One of the most common brown algae species along the northern Atlantic coastline is Sargassum, also called gulf weed and is a member of the order Fucales which also includes the rockweeds (Fucus and Ascophyllum). Of all the common seaweeds this one most resembles a true plant. It is easy to confuse the parts of Sargassum with those of a plant. But those lance shaped structures that look like leaves are fronds. The berry-like parts along the branch are small air bladders that assist with flotation. The branch itself is a stipe. And while most species of Sargassum are planktonic or floating in the water, the common species on Cape Cod, Sargassum filipendula, is attached to rocks by means of a small root-like holdfast.
Sargassum is the seaweed that is floating in huge mats in the Sargasso Sea, a part of the North Atlantic Ocean. The mats are a floating zoo of many different marine animals. Some of these are attached species such as bryozoans and hydroids. Others swim with the seaweed including several species of fish. Animals find shelter and food among these mats of algae. Not only do the air bladders help the algae float, but this brings the fronds to the surface to maximize the process of photosynthesis.
Sargassum is considered holopelagic which means that it spends its entire life cycle floating in the open ocean. There are several animal species that are endemic to this marine habitat. These include a crab, shrimp, and pipefish that specialize in living in and among the fronds of Sargassum. The crab (Portunus sayi) even mimics the Sargassum, offering it a special form of camouflage.
The floating species of Sargassum reproduce vegetatively by a process called fragmentation. The attached species can reproduce sexually and are quite similar to the other members of the Fucales. Male structures called antheridia release motile sperm which fertilize the eggs in the female structures called oogonia. Both of these structures are housed in the conceptacles. Once fertilization is successful a zygote develops releasing young gemlings that attach to a substrate and grow into the adult.
Like most seaweeds there are many commercial and industrial uses for Sargassum. Most marine algae are a good source for iodine so Sargassum has been used in alternative medicine to treat goiters. Like other members of the brown algae Sargassum is also a source of alginate which is used as a stabilizer in many food items and cosmetics. This seaweed has been applied to soil as a conditioner and fertilizer. And in some parts of the world Sargassum is consumed directly as a food source.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.