Jellies Down Deep
From Goo to Zoo
When Bruce Robison was just starting out in marine biology, the study of deep-sea life usually involved dragging a net behind a ship. This method was efficient but selective, he recalls. Trawl samples gave scientists a skewed picture of what populates the oceanic water column: large numbers of fishes, crustaceans, and squids—the hard-bodied animals the nets could actually snare—plus “a handful of goo” that was tossed overboard.
But the goo is a crucial piece of the oceanic puzzle, Robison realizes now. A deep-sea ecologist at the Monterey Bay Aquarium Research Institute, Robison has pioneered the use of submersible robots to study jellyfish and other gelatinous invertebrates in their native deep-sea environment. Once you enter their home, these organisms, known collectively as jellies, are hard to miss. As it turns out, they are a dominant form of life in the ocean, far more abundant than previously realized. Robison estimates that as much as 40 percent of the biomass in the open ocean is bound up in the bodies of gelatinous invertebrates.
“Jellies are a completely surprising component of the deep-sea food web,” Robison says. “Our present understanding of where jellies fit into the way the world works is far from complete. But it’s very clear they are a significant part of deep-ocean communities.”
“Jelly” is a generic term that marine scientists use to describe transparent, gelatinous invertebrates that float freely in the ocean. Jellies encompass more than just jellyfish, which themselves include about 200 species in the class Scyphozoa (phylum Cnidaria). Jellies come in all sizes, from the microscopic to dozens of feet long, and in uncounted forms. Their membership consists of species from widely divergent taxonomic groups, including true jellyfish from the phylum Cnidaria, comb jellies from the phylum Ctenophora, sea snails and sea slugs from the phylum Mollusca (most mollusks, such as the familiar, hard-bodied clams and mussels, are not jellies), and a small group from the phylum Chordata (which mostly includes non-gelatinous animals such as birds, reptiles, and people). Jellies are defined not by a single, shared evolutionary ancestry, but rather by the outward fact that they all have gelatinous bodies.
Through the use of remotely operated submersible vehicles, or ROVs, scientists at MBARI have gained unprecedented access to the jellies’ realm. A scientific ROV is essentially a swimming robot outfitted with research equipment such as sampling containers, headlights, and high-resolution video cameras. While the vehicle dives deep into the cold undersea darkness, scientists sit comfortably aboard a ship on the sea surface, controlling the ROV movements remotely and watching its video feed on a bank of screens. Manned submersibles are also used in studying jellies, but an ROV, freed from its human occupant, can run longer without resurfacing and makes an excellent camera platform.
