Table 1.

Postulated links and interactions between key species in the conceptual model of the studied kelp/sea urchin ecosystem, including the hypothesized impact of ocean warming (i.e., just the southern recovery area) and crabs on sea urchins in the two recovery areas (a southern and a northern area). Observed patterns from this study (if any) and the type of observation/statistic are described. The degree of support for the hypothesized links from other kelp–urchin studies are classified into strong, medium, or weak, and as causal or correlative. The references of the other studies are given

Interaction/Description	Degree of support other studies	Observed patterns in this study	References
Sea urchin ↔ kelp
1. Green sea urchins in high densities are grazing kelp and maintaining barren grounds	Strong causal	Negative correlation between kelp and sea urchin occurrence	Norderhaug and Christie (2009), Propp (1977), Rinde et al. (2014), Skadsheim et al. (1995), and Sivertsen (1997, 2006)
2. Kelp forests house sea urchin predators that regulate sea urchin abundance	Medium correlative	Sea urchins rarely observed inside kelp forests	Norderhaug and Christie (2009), Skadsheim et al. (1995), and Steneck et al. (2013)
Kelp → crab
3. Kelp forests are habitat for Cancer crabs	Strong causal		Christie, Fredriksen, and Rinde (1998), Fagerli et al. (2014), Steneck et al. (2013), and Woll et al. (2006)
Crab → sea urchin
4. Cancer crabs feed on sea urchins	Strong causal	Observations in field	Fagerli et al. (2014), and Steneck et al. (2013, 2004)
5. Cancer crabs reduce sea urchin populations	Correlative	An inverse pattern of abundance in time and space. Low proportion of barrens in areas with crab landings, and high proportions in areas without.	Steneck et al. (2013, 2004)
6. Red king crabs feed on sea urchins	Strong causal	Observations in the field	Gudimov et al. (2003), Jørgensen and Primicerio (2007), Oug and Sundet (2008), and Pavlova (2009)
7. Red king crabs reduce sea urchin populations	Correlative	An inverse pattern of abundance in time and space of crab landings and sea urchin density. Sea urchins on predator refuge habitats	Gudimov et al. (2003) and Oug and Sundet (2008)
Kelp → cod
8. Kelp forests are a habitat for coastal cod, particularly juveniles	Strong causal	Own unpublished results	Keats et al. (1987) and Norderhaug et al. (2005)
Cod → crab
9. Coastal cod feed on edible crabs	Strong causal	Observations in the field	Holt (1890), Link and Garrison (2002), Norderhaug et al. (2005), and Steneck et al. (2013)
10. Coastal cod population size influences edible crab populations	Weak correlative	An inverse pattern of abundance in time and space of cod and Cancer crab landings.	Steneck et al. (2013) for Cancer spp.
11. Coastal cod feed on king crabs	Strong causal		Dvoretsky and Dvoretsky (2009), Falk‐Petersen et al. (2011), and Livingston (1989)
12. Cod population size influences the size of king crab populations	Weak correlative	An inverse pattern of abundance in time and space of cod and king crab landings	Livingston (1989) for snow crabs
Temperature → sea urchin
13. Temperature increase is negative for sea urchins	Strong causal	Temporal and spatial correlations in the mid‐Norway	Fagerli et al. (2013, 2014), Rinde et al. (2014), Stephens (1972), and Siikavuopio et al. (2006, 2012)
Temperature → crab
14. Temperature increase is positive for the edible crab and results in northward movement of the crab	Medium correlative	Temporal and spatial correlations in the mid‐Norway)	Brattegard (2011), Lindley and Batten (2002), Lindley and Kirby (2010), and Woll et al. (2006)