Not sure if this is what you are looking for but this report has a nice summary of biomass conversions for benthos and other species with references to other literature. 

Carie Hoover

Cauffopé, G, and S J J Heymans. 2005. “Energy Contents and Conversion Factors for Sea Lion’s Prey.” In Food Web Models and Data for Studying Fisheries and Environmental Impacts on Eastern Pacific Ecosystems, edited by S Guenette and V Christensen, 13(1):225–237. Fisheries Centre Research Reports.

Hi Juan Carlos,

not sure if it contains exactly what you need, but you might check out Tom Brey's database at http://www.thomas-brey.de/science/virtualhandbook/navlog/index.html

some of its contents are explained in a MEE paper: http://www.researchgate.net/publication/227825782_An_empirical_model_for_estimating_aquatic_invertebrate_respiration/file/79e415033392f2b1ca.pdf

Article An empirical model for estimating aquatic invertebrate respiration

Hi Juan Carlos,

I help you with some publications.

http://www.sciencedirect.com/science/article/pii/0022098188900627#

www.int-res.com/articles/meps/140/m140p251.pdf

Article Weight-to-weight conversion factors for marine benthic macro...

It depends on what purpose and to what detail of your study is about. I used energy content (in calorie/gram) in analysis of milkfish pond benthic algae system. i assumed if you are interested in fish production prediction, simple dried matter in terms of ash-freed weight may be good enough at least on an early stage.

Thanks