The relative contribution of fleshy epiphytic macroalgae to the production of temperate maerl (rhodolith) beds

Maerl beds are composed of unattached red calcareous coralline algae. When located in shallow ecosystems, these macroalgae provide substrates for the development fleshy epiphytic macroalgae, which contribute to productivity maerl beds. To assess importance their contribution, we estimated primary production main taxa (Solieria chordalis or Rhodomelaceae), growing 2 distinct Lithothamnion corallioides Bay Brest (Brittany, France), characterized by different depths and incident irradiances. We algal photosynthetic parameters derived from photosynthesis-irradiance curves calculated incubations photo-respirometry chambers at irradiances dark. A comparison with results previously obtained L. showed that studied there were no differences between its terms photo-acclimation low However, had higher efficiencies rates per unit biomass chlorophyll a than species. Estimations net surface area bed indicated account 25% productivity. Interactions may affect respective contributions. In deepest beds, shading have detrimental impact on production, whereas shallowest protect photoinhibition under high