Marine Phyla Pages -- Coastal Carolina University
MACROALGAE
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General Overview1
http://seaweed.ucg.ie/defaultthursday.html
Algae are very simple chlorophyll-containing photosynthetic organisms. The term "algae" is used very loosely because defining them is very difficult. In general, they are simple autotrophic organisms composed of one cell, or grouped together in colonies, or as organisms with many cells, sometimes collaborating together as simple tissues. The larger algae species, visible to the naked eye, are called macroalgaes. A more common term for most marine macroalgae is "seaweed." Despite their size, they are non-vascular, have tissues no more than 2 cells thick to allow diffusion of materials with the environment (though some species are "thicker" with porous networks to allow deeper water penetration into the tissues), and are often multi-nucleated. Marine macroalgae are divided into 3 phyla: Chlorophyta (green algae), Phaeophyta (brown algae), and Rhodophyta (red algae).
Though many marine macroalgae species look like plants, their parts have different names and different functions. An entire macroalgae individual is called a "Thallus." It is attached, or cemented to a substrate with a "Holdfast." The holdfast is not the same thing as a root, and does not absorb or transport water or nutrients to the rest of the thallus. It is strictly for attachment. The "stipe" and "blade" are analagous to stems and leaves, respectively. Water, nutrients, and gasses are exchanged directly across the blade. Many species have a "pneumatocyst," or air bladder, to keep them upright in the water column..
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Algal reproduction is highly variable by species and therefore confusing to summarize. Generally, most species have a prominent alternation of generations, between diploid (2n) "sporophyte" generations and haploid (1n) "gametophyte" generations. In some cases, the two forms are macroscopically indistinguishable (for example, Ulva or sea lettuce), and in other cases they are quite different (for example, kelp, where the sporophyte is much bigger, or other species where only the gametophyte forms a thallus). For many species, asexual fragments can also grow to form a new thallus.
A common algal life cycle would include an alternation of sporophyte and gametophyte generations, where depending on the cycle, gametes (1n) can fuse to make a 2n sporophyte (fertilization), and/or spores (either 1n or 2n) can grow into a 1n or 2n thallus. In some species, the sporophyte forms 2 gametes which fertilize to form a new sporophyte (sounds like us!). These are just a few of the existing variations.
The autotrophic (photosynthetic) pigments are variable and are the basis of classification; all have chlorophyll a; some have b, others c; all have accessory pigments of some kind e.g. phycocyanin (blueish), phycoerythrin (reddish), carotenes (yellow-brown), xanthophylls (brown).
http://seaweed.ucg.ie/defaultthursday.html
Some are partially heterotrophic (get energy from non-photosynthetic sources also). Marine macroalgae species have great variation in size, from unicellular and 3-10 µm (microns) to giant kelps up to 70 meters long and growing up to 50 cm per day.
http://www.sanctuaries.nos.noaa.gov
Algae are found just about everywhere on earth: in the sea, in rivers and lakes, on soils and walls, in animals and plants (as symbionts - partners collaborating together); in fact just about everywhere where there is light with which to photosynthesize.
Links
1. http://seaweed.ucg.ie/defaultthursday.html
2. http://www.sanctuaries.nos.noaa.gov/pgallery/pgfagatele/living/living_12_100.html