Age class distribution and density of kelps
To investigate the demographic structure of the Hansneset kelp forest, the age and density of kelp specimens was documented at 2.5, 5 and 10m depth. The seasonal growth rhythm of kelps results in the formation of annual growth rings, which can be used for age determination in adult kelps ((Parke, 1948); for discussion see Bartsch et al., (2016)). The minimum age of kelp individuals was determined by counting the annual growth rings of a thin cross section taken from the stipe just above the holdfast. Small delicate kelp individuals with ≤5cm stipe length and specimens without growth rings were considered juveniles (<1 year old). For a minority of kelp individuals, the age was not recorded (A. esculenta : n = 4; ‘Digitate Kelps’: n = 21; S. latissima : n = 6) but calculated using a regression formula from stipe length and age following Rinde & Sjøtun (2005) (Appendix 1).