Article: The morphology and ecology of a mound-building coralline alga (Neogoniolithon strictum) from the Florida Keys

The coralline alga Neogoniolithon strictum Setchell and Mason, 1943 is a major component of carbonate mound-building communities in the Florida Keys. This paper investigates the morphology, variation, and occurrence of growth forms, and the responses of this coralline alga to differing environmental conditions. Tavernier Key is an emergent back reef mound with a windward zonation of carbonate-producing communities. The windward shallow-subtidal and intertidal zones are dominated by the branching N. strictum. This facies is divided into three subfacies. A framework subfacies of in situ, branching N. strictum thalli occupies the sheltered shallow-subtidal areas. A rhodolith subfacies occurs in intertidal, moderately exposed parts of the mound. Rhodoliths are generated from collapsed sections of the framework and branches show increasing amounts of redirected growth as rhodoliths are transported shorewards away from the framework subfacies. Exposed areas on the north-east of the mound are characterized by a gravel patch subfacies. These gravel patches have clean, sandy gravels that migrate shorewards during storms over the muddy inshore Thalassia beds. The main palaeoecological conclusions arising from this work are the narrow depth range of the Neogoniolithon facies, the morphological response of this coralline to low-water level and hydraulic energy, and the preservation of growth forms and facies in rhodolith cores.