Kjell Magnus Norderhaug1, Portia Kleiven1, Thomas Wernberg1, Ann-Elin Synnes2, Karen Filbee-Dexter1, Sigurd Espeland1, Jonas Thormar1, Kyrre Kartveit1, Lene Christensen1, Even Moland1
1Institute of Marine Research IMR, Norway - 2NIVA, Norway
As we are progressing through the Anthropocene, it is imperative to understand how ecosystems degraded by historical impacts respond to future pressures. Particular attention should be directed at changes in distribution and function of foundation species due to their disproportionally important ecological roles. Forest forming kelp is in decline and are being replaced by turf-forming algae in coastal areas globally, as a consequence of increasingly severe marine heatwaves. This replacement represents a miniaturization of the three-dimensional habitat and a change in habitat functions for many associated species. Ecologically, economically and culturally important coastal fish species depend on kelp forests in different life stages from egg to adult and may be affected in various ways. Many of these species already suffer from centuries of overexploitation, severely reducing abundances, truncating sizes and changing age distributions. Here we studied the overfished kelp forest ecosystems of Skagerrak and assessed the impact of the transition from kelp to turf on the associated fish communities. Specifically, we analyzed differences in abundance, body size and composition of benthic fish at sites with variable cover of kelp and turf. We found higher abundances of small fish with increasing cover of turf relative to kelp. This difference was mainly due to higher abundances of gobies on turf, and to a lesser extent due to presence of smaller individuals of the most abundant fish families labridae, gadidae or gobidae. Thus, by favoring small fish species, marine heatwaves exacerbate size distribution effects in these fish communities with many stocks already suffering from overfishing.
Biography
Norderhaug’s main field of interest is coastal ecosystems and in particular kelp forests. His research focus on the importance of these marine forests, their ecology and how they are impacted by human activity. To an increasing degree his research is directed towards understanding change on large spatiotemporal scales. He has long experience with environmental monitoring with focus on how eutrophication and climate change affect coastal ecosystems.