THE ABUNDANCE AND SIGNIFICANCE OF A CLASS OF LARGE, TRANSPARENT ORGANIC PARTICLES IN THE OCEAN

Polysaccharide-specific staining techniques reveal the existence and h igh abundance of a class of large, discrete, transparent particles in seawater and diatom cultures formed from dissolved exopolymers exuded by phytoplankton and bacteria. Transparent exopolymer particles (TEP), ranged from 28 to 5000 particles ml-1 and from 3 to 100s mum in longe st dimension at five coastal stations off California. A high percentag e of seemingly free-living bacteria (28-68%) were attached to these tr ansparent sheets and films, suggesting that they may alter the distrib utions and microenvironments of marine microbes in nature. Preliminary coagulation experiments demonstrated that TEP are major agents in the aggregation of diatoms and in the formation of marine snow. The exist ence of microbial exudates acting as large, discrete particles, rather than as dissolved molecules or as coating on other particles, suggest s that the transformation of dissolved organic matter into particulate form in the sea can occur via a rapid abiotic pathway as well as thro ugh conventional microbial uptake. The existence of these particles ha s far reaching implications for food web structure, microbial processe s, carbon cycling and particulate flux in the ocean.