Abundance, size distribution and bacterial colonization of transparent exopolymeric particles (TEP) during spring in the Kattegat

Abstract

The abundance, size distribution and bacterial colonization of transparent exopolymeric particles (TEP) were monitored in the Kattegat (Denmark) at weekly intervals throughout the spring (February-May) encompassing the spring diatom bloom. These recently discovered particles are believed to be formed from colloidal organic material exuded by phytoplankton and bacteria, and may have significant implications for pelagic flux processes. During this study, the n umber concentration of TEP (>1 μm) ranged from 3 x 103 to 6 x 104 ml-1 and the volume concentration between 0.3 and 9.0 p.p.m.; they were most abundant in the surface waters subsequent to the spring phytoplankton bloom. The range of TEP (encased) volume concentration was similar to that of the phytoplankton, although at times TEP volume concentration exceeded thai of the phytoplankton by two orders of magnitude. The TEP size distribution followed a power law, with the abundance of particles scaling with particle diameter ((β+1)). The seasonal average estimate of β (2.3) was not significantly different from three, consistent with TEP being formed by shear coagulation from smaller particles. However, date-specific estimates of β differed significantly from three, probably because TEP are fractal. All TEP were colonized by bacteria, and bacteria were both attached to the surface of and embedded in TEP. Yet the number of attached bacteria per TEP was related neither to the surface area nor the volume, but rather scaled with TEP size raised to an exponent of ~1.5. We argue thai this is consistent with TEP being fractal. Between 0.5 and 20% of the total bacterial population were attached to TEP. Crude estimates of TEP carbon concentrations combined with considerations of turnover times suggest that TEP and their colloidal precursors may represent a hitherto understudied but potentially significant pathway for dissolved organic carbon in the ocean.