Such complications forced this overly simplistic scheme to give way in 1975, when the late Frank H. Rigler, a zoologist at the University of Toronto,…

Such complications forced this overly simplistic scheme to give way in 1975, when the late Frank H. Rigler, a zoologist at the University of Toronto, published an influential critique of the concept. It was then that William E. Odum (of the University of Virginia”s Department of Environmental Sciences) and Eric J. Heald (of the University of Miami”s Rosenstiel School of Marine and Atmospheric Sciences) pointed out that more precise estimates of trophic level could be obtained from actual observations of diet. Their advance, as followed in current practice, treats trophic level as an empirically determinable property of a species–like average size or metabolic rate. So how exactly do marine biologists estimate trophic level for a given species?