APPLICATIONS OF THE FORAMINIFERAL PROPAGULE BANK: A NOVEL APPROACH TO UNDERSTANDING THE ECOLOGY OF FORAMINIFERA

Reproduction in the foraminifera generally produces large numbers of tiny juveniles that measure just 10s of microns in most species. These small juveniles function as propagules and can be entrained in the water column where they undergo passive dispersal both within and beyond the distribution limits of conspecific adults. These juveniles form a “propagule bank,” broadly analogous to a seed bank, that resides within the fine sediment fraction (<63 microns) of many depositional marine systems. At any given site, this propagule bank may include both young produced by local populations as well as those that have dispersed from more distant regions. Propagules of some species may lie in a cryptic or dormant state for months or even years under conditions that are suboptimal for growth. Given appropriate environmental conditions, however, these propagules can grow into adult agamonts (most) or gamonts (some) and subsequently reproduce. The propagule bank provides a novel tool that can be manipulated experimentally to address a number of ecological questions regarding benthic foraminifera. For experimental purposes, we separate the propagule bank from adult foraminiferans, larger benthic organisms and coarse material by sieving. The fine sediment fraction is retained for experiments, and the coarse fraction is used to assess the live and dead in situ assemblages. By growing foraminiferans from propagules under controlled environmental conditions, we can identify responses of certain species to specific ranges of important environmental parameters such as temperature and salinity, responses to a specific pollutant or combination of pollutants at known concentrations, and gain insight into the distance over which different taxa disperse by identifying “exotic” taxa that grow from propagules at a given site. This experimental approach gives us a tool for examining opportunistic species and potential foraminiferal bioindicators.