Poster Presentation Australian Marine Sciences Association 2025 Conference

Photosynthesis and Photosynthetic Electron Transport in the soft coral Sinularia spp and its zooxanthellae. (#139)

Raymond J. RITCHIE 1 , Suhailar SMA-AIR 1 , Thanongsak CHANMETHAKUL 2 , Vipawee DUMMEE 1
  1. Prince of Songkla University - Phuket, Thailand, Kathu, PHUKET, Thailand
  2. Faculty of Science and Technology, Phuket Jajabhat University, Phuket, Thailand

Photosynthesis in the soft coral Sinularia spp. (Cnidaria: Anthozoa: Octocorallia: Alyonacea) was measured using Pulse Amplitude Modulation fluorometry (PAM) of colonies and cultured zooxanthellae. Yield decreased exponentially with increasing irradiance, Ymax ≈ 0.5 in hospite and of zooxanthellae.  Optimum irradiance for ETR (Eopt) ≈ 200 µmol photon m-2 s-1 with strong photoinhibition at higher irradiances. Maximum ETR (ETRmax) in hospite ≈ 200 µmol e- g-1 Chl a s-1. Cultured zooxanthellae Eopt ≈ 172 µmol photon m-2 s-1), ETRmax ≈ 207 µmol e- g-1 Chl a s-1 or Pgmax ≈ 51.6 µmol O2 g-1 Chl a s-1. O2-electrode based respiration rate of the zooxanthellae ≈ 10.45 µmol O2 g-1 Chl a s-1. Maximum Pg/R ratio at optimum irradiance, 4.93 ± 1.27.  Photochemical Quenching (qP) decreased exponentially with increasing irradiance (half point for qP (½EqP) ≈ 150 µmol photon m-2 s-1) in the octocoral and the cultured zooxanthellae.  Non-Photochemical Quenching (NPQ) followed a simple exponential saturation curve in the octocoral (tentacles: NPQmax ≈ 0.625, NPQ half point (½ENPQ) ≈ 173 µmol photon m-2 s-1; stump: NPQmax ≈ 0.425, ½EqP ≈ 199 µmol photon m-2 s-1, NPQ of cultured zooxanthellae was very low (NPQmax  ≈ 0.05 at 551 µmol photon m-2 s-1).

  1. Ritchie, R.J., Suhailar Sma-Air, S., Chanmethakul, T., Dummee, V. (2025). Photosynthesis and Photosynthetic Electron Transport in the soft coral Sinularia spp and its zooxanthellae. Submitted to Coral Reefs.