Download Chapter_7 - South Johnston High School

Chapter 7:
Multicellular
Primary
Producers
• Most primary productivity done
by phytoplankton
Multicellular Algae
• Seaweed (macroalgae) inhabit the oceans
• Red, brown, and green in color
• Phycologists/algologists study seaweeds
and phytoplankton
Distribution of Seaweeds
• Most are benthic
• Grow on rocks, sand,
mud, coral, and other
organisms
• Are parts of fouling
communities
– Plants and animals that
live on pilings, bulkheads,
boat hulls, moorings, and
other artificial surfaces
• Inhabit 2% of seafloor
• Effects of light:
– Numbers vary by depth,
latitude, sea conditions,
and season
– Red algae is at greatest
depth
– Green algae at
shallowest depth
– Brown algae is at
intermediate depths
• Effects of temperature:
– Greatest diversity is
at tropical waters
• Decreases as you
get farther north
or south of the
equator
Structure of Seaweeds
• Body is called the thallus
– All but a few cells are
photosynthetic
– Lacks vascular tissue
– No stems, roots, or leaves
– Can occur in complex
shapes
• Holdfast attaches thallus
to a surface
• Stipe: stemlike region
between holdfast and
blade
Biochemistry of Seaweeds
• Photosynthetic pigments
– Due to wavelengths of light
not absorbed by seaweed
pigments
– Chlorophyll absorbs blue and
red wavelengths of light
• Pass green light
– Accessory pigments absorb
different wavelengths of light
• Pass energy to chlorophyll for
photosynthesis
• Can protect chlorophyll from
damage by light
• Cell wall composition
– Primarily cellulose
– Many secrete a slimy gelatinous mucilage
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•
•
•
Made of sugar polymers
Covers their cells
Can hold a great deal of water
Acts as protective covering to prevent desiccation
– Can have a cuticle
• Multilayered covering of protein
• Food reserves
– Excess sugars converted into polymers
• Stored as starches
– Unique sugars and alcohols can be used
as antifreeze at high latitudes
Reproduction in Seaweeds
• Asexual
– Fragmentation: thallus
breaks into pieces
• Each new piece grows into
new alga
– Spore formation
• Sexual
– Fertilization of
gametes to form a
zygote (fertilized egg
cell)
Green Algae (Chlorophyta)
•
•
•
•
•
Contain pigments like in vascular plants
Most are freshwater species
Seasonal sources of food for marine animals
Contribute to formation of coral reefs
Structure: unicellular or small multicellular
filaments, tubes, or sheets
• Response to herbivory:
– Rapid growth and release of huge
numbers of spores and zygotes prevent
elimination of their populations by
herbivores
– Small size allows them to occupy crevices
on rocky shores and reefs
Red Algae (Rhodophyta)
•
•
•
•
Primarily marine (98%)
Highest diversity among seaweeds
Mostly benthic
Are not always red
• Structure:
– Almost all are multicellular
– Less than 1m long
– Thallus varies widely in shape
and organization
• Response to herbivory:
– Food source for sea urchins, fish,
mollusks, and crustaceans
– Do not produce many toxins to deter
herbivores
– Can make thallus less edible
– Can change growth patterns to make
it more difficult to graze
• Commercial uses:
– Agar
– Thickening agent in ice cream, pudding,
and salad dressings
– Source of food
– Animal feed and fertilizer
Brown Algae (Phaeophyta)
• Ex: rockweeds, kelp, sargassum weed
• 1500 species  marine
• Range in size from microscopic and filamentous
to giant
• Distribution:
– More diverse and abundant along coastlines of
high latitudes
– Less diverse in the tropics
• Structure:
– Well-defined thallus
– Develop large, flat, leaflike blades
– Gas-filled bladders
• Help buoy the blade to get maximum sunlight
exposure
– Cell walls composed of cellulose
• Habitat: found from low tide
line to a depth of 10m
• Commercial products:
– Thickening agents in textile,
dental, cosmetic, and food
industries
– Source of iodine
– Used as food
– Cattle feed
Marine Flowering Plants
• General characteristics:
– Presence of xylem (carries water) and
phloem (carries nutrients)
– Reproduce by seeds (protected by a fruit)
– Roots, stems, and leaves
Invasion of the Sea by Plants
• New source of habitat and food
• Compete with seaweeds for light and other
benthos for space
• Bodies composed of polymers (cellulose,
lignin) that most marine organisms cannot
digest
• Have few competitors
Seagrasses (Hydrophytes)
• Live beneath the water
• Only ones that are truly marine
• 60 species (0.02%)
• Classification and distribution:
– Not true grasses
– Related to lilies and other freshwater
plants
– Inhabit temperate zones and higher
latitudes
– Others are tropical and subtropical
• Structure:
– Form from vegetative growth
– Roots, stems, leaves
– Aerenchyme
• Gas-filled tissue
• Provide buoyancy to leaves
• Potential for invasion by pathogenic
fungi
• Reproduction:
– Fragmentation, drifting, and plant re-rooting
– Some do not flower
– If they flower, they lack showy petals
• Small and inconspicuous
• Male or female
– Hydrophilous pollination
• Ecological roles:
– Primary producers 
food for herbivores
– Depositing and
stabilizing coastal
sediments reduces
turbidity
– Beds provide
habitats for many
marine species
Salt Marsh Plants
• Less adapted to marine life
• Must be exposed to air to flourish
– Restricted to intertidal zone
• Biological filter for terrestrial runoff on its
way to the sea
• Must tolerate higher sediment salinities
• Classification and distribution:
–Well developed along slopes of river
deltas and shores of lagoons and
bays
–Distribution is limited at high and low
latitudes
• Structure:
– Grows in tufts of vertical
stems (culms) connected by
rhizomes
– Each vertical stem produces
additional stems (tillers) at
its base
– Roots connected at culms
– Plants stand as high as 3m
• Well-drained nutrient-rich
soils
– Flowers pollinated by wind
• Seeds drop to the
sediment or are carried by
water currents
• Adaptations to a saline environment:
– Facultative halophytes
• Can tolerate salty and freshwater
conditions
– Tend to lose water to their environment by
osmosis
– Thick, water-retaining succulent parts
• Ecological roles:
– Detritus supplies nutrient needs for fish and
shellfish
– Shallow roots and rhizomes
• Helps stabilize coastal sediments
• Prevents shoreline erosion
– Accumulate and stabilize sediments
• Recycles phosphorous
• Filter runoff from coastal areas
– Removes toxic pollutants
• Maintains water quality
– Removes excess nutrients
Mangroves
• Trees and shrubs of tropical waters
• Little is submerged by the tide
• Classification and distribution:
– 54 species
– Specialized roots that descend to or rise from the
sediment
– Thrive along protected tropical shores with limited wave
action, low slope, high rates of sedimentation, and soils
that are waterlogged, anoxic, and high in salts
– Occur at low latitudes
– Associated with saline lagoons
– Found in tropical estuaries, islands, and atolls
– Dominant vegetation in mangrove swamps or mangals
• Structure:
– Roots
• Adapted to grow in loose,
shallow, anoxic, saline
sediments
• Many above ground (aerial)
• Ability to prevent salts from
entering the system from the
sediment
• Leaves
– Simple, oval, leathery,
and thick
– Never submerged by
flood tide
– Salt glands can secrete
a concentrated salt
solution
• Ecological roles:
– Root systems stabilize
sediments
– Aerial roots aid deposition
of particles
– Canopy is host to many
insects and birds
– Nursery and refuge to many
animals
• Reproduction:
– Simple flowers pollinated
by wind or bees