Germination and early-stage development in the seagrass, Zostera muelleri Irmisch ex Asch. in response to multiple stressors

Episodic freshwater events within coastal environments may influence germination and early-stage seedling development within the seagrass Zostera muelleri. Hypocotyl hairs have the potential to provide anchorage to sediments, initiate geotropism and facilitate water uptake. To this point, production of these structures in seagrasses has received little attention in the literature though they may significantly influence their ability to maintain populations within estuarine environments. Early-stage development of Z. muelleri was examined under various salinity, temperature and light conditions using a fully factorial design. We found that germination rates declined significantly with increasing salinity, with the greatest germination occurring in treatments subjected to 24-h darkness at either 15 or 20 °C. Hypocotyl hair initiation was influenced by both temperature and salinity. Seeds which germinated at 20 °C in 24-h darkness had significantly more germinants developing hypocotyl hairs than the other treatments. Although the initiation of hypocotyl hairs was generally greater under higher salinity concentrations, germinants subjected to lower salinity conditions had a greater likelihood of developing fully extended hypocotyl hairs. Based on our results, freshwater pulses that occur shortly after seed maturation could initiate year round germination in temperate regions. Furthermore, germinants stored at salinities of less than 16ppt showed greater elongation of hypocotyl hairs, indicating such pulses would also aid in the development of these structures. The timing of freshwater pulses may exert control over the recruitment and long-term survival of the species.