Effect of Turbidity and Intermittent Sediment Deposition on the Photosynthetic Efficiency of Non-Geniculate Crustose Coralline Algae

Abstract

Non-geniculate crustose coralline algae (NCA) are important in algal reef ecosystems, yet their physiological responses to turbidity and sediment burial remain insufficiently understood. We examined how six turbidity levels (0-300 mg L-1) and four sediment deposition depths (0-3 cm) affected two dominant species, Sporolithon sp. and Phymatolithon sp. Under turbidity treatments, for Sporolithon sp., Fv/Fm was lowest at 0 mg L-1 (0.43 +/- 0.01) and highest at 250 mg L-1 (0.62 +/- 0.01). ETRmax increased markedly under 150 mg L-1 (17.94 +/- 0.27) but declined under 300 mg L-1 (5.33 +/- 0.19). In Phymatolithon sp., turbidity levels of 150-250 mg L-1 produced consistently higher Fv/Fm values (0.58-0.60) and the lowest ETRmax occurred at 300 mg L-1 (5.71 +/- 0.34). Sediment burial caused strong early reductions in photosynthetic performance. In Sporolithon sp., all burial depths except 0 cm caused significant Fv/Fm declines within five days (decrease to 0.46). After 45 days, ETRmax ranged from 9.28 +/- 0.38 at 0 cm to 4.02 +/- 0.11 at 3 cm, with intermediate values at 1 and 2 cm. Phymatolithon sp. showed rapid declines in Fv/Fm at all depths (1 to 3 cm) before partial recovery after 15-20 days. Overall, moderate turbidity (150-250 mg L-1) provided protective light attenuation, whereas sediment deposition imposed strong early physiological stress. The contrasting responses of the two species highlight different adaptive strategies for surviving low-light and sediment-rich environments.