60.4 Saturday, Jan. 5 Tritrophic interactions involving a global climate regulator mediate foraging in marine top predators: Evidence from a 50-year seabird dietary database in the Southern Ocean SAVOCA, M.S.*; NEVITT, G.A.; Univ. of California, Davis email@example.com
Dimethyl sulfide (DMS) has been studied intensively in the context of global climate regulation, and has also been implicated as a key signal molecule in foraging cascades. It has been suggested that seabirds and other marine predators use DMS released by depredated phytoplankton as a foraging cue to locate zooplankton prey. However, the dietary links between DMS attraction and trophic foraging level have never been explicitly demonstrated. We conducted a meta-analysis to explore the hypothesis that DMS mediates a tritrophic interaction in a marine system. We focused on 18 species of Antarctic and sub-Antarctic procellariiform seabirds for which experimental data on chemical attraction were available. If DMS is an infochemical facilitating a tritrophic cascade, we predicted that the diets of DMS-tracking species would contain significantly higher proportions of primary consumers (e.g. crustacea) than other food types (cephalopods and fish). Our results supported this prediction (proportion crustacea: 0.814 ± 0.039, proportion cephalopod: 0.065 ± 0.019, proportion fish: 0.108 ± 0.024; F5,274=42.67, P<0.001). We further explored this hypothesis by examining the diets of species responsive to 3-methyl pyrazine, a scented compound associated with the next highest trophic level, depredated crustacea. These analyses were consistent in showing essentially the opposite relationship: the diets of non pyrazine-tracking species were significantly more reliant on primary consumers than other food types (proportion crustacea: 0.564 ± 0.053, proportion cephalopod: 0.235 ± 0.042, proportion fish: 0.195 ± 0.034; F5,274=17.18, P<0.001). Together, this provides strong evidence that DMS, a globally important climate regulator, also functions in ecological contexts to facilitate a tritrophic interaction in the pelagic marine environment.