thalli (sporophyte & gametophyte) Sporophyte generation (2n) goes through meiosis and makes haploid (n) spores Spores divide and develop into second kind of thallus, a haploid (n) gametophyte generation Gametophytes produce haploid gametes which unite to produce a diploid zygote Sometimes separate male and female thalli Sometimes male and female gametes produced in one thallus

Reproduction in sea lettuce (Type 1)

Reproduction in red algae (Type 2) Unique to red algae Similar to type 1, but involves a 3rd generation called carposporophyte (2n) from fusion of gametes Carpospores are diploid spores produced by the carposporophyte which develop into sporophytes

Reproduction in red algae (Type 2)

Reproduction in rockweeds (Type 3) Easiest to understand Similar to reproduction in animals NO ALTERNATION OF GENERATIONS One thallus (2n) Thallus produces haploid gametes by meiosis After fertilization, zygote develops into a new diploid thallus

Reproduction in rockweeds (Type 3)

Reproduction in green algae (Type 4) Dominant thallus is haploid and produces haploid gametes On fertilization, gametes form a diploid zygote Meiosis takes place in the zygote, resulting in haploid spores Each spore develops into a haploid individual and it begins again…

Reproduction in green algae (Type 4)

Economic Importance mariculture: China, Japan, Korea fertilizer, food additives phycocolloids: gelatinous chemicals, used in food processing, suspensions & gels algin: stabilizer/emulsifier in diary products carageenan: from red algae (Irish moss/Chondrus), used as emulsifier (pudding, dairy products) agar: used to form jellies, to protect meats in canning, as thickener, pharmaceuticals, cosmetics

Flowering Plants (angiosperms): Dominant plants on land, few are marine True leaves, stems, roots Xylem and phloem to transport water, nutrients, food from photosynthesis Grouped in Kingdom Plantae Reproduction involves a dominant sporophyte with a flower as the reproductive organ

Seagrasses: not true grasses, closest relatives are lilies horizontal stems (rhizomes) that grow beneath sediment flowers are small, pollen carried by water currents seeds dispersed by water currents, in feces of fish and other animals (!) eelgrass (Zostera) is most widely distributed of the 60 known species of seagrass

Zostera Temperate and tropical regions Shallow, well-protected coastal waters (bays, estuaries) Flat, ribbon-like leaves Common in oxygen-poor sediments Zostera beds are highly productive and provide food to variety of animals

Zostera

Surfgrass Unusual seagrass Inhabits rocky coasts exposed to wave action May become exposed at low tide Pacific coasts of North America Research seagrass beds

Surfgrass

Salt-Marsh Plants: Cordgrasses are true members of grass family Not marine species Land plants tolerant of salt Do not tolerate total submergence by seawater Live in salt-marshes and soft-bottom coastal areas Temperate regions Habitat and breeding grounds for fish Erosion control, natural water purification

Salt-Marsh Plants Leaves are always partly exposed to air Salt glands in leaves excrete excess salt Halophytes= salt-tolerant plants Pickle weed (Salicornia) is another example

Cordgrass

Pickle weed

Mangroves: Trees and shrubs adapted to live along tropical and subtropical shores around the world Land plants that can tolerate salt Muddy or sandy shores protected from waves Include up to 80 different species of flowering plants

Red Mangroves Red mangroves (tropics and subtropics)—extreme northern and southern limits of red mangrove are areas where killing frosts begin Salt marshes replace red mangroves in areas exposed to frost

Red Mangrove

Red Mangrove Leaves are thick to reduce water loss Seeds germinate while still attached to parent tree Develop into seedlings as long as 30 cm before falling from the parent Seedlings stick in muddy sediment or float in the water to new locations