Relationship between waterfowl and the seagrass Ruppia maritima in a southwestern Atlantic coastal lagoon

We evaluated the distribution of waterfowl in relation to a seagrass (Ruppia maritima) patch, to infauna, and on its relationship with substrate characteristics. An experiment performed in the Mar Chiquita coastal lagoon (37 degrees 46'S, 57 degrees 27'W; Argentina), was used to evaluate the effect of herbivory on widgeon grass, R maritima control plots of equal size, located between bird exclosures, were exposed to herbivory. The experiment ran for 31 d, starting on December 1, 1994. Censuses showed that black-necked swan ((x) over bar = 50 birds ha(-1). SD = 37, n = 10) and coots ((x) over bar = 42 birds ha(-1), SD = 28, n = 10) were the most important (always present) of the waterfowl seen feeding on R. maritima. The results of the experiment showed greater leaf lengths, lower belowground (rhizomes and roots) biomass, greater aboveground (leaves and shoots) biomass, and greater abundance of the polpchaete Heteromastus similis in exclosure plots. There were no exclosure effects on total biomass (belowground plus aboveground), reproductive parts (fruits and pre- and postpollination flowers), or abundance of most benthic infauna. Topographic survey showed that sediment surface was higher within the R. maritima patches, but there were no significant differences in granulometric composition. Surveys also showed that bird distribution was strongly associated with the presence of R. maritima.