THE INFLUENCE OF VEGETATION, SALINITY, AND INUNDATION ON SEED BANKS OF OLIGOHALINE COASTAL MARSHES

Sea level rise may alter salinity and inundation regimes and create pa tches of open water in oligohaline coastal marshes, potentially affect ing the composition and germination of seed bank species. We conducted seedling emergence experiments to: (1) examine the effects of standin g vegetation on the seed banks of three oligohaline marsh communities in coastal Louisiana (dominated by Paspalum vaginatum Sw., Sagittaria lancifolia L., or Spartina patens (Ait.) Muhl., respectively); and (2) investigate the effects of salinity and inundation regime on germinat ion of seed bank species. We also studied the effect of a temporary in crease in salinity (to simulate a salt water intrusion event) on the v iability of buried seeds. We found that the presence or absence of veg etation within a community affected the abundance of some species in t he seed bank but had little effect on species composition. Also, the s eed banks of the three communities exhibited considerable overlap in s pecies composition and had similar species richness (10-11) and divers ity (antilog Shannon-Weaver diversity index = 6.5-7.1), despite differ ences in vegetation type. Higher salinities and flooding reduced seedl ing emergence for most species; few species emerged at salinities abov e four parts per thousand (ppt), and only Sagittaria lancifolia and El eocharis parvula germinated well under flooded conditions. A temporary increase in salinity did not affect species richness or seedling emer gence of most species. Our results suggest that differences in vegetat ion may have little effect on the composition of seed banks of oligoha line marshes. However, higher salinities and greater depth and duratio n of inundation (anticipated as global sea level continues to rise) ma y decrease recruitment of seed bank species, reducing their abundance in oligohaline marsh communities.