Abstract
BackgroundRed coralline algae are critical components of tropical reef systems, and their success and development is, at least in part, dependent on photosynthesis. However, natural variability in the photosynthetic characteristics of red coralline algae is poorly understood. This study investigated diurnal variability in encrusting Porolithon sp. and free-living Lithophyllum kotschyanum. Measured parameters included: photosynthetic characteristics, pigment composition, thallus reflectance and intracellular concentrations of dimethylsulphoniopropionate (DMSP), an algal antioxidant that is derived from methionine, an indirect product of photosynthesis. L. kotschyanum thalli were characterised by a bleached topside and a pigmented underside.ResultsMinimum saturation intensity and intracellular DMSP concentrations in Porolithon sp. were characterised by significant diurnal patterns in response to the high-light regime. A smaller diurnal pattern in minimum saturation intensity in the topside of L. kotschyanum was also evident. The overall reflectance of the topside of L. kotschyanum also exhibited a diurnal pattern, becoming increasingly reflective with increasing ambient irradiance. The underside of L. kotschyanum, which is shaded from ambient light exposure, exhibited a much smaller diurnal variability.ConclusionsThis study highlights a number of dynamic photoinhibition strategies adopted by coralline algae, enabling them to tolerate, rather than be inhibited by, the naturally high irradiance of tropical reef systems; a factor that may become more important in the future under global change projections. In this context, this research has significant implications for tropical reef management planning and conservation monitoring, which, if natural variability is not taken into account, may become flawed. The information provided by this research may be used to inform future investigations into the contribution of coralline algae to reef accretion, ecosystem service provision and palaeoenvironmental reconstruction.
Highlights
Red coralline algae are critical components of tropical reef systems, and their success and development is, at least in part, dependent on photosynthesis
Contrasting diurnal patterns were observed for the topside of L. kotschyanum and Porolithon sp
At 07 h00, rETRmax of the topside of L. kotschyanum was significantly higher than Porolithon sp. and the underside of L. kotschyanum (F2 = 12.52, p = 0.001)
Summary
Red coralline algae are critical components of tropical reef systems, and their success and development is, at least in part, dependent on photosynthesis. Measured parameters included: photosynthetic characteristics, pigment composition, thallus reflectance and intracellular concentrations of dimethylsulphoniopropionate (DMSP), an algal antioxidant that is derived from methionine, an indirect product of photosynthesis. Red coralline algae (Rhodophyta: Corallinales) are found in coastal areas worldwide, encrusting rocks or growing as free-living individual thalli, which are known as maerl or rhodoliths [1]. The success and development of coralline algae is, at least in part, driven by photosynthesis, yet comparatively little research has investigated their photosynthetic characteristics [12]. Light quality has a significant effect on the photosynthetic capacity of red algae: blue light can stimulate pigment and protein production, whilst red light can promote growth [21]
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