In situ observations have also revealed similarities and subtle distinctions in feeding by highly disparate species. The isopod Acanthamunnopsis milleri collects particles from the surrounding water using fine, stiff bristles distributed along its elongate arms, then draws the arms past its mouth to remove the accumulated food. We have observed the pelagic red crab Pleuroncodes planipes feeding in a similar manner. In contrast, another isopod, Munneurycope murrayi, collects clumps of aggregated marine snow such as discarded larvacean houses from the water column. The long, retractile filaments of the vampire squid, Vampyroteuthis infernalis were widely believed to be sensory structures until we observed them in situ being used to collect detritus and marine snow aggregates, which were subsequently drawn through the arms and to the mouth for ingestion.

In all of these cases gut content analyses alone would not have allowed us to distinguish between these different feeding modes and food types.

Searching the VARS database with a much broader scope has yielded a detailed description of the deep pelagic food web of Monterey Bay. Based on 743 independent feeding events, our published results indicate that gelatinous predators – siphonophores, medusae, and ctenophores – are key carnivores, comparable to fish and squid in their importance within the food web. This study also examines how gelatinous predators, once believed to be a trophic “dead-end,” are fully integrated into overall food web structure.

A detailed investigation of the feeding of abundant squids in the genus Gonatus involved mining the VARS database for observations of feeding, as well as targeted dive time to seek out these predators. The surprising results showed that in addition to the small fishes we expected them to consume, gonatid squids also showed a high degree of cannibalism.

Filter-feeding gelatinous animals like giant larvaceans, salps, and doliolids mediate sinking particle flux, in some cases transporting substantial amounts of carbon into the deep sea. Other predatory gelatinous animals like large siphonophores and medusae directly consume micronektonic animals (e.g., crustaceans, fishes, and small cephalopods), and are in turn consumed by pelagic predatory fishes like opah and tunas. In this way, dominant gelatinous animals serve as critical trophic nodes in epipelagic, mesopelagic, and bathypelagic food webs, necessitating ecological study of their overall roles.