Jellyfish
Although most jellyfish live well off the ocean floor and form part of the plankton, a few species are closely associated with the bottom for much of their lives and can be considered benthic. The upside-down jellyfish in the genus "Cassiopea" typically lie on the bottom of shallow lagoons where they sometimes pulsate gently with their umbrella top facing down. The tiny creeping jellyfish "Staurocladia" and "Eleutheria" cannot swim, and "walk" around on seaweed fronds or rocky bottoms on their tentacles. Most hydromedusae and scyphomedusae that live in coastal habitats find themselves on the bottom periodically, where they may stop swimming for a while, and certain box jellyfish species also rest on the sea bed in shallow water. Even some deep-sea species of hydromedusae and scyphomedusae are usually collected on or near the bottom. All of the stauromedusae are found attached to either seaweed or rocky or other firm material on the bottom.
Jellyfish
Jellyfish are eaten by humans in certain cultures, being considered a delicacy in some Asian countries, where species in the Rhizostomae order are pressed and salted to remove excess water. They are also used in research, where the green fluorescent protein, used by some species to cause bioluminescence, has been adapted as a fluorescent marker for genes inserted into other cells or organisms. The stinging cells used by jellyfish to subdue their prey can also injure humans. Many thousands of swimmers are stung every year, with effects ranging from mild discomfort to serious injury or even death; small box jellyfish are responsible for many of these deaths. When conditions are favourable, jellyfish can form vast swarms. These can be responsible for damage to fishing gear by filling fishing nets, and sometimes clog the cooling systems of power and desalination plants which draw their water from the sea.