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

Zn Qui-Minet , Dominique Davoult (1) , J Grall (2) , Sophie Martin (1)

1 ADMM - Adaptation et diversité en milieu marin
2 IUEM - Institut Universitaire Européen de la Mer

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

Mots clés: maerl; fleshy epiphytic macroalgae; photosynthesis; productivity; red algal physiology; Solieria chordalis; filamentous Rhodomelaceae

Domaines: Biodiversité et Ecologie; Océanographie

Zn Qui-Minet, Dominique Davoult, J Grall, Sophie Martin. The relative contribution of fleshy epiphytic macroalgae to the production of temperate maerl (rhodolith) beds. Marine Ecology Progress Series, In press, 693, pp.69-82. ⟨10.3354/meps14089⟩. ⟨hal-03692321⟩