Norwegian Institute of Water Resources (NIVA) - Tromsø

Restoration Project

Norwegian Institute of Water Resources (NIVA) - Tromsø

Restoration Objective:

The aim of this study was to investigate whether kelp may recover if the abundance of urchins is reduced in a small-scale pilot study. This could provide value by using the profitable commercial harvest of urchins to restore the valuable ecosystem services of kelp forests.

Site Selection Criteria:

Shallow, sheltered sites with high current flow were selected. These sites were dominated by sea urchins and had no visible kelps/seaweeds.

Cause Of Decline:

The kelp species Saccharina latissima and Laminaria hyperborea form highly productive dense forests in the sublittoral zone along the Norwegian coast, providing habitat, food, nutrients, and shelter to numerous species. The total kelp forest area along the Norwegian coast line was estimated to be about 7900 km2 in 2011, but this is estimated to be less than 50% of the original coverage, with an estimated 9800km2 of kelp forest lost. The causes of kelp forest loss include climate change, increased runoff of particles, increased nutrients and growth of filamentous algae. However the major cause is overgrazing caused by high densities of sea urchins.

Key Reasons For Decline:


Scientific Paper

Regrowth of kelp after removal of sea urchins (Strongylocentrotus droebachiensis). NIVA-report ISSN 1894-7948

P. Carlsson, H. Christie

Site Observations:

Observation Date

29th Oct 2018

Action Summary:

Three underwater cages (9m2 each) were deployed outside Tromsø, Northern Norway during Autumn 2018. All urchins (Strongylocentrotus droebachiensis) were removed from within these cages (300-600/cage) continuously until Summer 2019.

Lessons Learned:

There was short term success in algal recruitment, however once a high density of kelps were achieved in the cages, encroachment of sea urchins increased.

Project Outcomes:

The first kelp individual appeared in mid-March, and by the end of May, the seafloor in the cages had 80-100% coverage of algae. The kelp species Alaria esculenta were growing on the nets as well. Algae composition was dominated by the brown algae Desmarestia sp. and Alaria esculenta. Some sugar kelp individuals (Saccharina latissima) were also present.

Key Reasons For Decline:


Area of Restoration (Ha)


Indicator Data:


Ending Value:

Starting Value:

Presence / Absence of Kelp

Cost Year:400000
Cost Currency:NOK
Total Cost:400,000