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 (⁓2,500 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 offered kelp blades were not consumed at latitudes where phlorotannin contents were very high also 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.

Methods
The dataset was collected during fieldwork occurred in austral-summer 2018-2019. Tethering assays were deployed in 12 sites along the Chilean coast, using three different prey items: porcellanid crabs, squidpops and seaweed. In each site, data was collected on the day and 24 h after the deployment of the assay. Environmental and habitat data from the site was collected either on the day of the deployment or the day after. A multiparameter was used to obtain water quality measurements YSI-95. Habitat data was taken from photoquadrants. Species abundances were counted via visual transects.