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

Abstract

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.

Levelling-up rhodolith-bed science to address global-scale conservation challenges

“…Indeed, compared to sand or muddy seabeds, the habitat formed by rhodolith beds has higher primary and secondary productivity. Primary producers, including rhodoliths themselves but also associated macro-and J o u r n a l P r e -p r o o f microalgae, contribute substantially to habitat primary productivity and biogenic carbonate production (Martin et al, 2007;Amado-Filho et al, 2012a;Schubert et al, 2019;Teed et al, 2020;Qui-Minet et al, 2022). Moreover, provision of complex habitat structures increases the faunal biomass in rhodolith beds and, consequently, their associated secondary productivity (Bordehore et al, 2003;Steller et al, 2003;Gabara et al, 2018;Moura et al, 2021;Stelzer et al, 2021).…”

“…(2) Direction and magnitude of rhodolith-bed carbon fluxes (carbon 'sink-source' duality), which are associated to community productivity (Martin et al, 2007;Qui-Minet et al, 2022);…”

Epiphytic Algae on Dominant Macrophytes in Lotic Ecosystems in the Eastern Flanks of Mount Cameroon

“…Microalgae such as the cyanobacteria have nitrogen fixation abilities [20]. Epiphytic algae according to some authors account for more primary production than their macrophytic hosts [21,22] and are also involved in trophic interactions [23].…”