Absence of a Large Brown Macroalga on Urbanized Rocky Reefs around Sydney, Australia, and Evidence for Historical Decline(1).

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 ∼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.