Effect of dissolved polyunsaturated aldehydes on the size distribution of transparent exopolymeric particles in an experimental diatom bloom

Abstract

Diatoms constitute a widespread group of phytoplanktonic species that thrive in coastal waters and produce episodical blooms. During these blooms, these diatoms release several organic compounds into the environment. Two types of organic molecules released by diatoms are the polyunsaturated aldehydes (PUA) and exopolymeric substances (EPS). EPS can spontaneously form particles called transparent exopolymeric particles (TEP). Spatial and temporal distributions of both, PUA and TEP, are linked to phytoplankton abundance, and peaks of both have been reported after diatom bloom episodes in the photic zone. For the first time, we have inferred interactions between both kinds of compounds by analyzing the effects of a mix of dissolved PUA (heptadienal, octadienal and decadienal) on TEP production in experimental microcosms. Our results show that the presence of dissolved PUA significantly increased TEP size and generated larger aggregates (>200 μm) towards the end of the bloom period, probably by increasing TEP stickiness. Since TEP production in nature enhances particle aggregation and carbon export from euphotic to deeper zones in aquatic ecosystems, this could imply important effects on the vertical flow of materials in the pelagic system and changes in the size distribution of available food particles after bloom events of PUA-producer species.