Ecotype-specific light intensity responses in Sargassum horneri: bloom-forming vs. benthic forms

Area of Science:

• Marine Botany
• Photosynthetic Physiology
• Ecological Adaptations

Background:

• Sargassum horneri exhibits distinct floating and benthic ecotypes.
• Understanding ecotype-specific responses to light is crucial for predicting population dynamics.

Purpose of the Study:

• To compare the light-driven physiological adaptations of floating and benthic Sargassum horneri ecotypes.
• To determine the impact of varying light intensities on photosynthetic performance and stress resilience.

Main Methods:

• Exposure of both ecotypes to five light intensities (50–600 μmol photons m⁻² s⁻¹).
• Measurement of relative growth rate (RGR), maximum photochemical efficiency (Fv/Fm), and relative electron transfer rate (rETRmax).
• Analysis of pigment synthesis, light saturation point (Ik), tissue carbon storage, and antioxidant enzyme activity (CAT, GR).

Main Results:

• Both ecotypes displayed bell-shaped RGR curves, with optimal growth at different light intensities.
• High light (600 μmol photons m⁻² s⁻¹) inhibited Fv/Fm and rETRmax, more severely in the floating ecotype.
• Benthic S. horneri showed greater resilience, higher soluble protein and UV-absorbing compounds under elevated light.

Conclusions:

• Sargassum horneri ecotypes exhibit distinct physiological adaptations to light intensity.
• Benthic S. horneri demonstrates superior photosynthetic performance and resilience under high-light conditions compared to the floating ecotype.
• Benthic S. horneri possesses the plasticity to potentially thrive and proliferate in surface waters with transient high-light exposure.