POPULATION DYNAMICS OF FORAMINIFERA IN MANGAL SWAMPS AND MARSHES

Seasonal trends of tropical intertidal foraminiferal communities have been poorly investigated, but that of their temperate counterparts are better understood to display either annual or intrannual periodicity. Seasonal patterns in live foraminiferal densities (LFDs) were investigated at Caroni Swamp (March 2011 to May 2013) and Claxton Bay (July 2012 to 2013; Trinidad). These were compared to population dynamics at temperate Cowpen Marsh (May 1995 to 1996) and Brancaster Marsh (November 1995, March, May and August 1996; UK). Quantitative methods used were: statistical comparison of monthly LFDs within seasons; time series analysis (TSA); cross correlations with abiotic variables (only at tropical locations); and identifying major assemblage turnovers using a novel approach, the assemblage turnover index (ATI) and the conditioned on boundary index (CoBI). Foraminiferal populations at the temperate marshes displayed seasonal population growth in warmer months (summer and spring) and decline in cooler months (autumn and winter). At the tropical swamps population growth was aseasonal. At Caroni Swamp, major assemblage turnovers coincided with periods of seasonal change in one year but were not reproduced in the following year, and neither agglutinated or calcareous species showed seasonal preference. At Claxton Bay, however, preferential growth of agglutinated species occurred during the dry season and of calcareous species during the wet season. This pattern was related to higher sediment organic content and lower sediment pH concentrations during the wet season, and vice versa in the dry season. Foraminiferal population dynamics differed between the tropical locations, mainly due to geographic differences that result in different hydrodynamic features, such as flushing and retention times.