Absence of a large brown macroalga on urbanized rocky reefs around Sydney, Australia, and evidence for historical decline

Loss of habitat- forming algae is increasingly prevalent in temperate marine ecosystems. Here, we document absence of an important habitat- forming macroalga, Phyllospora comosa ( Labill.) C. Agardh, along an urbanized coast in New South Wales ( NSW), Australia. Dense Phyllospora canopies were common on shallow sublittoral reefs north and south of Sydney. In contrast, we did not find a single individual along similar to 70 km of rocky coastline in the Sydney metropolitan region, despite historical evidence to suggest that it was very common half a century ago. Recolonization of this important habitat- forming alga has not occurred on Sydney reefs despite improved water quality, protection of its habitat, and frequent long- distance dispersal of Phyllospora wrack. While there are obvious limitations, historical information can be useful for identifying potential shifts in community structure to increase our understanding of contemporary ecological patterns.