Its long planktonic larval period and short life cycle make able to colonise new areas and increase dramatically in number if food supplies are favourable.

[17] A 2020 molecular analysis by Bazzicalupo et al. found no consistent genetic differences between B. leachii subspecies, and recommended that this classification scheme be abandoned.

In their view, B. leachii is a morphologically variable species with a pantropical distribution and limited gene flow between Indo-Pacific and Atlantic populations.

[20] Rather than being carried in ballast water like many other species invading the Mediterranean, B. leachii probably arrived naturally as sea surface temperatures that would normally prevent it entering the Strait of Gibraltar have shifted north with climate change.

[21] The species is usually found in protected marine bays and estuaries, tidal pools, occurring in the intertidal zone and down to at least 10 m.[22] It is a benthic detritivore which grazes for food on muddy or sandy bottoms.

[23] This sea hare may be found in dense concentrations or singly; it follows a daily rhythm, assembling in groups at sunset and dispersing in the morning.