1. Chapter 6
Seaweeds and Plants

2. Primary Producers Those that use light to perform photosynthesis
Are always exceptions
A few seaweeds that are not primary producers but are parasites of other seaweeds

3. Seaweeds AKA: Macrophytes or Macroalgae Are all multicellular
Classified/characterized based on structure as well as types of pigments and food products they store

4. Structure of seaweed
Wide range of growth forms and complexity of structures
The complete body is known as the thallus
Can be a filament, a thin leafy sheet, or
giant kelp
The leaf-like flattened portions of
the thallus are blades
Main photosynthetic region
Note: all portions of thallus can
photosynthesize as long as they have
chlorophyll

5. distinct stem-like structure called stipe
Gas-filled bladders, pneumatocysts, sometimes keep the blades close to the sea surface
Mixture of gases includes CO
Maximizes their exposure to the sunlight
distinct stem-like structure called stipe
Provide support
Where blades originate from
The holdfast looks like roots and attaches the thallus to the bottom
Do not absorb significant amounts
of water/nutrients, or penetrate
through sand/mud like tree roots
Water and nutrients are picked
up directly through the thallus

6. Types of seaweed 3 Basic types Green Red Brown
Hard to recognize groups by color in nature because of the proportion of chlorophyll and other pigments can vary

7. Green Algae Most live in freshwater and terrestrial environments
Only 10% of 7,000 species are marine
Bays, estuaries, isolated tide pools on rocky coasts
Most have a simple thallus
Thought that land plants evolved from green algae
Have some pigments and food reserves
End 4/13

8. Filamentous green algae are common on rocks in shallow water and tide pools
May be branched or unbranched
Enteromorpha
Thin thallus in the form of a hollow tube
Sometimes flourish in polluted areas
Ulva (AKA sealettuce)
Paper-thin sheets with varying shapes depending on environmental factors
Polar to tropic waters
Valonia
Form large spheres or spherical clusters in tropics and subtropics
Several other green algae consist of thin filaments or tubes (siphons) formed by a single cell with multiple nuclei
Caulerpa, Codium (Dead man’s fingers)
Halmedia (Calcareous green alga)
Numerous segments with deposits of calcium carbonate
Plays important role in forming coral reefs

9. Brown Algae Olive green to dark brown color
Due to yellow-brown pigments (fucoxanthin)
Almost all of the approx 1500 species are marine
Dominant primary producer on temperate and polar rocky coasts
Include largest and most complex seaweeds
Simplest have a finely filamentous thallus
Ectocarpus

10. Dictyota have a flat and branched thallus
Padina have a fan shaped and lightly calcified thallus
Both tropical and subtropical
The thallus of most species of
Desmarestia is branched in many way
Found in cold waters
Some of brown algae are exposed at low-tides at the middle and upper levels of rocky shores
Thick, leathery thalli can withstand exposure to air

11. Many species have gas-filled floats
Rockweeds, wracks, Fucus, found in temperate shores
The knotted seaweed (Ascophyllum) is found along temperate Atlantic coasts

12. In warm waters like the Gulfs of Mexico and California these temperate species are replaced by sargasso weed (Sargassum)
Has pneumatocysts
Most species grow on rocks but at least 2 float offshore in huge masses
The sargasso sea
An area in the Atlantic north of the West Indies
Seaweed drifts in other regions of the world
Gulf of Mexico

13. Kelps are the most complex and largest of all brown algae
Most found below low tide in temperate and sub polar latitudes
Can provide food and shelter for many other organisms
Some consist of a single large blade up to 3 meters in length
Laminaria
Blades are harvested for food in several parts of the world
Several blades may grow from a single holdfast
In some species the blade is spilt/branched

14. Agarum and Alaria Postelsia
A rib runs along the middle of the single blade
Postelsia
AKA sea palm
Grows on intertidal rocks exposed to heavy waves
Occurs in thick clusters from central California to British Columbia

15. Another large kelp is Pelagophycus
2 Branched forms
Feather-boa kelp (Egregia)
Southern Sea Palm (Eisenia)
Both are common on Pacific rocky shores
In the Pacific the largest kelps are found in deeper water just below the lowest tide level
The bull kelp (Nereocystis) has a whip-like stipe up to 30m long with a large spherical pneumatocyst at the upper end
Another large kelp is Pelagophycus
Similar to bull kelp, but has impressive antler-like branches

16. Macrocyotis is the largest of the kelps
massive holdfast attached to hard bottoms
Several long stipes grow from holdfast where elongated blades develop
At the base of each blade a pneumatocyst eventually develops
can grow 50 cm or more per day in optimal conditions
form dense and very productive kelp beds or forests in colder waters of the N and S Pacific
Harvested by chopping off the tops for the extraction of several natural products
Among the richest most productive environments in marine realm

17. Red Algae (Phylum Rhodophyta)
More species in this category than green and brown combined
The red color is due to pigments called phycobilins which mask chlorophyll
Most are red, may have different colors depending on their daily exposure to light

18. The group is essentially marine in shallow-water environments
Some are harvested for food and for the extraction of various products
The structure of the thallus of red algae doesn’t show the wide variation in complexity and size shown in brown algae

19. Some become greatly simplified in structure by becoming parasites of other seaweeds
A few have lost all trace of chlorophyll and have become heterotrophs depending entirely on their host for nutrition
Most are filamentous
Thickness, width, and arrangement vary a great deal

20. Some species of Gigartina have large blades as long as 2m
Dense clumps are more common on the upper levels of rocky shores that are exposed at low tide
Longer and flatter branches dominate in areas less exposed to air and in deeper water
Shown in species of Gelidium and Gracilaria
Endocladia forms wiry clumps on rocky shores from Alaska and S California
Some species of Gigartina have large blades as long as 2m
Among most massive of red algae

21. The most common growth form is a thallus with thin large blades
species of Porphyra are common on rocky shores above the lowest tide from polar to tropical coasts
The most common growth form is a thallus with thin large blades
Rhodymenia is common in N. Atlantic
Blades reach 1m in length
Irish mass (chondrus) is N. Atlantic red alga
It can tolerate wide ranges of temperature, salinity and light
Shape varies greatly in response to these physical factors

22. Coralline algae are red algae that deposit calcium carbonate within cell walls
Important in several marine environments
Calcified thallus takes a variety of shapes
Thin disks growing over other seaweeds
Branches with many joints
Smooth or rough encrusting growths on rocks
Color varies from light to intense reddish-pink; dead ones are white
Warm water coralline are actively involved in formation and development of coral reefs
Others thrive in temperate and polar waters often attaining large size

23. Life History Reproduction is a complex affair in seaweeds
Asexual, or vegetative, reproduction is common
It may be more important than sexual reproduction in most species

24. Fragments of the thallus can grow into new individuals
floating masses of Sargassum of Sargasso Sea
Some seaweeds produce spores
cells specialized for dispersing to new locations or persisting through unfavorable conditions
Some are protected by resistant cell walls
Others have flagella for movement and are known as zoospores

25. The production of gametes is a key event in sexual reproduction
Gametes produced by all members of a seaweed species may be similar in appearance or may consist of larger non-motile eggs and smaller sperm that can swim by flagella
Male gametes in the red algae lack flagella and are non-motile
They may be released in strands of slime
Male and female gametes may be formed in the same thallus but the chances are good that fusing gametes will be from separate thalli

26. Seaweeds may also produce haploid spores or gametes by meiosis
Cells of seaweeds, as well as humans and clams, divide and produce identical cells by mitosis
Seaweeds may also produce haploid spores or gametes by meiosis
The existence of diploid and haploid cells is fundamental in understanding the often complex life histories of seaweeds
The life histories can be divided into 4 types

27. 4 types of seaweed life history
Most common among all three groups of seaweeds
Involves 2 types of thalli
Diploid (2n) sporophyte generation that through meiosis produces not gametes by haploid (1n) spores
Except in red algae these
spores are typically motile
They divide and develop into
the second kind of thallus

28. A haploid (1n) gametophyte generation
the one that produces haploid gametes
In some species there are separate male and female thalli
In others, both types of gametes are produced by every thallus
The gametes are released and, with fertilization, produce a diploid zygote that develops into the diploid sporophyte
a life history with two generations, a sporophyte and a gametophyte, is an example of a phenomenon of alteration of generations
In some algae such as sea lettuce and the brown Dictyota, the sporophyte and gametophyte are structurally identical
On the other hand, in Kelps the large plant we see is the sporophyte, whereas the gametophyte is minute and barely visible

29. The third type, is similar to that of animals (including humans)
The second type, unique to the red algae, is more complex, involving alternation of three generations
The third generation a diploid carposporophyte results from the fusion of gametes
Carpospores, diploid spores produced by the carposporophyte, develop into sporophytes
The third type, is similar to that of animals (including humans)
There is no alteration of generations
Only one thallus and is diploid
Thallus produces haploid gametes by meiosis that creates a diploid zygote after fertilization
Some brown algae and some green algae

30. There are many known variations of these types of life history
The fourth type occurs in some green algae
The dominant thallus is haploid and produces haploid gametes
With fertilization the gametes form a diploid zygote
It is in the zygote in which meiosis takes place resulting in haploid spores
Each spore develops into a haploid individual, the only kind of thallus in the cycle
There are many known variations of these types of life history

31. Other interesting things about seaweed:
The development of gametes or spores can be influenced by the amounts of nutrients in the water, temperature, or by day length
High levels of nitrogen nutrients in the water cause the development of asexual spores in sea lettuce
Low levels stimulate the development of gametes instead

32. Release of gametes and spores can be triggered by the splashing of water in an incoming tide
Also by the cycles of the moon
Or chemical messengers received from cells of the opposite sex
In some seaweeds the release of male and female gametes is timed to take place at about the same time

33. Economic Importance
Around the world, workers harvest seaweeds to be used in many ways
Most obvious is as a food source (red and brown algae)
Farming of seaweed, mariculture, is a big business in China, Japan, Korea, and other nations
Seaweed produces several types of gelatinous chemicals, phycocolloids
Used in food processing and in manufacture of different products
Valuable for their ability to form viscous suspensions or gels even at low concentrations

34. One important phycocolloid, algin
Used extensively as a stabilizer and emulsifier in manufacture of dairy products (ice cream, cheese and toppings which need to be smooth and not likely to separate)
Page 114 for more examples
A major source for algin for commercial uses is the giant kelp
West coast of temperate N America (California)
Collected by large barges with rotating blades that cut and collect the stipes and fronds to a depth of 1-2m below the surface
Stipes quickly grow back toward the surface
Another source is Laminaria
Harvested in North Atlantic

35. The second phycocolloid is carrageenan
Obtained from red algae (Irish moss) in N Atlantic and Eucheuma in the tropics
Valued as an emulsifier
Gives body to dairy products and a variety of processed foods like instant pudding
Another is agar
Extracted for its ability to form jellies
Protects ham, fish, and meats during canning
Low calorie foods (not digestible by humans)
Thickener
Other examples page 114
Biologists will use it as a medium in which to grow bacteria and mold
Obtained from red algae

36. Can also be used for fertilizer, food additives in animal feeds, and wound dressings in hospitls
Coralline algae are sometimes used in Europe to reduce the acidity of soils
Some red seaweeds are marketed as nutritional supplements

37. Flowering Plants
The 250,000 species of flowering plants, angiosperms are dominant on land but few live in the ocean
Have true leaves, stems, and roots that are all provided with specialized tissues to transport water, nutrients, and food manufactured by photosynthesis
Reproduction involves a dominant sporophyte that features an elaborate reproductive organ, the flower

38. Of all of the flowering plants, only the seagrasses are truly marine
Often live submerged by seawater, rarely exposed at low tide
Salt-marsh grasses and mangroves inhabit estuaries and shores protected from the wave action
They are not at home in the ocean and usually only their roots are covered by water at high tide
There are also many flowering plants adapted to colonize coastal areas exposed to salt-laden winds and occasional sea spray
Do not tolerate immersion in seawater
May be found on sand dunes or living along the edges of salt marshes

39. Seagrasses
Superficially resemble grass but are actually not grass at all
Closest relatives seem to be from the lily family (showing that they evolved from land plants)
Have adapted to life in the marine environment
Have horizontal stems called rhizomes
Commonly grow beneath the sediment

40. Roots and erect shoots grow from the stems
Seagrass flowers are typically very small and inconspicuous because there is no need to attract insects for pollination
The pollen that contains the sperm is carried by water currents
Often released in strands
Tiny seeds result from successful fertilization
Seeds are dispersed by water currents and perhaps in the feces of fish and other animals that browse on the plants

41. Eelgrass is most widely distributed of the nearly 60 species of seagrass known
Found in many temperate and tropical regions around the world
Inhabits shallow, well-protected coastal waters such as bays an estuaries
Has distinctively flat, ribbon like leaves
Common in oxygen-poor sediments
Thick eelgrass beds are highly productive and provide shelter and food to a variety of animals

42. Surf grass inhabits rocky coasts exposed to wave action
May be exposed at low tides
Found on Pacific coast of North America

43. Salt-Marsh Plants Cordgrasses are true members of the grass family
Not really marine species, but land plants that tolerate salt
Do not tolerate total submergence by seawater
Live in salt marshes and other soft-bottom coastal areas in temperate regions
Highly productive and provide habitat and breeding grounds for many species important to fisheries
Offer protection against erosion and provide natural water purification systems

44. Salt glands in the leaves excrete excess salt
Inhabit the zone above mudflats that becomes submerged by seawater only at high tide
Leave are always partly exposed to air
Salt glands in the leaves excrete excess salt
Other salt-tolerant plants, halophytes, are found at higher levels on the marsh
Pickle weed

45. Mangroves
Trees and shrubs adapted to live along tropical and subtropical shores
Flourish along muddy or sandy shores protected from waves
Depending on location, there are different adaptations that mangroves have especially regarding water loss from salty environments

46. Red mangrove leaves are thick to adapt to water loss
Some other mangroves have seeds that germinate while still attached to the parent tree
They develop into elongated pencil shaped seedlings as long as 30 cm (1ft) before falling from the parent
Successful one stick in the soft muddy sediment or float in the water to be carried by currents to new locations