Cave crustaceans

This is a group entry for the small crustaceans that live where the light stops. Maltese sea caves have a recognisable zonation: a bright entrance with algae and sponges, a dim middle section, and a dark inner zone where the water barely mixes, food is scarce, and the walls carry white or grey bacterial films that look like a thin coating of paint or mucus. It is in that inner zone that the specialists live.

The best-documented Maltese site is Għar Ħarq Ħamiem at St George's Bay in St Julian's, an anchialine cave with fresh water sitting over brackish water over near-seawater, two chambers, a sharp thermocline in the top few metres and a lower chamber running to around 50 m. It is a Site of Scientific Importance and an Area of Ecological Importance, and in 2024 the eyeless amphipod Neogammarus karamani was recorded there for the first time in the Maltese islands. Alongside amphipods, the fauna of such caves is dominated by copepods, ostracods, isopods and small mysid shrimps of the genus Hemimysis, which hang in reddish swarms under dark ceilings.

Be careful with the stories. Divers often talk about a local "albino shrimp", and pale, weakly pigmented shrimps of the ordinary reef genera do turn up in Maltese cave darkness, along with the golden coral shrimp Stenopus spinosus and prawns of the genus Palaemon in the twilight zone. But no blind endemic cave shrimp has been formally described from Malta, and what is confirmed in the literature is the eyeless amphipod, the copepods and the bacterial films, not a white shrimp.