Biomonitoring of hypoxia and sulfide stress in three sub-tropical seagrasses

Hypoxia and sulfide exposure, increased using glucose, are considered major environmental stressors in seagrass communities. Quantum efficiency, total soluble protein and catalase activity were quantified to evaluate the applicability of each of these bioindicators to detect environmental stress in three tropical seagrass species, Thalassia testudinum (Banks ex Kèoenig), Halodule wrightii (Ascherson) and Syringodium filiforme (Kuetz). Hypoxia + sulfide treatments significantly decreased the quantum efficiency of all three species, but showed no response in protein and catalase activity. Although no treatment effect was found, catalase activity was enhanced in T. testudinum leaves and H. wrightii roots relative to other tissues, while S. filiforme showed no location-specific catalase activity. These results indicate that quantum efficiency is a more sensitive indicator than protein and catalase activity to hypoxia and sulfide stress in seagrasses.