Micro-scale processes ubiquitously shape the marine ecosystem, from the structure of the trophic web to the fate of the chemical compounds that enter the biogeochemical cycles. In the patchy turbulent environment of the ocean, the interaction between the microorganisms at the base of the marine trophic web is mediated by the chemoresponse to ephemeral chemical stimuli. In this study, we examined the chemical responses of various model marine protists to DMSP, a naturally occurring organic sulfur compound present in most marine phytoplankton, as well as its byproducts DMS and Acrylate. The organisms studied belong to three different trophic modes: <em>Oxyrris marina</em> (an osmotroph), <em>Gyrodinium dominans</em> (a phagotroph), and <em>Karlodinium armiger</em> (a mixotroph). We analyzed the behavioral changes induced by the chemical stimuli by using a conventional capillary asset, broadly used in chemotaxis studies, along with an automated image analysis technique to track the individual trajectories of the swimming organisms. Our results indicate that all organisms exhibit a strong chemoattraction to DMSP, mild chemoattraction to DMS, and no chemorepulsion towards Acrylate, which contradicts previous studies. We also noted a chemokinetic response of <em>Gyrodinium d.</em> to DMSP, as it altered the organism's swimming behavior in terms of speed and motility patterns. These findings could offer further understanding of how marine protists utilize these compounds and provide a deeper insight on the distinct foraging strategies employed by individual organisms depending on their trophic mode.

Primary Presenter: MEDEA ZANOLI, Mediterrenean Institute of Advanced Studies (IMEDEA) (medeazanoli@gmail.com)

Authors:

Queralt G&#252;ell, Institute of Marine Sciences (ICM-CSIC)  (queraltguell@icm.csic.es)

Rafel Sim&#243;, Institute of Marine Sciences (ICM-CSIC)  (rsimo@icm.csic.es)

Idan Tuval, Mediterranean Institute for Advanced Studies (IMEDEA)  (ituval@imedea.uib-csic.es)

Medea Zanoli, Mediterranean Institute for Advanced Studies, Esporles,   (medea@imedea.uib-csic.es)