Biemna variantia

Biemna variantia is found in the Arctic Ocean and northern Atlantic Ocean, from the Gulf of Saint Lawrence and Greenland to the Barents Sea and the North Sea. It is also known from the English Channel and as far south as Portugal, the Canary Islands and the Alboran Sea, at the western end of the Mediterranean Sea. It grows on vertical rock faces where there is moderate water movement, under boulders and on stones, gravel and mud, at depths varying from the intertidal zone to 1,600 m (5,200 ft). This sponge tolerates brackish water and is not uncommon in estuaries.^[2]

Like other sponges, Biemna variantia draws in water through small pores, filters out organic particles less than 3μm in diameter, and expels the water through the oscula; its diet consists mostly of bacteria, unicellular algae, and organic debris. The sponge is a hermaphrodite and can reproduce both sexually and asexually. Male and female gametes are produced at different times, so self-fertilisation does not occur. After fertilisation, the embryos are brooded inside the sponge, and when they reach the last embryonic stage, they pass out through the oscula into the water column.^[2] They drift with the plankton, and after a few days, they settle on the seabed, attach themselves to the substrate and become juvenile sponges. Asexual reproduction is via budding, or by fragmentation, a process that occurs when pieces of sponge become detached.^[2]