48
mal fauna; filter-feeders proliferate in the surrounding area. In the back-arc basins
of the Western Pacific, hydrothermal fields can be colonised by large gastropods,
mytilids, Alvinellidae worms, coral (Fig. 2.11), with, on the periphery, cirripede
crustaceans (Fig. 2.12), sponges or brisingida asteroids. Even if the fauna of each
unit is unique, all these hydrothermal ecosystems function in the same way.
Fig. 2.11  Coral and cidarid
urchin on the periphery of
active hydrothermal systems
on the Mid-Atlantic Ridge
Fig. 2.12  Cirripedes on the
periphery of an active hydrothermal site in Lau Basin,
Pacific
J. Galéron