Transcript Avicennia germinans

Chapter 7
Multicellular Primary
Producers
© 2006 Thomson-Brooks Cole
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.
© 2006 Thomson-Brooks Cole
Key Concepts
• 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.
© 2006 Thomson-Brooks Cole
Key Concepts
• Salt marsh plants and mangroves
stabilize bottom sediments, filter runoff
from the land, provide detritus, and
provide habitat for animals.
© 2006 Thomson-Brooks Cole
Multicellular Algae
• 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)
• Scientists who study seaweeds and
phytoplankton are called phycologists
or algologists
© 2006 Thomson-Brooks Cole
Distribution of Seaweeds
• Most species are benthic
• 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
© 2006 Thomson-Brooks Cole
Distribution of Seaweeds
• Effects of light on seaweed distribution
– chromatic adaptation, proposed in the
1800s, was accepted for 100 years
• chromatic adaptation—the concept that the
distribution of algae was determined by the
light wavelengths absorbed by their accessory
photosynthetic pigments, and the depth to
which these wavelengths penetrate water
– such zonation does not occur
– distribution depends more on herbivory,
competition, pigment concentration, etc.
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Distribution of Seaweeds
• Effects of temperature on seaweed
distribution
– diversity of seaweeds is greatest in
tropical waters, less in colder latitudes
– many colder-water algae are perennials
(living more than 2 years)
• only part of the alga survives colder seasons
• new growth is initiated in spring
– intertidal algae can be killed if
temperatures become too hot or cold
© 2006 Thomson-Brooks Cole
Structure of Seaweeds
• Thallus—the seaweed body, usually
composed of photosynthetic cells
– if most of it is flattened, it may be 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
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Biochemistry of Seaweeds
• Photosynthetic pigments
– Color of thallus = wavelengths of light not
absorbed by the seaweed’s pigments
– All have chlorophyll a plus:
• chlorophyll b in green algae
• chlorophyll c in brown algae
• chlorophyll d in red algae
– Chlorophylls absorb blue/red, pass green
– Accessory pigments absorb various colors
• e.g. carotenes, xanthophylls, phycobilins
© 2006 Thomson-Brooks Cole
Biochemistry of Seaweeds
• Composition of cell walls
– Primarily cellulose
– May be impregnated with calcium
carbonate in calcareous algae
– Many seaweeds secrete slimy mucilage
(polymers of several sugars) as a cell
covering
• holds moisture, and may prevent desiccation
• can be sloughed off to remove organisms
– Some have a protective cuticle—a multilayered protein covering
© 2006 Thomson-Brooks Cole
Biochemistry of Seaweeds
• Nature of food reserves
– Excess sugars are converted into polymers
– Stored as starches
– Unique sugars and alcohols may be used
as antifreeze substances by intertidal
seaweeds during cold weather
© 2006 Thomson-Brooks Cole
Reproduction in Seaweeds
• Fragmentation—asexual reproduction in
which the thallus breaks up into pieces,
which grow into new algae
– drift algae—huge accumulations of seaweeds
formed by fragmentation
• Asexual reproduction through spore
formation
– haploid spores are formed within an area of the
thallus (sporangium) through meiosis
– sporophyte—stage of the life cycle that produces
spores, which is diploid
© 2006 Thomson-Brooks Cole
Reproduction in Seaweeds
• Sexual reproduction
– gametes fuse to form a diploid zygote
– gametophyte—stage of the life cycle that
produces gametes
– gametangia—structures where gametes
are typically produced
• Alteration of generations—the
possession of 2 or more separate
multicellular stages (sporophtye,
gametophyte) in succession
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Green Algae
• Structure of green algae
– Most are unicellular or small multicellular
filaments, tubes or sheets
– Some have a coenocytic thallus consisting
of a single giant cell or a few large cells
containing more than 1 nucleus and
surrounding a single vacuole
• the cell grows and the nucleus divides
– There is a large diversity of forms among
green algae
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Green Algae
• Response of green algae to herbivory
– 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 strong jaws
and fill stomachs with non-nutrient minerals
• many produce repulsive toxins
© 2006 Thomson-Brooks Cole
Green Algae
• Reproduction in green algae
– the common sea lettuce, Ulva, has a life
cycle that is representative of green algae
– basic alternation of generations between
the sporophyte and gametophyte stages
• sporophytes and gametophytes are nearly
identical
• spores and gametes are similar, but spores
have 4 flagella while gametes have 2
• gametes of opposite mating types must fuse
for fertilization to occur
© 2006 Thomson-Brooks Cole
Red Algae
• Primarily marine and mostly benthic
• Red color comes from phycoerythrins
– Thalli can be many colors, yellow to black
• Structure of red algae
– Almost all are multicellular
– Thallus may be blade-like, composed of
branching filaments, or heavily calcified
• algal turfs—low, dense groups of filamentous
and branched thalli that carpet the seafloor
over hard rock or loose sediment
© 2006 Thomson-Brooks Cole
Red Algae
• Response of red algae to herbivory
– making their thalli less edible by
incorporating calcium carbonate
– changing growth patterns to produce
hard-to-graze forms like algal turfs
– evolving complex life cycles which allow
them to rapidly replace biomass
– avoiding herbivores by growing in crevices
© 2006 Thomson-Brooks Cole
Red Algae
• Reproduction in red algae
– 2 unique features of their variety of life
cycles:
• absence of flagella
• occurrence of 3 multicellular stages: 2
sporophytes in succession and one
gametophyte
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Red Algae Life Cycle
• sperm from male gametophyte forms zygote
on part of female gametophyte, then divides
– carposporophyte—unique red algae stage which
develops from the female gametophyte once the
attached zygote begins to divide
• carposporophyte produces non-motile
diploid spores called carpospores
• carpospores settle, germinate, and grow into
an adult alga called a tetrasporophyte
• tetrasporophyte releases non-motile haploid
tetraspores which grow into gametophytes
© 2006 Thomson-Brooks Cole
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 animal hosts
– consolidation—process of cementing loose
bits and pieces of coral together
• red coralline algae precipitate calcium
carbonate from water and aid in consolidation
of coral reefs
© 2006 Thomson-Brooks Cole
Red Algae
• Commercial uses of red algae
– phycocolloids (polysaccharides) from cell
walls are valued for gelling or stiffening
• e.g. agar, carrageenan
– 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
© 2006 Thomson-Brooks Cole
Brown Algae
• Familiar examples:
– rockweeds
– kelps
– sargassum weed
• 99.7% of species are marine, mostly
benthic
• Olive-brown color comes form the
carotenoid pigment fucoxanthin
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Brown Algae
• Distribution of brown algae
– more diverse and abundant along the
coastlines of high latitudes
– most are temperate
– sargassum weeds are tropical
© 2006 Thomson-Brooks Cole
Brown Algae
• Structure of brown algae
– bladders—gas-filled structures found on
larger blades of brown algae, and used to
help buoy the blade and maximize light
– cell walls are composed of cellulose and
alginates (phycocolloids) that lend
strength and flexibility
– trumpet cells—specialized cells of kelps
that conduct photosynthetic products (e.g.
mannitol) to deeper parts of the thallus
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Brown Algae
• Reproduction in brown algae
– usual life cycle = alternation of
generations between a sporophyte (often
perennial) and a gametophyte (usually an
annual)
– rockweed (Fucus) eliminates gametophyte
stage; meiosis occurs on inflated tips of
the sporophyte, fertilization in the water
– rhizoids—root-like structures which attach
the fertilized egg and grow into a holdfast
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Brown Algae
• Brown algae as habitat
– kelp forests house many marine animals
– sargassum weeds form floating clumps
that provide a home for unique organisms
• Commercial products from brown algae
– thickening agents are made from alginates
– once used as an iodine source
– used as food (especially in the Orient) and
cattle feed
© 2006 Thomson-Brooks Cole
Marine Flowering Plants
• 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 an embryonic plant
and supply of nutrients surrounded by a
protective outer layer
© 2006 Thomson-Brooks Cole
Marine Flowering Plants
– 2 types of seed plants:
• conifers (bear seeds in cones)
• flowering plants (bear seeds in fruits)
– all conifers are terrestrial
– marine flowering plants are halophytes,
meaning they are salt-tolerant
© 2006 Thomson-Brooks Cole
Invasion of the Sea by Plants
• Flowering plants evolved on land and
then adapted to the marine
environment
• Flowering plants compete with
seaweeds
• Their bodies are composed of polymers
like cellulose and lignin that are
indigestible to most marine organisms
• A single species may dominate longterm; other organisms depend on it
© 2006 Thomson-Brooks Cole
Seagrasses
• Seagrasses are hydrophytes (they
generally live beneath the water)
• Classification and distribution of
seagrasses
– 12 genera in 5 families of 3 clades (groups
with a common ancestor)
• 1 clade = eelgrasses and surf grasses
• 2nd clade = paddle grasses (Halophila), turtle
grasses, and Enhalus
• 3rd clade = paddle grass (Ruppia), manatee
grasses, and shoal grasses
© 2006 Thomson-Brooks Cole
Seagrasses
– ½ of the species inhabit the temperate
zone and higher latitudes; other ½ are
tropical and subtropical
• 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
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Seagrasses (Structure)
– stems
• have cylindrical sections called internodes
separated by nodes (rings)
• rhizomes—horizontal stems with long
internodes with growth zones at the tips,
usually lying in sand or mud
• vertical stems arise from rhizomes, usually
have short internodes, and grow upward
toward the sediment surface
– roots
• arise from nodes of stems and anchor plants
• usually bear root hairs—cellular extensions
• allow interaction
with bacteria in sediments
© 2006 Thomson-Brooks Cole
Seagrasses (Structure)
– leaves
• arise from nodes of rhizomes or vertical stems
• scale leaves—short leaves that protect the
delicate growing tips of rhizomes
• foliage leaves—long leaves from vertical shoots
with 2 parts
– sheath that bears no chlorophyll
– blade that accomplishes all photosynthesis using
chloroplasts in its epidermis (surface layer of cells)
• undergo periods of growth and senescence
– blade life cycles affect epiphytes on seagrasses
© 2006 Thomson-Brooks Cole
Seagrasses (Structure)
– aerenchyme—an important gas-filled
tissue in seagrasses
• lacunae—spaces between cells in aerenchyme
tissues throughout the plant
– provide a continuous system for gas transport
• aerenchyme is reduced to microscopic pores at
nodes and where parts join to keep water out
• provides buoyancy to the leaves so they can
remain upright for sunlight exposure
• tannins—antimicrobials produced as a chemical
defense against invasion of the aerenchyme by
fungi or labyrinthulids
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Seagrasses
• Reproduction in seagrasses
– some use fragmentation, drifting and rerooting and do not flower
– flowers are usually either male or female
and borne on separate plants
– hydrophilous pollination
• sperm-bearing pollen is carried by water
currents to stigma (female pollen receptor)
– a few species produce seedlings on the
mother plant (viviparity)
© 2006 Thomson-Brooks Cole
Seagrasses
• Ecological roles of seagrasses
– role of seagrasses as primary producers
• less available and 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
© 2006 Thomson-Brooks Cole
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
along with the surrounding sediment
• the young of many commercial species of fish
and shellfish live in seagrass beds
© 2006 Thomson-Brooks Cole
Salt Marsh Plants
• Much less adapted to marine life than
seagrasses; must be exposed to air
• 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
• many kinds of shrubs and herbs
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Salt Marsh Plants
• Structure of salt marsh plants
– smooth cordgrass, which initiates salt
marsh formation, grows in tufts of vertical
stems connected by rhizomes
• culm—vertical stem
• tillers—additional stems produced by a culm at
its base which give a tufted appearance
– aerenchyme allows diffusion of oxygen
– flowers are pollinated by the wind
– seeds are dispersed by water currents
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Salt Marsh Plants
• Adaptations of salt marsh plants to a
saline environment
– facultative halophytes—plants that can
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
– shrubs and herbs have succulent parts
© 2006 Thomson-Brooks Cole
Salt Marsh Plants
• Ecological roles of salt marsh plants
– contribute heavily to detrital food chains
– help stabilize coastal sediments and
prevent shoreline erosion
– rhizomes of cordgrass help recycle the
nutrient phosphorus through transport
from bottom sediments to leaves
– remove excess nutrients from runoff
– are consumed by terrestrial animals (e.g.
insects)
© 2006 Thomson-Brooks Cole
Mangroves
• Classification and distribution of
mangroves
– mangroves include 54 diverse species of
trees, shrubs, palms and ferns in 16
families
– ½ of these belong to 2 families:
• red mangrove (Rhizophora mangle)
• black mangrove (Avicennia germinans)
– others are white mangroves, buttonwood,
and Pelliciera rhizophoreae
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
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
– mangal—a mangrove swamp community
© 2006 Thomson-Brooks Cole
Mangroves
• Structure of mangroves
– representative of mangroves are trees
with simple leaves, complex root systems
– 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
© 2006 Thomson-Brooks Cole
Mangroves (Structure)
• anchor roots—branchings from the stilt root
beneath the mud
• nutritive roots—smaller below-ground
branchings from anchor roots which absorb
mineral nutrients from mud
• black mangroves have cable roots which arise
below ground and spread from the base of the
trunk
• anchor roots penetrate below the cable root
• pneumatophores—aerial roots which arise from
the upper side of cable roots, growing out of
sediments and into water or air
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Mangroves (Structure)
– leaves
• mangrove leaves are simple, oval, leathery
and thick, succulent like marsh plants, and
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 and then shedding them
© 2006 Thomson-Brooks Cole
Mangroves
• Reproduction in mangroves
– simple flowers pollinated by wind or bees
– mangroves from higher elevations have
buoyant seeds that drift in the water
– mangroves of the middle elevation and
seaward fringe have viviparity
• propagule—an embryonic plant that grows on
the parent plant
• hypocotyl—long stem hanging below the
parent branch on which the propagule grows
© 2006 Thomson-Brooks Cole
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
© 2006 Thomson-Brooks Cole