ABSTRACT
Primary productivity amongst plankton is influenced mainly by the intensity of light and the availability of nutrients. Nutrients clearly play an important role in determining the biofacies in upwelling systems, but related factors, such as temperature and oxygen, may also play an important role and it is commonly difficult to isolate one limiting factor from others. Because the circulation of surface ocean waters is organized into discrete currents or gyres, each with its own temperature range, the distribution of planktonic and benthic communities often shows sharp discontinuities at the boundaries of these water masses. Salinity generally only becomes an important limiting factor in marginal marine environments that are brackish or hypersaline. Rapid rates of sedimentation associated with storms, floods and turbidity currents may in some instances be recognized by escape burrows adjacent to which the sedimentary laminae are disturbed by the movement of the burrowing organism as it attempts to escape being buried.
