Uprooting of Zostera marina Shoots in Relation to Below-ground Biomass Reduction under Low Light and High Sulfide Conditions

Abstract

The objectives of this study were to investigate the effects of below-ground biomass reduction on the stability of eelgrass shoots in sediment to clarify the factors responsible for the loss of eelgrass shoots even with little disturbance by waves in Nagatsuraura Bay, Japan. The environmental conditions in eelgrass beds with and without root death were also investigated. Loss of roots without the dying-back symptoms led to the decrease in the stability of eelgrass shoots in the sediment, and would allow the uprooting of shoots with minimal disturbance. The decay of healthy root biomass of eelgrass was associated with a high sulfide concentration in sediment and/or low photosynthetic activity. In the sulfide concentrations between 0.5 mg/g D. W. and 2.0 mg/g D. W., eelgrass with high photosynthetic activity tended to experience less stunted roots compared to the shoots with low rates of photosynthesis. This result suggests that eelgrass with high photosynthetic activity seemed to prevent sulfide intrusion by supplying oxygen to below-ground tissues to maintain an oxic microsphere around the roots and by re-oxidizing sulfide to harmless sulfate.