Temperature Stratification and Monochromatic Light Break Dormancy and Facilitate On-Demand In Situ Germination in the Seagrass Halophila ovalis, with Seed Viability Determined by a Novel X-Ray Analysis

Abstract

The seagrass Halophila ovalis rapidly colonizes marine sediments from seed across a range of depth, light, and temperature conditions, making it ideal for restoration projects. Yet, presently, it is not a targeted restoration species as the biology of seed dormancy and germination is poorly understood. This study addresses that knowledge gap by experimenting with temperature and light pre-treatments with the aim to determine optimal conditions for high rates of seed germination. H. ovalis seeds were pre-treated ex situ by applying nine combinations of temperature and monochromatic light. Two thirds of the pre-treated seeds were placed at separate field sites in conditions suboptimal for natural germination while one third remained in ex situ culture under suboptimal germination conditions (17 °C). Seed viability was monitored to determine if storage conditions impacted viability. X-ray analysis revealed a general decline in viability with time in storage. To analyze the effectiveness of pre-treatments, we compared the results of ex situ and in situ germination. Pre-treating seeds with red light (673 nm) and a stepwise temperature increase (15–20–25 °C) yielded the highest germination success across field and laboratory culture conditions. This indicates that we can use temperature and monochromatic light pre-treatments to break seed dormancy in the laboratory and induce “on-demand” germination of seeds after delivery to field sites potentially leading to more efficient and successful restoration practices with this species. Similarly, the conditions required for breaking dormancy and germination in H. ovalis (red spectrum light and a stepwise temperature increase) represent conditions associated with spring river freshwater runoff and warming of estuaries and coastal seas in temperate Australia.