No abstract

There is considerable concern about conservation of biodiversity in highly disturbed and urbanized environments, although a very large proportion of biodiversity (i.e. the small and cryptic invertebrates) have been little studied in this regard. Many biogenic structures (e.g. coral reefs, mussel beds, foliose algae) provide habitat for a large number of small invertebrates. The features of these habitats to which these animals respond are complex and poorly documented. Invasive species are increasing in abundance and diversity in many disturbed estuaries, but most previous studies have concentrated on effects of invasive species on surrounding macroscopic assemblages. This study examines the assemblages of small invertebrates and algae living in natural patches of coralline turf and in patches of the invasive mussel, Mytilus galloprovincialis, on seawalls in Sydney Harbour. Although most taxa identified were common to both habitats, they were generally more abundant in turf than in the mussels, especially the more widespread and numerous taxa. Few taxa were unique to either habitat and those were generally sparse and patchy. In addition, there were relatively more smaller animals in the algal turf than in the mussels, although it is not known whether these were juveniles of adults present in both habitats, or different species. These data show that coralline turf and mussel beds do not provide similar intertidal habitat for associated assemblages and that overgrowth of natural biota by mussels may have strong indirect effects on associated assemblages. These warrant further experimental investigation, so that the effects of invasive species on local biodiversity can be better understood and managed.

No abstract

Artificial structures, such as seawalls, pilings and pontoons, are common features of urban estuaries. They replace natural structures or add to the amount of hard substratum in an area and provide habitats for many fish and invertebrates. Previous work has concentrated on fish or on the invertebrates that occupy the primary substratum of artificial structures. Mussels often grow on different types of structures (pontoons, pilings, seawalls and natural reefs) and provide a secondary substratum for other organisms to inhabit. Counting and identifying organisms associated with mussel beds is traditionally done to species level, which is very time-consuming. To save time, organisms in this study were identified to coarse levels of taxonomic resolution (a mix of taxa, such as class, order, family and genus), which showed similar patterns to those when particularly speciose and abundant groups were identified to species. This study tests hypotheses that the distribution and abundance of mobile and sessile organisms that inhabit mussel beds will differ among natural and various types of artificial structures. When the associated assemblages of mussel beds from different types of structures and from different locations were examined, assemblages varied according to the type of structure they inhabited and its location. Assemblages associated with mussels on pontoons differed consistently from those on other types of structures. Patterns in the assemblages were also consistent through time. These data show that the types and amounts of artificial structures added to an environment can affect the types, distribution and abundances of organisms living in biogenic habitats.