The Poor Knights lie close to the continental shelf and its upwelling of nutrient-rich waters. This lush food source flows close to the Islands and provides a continuous supply of food for filter feeders. Archways and vertical walls are thick with an astonishing array of encrusting life that support an incredible bio-mass of fish and other invertebrates. The shady recesses of archways and caves offer a haven to species usually only found at depth, and act as safe havens for juveniles. In the protected back recesses of Rikoriko Cave a sponge usually found only at 200 metres thrives just 10 metres below the surface.