Restoring seaweeds: does the declining fucoid Phyllospora comosa support different biodiversity than other habitats?

Abstract

Degradation and loss of natural habitats due to human activities is a main cause of global biodiversity loss. In temperate systems, seaweeds are a main habitat former and support extremely diverse communities, including many economically important species. Coastal urbanisation is, however, causing significant declines of key habitat-forming seaweeds. To develop successful management strategies such as seaweed habitat restoration, it is necessary to first determine what additional ecosystem values are likely to be added through restoration and to provide baseline data against which goals can be established and success can be measured. The habitat-forming fucoid Phyllospora comosa was once common on shallow subtidal reefs around Sydney, Australia’s largest city, but disappeared in the 1980s, coincident with heavy sewage outfall discharges. To provide the baseline data necessary for restoring and managing Phyllospora in areas from where it has disappeared, we quantified the community composition and abundance of fish and large invertebrates (abalone and sea urchins) in healthy Phyllospora habitats and compared them to those in Ecklonia radiata (the other major habitat-forming kelp in the region) as well as other common shallow subtidal habitats. Fish assemblage structure was similar between Phyllospora vs Ecklonia beds, but Phyllospora supported much greater numbers of abalone and urchins than any other habitat. This suggests that, in terms of some components of the biodiversity it supports, Phyllospora is functionally unique and not a redundant species. Restoring this seaweed will, therefore, also contribute to biodiversity rehabilitation by restoring unique faunal assemblages that are supported by Phyllospora, including economically important species.