I often try to imagine the open ocean world of the jellies, a place where the physical barriers are completely different than on land. Like floating in space, life in the ocean is a three-dimensional and any direction can be navigated with ease. Being free from the constraints of a surface means you aren’t required to follow the contours of hills or valleys or bends in the road. There aren’t any structures like houses or trees to hide behind, branches to block your view, no walls to obscure you. This is why when we put something in the open ocean, like a buoy or a mooring, it collects organisms. Physical bodies naturally recognize another physical body in a surfaceless space, and the surface acts like a magnet attracting life.
- Many hyperiid amphipods colored both white and orange in a common Mediterranean jellyfish. The purple is the jelly’s reproductive system. From Sonke Johnsen.
In the vast unmarked space, large animals are themselves a surface, a landing pad, nursery, and even food source for creatures smaller in size. Like jungle trees whose leaves, twigs, and boughs are home for birds, insects, and monkeys and whose fruits and nuts serve as their sustenance, large animals in the open ocean house an array of biota, and jellies are among the most inhabited. Two hundred species of crustaceans called hyperiid amphipods live exclusively on pelagic jellies. Most of them have huge eyes, bodies like segmented beetles, and a mop of frizzy legs that peek out from below.
Hyperiids have evolved just the right structures to parasitize jellyfish. Their mouths are small, all the better for eating jelly. Their legs are broad for clinging to the bell. Baby hyperiids burrow deep within the tissue of jellies and extend a sipping tube right into their digestive canal, continually sucking out a shake of predigested nutrition. These juveniles can’t swim, so the jellyfish not only provides sustenance, but a free ride as well, one that offers protection from predation and sinking. The jellyfish’s sting? Hyperiids are immune to it. They even eat the jellies’ tentacles, where stinging cells are concentrated.
But jellies aren’t just nibbled at by the smallest of creatures, the largest pose a threat too. Jellies are the only food on the menu for some of the open ocean’s giants, especially sea turtles and sunfish.
Sunfish, or Mola Mola, are the biggest, boniest fish in the sea. They can grow as large as a pickup truck and, because of their stunted tail, look a lot like the head of a swimming sumo wrestler. A diver off from the coast of Malta in the Mediterranean caught outstanding footage of a massive sunfish. Like open ocean jellies, this ancient creature is an ecosystem in its own right, host to a wig of barnacles and a beard of reeffish.
Scientists hoping to catch a glimpse into the world of leatherback turtless, which grow to 300 pounds on a diet jellyfish alone, recently fastened cameras on the shells of these reptiles. Hours of footage confirmed the sea turtles’ predilection for jellies. What I find stunning about this clip is the way the turtle accelerates on the sea nettle, attacking it like a hawk on a hare. For a jellyfish, life in a three-dimensional ocean with no physical place to hide is truly a jungle, with attacks coming from inside as well as outside.