Changes in Abiotic Drivers of Green Sea Urchin Demographics following the Loss of a Keystone Predator

Table 1

Examples of environmental variables that can influence sea urchin demographics in temperate urchin barrens.

Type of influence	Variable in this study	Scale in this study	Rationale	Expected influence +/-/?	Sources
Oceanographic	Sea surface salinity	Island	Strongylocentrotus spp. have a generally low tolerance to low and highly variable salinities	—	[21, 22, 26, 28, 44, 46, 95]
	Sea surface temperature	Island	Temperature can influence the behaviour, reproduction, grazing, and growth of green sea urchins. Particularly important in large-scale climate studies	Mixed
	Sea surface current velocity	Island	Can influence patterns of sea urchin demographics by driving recruitment and local community structure	Mixed
Bathymetric	Exposure	Site	Important local driver of sea urchin behaviour, size structure, and ecological function	Mixed	[15, 18–21, 29–31, 38, 44, 95, 96]
	Slope	Site	Slope will shape patterns of sea urchin behaviour in response to perturbation across depth ranges	+
	Slope variability	Site	Variability in slope can serve as a measure of complexity of local habitat, influencing sea urchin behavioural responses to perturbations across depth ranges	+
	Depth	Site	Depth will shape patterns of sea urchin behaviour and ecological function	Mixed
	Depth variability	Site	Variability in depth can serve as a measure of the complexity of the local habitat, influencing sea urchin behaviour and ecological function	+
	Shallow habitat	Site	The amount of shallow habitat within the foraging depths of sea otters and also in the ideal depth range for macroalgal production	+
	Deep habitat	Site	The amount of deep water inaccessible to sea otters that could serve as a deep water refugia	+
	Amount of shelf habitat	Site	The amount of habitat on the continental shelf (0-200 m water depth)	+
Geophysical	Shape	Island	Can influence local currents, weather patterns, and degree of coastal vs. oceanic influence. Geophysical structure of the shoreline can influence other environmental forces	?	[27, 96]
	Mean elevation	Island		?

Variables are listed by the type of influence. Rationale for inclusion was based on referenced sources with expected influence on urchin demographics: positive (+), negative (-), mixed, or unknown (?). This is not an exhaustive literature review and presents examples from temperate urchin barrens where sea otters are not a functional component of the ecosystem.