demosponges have been observed in breaches of the crater rim and presumably rely on incoming nutrient-rich water from the ocean, while crinoids, gorgonians, ophiuroids and sponges have been found on the western rift zone of vailulu'u. in non-hydrothermal areas, echinoderms, octocorals and sponges dominate the surfaces, and crabs, eels, octocorals and octopi have been observed in the summit areas. the eel populations have given that part of the volcano the nickname "eel city"; the eels subsist on food species transported by ocean currents, such as crustaceans.