Persistence of Zostera marina L. (eelgrass) seeds in the sediment seed bank

Two separate field experiments in the Newport River/Back Sound, North Carolina (NC) and the lower Chesapeake Bay (CB), Virginia were conducted in 2007 and 2008 to quantify the effects of time (6, 12, 15 months), seed source (mixed-annual, perennial NC; perennial CB), site (local environmental factors), and sediment type (fine, coarse) on the persistence of Zostera marina seeds in the sediment seed bank. It is here, at the southern limit of the species distribution along the western Atlantic, that the probability of population loss may be high and the importance of a seed bank in the resilience and recovery of these populations great. Experimental results indicate that viability of both NC and CB seeds decreased significantly after just 6 months in the sediment following the seasonal period of maximum germination and continued to decline over time with no seeds viable remaining in CB cores and < 5% of seeds remaining viable after 15 months in NC treatments. In these experiments time was the overriding factor affecting the persistence Z. marina seed banks for all treatments in both NC and CB and viability was not significantly affected by seed source, site, or sediment type. Based on the results of the in situ experiments, mixed-annual and perennial Zostera marina populations in North Carolina and perennial populations in Virginia produce transient seed banks (seeds viable < 12 months). The lack of a persistent seed bank may reduce the resilience of Z. marina at the limits of the species distribution to repeated stress events. As a result these populations may be particularly susceptible to disturbance with only a limited capacity for recovery if sexual reproduction is impaired.