Transparent exopolymer particle (TEP) dynamics in the eastern Mediterranean Sea

Depth and spatial distribution patterns of transparent exopolymer particles (TEP) were measured during 2 east to west cruise transects across the ultra-oligotrophic Levantine basin, eastern Mediterranean Sea (SESAME, September 2008; ISRLEV, July 2009), and at 2 stations 20 and 50 km offshore (2008). TEP distribution was examined relative to chlorophyll a concentrations, bacterial production, and alkaline phosphatase activity (APA), taken as a measure of phosphorus (P) stress. During the stratified period, TEP levels were highest in a 5 m surface layer and correlated positively with APA as P concentrations decreased. On the transects, TEP concentrations from both surface and depth (1000 m) samples increased from west to east, corresponding to a pattern of increasing oligotrophy. In pelagic waters, maximal rates of bacterial production and TEP concentrations were consistently measured in surface samples. These contained abundant large (170 mu m) TEP with numerous associated bacteria, possibly derived from algal or bacterial release or detritus. Lowest TEP concentrations were found in the deep chlorophyll maximum layer where TEP appeared as small (similar to 4 mu m) particles with only few attached bacteria. In deeper (300 to 1000 m) samples, both TEP concentrations and size increased, with most particles having associated bacteria. Our data augment previous studies on the formation of TEP and the subsequent utilization of this material by heterotrophic bacteria both in the euphotic zone and in deeper waters. Moreover, our study suggests that in ultra-oligotrophic environments such as the Levantine basin, TEP plays an especially important role in carbon cycling and transportation.