I think it might be a genus of family sargassaceae

It seems to be a Sargassum species

I think also that it is a Sargassum species.

small fronds of sargassum, maybe sargassum polyphyllum

Definitely agree with the consensus - Sargassum though couldn't guess at the actual species. 

Certainly looks like Sargassum - have a look at AlgaeBase there might be more information on there

I think that this macroalgae belongs to the genus Sargassum.

That is what I think. A Sargassum species but I don't know their scientific name.  :)

It is not a sargassum polyphyllum.

May be S. brachyphyllum?

It may be sargassum polycystum

http://www.algaebase.org/search/species/detail/?species_id=4111

It is a Sargassum, you should run the key to see which species it is

I agree with our colleagues. However Sargassum is one of the difficult groups. To many names and there is not a clear phylogeny for them. You can start as Brigitte said, looking a key from your geographic region. 

I agree with F. Pedroche.

I also agree with all  members views as Sargassum. In this connection, species as wightii Grev.in the Class Phaeophyceae under division Pheaophyta.

Sargassum as a genus. Which species is another story...

Same as every one, I would ID it as a Sargassum... You should look at recent works from Lydiane Mattio and colleagues on the species delineation within this genus

Sargassum yes.. is there a clear picture portraying the stem part?? or the air bladders??

Sargassum sp. confirm it looking at the stem and branching pattern...

S. polycystum's stem is more narrow. But S. brachyphyllum's stem don't others. Dear Enciso, We are waiting detail photographs of your samples. Would you share with us?

Just wait Sir until tomorrow. I'll go to beach later for gathering a fresh sample of young and mature.

Good behavior. Perhaps, we will help to you as detail that's time. Especially reproductive, folious and air structures parts of its, may be important.

It is right that a specis from Sargassum. But photographs are not very clear.

I agree with Reeta Jayasankar answer.

Pour moi, selon les images qui ne sont pas aussi clairs, il s'agit de Sargassum sp.

Donc il faut des échantillons afin de pouvoir déterminer avec plus de précision

Unidentified Seaweed in water

Another unidentified seaweed species photo.

Dear Enciso:

Your first photo was much better. You should take a picture more closely from stem, leave and reproductive organs are part of the samples. Not overwiev. If you can pull these features, we can help to you more easily.

Dear Enciso,

It is important to classify an alga to start to describe and focus on the taxonomic characteristics while the pictures do not reflect all taxonomic details.