EFFECTS OF TEMPERATURE AND SALINITY ON SHALLOW-WATER FORAMINIFERAL ASSEMBLAGES: AN EXPERIMENTAL APPROACH

Benthic Foraminifera are widely recognized as sensitive indicators of changing environmental conditions over a range of spatial and temporal scales. Shallow-water assemblages in particular have been applied to studies on pollution and other human-induced impacts as well as broader problems such as documenting the Holocene rise in sea level. Our understanding of the environmental tolerances of benthic Foraminifera stems largely from field-based studies in which patterns of distribution are correlated to environmental conditions. Shallow-water, field-based studies, however, may be less than conclusive because environmental conditions often vary widely throughout the year or even within a single tidal cycle. A novel experimental approach allows us to examine the effects of selected environmental parameters on the growth of species and assemblages in a controlled setting. As shown previously, small juveniles are the primary stage in which Foraminifera disperse, and the fine sediment fraction (<63 μm) found in depositional settings contains an abundant and diverse “seed bank” of tiny juvenile Foraminifera. The juveniles of this “seed bank” or “propagule bank” can be easily grown to adults in the laboratory under controlled conditions. Results to date examining the effects of temperature and salinity indicate that the “seed bank” collected from selected Sapelo Island mudflats produces very different assemblages depending on the experimental conditions under which they are grown. Temperature is more important than salinity in determining the species composition of assemblages, and at lower temperatures (12° C) assemblages are virtually indistinguishable regardless of salinity. At higher temperatures (22° C), however, salinity plays a significant role in determining the assemblage composition. Some species (Haynesina germanica, Psammophaga simplora) grew under all conditions, whereas others (Ammonia tepida, Elphidium excavatum, Miliammina fusca, Textularia spp., Triloculina oblonga) proved more limited. This method of growing foraminiferal assemblages under controlled conditions provides a better understanding of the environmental tolerances of individual species and will ultimately refine our interpretations of environmental change whether a result of natural causes or human impacts.