The answers to this question began to arise in the eighties when Professor Pérès, and group, said the different habitats in the Mediterranean Sea. I pray this literature review to discern any of the answers to your question.

AHOY Romain, 

I'm currently using biological traits to elucidate -from a functional approach- the composition and distribution of antarctic macrobenthic communities in a glacio-marine fjord.

I've used trophic guilds that includes some traits used by Mcdonald et al.(2010), and others from Paganelli et al.(2012):

• FEEDING MODE (Deposit feeder, Detritivore, Predator, Suspension/filter feeder, mixed trophic groups, inter alia)
• FOOD SOURCE (Surface, Subsurface, & Epibenthic)
• FOOD TYPE (Omnivory, Carnivory & Herbivory)
• MOTILITY (Motile, Discretely motile & Sessile)
• HABITAT (Free living, Parasite, Attached, Encrusting, Burrow dwelling, Tubiculous & Parasite)

My analysis mainly tilts to the trophic function but you can also use life history strategies like King & Mcfarlane (2003) did.

Salute! 

Poster Spatial distribution of the macrobenthos at the Mackellar In...

The benthic environment in deep water in the Med is much like that in the Atlantic - EXCEPT bottom temperatures are exceptionally warm.  11-13 C at great depth versus 3-4 C at comparable depths in the open Atlantic.  This limits the diversity of the deep fauna derived from the Atlantic to those species sufficiently eurythermal to occupy exceptionally warm bottom waters.  The temperature difference has also been a factor in faunal differentiation in the Med vs open Atlantic, with a number of endemic species known only from Med deep water.  The shallow sill at Gibraltar is a vicariant zoogeographic barrier and filter.  It is difficult or impossible for stenothermal, stenohaline larvae to cross this barrier in either direction and survive the change in salinity and temperature.

For seaweeds and seagrasses, I would consider temperature (one of the most important traits of Mediterranean flora is the existence of vicariated populations of tropical species, e.g. Digena simplex, Halymeda tuna, Anadyomene stellata..., and Mediterranean endemisms such as Posidonia oceanica, Cystoseira elegans or Cystoseira spinosa among others), growth rate, life cycle (perennial/annual) and herbivore defenses in comparison with European Atlantic species. I mean if you consider that the European Atlantic seascape is dominated by high productive macrophytes such as kelps (Saccorhiza polyschides, Laminaria digitata...) and Mediterranean seascape is dominate by slow growing macrophytes (Posidonia oceanica, Cystoseira tamariscifolia, corallinales in depth waters), I think that those traits could be useful to distinghish these areas. Of course, it depends largely of regional oceanography and local conditions (e.g. river proximity).