National Geographic : 1994 Aug
in 1977. We donned our protec tive suits, loaded the truck with buckets, and drove out at dusk. Almost as soon as we began to search the waters, a shark glid ed into view among the pilings. We decided not to wade in to catch our quarry. Soon three large green turtles, each nearly three feet long, appeared, slowly swimming back and forth in the pools of light shining from the pier. Something about the way those turtles cruised through the water made me wonder if they might be looking for jellyfish. I didn't wonder long. From the darkness came a box jelly the size of a grapefruit, lan guidly pulsing toward the pier. We watched it dodge the dan gerous pilings. This once per plexing behavior now excited us, since Peggy and Martin had proved that Chironex can easily see objects the size of pilings. Then, as I prepared to lower my net, out from beneath the pier came the three turtles. The box jelly didn't have a chance. The fastest of the turtles chased it down and consumed it in two quick bites. The sight was startling. This creature that can kill in an instant was being casually dined on, tentacles and all, by an enemy obviously immune to its defenses. During the next hour two more box jellies appeared. The turtles finished each one off before we could even pick up our nets. How did the sea turtles do it? No one knows exactly. Perhaps there is some protection afford ed by the lining of their digestive system-which may also be what allows them to eat glass sponges with ease. Sea turtles have been found with as much as a pound of the sponges' sharp siliceous spicules in their diges tive systems. There may be another explanation, one that science has not yet found. But now it was time to pack our gear and go home. I lingered for a moment, hoping to catch a last glimpse of a box jelly and marveling at how much we had learned about Chironex since the days of feeding Charlie by hand 17 years earlier. Yet we had just discovered that this most venomous of creatures faces its own vulnerabilities. Once again, as it has so often, the unseen life beneath the dark sea had enlightened us in an unexpected way. O Cast-iron gut may help the hawksbill turtle snack with impunity. Still, the box jelly's stinging capsules are, says biologist Robert Hartwick, "perhaps the most com pact, complex, and effective weapons developed by any animal other than man."