Friday Harbor Marine Laboratories, University of Washington
San Juan Island, Washington
Archival Pigment Print
While jellyfish are usually planktonic swimmers, this one is typically found on the bottom during the day. Negatively buoyant, it perches on its tentacles like a spider on its legs, feeding on tiny animals that crawl on the sand. At night, it pulses its bell to rise a few meters above the bottom, where it catches small organisms that themselves emerge from the sediment to feed. The jellyfish’s daily vertical migrations are probably instructed by the tiny eyespots trimming the bell margin—spots that don’t seem to form images but detect light. One study found that as light levels decreased, the animal pulsed its bell more quickly, which explains how it rises into the water column when the sun sets.