Constructing replacement habitat for specialist and generalist molluscs—the effect of patch size

Urban shorelines are threatened by ‘armouring’ from anthropological constructions that are replacing the natural intertidal habitat at an increasing rate. In places, intertidal boulder fields are listed as threatened habitats in urbanized areas. On sheltered shores, these habitats support diverse assemblages, including specialist species, many of which are rare that predominantly or only live under boulders. Activities associated with urbanization threaten these habitats and this specialist biota. Thus, there is a need to learn how to restore these habitats for these assemblages. Most studies of intertidal habitat replacement have focused on habitats dominated by large plants, e.g. mangroves, or by animals that create habitat, e.g. oyster reefs, although previous work has shown that invertebrates will colonize newly created patches of quarried boulders. Here, colonization of newly created patches, either of 50 (50B patches) or 100 (100B patches) quarried boulders replicated in 2 intertidal sites in New South Wales, Australia, is described. Rare specialist and common widespread animals readily colonized these patches, with most of the species randomly distributed between the patch sizes. Of those that did show differences between patch sizes, some species were more abundant on the 100B patches, whereas other related species showed the opposite pattern. After a few weeks, most of the species were as abundant in these patches as on natural boulders. There was no consistent tendency for abundances or diversity to be smaller on the artificial patches than on natural boulders. It is clearly cheap and easy to build an intertidal boulder habitat which is rapidly used by many different common and rare animals. This may assist with the conservation of these fauna living in urbanized environments, where much of their natural habitat has been lost.