ENVIRONMENTAL-REGULATION OF SEED-GERMINATION IN ZOSTERA-MARINA L (EELGRASS) IN CHESAPEAKE BAY - EFFECTS OF LIGHT, OXYGEN AND SEDIMENT BURIAL

The effects of light, oxygen and sediment burial on seed germination of Zostera marina L. were tested in two experiments beginning in 1987 and 1988. In 1987, seeds were placed in flow-through clear plastic tubes or buried at depths of 5, 15 and 25 mm in pots filled with seagrass sediments and held in an outdoor running seawater tank at ambient temperature, salinity and solar irradiance. The seeds began germinating in the sediments when water temperatures dropped to 15-degrees-C in mid-October and nearly all were germinated by December. Seeds held in the plastic tubes did not begin to germinate until mid-January. Again in 1988, seeds planted in pots germinated in October when temperatures decreased to 15-degrees-C; germination in the oxygenated water column was again delayed throughout the autumn and winter. However, seeds held in the water column in clear vials of deoxygenated water, without sediment, displayed a pattern of rapid fall germination identical to that of the sediment treatments. No consistent effect of light and dark treatments was observed in the water-column seeds. We conclude that eelgrass seeds are well adapted for germination in anoxic conditions and that seed germination in this region is keyed to not only seasonal temperature changes, but also oxygen availability.