Mesopelagic fishes and prokaryotes: food for thought

14 Juliol 2017
Sala d'Actes
Impartida per: 
Dr. Xosé Anxelu G. Morán
King Abdullah University of Science and Technology, Thuwal, Saudi Arabia


The recent finding that mesopelagic fish biomass is one order of magnitude higher than previously thought has boosted studies about their role in ocean biogeochemical cycles. Diel vertical migrations of these small fishes represent a rapid, massive transfer of organic matter to impoverished mesopelagic layers during daytime. However, its effect on heterotrophic bacteria and archaea remains unknown. A series of experiments conducted at one 700 m deep station in the central Red Sea suggest that mesopelagic fishes represent an important food source for heterotrophic prokaryotes inhabiting the 450-550 m layer. We have documented dissolved organic carbon (DOC) consumption rates of up to 5 µmol L-1 d-1 in parallel to sustained increases in heterotrophic prokaryotes biomass during short-term incubations. Mesopelagic microbes were significantly larger than their counterparts from shallower depths and they also showed higher growth efficiencies, indicating the existence of labile organic compounds. Dissolved organic matter C:N ratios and fluorescent properties do not support the contention that deep stocks are uniformly refractory. Incubations conducted in different seasons and at different times of the diel cycle (i.e. noon vs. midnight, and monitoring the fish arrival at sunrise) together with transplantation experiments consistently support the existence of previously overlooked DOC hotspots that may change our view of the functioning of microbial food webs in the twilight ocean.


Brief biography

Dr. Xosé Anxelu G. Morán is Associate Professor of Marine Science affiliated to the Red Sea Research Center at King Abdullah University of Science and Technology in Thuwal (Saudi Arabia). He obtained his PhD in Biology (University of Oviedo/Uviéu, Spain) in 1999. After completing postgraduate and postdoctoral stays at the Institute of Marine Sciences (ICM-CSIC) in Barcelona under the supervision of Dr. Marta Estrada, he became senior researcher at the Spanish Institute of Oceanography (IEO) in Gijón/Xixón from 2001 to 2014. In 2008 he was on a sabbatical at the MBL in Woods Hole (USA). His research interests revolve around marine microbial ecology and biogeochemistry, focused on the role of microbial plankton in biogeochemical carbon cycling. His current work includes the trophic relationships between bacterioplankton and phytoplankton, the metabolic ecology of prokaryotes and the interactions between dissolved organic matter and microbes in oligotrophic environments, particularly in the Red Sea, ultimately aimed at understanding the response of marine microbiota to global change. He has been co-chair of the ICES Working Group of Phytoplankton and Microbial Ecology (2009-2015).