Nutrient enrichment outweighs effects of light quality in Zostera marina (eelgrass) seed germination

•Light quality significantly influences seed germination percentage and mean germination time.•The influence of light were outweighed and the MGT decreased significantly under nutrient enrichment.•Optimal light conditions and adequate fertilization is expected to enhance the success of future transplantation programs.

In a set of 6-week germination experiments, we investigated the single effects of different light conditions (single red; single blue; red: blue mixtures 1:1; red: blue mixtures 1:2; red: blue mixtures 2:1; white and dark) and the interactive effects of enriched water column nutrients (nitrogen-N and phosphorus-P) and light conditions on the germination percentage, and mean germination time (MGT) of the seagrass, Zostera marina. When incubated in natural seawater, seed germination was enhanced by red and blue light as well as darkness, with the highest germination percentage in R: B = 1:1 (63 ± 6.0%). Seeds under white light showed the lowest germination percentage (26.9 ± 2.37%), and had significant differences with the other 6 light conditions (p < 0.05). When seeds were incubated under nutrient enrichment, the significant influences of light were outweighed, the germination percentages under all light conditions could maintain at a similar level (57.78%-68.89%). The MGT of seeds incubated in natural seawater was between 27.70 and 30.51 days, and this value decreased to 24.13-27.10 days under nutrients enrichment, with significant differences under all light conditions (p < 0.05). This experiments revealed that Z. marina seeds were nutrient limited and light quality had significant influences on seed germination in natural seawater, but nutrient enrichment would outweighs the effects of light quality, which indicates an important unexplored force involved in seagrass population dynamics and gives insights for seagrass restoration projects based on seed applications.