Trophic complexity in marine sediments: new evidence from the Gulf of St. Lawrence

The potential for predatory infaunal species to increase trophic complexity in marine sedimentary habitats has been debated in the past; however, the status of predatory infauna as a distinct trophic level remains controversial. Specifically, it is unclear whether these assemblages can be accurately depicted by a 3-level trophic model in which predatory infauna constitutes a critical intermediate trophic link between epibenthic predators and other infauna. Here, we specifically address whether the key requirement for recognition of a 3-level trophic structure (namely that 'epibenthic predators must selectively prey on predatory infauna') is supported by new experimental evidence from 2 contrasting habitats in the Gulf of St. Lawrence, Canada. Our results unambiguously support a 3-trophic level model and raise a series of questions on the current understanding of the trophic structure of marine sedimentary habitats.