The influence of increased seawater HCO3− concentration on the survival, growth and physiology of the eelgrass Zostera marina

Abstract

Inorganic resources are a key determining factor in the growth process of seagrass; however, the process and mechanisms involved in the promoting effect of increased seawater HCO3− concentration on seagrass growth and propagation under controlled conditions are poorly understood. We subjected shoots of the eelgrass Zostera marina to different seawater HCO3− levels [2 (control), 5, 10, 15 and 20 mmol L−1] for 6 weeks under controlled, mesocosm conditions. We measured eelgrass response in terms of survivorship, growth, propagation, productivity, carbonic anhydrase, leaf pigmentation and carbohydrate concentrations. The ramet frequency of Z. marina reached 58.7% when exposed to 5 mmol L−1, which was 1.3 times higher than that of shoots under the control condition. Survival analysis combined with growth assessment suggested that the optimal range of seawater HCO3− concentration for the propagation of Z. marina shoots was 4.8–5.5 mmol L−1. The promotion of survival and propagation of Z. marina that stemmed from seawater HCO3− concentration mainly depended on the increase in chlorophyll content and accumulation of nonstructural carbohydrate. The total chlorophyll content of Z. marina leaves exposed to 5 mmol L−1 was 1.1 times higher than that of shoots under the control condition. The results provide valuable data that could prove helpful in the development of efficient artificial propagation technology for Z. marina shoots.