Algae Part I

ALGAE

The algae are an ancient group of aquatic plants. (Some taxonomists consider the algae to be Protoctists but
this approach will not be followed here.)
There are thought to be about 23,000 species of algae.

There are 3 features which distinguish the algae from other plants;-

Body plan: There is no specialisation of the algal body into root, stem, leaves with vascular tissue. The photosynthetic portion of the alga is a thallus while the attachment portion comprises hair-like rhizoids. For this reason, old classification systems put the algae into a grouping known as the Thallophytes.

No Embryo: For most algae, sperm and eggs fuse in the open water and the zygote develops into a new plant without any protection. For other plant groups the zygote develops into an embryo within the protection of the parent plant. For this reason, old classification systems termed all other plant groups Embryophytes.

Reproductive structures: The gametes are produced within a single cell. There is no jacket of sterile cells protecting the gametes.

Release of algal sperm cells from a single cell Moss egg cell surrounded by sterile cells

Being aquatic, algae are

marine
freshwater
terrestrial

Terrestrial algae are effectively surviving in an aquatic environment on land. Soil algae survive in a film of soil water.
The other major group of terrestrial algae are those in lichen symbioses.

Lichens comprise algae and fungi in partnership. The fungus provides an outer weft of mycelia which creates a humid protected environment for the alga to live and photosynthesise (and feed the fungus!).

Fungal layer

Algal layer

Fungal Layer

Interestingly, lichens have distinctive morphologies and so these associations have traditionally been given
genus & species names as if they were discrete organisms.

Crustose lichen on rock	Fruticose lichen

As terrestrial plants the algae have a unique role as pioneer plants. They grow on bare rock, providing there is moisture.
The rock weathers and crumbles. The algae die. The mineral contribution of the rock and the organic remains of
the algae lead to formation of soil. This pioneering activity therefore paves the way for more demanding plants
to invade. A succession such as this is precisely what would have occurred when the islands of the Caribbean first
emerged from the sea.

Within the aquatic environment, there are two broad niches;-

planktonic - floating algae.
For micro-algae these often have strange shapes which help keep the algae
suspended as well as serve an anti-predation role.

benthic - attached algae.
These are algae anchored to the substratum

USES

Algae are primary producers, i.e. they are the start of the food chain. One third of all the carbon fixed on this planet is achieved by algae, largely in the oceans!

Seaweeds are used as fertilisers and even food (by the Japanese, Irish, Welsh and even some of us here in the Caribbean who enjoy "sea moss" ).

Extracts from the cell walls of (typically brown & red) algae provide the polysaccharides agar and carageenan. These are used as thickening agents in food, in surgical dressings and in microbial media.

Diatomaceous earth. The skeletons of a group of algae, the diatoms, are glass-like and this material is put to a variety of uses, such as abrasives (it used to be used in toothpaste!), reflective road signs, swimming pool filters.

A suspension of diatoms

ALGAL CLASSIFICATION

Algae are largely classified on the basis of:-

colour (photosynthetic pigments)
storage material
flagella
cell wall

The algae are a very heterogenous grouping. Taxonomically each group (greens, reds etc) is considered a division which means that while all algae share the feature of being simple plants, each group is as distinct from the next as ferns are compared to flowering plants!

You should consult handout 3, summarising the characteristics of the major algal groups.
Click here, if you want to look at photomicrographs of various algal groups.

In this course we will focus on three groups

Chlorophytes (green algae)
Phaeophytes (brown alage)
Rhodophytes (red algae)

Nevertheless, there are other groups you should be aware of.

Cyanobacteria
Anabaena
These are blue green bacteria traditionally called blue green algae. Click here to go on the web and see photomicrographs of a range of blue-greens. As discussed before, these are not even eukaryotes. The fact, however, that they are microscopic and photosynthetic has traditionally led to their receiving consideration in courses like this. Cyanobacteria were probably the first photosynthetic organisms and have been around for about 3.5 billion years. They exist as unicells, colonies or filaments. They have a bacterial type cell wall, no nucleus and no flagella. In addition to bacterial chlorophyll they have the pigments phycocyanin and phycoerythrin. Blue-greens are responsible for nitrogen fixation on land and in water. Like green algae, they can form lichen symbioses with fungi.

Chlorophytes

These are closest to the higher plants in many ways and are considered their ancestors

photosynthetic pigments - chlorophylls a & b, ß-carotene
cell wall - cellulose-rich
reserves - starch

This is a very diverse group, showing almost the full spectrum of morphological possibilities - from unicells to macroalgae. We will look at this in Algal Structure & Reproduction.

Euglenophytes

Click Euglena to go on the web and see what this organism looks like.
These organisms are unicellular flagellates. They resemble green algae in in their photosynthetic pigments (chlorophylls a & b, ß-carotene) but

they store paramylon (a ß1,3 glucan) and fat
lack a cell wall but have a pellicle (protein plates underly the cell membrane)
can be heterotrophic (hence these organisms are often considered to be animals!)

Euglena can cause algal blooms.

Phaeophytes

These are the brown algae.

Sargassum on an exposed shoal

These are almost all marine macro-algae.
They contain clorophylls a & c and the brown carotenoid fucoxanthin.
They store a ß1,3 glucan called laminarin.

Chrysophytes

These are the golden-brown algae. Link this group in your mind to the brown algae. They share many of their features (same pigments, same storage reserves) but occupy a different niche - they are microscopic and planktonic unlike the browns which tend to be attached seaweeds. In fact, some taxonomists put the brown and golden-brown algae in the seame Division.

Diatoms are probably the most important members of this group.

They have an outer case or frustule made of silica and are motile.

There are many sites on the web which allow you to see the vast array of diatom diversity.

http://www.bgsu.edu/Departments/biology/algae/index.html
http://www.comet.net/gek/phytoc.htm
http://baldrick.kc.kuleuven.ac.be/~karls/bionet/aquadata/kiesel/biokieng.htm

Rhodophytes

These are the red algae and are mainly marine macro-algae (seaweeds). They have;-

a red pigment, phycoerythrin, (in addition to chl a) which allows them to photosynthesise in deep waters
no motile stage (male gametes have no flagella)
as reserve a form of starch (floridean starch)
a complex life cycle of 3 phases (not to be considered in this course)

This is Gracilaria, known in the Caribbean as "sea moss". As botanists, avoid this name as "moss" has a very precise botanical meaning, viz. a group within the Bryophytes!
Gracilaria is dried and boiled to provide a drink of dessert, supposedly with health-giving (even aphrodisiac!) properties.

Pyrrophytes

This is a diverse group of reddish-brown micro-algae. They inhabit both freshwater and marine habitats.The most important group within the Pyrrophytes is probably the dinoflagellates.

Dinoflagellates;-

typically have the cell wall below the cell membrane like armour plating (analagous to the pellicle of Euglenoids except it is not proteinaceous)
have 2 flagella, one trailing, the other beating transversely
have a spinning motion, like a top
are responsible for the algal blooms known as "red tides"
"ciguatera poisoning" which can result from eating large fish like barracuda in the northern Caribbean is caused by a dinoflagellate toxin which has accumulated in the fish flesh

We have now had a look at the main taxonomic groups in the Algae.
Click the button to move on to their structural & reproductive diversity.

	Body plan: There is no specialisation of the algal body into root, stem, leaves with vascular tissue. The photosynthetic portion of the alga is a thallus while the attachment portion comprises hair-like rhizoids. For this reason, old classification systems put the algae into a grouping known as the Thallophytes.
	No Embryo: For most algae, sperm and eggs fuse in the open water and the zygote develops into a new plant without any protection. For other plant groups the zygote develops into an embryo within the protection of the parent plant. For this reason, old classification systems termed all other plant groups Embryophytes.
	Reproductive structures: The gametes are produced within a single cell. There is no jacket of sterile cells protecting the gametes.

	Algae are primary producers, i.e. they are the start of the food chain. One third of all the carbon fixed on this planet is achieved by algae, largely in the oceans!
	Seaweeds are used as fertilisers and even food (by the Japanese, Irish, Welsh and even some of us here in the Caribbean who enjoy "sea moss" ).
	Extracts from the cell walls of (typically brown & red) algae provide the polysaccharides agar and carageenan. These are used as thickening agents in food, in surgical dressings and in microbial media.
	Diatomaceous earth. The skeletons of a group of algae, the diatoms, are glass-like and this material is put to a variety of uses, such as abrasives (it used to be used in toothpaste!), reflective road signs, swimming pool filters.