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?