Light Absorption in Coralline Algae (Rhodophyta): A Morphological and Functional Approach to Understanding Species Distribution in a Coral Reef Lagoon

Abstract

Red coralline algae are a cosmopolitan group with the ability to precipitate CaCO 3 within the walls of their vegetative cells. The resultant carbonate structure is key for explaining their ecological success, as it provides protection against herbivores and resistance to water motion. However, its potential contribution to enhance thallus light absorption efficiency through multiple light scattering on algal skeleton, similar to the effect documented for scleractinian corals, has not been yet investigated. Here, we initiate this analysis, characterizing thallus optical properties of three coralline species, which differed in pigment content and thallus mass area (TMA, gDW m −2 ). The three species, the rhodolith Neogoniolithon sp., the crustose coralline alga (CCA), Lithothamnion sp., and the articulated alga Amphiroa tribulus, represent the more distinctive coralline growth-forms and are able to colonize contrasting light environments in Caribbean coral reefs. The thicker thalli of the rhodoliths were the most efficient light collectors, as evidenced by their higher pigment absorption efficiency (a * Chla ; m 2 mgChla −1 ) and photosynthetic rates per unit area. This could explain rhodolith success in oligotrophic, highly illuminated reef environments. In contrast, the thinner thalli of the CCA, a low-light specialist, showed the highest metabolic rates normalized to mass and the highest light absorption efficiencies per unit mass (a * M ; m 2 gdw −1 ). Therefore, the ecological success of the CCA in cryptic habitats within the reef cannot be explained only by its low-light physiology, but also by its capacity to reduce the structural costs of their thalli, and thus of its new growth. Lastly, the ecological success of Amphiroa tribulus, which displayed intermediate values for the efficiency of light absorption, metabolic rates and TMA, was explained by its ability to construct the largest light collectors (algal canopies) thanks to the presence of flexible, non-calcified segments (genicula). This ability enables enhanced photosynthetic and carbonate production at the organism/canopy level. The resulting fragile canopy survives best within the protection provided by colonies of the lettuce coral Agaricia agaricites. In conclusion, our study demonstrates the utility of optical traits as powerful tools to investigate differences in the competitive abilities, abundances and niche distribution among algal species and/or growth-forms.

Acclimation of a rocky shore algal reef builder Neogoniolithon sp. to changing illuminations

“…Furthermore, results obtained following fluorescence analyses according to the protocol developed by Ruban and colleagues (Ruban ) correlated with apparent damage to PSII centers following high illumination (Fig. b), strongly supporting photodamage as an important component (Vásquez‐Elizondo and Enríquez ).…”

“…Yet, for the Ruban protocol to be fully adopted for measurements on CCAs, the effect of calcification on the light field may have to be incorporated. The CaCO 3 within the cell walls modifies the photon flux reaching the photosynthetic apparatus (Vásquez‐Elizondo and Enríquez ), but the impact of light intensity on changes in this parameter was not examined.…”

“…The results indicate that antennae‐related photoprotection and vast changes in pigment pool size and composition play an important role in the alga's acclimation to different light levels. Possibly, this sensitivity to high illumination and antenna changes were previously overlooked due to the masking effects of surrounding rock structure and other inhabitants (Vásquez‐Elizondo and Enríquez ). Finally, information is missing on the extent to which the CO 2 concentrating mechanism in CCAs (Cornwall et al ; Hofmann and Heesch ) participates in the dissipation of excess light energy as observed in many other micro and macroalgae (Tchernov et al ).…”

“…a,b). While the calcification process is strongly affected by ambient conditions, it also modifies the optical properties, hydrology, minerology, and pH in its proximity (Pentecost ; Moore and Burne ; Chisholm ; Riebesell et al ; Kingsley et al ; Schulz et al ; Bach et al ; Littler and Littler ; Venn et al ; Diaz‐Pulido et al ; McCoy and Kamenos ; Hofmann et al ; Le Goff et al ; Taylor et al ; Vásquez‐Elizondo and Enríquez ; Williamson et al ), and references therein. In a recent study, Hofmann and colleagues used microelectrodes and inhibitors of carbonic anhydrase and bicarbonate transporters to measure ionic fluxes associated with photosynthesis and calcification in a tropical CCA (Hofmann et al ).…”

“…Despite the importance of the CCAs, information on their acclimation to the large range of light intensities in their habitat, and changes therein, is scarce. In recent studies Vásquez‐Elizondo and colleagues (Vasquez‐Elizondo and Enriquez ; Vásquez‐Elizondo and Enríquez ) provided an in‐depth insight on the effects of calcification, pigment content, and thallus mass area on the light field, but the effect of the light intensity during growth on these parameters was not examined.…”