Properties of sea grass and sand flat sediments from the intertidal zone of St. Andrew Bay,Florida

Organic and carbonate carbon and textural properties of the substrates underlyingHalodule wrightii andThalassia testudinum sea grass beds in the intertidal zone of St. Andrew Bay, Florida were compared to adjacent unvegetated sand flats by physiographic divisions within the bay and to the subtidal slopes of the bay. Sea grass and sand flat sediments were principally fine-grained quartz sands. The mean particle-size of the sea grass sediments were finer-grained than those of the sand flats only in the west arm and lagoon of the bay. Size-frequency distributions of the sea grass sediments were generally slightly more negatively skewed and more leptokurtic than those of the sand flats. The sea grass sediments were less well sorted than were the sand flat sediments. The average organic and carbonate carbon contents of the sea grass beds were 1.9-fold greater than that of the sand flats but much less than that of the subtidal sea grass meadows. In the areas of pollution, sea grasses were absent; near this areaHalodule wrightii was the dominant sea grass.