The ecology of Sargassum pteropleuron Grunow (Phaeophyceae, Fucales) in the waters off South Florida

Abstract

A comparison is made of the effects of seasonal temperature change upon the metabolism of Sargassum pteropleuron Grunow and the growth of S. polyceratium Montagne, species forming geographically adjacent populations off the Atlantic coast of South Florida. Apparent net photosynthetic and dark respiratory rates of S. pteropleuron did not vary significantly during the periods of high water temperature from mid summer to autumn. A significant decline in net photosynthetic rates coincided with senescence of the annual axes and the declining water temperatures of winter. The seasonal pattern of metabolism was similar to that reported for growth of S. pteropleuron. By contrast, growth of S. poiyceratium was maximal from the mid fall to mid winter. Senescence of the annual axes reduced the plants to perennial holdfasts by midsummer. This dissimilar response of two species of Sargassum forming geographically adjacent populations to seasonal environmental fluctuations is discussed in relation to the phenology of seaweeds in the tropics.