Population development and ecophysiology of the sea urchins Strongylocentrotus sp. in Porsangerfjorden, Finnmark, Norway

In August 2023, three researchers of the Alfred Wegener Institute (AWI) and the University of Bremen visited the Holmfjorden Research Station of the Norwegian Instutute of Marine Research (IMR). Marie Koch (AWI) and Simon Jungblut (Uni Bremen) had been at the station in summer 2022 already for conducting an ecophysiological temperature experiment with the green sea urchin Strongylocentrotus droebachiensis. Additionally, they sampled specimen of S. droebachiensis and its conspecific, S. pallidus, from the environment for microbiome and enzyme analysis as well as macrozoobenthos species for creating a genetic barcode library as a basis for future eDNA studies.

With the help of Chiara Sickert (Uni Bremen), Marie and Simon re-visited the Holmfjorden Research Station now again for 7 days to evaluate the status of the sea urchin populations in the bay next to the station and to take more environmental samples. Also, some gaps in the macrozoobenthos collection of last year have now been closed.

First results indicate that especially the population of S. droebachiensis increased by 20% in comparison to 2022 to on average over 160 individuals per m² in the barren area of the bay. Additionally, we observed a substantial number of cases of cannibalism or intraguild predation (esp. with Echinus esculentus victims). This might be caused by stress reactions due to high densities or by infestation with pathogens or eventually parasites. Parasites, however, have not been detected during the environmental sampling of sea urchins. The sea urchin population and its environmental impact (e.g., the formation of the barren area in the bay and potentially other fjord areas) should be monitored in future campaigns.


Photos: Simon Jungblut & Chiara Sickert

Marie Koch, Chiara Sickert and Simon Jungblut (from left) ready to sample sea urchins in the bay next to the Holmfjorden Research Station
The counting quadrat (1 sqm) placed in the barren area of the Holmfjorden bay
Holmfjord seaweed diversity from above
Chiara Sickert measuring and weighing sea urchins
Green and purple color morphs of the sea urchin Strongylocentrotus droebachiensis from Holmfjord
Echinus esculentus cannibalized by several Strongylocentrotus droebachiensis in the Holmfjorden bay
Examples for the purple and green color morph of Strongylocentrotus droebachiensis
Cannibalized individual of Strongylocentrotus droebachiensis

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