Predators of the destructive sea urchin Strongylocentrotus droebachiensis on the Norwegian coast

Cw Fagerli,S Fredriksen,Mf Pedersen,H Christie,Km Norderhaug

doi:10.3354/meps10701

Cw Fagerli, S Fredriksen + Show 3 more

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https://doi.org/10.3354/meps10701

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Abstract

In central Norway, populations of the green sea urchin Strongylocentrotus droe- bachiensis are collapsing, but the factors controlling its population density have not yet been elucidated. Through field sampling, we identified several sea urchin predators and investigated their predation rates on recently settled S. droebachiensis in laboratory experiments. Tethering experiments in kelp forest and on barren ground study sites in the area where sea urchin popula- tions are collapsing confirmed predation by some of the predators tested in laboratory experi- ments. The edible crab Cancer pagurus was the most efficient sea urchin predator, and it was more abundant at kelp forest sites than on barren grounds. Stocks of C. pagurus have increased dramatically in central Norway since the 1990s, and predation by C. pagurus may contribute to the decline in sea urchin densities, allowing kelp recovery and conferring resilience of the new kelp forest state.

Highlights

On the coast of central Norway, kelp Laminaria hyperborea (Gunnerus) Foslie forests are recovering from extensive overgrazing and more than 4 decades of sea urchin dominance (Norderhaug & Christie 2009)
No juvenile sea urchins were found under roofing tiles in kelp forest, while individuals from all predator species were identified in both habitats, not in all sampling periods (Fig. 3)
The remaining predators showed no significant differences in mean abundance between barren ground and kelp forest sites

Summary

Introduction

On the coast of central Norway, kelp Laminaria hyperborea (Gunnerus) Foslie forests are recovering from extensive overgrazing and more than 4 decades of sea urchin dominance (Norderhaug & Christie 2009). F. Müller, 1776 seems related to a failure in recruitment, which has coincided with increasing ocean temperatures (Fagerli et al 2013). 1776 seems related to a failure in recruitment, which has coincided with increasing ocean temperatures (Fagerli et al 2013) Throughout this period of increasing water temperatures and kelp recovery, an abrupt increase in the abundance of the edible crab Cancer pagurus Linnaeus, 1758 has taken place (Woll et al 2006). As a likely sea urchin predator, the increase in C. pagurus may contribute to the on-going process of kelp recovery

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