Reproduction

 

Sargassum has two different methods of reproduction.  The pelagic species reproduce asexually through fragmentation. As the older parts of free-floating sargassum decay, the younger parts break off and continue to grow.

In other sargassum, reproduction is oogamous. The male gamete is mobile, while the female gamete remains immobile. Conceptacles form on receptacles and are either male or female. In male conceptacles, antheridium form. The oval antheridium have two walls, an outer exochite and an inner endochite, which is gelatinous. The are held within the conceptacle by a stalk. Once they mature they detach from the stalk and leave through ostiole.

Oogonium form inside receptacles. Once they are mature, they come out of the ostiole, but remain attached by a gelatinous stalk.  Antheridium use anterior flagella to attach to the oogonium. Although many attach, only one antheridium enters the oogonium in fertilization. The antheridium and the egg inside the oogonium fuse, forming a zygote. The zygote divides into lower cells and upper cells.  The lower cells form the rhizoid, and the upper cells form the sporophyte of sargassum.  The new sargassum is diploid, containing complete sets of chromosomes from both parents.

The success of pelagic sargassum has played a part in the seaweed becoming a problem in many coastal areas. The vegetative reproduction means that there can be an almost endless supply of new seaweed. While sargassum mats create a vital ecosystem for a great number of species, aside from baby sea turtles who eat the seaweed, most animals use the mats for habitat, eating other organisms living in the sargassum.  

Sargassum thrives in warm water. As it floats above other species, it outcompetes other seaweeds for the sunlight it needs. Its reproduction through fragmentation give it an advantage: any harm that comes to a mat of sargassum can lead to the creation of new sargassum.