Anchialine pools are brackish surface water bodies that have a subterranean connection to the sea. They are associated with carbonate substrates and lava flows on the coast and have a stronger terrestrial influence than other subterranean systems. Exposure to the surface enables algal primary producers to inhabit the water column and the benthos. Diversity and productivity of these aquatic ecosystems increases with age and connectivity to the sea. Some anchialine pools are highly insular, with molluscs and crustacean species found nowhere else.