Dear Dr.Noreddine, for estimatiing the biomass  in intertidal habitats, the  quadrate method which is a simple and reliable method.  For estimation of biomass, quadrats of 0.25 × 0.25 m were sampled on the rocky surfaces. Plant materials present in the quadrats were taken with a scalpel and brought to the laboratory in the plastic bags containing seawater to prevent drying of plants. Plant materials were cleaned properly and material was dried in an oven at 60°C. Each month 3 to 4 samples were collected and biomass was expressed as gram dry weight per m² (g.m-2). 

Thank you and best of luck with your work.

I would recommend the following paper:

Chopin, T., 1997 - Marine biodiversity monitoring. Protocol for monitoring of seaweeds.  Environment Canada, Ecological Monitoring and Assessment Network, Ottawa, 40 p. 

Also available at http://www.eman-rese.ca/eman/ecotools/protocols/marine/seaweeds/seaweeds_marine_e.pdf

All the best,

Dear Dr. Noreddine,

It seems that the link above does not work any longer. The document is posted on my ResearchGate page and I hope you can access it that way. If not, send me your email address and I will send the document as an attachment.

Sorry for the inconvenience and all the best,

Thierry Chopin