Physiology of maerl algae: Comparison of inter‐ and intraspecies variations

Abstract

Free‐living red coralline algae play an important role in the carbon and carbonate cycles of coastal environments. In this study, we examined the physiology of free‐living coralline algae‐forming maerl beds in the Bay of Brest (Brittany, France), where Lithothamnion corallioides is the dominant maerl (i.e., rhodolith) species. Phymatolithon calcareum and Lithophyllum incrustans are also present (in lower abundances) at a specific site in the bay. We aimed to assess how maerl physiology is affected by seasonality and/or local environmental variations at the inter‐ and intraspecific levels. Physiological measurements (respiration, photosynthetic, and calcification rates) were performed using incubation chambers in winter and summer to compare (1) the dominant maerl species at three sites and (2) three coexisting maerl species at one site. Comparison of the three coexisting maerl species suggests that L. corallioides is the best adapted to the current environmental conditions in the Bay of Brest, because this species is the most robust to dissolution in the dark in winter and has the highest calcification efficiency in the light. Comparisons of L. corallioides metabolic rates between stations showed that morphological variations within this species are the main factor affecting its photosynthetic and calcification rates. Environmental factors such as freshwater inputs also affect its calcification rates in the dark. In addition to interspecies variation in maerl physiology, there were intraspecific variations associated with direct (water physico‐chemistry) or indirect (morphology) local environmental conditions. This study demonstrates the plasticity of maerl physiology in response to environmental changes, which is fundamental for maerl persistence.

Rhodolith Physiology Across the Atlantic: Towards a Better Mechanistic Understanding of Intra- and Interspecific Differences

“…On the other hand, temperature and light were identified as strong environmental drivers for rhodolith light calcification, which was reflected in increased G Light towards lower latitudes. This is consistent with higher summer calcification rates reported for cold-and warm-temperate rhodolith species (Sordo et al, 2020;Qui-Minet et al, 2021). Dark calcification rates, on the other hand, seemed to be related to species identity rather than environmental conditions, which is in accordance with other comparative studies for crustose coralline algae (Chisholm, 2000) and rhodoliths (Qui-Minet et al, 2021;Schubert et al, 2021a).…”

“…This assumption is supported by recent studies that showed a high plasticity in inorganic carbon uptake strategies for photosynthesis (Hofmann and Heesch, 2018;Zweng et al, 2018;Bergstrom et al, 2020). Also, comparisons among different species, from the same habitat, suggest a variability in the strength of the coupling between photosynthesis and calcification (Vaśquez-Elizondo and Enrıquez, 2016;Qui-Minet et al, 2021). The direct relationship between these processes was demonstrated early on (Digby, 1977;Pentecost, 1978;Borowitzka, 1981;Borowitzka, 1987) and is supported by recent studies (e.g., Martin et al, 2013;Vaśquez-Elizondo and Enrıquez, 2016;Sordo et al, 2019), which showed a decline in calcification upon inhibition of photosynthesis (Hofmann et al, 2016;McNicholl et al, 2019).…”

“…Overall, coralline algal species have been shown to express a high variability regarding their physiological performance under similar environmental conditions (e.g., Chisholm, 2000;Chisholm, 2003;Vaśquez-Elizondo and Enrıquez, 2016;Qui-Minet et al, 2021;Schubert et al, 2021a), which suggest differences in physiological mechanisms and/or the extent to which they are expressed. This assumption is supported by recent studies that showed a high plasticity in inorganic carbon uptake strategies for photosynthesis (Hofmann and Heesch, 2018;Zweng et al, 2018;Bergstrom et al, 2020).…”

“…This link has been related to an elevation of the pH at the calcification site due to photosynthetic activity. Considering differences in species' metabolic rates (Chisholm, 2000;Chisholm, 2003;Vaśquez-Elizondo and Enrıquez, 2016;Qui-Minet et al, 2021) and morphological traits, which affect pH conditions in the diffusive boundary layer (DBL; Cornwall et al, 2017;Schubert et al, 2021a) that are positively correlated with the pH of the calcifying fluid (pH cf ;Comeau et al, 2019a), it can be assumed that its strength varies among species. Furthermore, coralline CaCO 3 precipitation in the dark, with lower and highly variable rates among species (e.g., Chisholm, 2000;Vaśquez-Elizondo and Enrıquez, 2016;Qui-Minet et al, 2021;Schubert et al, 2021a), and when photosynthesis is inhibited (Hofmann et al, 2016; suggests that calcification is partially independent from photosynthesis.…”

“…Reviewing available information for rhodoliths, it becomes evident that only a few studies have focused on a general physiological characterization, including information on specific rates of photosynthesis and/or calcification, productivity estimates, seasonal variation in physiological rates and/or a physiological comparison among species (Littler et al, 1991;Payri, 1997;Martin et al, 2006;Martin et al, 2007a;Martin et al, 2007b;Sordo et al, 2020;Qui-Minet et al, 2021;Schubert et al, 2021a). Even less information is available regarding the mechanisms driving rhodolith photosynthesis and calcification (Cornwall et al, 2017;Hofmann and Heesch, 2018;Zweng et al, 2018).…”