B. Order Fucales Fucus and Sargassum

 

Fucus is one of the toughest algae commonly found on rocky shores and in intertidal zones

Their 2N bodies are exposed at low tide to the sun, dessicating winds and the pounding of waves.

Up to 2m long, the dichotomously branched body is held to the bottom substrate by holdfasts; when submerged, air bladders on the blades float the leaf like extensions up to the light.

Photosynthetic rates of these frequently exposed marine algae are 1-7x as great in air as in water...

Fucus blades are pretty complicated for an algae, with an epidermis ( outer protective layer) , cortex ( filler layer) and a central region

The ends of the branches are swollen with hydrophilic compounds = receptacles

Over the surface of receptacles are conceptacles- small cavities in which some cells produce either eggs or sperm; conceptacles can contract at low tide, squeeze out gametes which meet in water to form zygote; settles down grows into newindividual

 

 

 

Sargassum: unlike the rock-beaten family above, free floating sargassum have vreated their own ecosytem....

In this ecosystem no animals are strict herbivores, but rather they are omnivores, switching between diets of eating algae and animals. This may in part be due to the rubbery, biochemically rich nature of Sargassum or the lack of protein.

Sargassum - Brown Algae Sargassum is distributed in warmer cllimes than the kelps we discussed before. There are 15 species of this brown algae, and each has an air bladder.

The Sargasso Sea is a free-floating (pelagic) kelp-dominated ecosystem in the western North Atlantic. It is bounded by the Gulf Stream, the Canaries Current, and other currents which together produce an ever circulating boundary.

Two species constitute the majority of the algae here, primarily Sargassum natans, and most of the rest is Sargassum fluitans. These two species apparently evolved from other anchored species of Sargassum, providing the basis of this uniqe ecosystem.

Sargassum stays afloat by producing gas-filled bladders which act like buoys. You can see these in the picture at left; the picture also shows the typical jagged-edged blades.

Such a floating ecosystem of course will have difficulties in acquiring nutrients, and will therefore be severely limited by access to such nutrients. Many of the organisms which live here survive by being generalists, not limiting themselves to a single food source but making use of whatever is available.

 

The accumulated mats of Sargassum support a wide variety of animal life, some of which depend on the kelp for only a part of their life. Other organisms spend their whole life among the algae, and this diversity of life has been called a "floating jungle".

Some of the more unusual forms include fish and crabs which are camouflagued to look like Sargassum.

Perhaps the best known of these is the pipefish Syngnathus pelagicus, a relative of the seahorse. This fish is brownish-green, and is covered by flaps of skin which resemble the kelp blades. There are more than 50 fish species whose lives are linked to Sargassum, and a myriad of invertebrates, including gastropods, polychaetes, bryozoans, anemones, and sea-spiders. The most numerous inhabitants are hydroids and copepods.


C. Order Ectocarpales Ectocarpus see text for picture

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