PhD defence: Èric Jordà Molina

Thesis title​​​:

Spatio-temporal dynamics of soft-bottom macrobenthic communities in a rapidly changing Arctic: a case study of the Northwestern Barents Sea

Trial lecture topic:

Tipping points in the Arctic marine ecosystem

Evaluation Committee:

• Scientist Thomas Soltwedel, Alfred Wegener Institute for Polar and Marine Research, Germany
• Associate Professor Marie Nordström, University of Helsinki, Finland
• Professor Leslie R. Noble, Nord University

Supervisory Committee:

• Main supervisor: Professor Henning Reiss, Nord University
• Co-supervisor: Associate Professor Arunima Sen, The University Centre in Svalbard (UNIS)
• Co-supervisor: Adjunct Professor Paul Renaud, The University Centre in Svalbard (UNIS)
• Co-supervisor: Professor Bodil Bluhm, University of Tromsø (UiT)
• Co-supervisor: Research Scientist Mark Silberberger, Institute of Oceanology PAN, Poland

Thesis summary​:

The seafloor of the Barents Sea shelf hosts one of the most productive benthic assemblages of the Arctic seas. In particular, macrofaunal organisms (e.g. annelid worms, crustaceans, molluscs and others) that live in and on marine sediments have critical roles in the recycling of organic matter that sinks from the overlying waters to the seafloor. At the same time, the biological composition of these communities is highly spatially structured by environmental parameters and processes of the overlying waters and the seafloor environment. Hence, unprecedented rates of ocean warming and sea ice retreat driven by climate change are expected to cause significant biological shifts in the northwestern Barents Sea ecosystem in the coming decades, potentially leading to a re-organization of macrofaunal communities.

After investigating the dynamics and patterns of macrofaunal communities of this region at different spatio-temporal scales, the results of the present thesis have documented that significant fluctuations occurred in macrofaunal composition throughout the first two decades of the 21st century in conjunction with warm water anomalies caused by increased frequency of Atlantic water inflow in Arctic domains of the Barents Sea. Also, macrofauna communities of this region are highly decoupled from short-term variations of phenological processes occurring in the overlying water column, suggested by little seasonality in the composition and function of benthic assemblages. However, an experimental approach corroborated that benthic remineralization rates will most likely increase in a predicted warmer and more productive Barents Sea, leading to changes in carbon cycling and biogeochemical processes.

This thesis contributes to a better understanding of the temporal and spatial dynamics of benthic ecosystems in the Arctic and provides extensive new knowledge relevant to the effective management of the Barents Sea ecosystem, a system heavily impacted by the effects of ongoing climate change.