Photosynthesis rates of seagrass and macroalgae measured in situ by pulse-amplitude modulated (PAM) fluorometry

Photosynthesis, a fundamental process, sustains coastal vegetated ecosystem services. Pulse-Amplitude Modulated fluorometry was a non-invasive method used to assess the photosynthetic efficiency of seagrass and macroalgae in dynamic coastal environments. The aims of this study were to explore the photosynthesis rate of seagrass and macroalgae in different island morphogenesis that have coastal dynamics. The study was located in Pari Islands, Karimunjawa National Park, and Sebesi Island from March to June 2024. Seagrass leaves and macroalgae thalli were clamped with magnetic sample holder, then connected to the fluorometer sensor cable for measuring photosynthesis rate. Macroalgae had a higher photosynthesis rate compared to seagrasses, macroalgae could have ETR values of up to 400 μmol electrons m-2 s-1, while seagrass could have ETR values of up to 200 μmol electrons m-2 s-1. Non-calcareous macroalgae had a higher photosynthesis rate than calcareous macroalgae. Seagrass and macroalgae on hilly islands had higher photosynthesis rates than flat islands. The rate of photosynthesis of macroalgae on Sebesi (volcanic island) was higher than on tectonic islands, and the rate of photosynthesis of seagrass on Karimunjawa (tectonic islands) was higher than on volcanic islands because it was affected by the damage of seagrass by the tsunami on Sebesi Island.