David R. Currie

Epibenthic community structure in Port Phillip Bay, Victoria, Australia

Epibenthic community structure in Port Phillip Bay was examined from quantitative diver samples collected at 30 depth-stratified stations during 1998. Analysis of variance showed a strong trend of decreasing epibenthic abundance, biomass and species diversity with depth. Reductions in these three parameters were most pronounced over shallow inshore waters and could be attributed largely to decreases in the abundance of the heavy, mat-forming ascidian Pyura stolonifera with depth. Four epifaunal community groupings, closely reflecting differences in sediment and habitat type within the bay, were identified from ordinations of species abundance and biomass data. The four epifaunal groupings also closely matched distributional patterns observed in other studies in both demersal fish and infaunal communities. Epifaunal communities in the bay were dominated by filter-feeding organisms which accounted for nearly 95% of the total species abundance and 98% of the total species biomass. Seven of the 63 epibenthic organisms collected during the survey are exotic introductions to the bay (Sabella spallanzanii, Ascidiella aspersa, Styela clava, Styela plicata, Ciona intestinalis, Pyromaia tuberculata and Asterias amurensis). As many of these species are widespread and abundant (35% of all individuals), their effects on the ecology of Port Phillip Bay are likely to be significant.

Infaunal macroinvertebrate assemblages of the eastern Great Australian Bight: effectiveness of a marine protected area in representing the region’s benthic biodiversity

Marine reserves are used widely throughout the world to conserve biodiversity, but in many instances uncertainties exist over how well these areas represent biodiversity at a regional scale (i.e. 100–1000 km). In the present study, infaunal assemblages were examined in the eastern Great Australian Bight (GAB) to evaluate the efficacy of the Benthic Protection Zone of the GAB Marine Park in representing regional biodiversity. Distributional patterns in infauna were further examined in relation to epifaunal species composition and environmental conditions to investigate structural forcing. Grab samples of infauna were collected from the same 65 sites sampled in an earlier survey of epifauna. In total, 240 taxa belonging to 11 phyla were collected. Most taxa were uncommon, with 96% representing less than 2% of the total number of individuals collected and 39% occurring at only one site. Unlike the epifauna, the infauna of the eastern GAB does not appear to be particularly diverse. Sessile filter feeders dominated the infaunal communities of the inner shelf, whereas motile, deposit-feeding organisms dominated the shelf break. As was the case with the epifauna, the highest numbers of taxa and individuals were recorded near the head of the bight and in inner-shelf waters off the western Eyre Peninsula, where productivity is enhanced by upwelling. Cluster analysis identified three community groupings, which were strongly correlated with depth. All three communities and 72% (172) of the 240 taxa collected were represented within the Benthic Protection Zone of the GAB Marine Park, confirming findings from the epifaunal survey that this protected area is well placed to represent the benthic biodiversity of the eastern GAB.

Demosponge Biodiversity in the Benthic Protection Zone of the Great Australian Bight

Summary The Benthic Protection Zone (BPZ) situated in the South Australian section of the Great Australian Bight (GAB) protects marine benthos from anthropogenic disturbances of the sea floor. However, little is known of the marine benthic fauna occurring within the zone. In a baseline study during 2001/02, epibenthic sled sampling of sites inside the BPZ, and in other parts of the eastern GAB, yielded 351 species of sponge. Of these, 109 demosponge species from 32 families and 61 genera were found in the BPZ. Sponge community composition changes across the shelf, with the highest diversity of sponges occurring in shallow inshore waters, declining with increased depth and distance offshore. The sponge fauna is dominated by species occurring in temperate Australia, with little affinity to fauna in tropical Australia.

Biophysical Factors Affecting the Distribution of Demersal Fish around the Head of a Submarine Canyon Off the Bonney Coast, South Australia

We sampled the demersal fish community of the Bonney Canyon, South Australia at depths (100–1,500 m) and locations that are poorly known. Seventy-eight species of demersal fish were obtained from 12 depth-stratified trawls along, and to either side, of the central canyon axis. Distributional patterns in species richness and biomass were highly correlated. Three fish assemblage groupings, characterised by small suites of species with narrow depth distributions, were identified on the shelf, upper slope and mid slope. The assemblage groupings were largely explained by depth (ρw = 0.78). Compared to the depth gradient, canyon-related effects are weak or occur at spatial or temporal scales not sampled in this study. A conceptual physical model displayed features consistent with the depth zonational patterns in fish, and also indicated that canyon upwelling can occur. The depth zonation of the fish assemblage was associated with the depth distribution of water masses in the area. Notably, the mid-slope community (1,000 m) coincided with a layer of Antarctic Intermediate Water, the upper slope community (500 m) resided within the core of the Flinders Current, and the shelf community was located in a well-mixed layer of surface water (<450 m depth).

Evaluating the effects of reserve closure on algae, invertebrate and fish assemblages at a temperate South Australian marine reserve

Differences in the reef biota between the Point Labatt Marine Reserve and adjacent unprotected reference areas were examined following an 18-year period of protection from fishing. Quantitative measures of fish, invertebrates and algae were obtained by divers at 1 6 depth-stratified locations inside and outside the reserve, and the significance of differences examined using a combination of univariate (ANOVA) and multivariate (MDS) analyses. Strong depth-related differences in the composition and abundance of algae and invertebrates were observed, both inside and outside the reserve. These community differences were most pronounced in shallow near-shore waters (<10 m depth), and were largely due to variations in the abundance of a small group of species with widespread distributions. Spatial patterns in fish were not closely related to depth, and it appears that trophic linkages between fish and the underlying algal and invertebrate assemblages at Point Labatt are either weak or occur at spatial scales larger than that covered in this study. No significant reserve-related differences were detected in the abundance, diversity or community structures of algae, invertebrates and fish examined in this study. In many cases this is because the biological attributes measured were highly variable in space, and required more intensive sampling regimes to improve statistical precision. This study emphasizes the need for more robust survey designs and their timely implementation in marine conservation planning processes.

The Distribution and Trophodynamics of Demersal Fish from Spencer Gulf

Abstract This paper describes the composition, distribution and diets of demersal fishes collected from Spencer Gulf during a quantitative Gulf-wide trawl survey in February 2007. A total of 132 fish species from 65 families were collected from the 120 trawl shots. Degens leatherjacket, Thamnaconus degeni, was the most abundant species collected (627 ± 239 ha−1). This fish was also dominant in terms of biomass, and accounted for more than 40% of the total catch weight. Most other species (95%) had mean biomasses ranging from less than 1 to 515 g ha−1, and individually contributed less than 3% to the overall catch. Correlation analyses revealed a broad latitudinal gradient in fish abundance, biomass and richness. All three parameters generally increase towards the south of the Gulf, in association with increasing water depths and decreasing water temperatures. Multivariate cluster analyses confirmed the presence of a strong environmental gradient between the north and south of the Gulf, and highlight the presence of three distinct fish assemblages (north, central and south) that are closely allied with changes in depth. Small subsets of species with restricted distributions characterised each regional assemblage. Dietary examinations of the stomach contents of 871 fish representing 107 species were also undertaken during this study. Five feeding guilds were identified from cluster analysis of the stomach contents. These included groups of fish feeding primarily on echinoderms (2 spp), other fish (13 spp), molluscs (11 spp), crustaceans (52 spp) and worms (23 spp). Atrophic model was constructed to evaluate levels of food consumption for each fish, and to assess regional differences in the composition and total volume of prey eaten. Total food consumption was estimated to decrease progressively towards the top of the Gulf, with daily food consumption rates in the northern region (219.55 g ha−1 day−1) more than seven times lower than those in the south of the Gulf (1580.99 g ha−1 day−1). Crustaceans and annelids were the two most important prey items consumed by demersal fish in all three biomes of the Spencer Gulf (north, central, south), and comprised more than 30% and 18% of the total diet, respectively. Our model suggests that almost half a kilogram of crustaceans and worms are consumed daily per hectare in the south of the Gulf. All other prey groups (e.g. molluscs, bryozoans, echinoderms, sponges) are eaten in much smaller volumes, and are individually consumed at daily rates of less than 127 g ha−1 in each biome. Estimates of consumption were broadly consistent with other temperate Australian estuaries. However, as no seasonal replication of sampling was undertaken it remains unclear if observed spatial patterns and trends are temporally robust.

Macrofaunal Patterns in and around du Couedic and Bonney Submarine Canyons, South Australia

Two South Australian canyons, one shelf-incising (du Couedic) and one slope-limited (Bonney) were compared for macrofaunal patterns on the shelf and slope that spanned three water masses. It was hypothesized that community structure would (H1) significantly differ by water mass, (H2) show significant regional differences and (H3) differ significantly between interior and exterior of each canyon. Five hundred and thirty-one species of macrofauna ≥1 mm were captured at 27 stations situated in depth stratified transects inside and outside the canyons from 100 to1500 m depth. The macrofauna showed a positive relationship to depth in abundance, biomass, species richness and community composition while taxonomic distinctness and evenness remained high at all depths. Biotic variation on the shelf was best defined by variation in bottom water primary production while sediment characteristics and bottom water oxygen, temperature and nutrients defined biotic variation at greater depth. Community structure differed significantly (p<0.01) among the three water masses (shelf-flowing South Australian current, upper slope Flinders current and lower slope Antarctic Intermediate Water) (H1). Although community differences between the du Couedic and Bonney regions were marginally above significance at p = 0.05 (H2), over half of the species captured were unique to each region. This supports the evidence from fish and megafaunal distributions that the du Couedic and Bonney areas are in different bioregions. Overall, the canyon interiors were not significantly different in community composition from the exterior (H3). However, both canyons had higher abundance and/or biomass, increased species dominance, different species composition and coarser sediments near the canyon heads compared to outside the canyons at the same depth (500 m), suggestive of heightened currents within the canyons that influence community composition there. At 1000–1500 m, the canyon interiors were depauperate, typical of V-shaped canyons elsewhere. The large number of species captured, given the relatively low sampling effort and focus on the larger macrofauna, support previous studies that identify the South Australian coast as a high biodiversity area.