Environmental and local habitat variables as predictors of trophic interactions in subtidal rocky reefs along the SE Pacific coast

Temperature generally drives latitudinal patterns in the strength of trophic interactions, including consumption rates. However, local community and other environmental conditions might also affect consumption, disrupting latitudinal gradients, which results in complex large-scale patterns. This study assessed the relative effect of environmental variables and local consumer communities on predation and herbivory along more than 22 degrees of latitude (∼2500 km) of the Chilean coast. Consumption assays with animal prey (porcellanid crabs and squidpops) and the kelp Lessonia spp. were used to assess predation (after 2 h and 24 h) and herbivory (after 24 h) at 12 study sites where important environmental variables (seawater characteristics, habitat features and consumer community characteristics) were measured. For each prey type, we aimed to identify the variables that best explained variation in consumption. Predation rates were positively related to temperature, but also with dissolved oxygen and higher salinities, all variables that are thought to favour higher metabolic rates in consumers. Local habitat characteristics (i.e. higher bare rock cover) negatively affected predation rates on porcellanid crabs, likely because large predatory fish feeding on crabs (which also explain higher crab consumption) are less abundant in seaweed-free areas (kelp or understory algae). There was a decrease in herbivory with higher understorey algae cover, possibly due to the presence of alternative, more palatable seaweeds. The fact that the offered kelp blades were not consumed at latitudes where phlorotannin contents were very high suggests a relationship between consumption and seaweed palatability. Since many of the explanatory variables did not show a strict latitudinal trend, large-scale consumption patterns can vary with sources of local variation that affect the consumer metabolism, foraging efficiency and consumption pressure.