Table 1. List of environmental variables used in analysis.

Variable	Short	Description	Reference
Natural
Macroalgal biomass	ALG	Macroalgal wet weight per unit area	NaGISA data
Substrate category	SUB	Categories: bedrock, sandstone, large boulders, boulders and cobbles, rocks embedded in soft sediment	NaGISA data
Sea-surface temperature	SST	climatological summer mean value, averaged between 1985 and 2001, derived from the 4 km resolution AVHRR Pathfinder Project version 5.0 by the NOAA NODC	[125]
Chlorophyll-a	CHA	SeaWiFS reprocessing 5.2 by the NASA GSFC Ocean Color Group, averaged 1997-2009, 9 km resolution	[126]
Primary productivity	PP	mg carbon m−2 d−1, Vertically Generalized Production Model (VGPM) for SeaWiFS, averaged 1997–2007, 18 km resolution	[127]
Salinity	SAL	HYCOM predictive model, National Ocean Partnership Program, average for 2003, 1/12° resolution	http://www.hycom.org/
Anthropogenic
Inorganic pollution	INP	urban runoff estimated from land-use categories, US Geologic Survey (http://edcsns17.cr.usgs.gov/glcc/)	[55]
Organic pollution	ORP	FAO national pesticides statistics (1992–2002), (http://faostat.fao.org)	[55]
Nutrient contamination	NUTC	FAO national fertilizers statistics (1992–2002), (http://faostat.fao.org)	[55]
Marine-derived pollution	MARP	port data 1999–2005, proportional to commercial shipping traffic	[55]
acidification	AC	aragonite saturation state 1870–2000/2009, 1 degree lat/long resolution	[55]
invasive species incidence	INV	cargo traffic 1999–2003	[55]
human coastal population density	HUM	LandScan 30 arc-second population data of 2005	[55]
shipping activity	SH	commercial ship traffic 2004–2005	[55]