| dc.description | The goal of the research was to document and interpret short and long-term changes in growth and abundance of seagrasses (Thalassia testudinum, Syringodium filiforme) in Barbados. The short-term changes were in response to a 15-month discharge of turbid water into St. Lawrence Bay; the long-term changes were over the 25-year period 1969--1994. To facilitate interpretation of the changes, effects of seasonality and shoot age on Thalassia were investigated, and nutrient and light competition between Thalassia and Syringodium was assessed. Seasonal variation was observed in growth of Thalassia, being highest when nutrient availability (leaf nutrient levels) was highest. Effects of shoot age on Thalassia leaf growth were investigated in 3 shoot age categories. Most growth variables increased with shoot age, with shoot age explaining more of the variance in younger than older shoot age categories. Thalassia abundance and growth decreased significantly during the 15-month discharge event in St. Lawrence Bay, probably through reduced light levels. Syringodium abundance increased during the event, probably through increased nutrient availability, suggesting that Thalassia may be the more effective nutrient competitor. This may result from the higher belowground to aboveground biomass ratio characteristic of Thalassia. In a canopy removal experiment, Syringodium inhibited Thalassia growth through light competition more than the reverse. This suggests that Syringodium is the more effective light competitor, possibly because of its higher aboveground to belowground biomass ratio. Thalassia abundance and growth decreased, and Syringodium abundance increased, between 1969 and 1994. The impact of a hurricane in 1980 may best explain the Thalassia loss, and the Syringodium increase may be a response to this loss. The decrease in Thalassia growth could result from increased light competition from Syringodium, from a long term decrease in coastal water clarity believed to have occurred in Barbados, or perhaps from a younger Thalassia shoot age distribution resulting from the hurricane impact. | en_US |
