Temporal variations in transparent exopolymer particles (TEP) associated with a diatom spring bloom in a subarctic ria in Japan

Abstract

Temporal variations in transparent exopolymer particles (TEP) were studied during a spring bloom (January to April 1998) in a subarctic ria on the northeast coast of Japan. A diatom-dominated bloom developed from mid-February. Two major peaks were recorded in the first and last week of March, during which chlorophyll concentrations reached the maximum of 12 μg 1-1. The TEP concentration increased sharply after the first peak, the pre-bloom average of 901 rising to 1442 μg xanthan equiv. 1-1. The maximum TEP value of 2321 μg xanthan equiv. 1-1 recorded at the surface coincided with the second bloom peak. After this peak, TEP concentration continued to be relatively high. The number of particles fluctuated between 1 and 3.4 × 105 ml-1 (size = 4 to 520 μm) with an increase in small-sized particles following the bloom decline. TEP concentrations in this bay were much higher (avg. 1344 μg xanthan equiv. 1-1) than reported elsewhere (avg. 147 to 308 μg xanthan equiv. 1-1). Although TEP increased considerably following the bloom, it was interesting to note the high pre-bloom concentrations despite low chlorophyll concentrations. This implied that a source other than phytoplankton was responsible for the release of exudates leading to TEP formation. Laboratory experiments confirmed our assumption that the significantly high background TEP was due to the additional formation of these particles from the extracellular exudates released by the macroalga Undaria pinnatifida, cultivated commercially in this bay. Thus, besides providing information from the subarctic coastal waters of Japan for the first time, our study also confirms the role of macroalgal exudates as an important additional source for the formation of TEP.