Light requirements for successful restoration of eelgrass (Zostera marina L.) in a high latitude environment - Acclimatization, growth and carbohydrate storage

- Transplants acclimatized to light conditions from 10 to 3 mol photons m− 2 day− 1, within 1.5 months.
- Lateral branching was significantly reduced at light levels below 5 mol photons m− 2 day− 1.
- Acclimatized eelgrass transplants could store carbohydrates at light levels down to 3 mol photons m− 2 day− 1.
- Rhizomes experienced loss of carbohydrates following transplantation and during severe shading.
- Severe shading revealed large temperature dependent effects on survival and general effects on morphology.

The short growth season in high latitude environments pose challenges for eelgrass restoration, particularly in areas that receive little light due to e.g. depth or reduced water quality conditions. In order to improve our understanding of the acclimatization potential of eelgrass to low light and the light requirement for successful restoration of eelgrass, an indoor mesocosm study was performed assessing three light (3, 5 and 10 mol photons m− 2 day− 1) and two temperature conditions (12 and 20 °C). The aim of the study was to determine if eelgrass transplants originating from a shallow donor meadow with high light could acclimatize to low light conditions and how different light conditions affect growth characteristics and carbohydrate storage of transplants. A second aim was to investigate how eelgrass grown under different light conditions cope during severe shading (zero light) under the two temperature conditions, and how severe shading affect the carbohydrate stock of transplants. The results demonstrate that eelgrass can acclimatize to light levels from 10 down to 3 mol photons m− 2 day− 1 by adjustments in morphology, pigmentation and growth strategy, but with a significant reduction in the production of lateral branches below 5 mol photons m− 2 day− 1. Temperature had a strong positive effect on shoot morphology and above ground biomass production independent of light treatment, but less effect on branching. Furthermore, the study shows that acclimatized eelgrass transplants can store carbohydrates at light levels down to 3 mol photons m− 2 day− 1, but that losses occur in relation to the transplantation process and as a result of severe shading. Survival of transplants during severe shading conditions demonstrated large temperature dependent effects, with no effects of previous light conditions. The results from this study provide important insight into the phenotypic response by eelgrass to environmental conditions and could have important implications for management and restoration of eelgrass in high latitude environments with respect to acclimatization potential and the minimum light requirement for successful restoration.