Matthew A. McArthur

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.

Developing physical surrogates for benthic biodiversity using co-located samples and regression tree models: a conceptual synthesis for a sandy temperate embayment

Marine physical and geochemical data can be valuable surrogates for predicting the distributions and assemblages of marine species. This study investigated the bio-environment (surrogacy) relationships in Jervis Bay, a sandy marine embayment in south-eastern Australia. A wide range of co-located physical data were analysed together with biological data, including multibeam bathymetry and backscatter surfaces and derivatives, parameters that describe seabed sediment and water column physical/geochemical characteristics and seabed exposure. Three decision tree models and a robust model selection process were applied. The models for three diversity indices and seven out of eight infaunal species explained 32–79% of the variance. A diverse range of physical surrogates for biodiversity were identified. The surrogates are presented in a conceptual model that identifies the mechanisms that potentially link to biodiversity patterns. While some surrogates may exert direct influence over organisms to exposure and chlorophyll-a, for example, most pointed to complex relationships between multiple biological and physical factors occurring in different process domains/zones. The reliable bio-environment relationships identified from co-located samples and conceptual models enabled a mechanistic understanding of benthic biodiversity patterns in a sandy coastal embayment that may have implications for marine environmental management.

Predictive mapping of soft-bottom benthic biodiversity using a surrogacy approach

A key requirement for informed marine-zone management is an understanding of the spatial patterns of marine biodiversity, often measured as species richness, total abundance or presence of key taxa. In the present study, we focussed on the diversity of benthic infauna and applied a predictive modelling approach to map biodiversity patterns for three study sites on the tropical Carnarvon shelf of Western Australia. A random forest decision tree model was used to generate spatial predictions of two measures of infaunal diversity, namely, species richness and total abundance. Results explained between 20% and 37% of the variance of each measure. The modelling process also identified potential physical surrogates for species richness and abundance, with sediment physical properties ranked as most important across the study region. Specifically, coarse-grained heterogeneous sediments were associated with higher infaunal species richness and total abundance. Seabed topographic properties were also important at the local scale. The study demonstrated the value of a surrogacy approach to the prediction of biodiversity patterns, particularly when the number of biological samples was limited. Such an approach may facilitate an understanding of ecosystem processes in the region and contribute to integrated marine management.

Infaunal biodiversity patterns from Carnarvon Shelf (Ningaloo Reef), Western Australia

Infaunaareimportantinmanyecologicalprocessesbuthavebeenrarelyconsideredinbiodiversityassessments ofcoralreefsandsurroundingareas.Wesurveyedinfaunalassemblagesandassociatedenvironmentalfactors(depth,seabed reflectance, sediment characteristics) in three areas (Mandu, Point Cloates, Gnaraloo) along the Carnarvon Shelf, Western Australia. This region supports Ningaloo Reef, a relatively pristine coral reef protected by the Ningaloo Marine Park and a Commonwealthmarinereserve.MacrofaunaweresampledwithaSmith-McIntyregrabandsievedthrough500mm.A total of 423 species and 4036 individuals was recorded from 145 grabs, with infauna accounting for 67% of species and 78% of individuals. Rare species (#2 individuals per species) represented 42% of the total assemblage. Assemblages were significantly different among all three areas, with the most distinct recorded from the southern-most area (Gnaraloo). Althoughassemblagesvariedsignificantlywithdepthandsedimentcomposition(mudandgravel),theserelationshipswere weak. Results from the current study broadly quantify macrofaunal diversity in the region and identify potential spatial and environmental patterns which will help inform future marine management plans, including the provision of baseline information to assess the efficacy of protected areas in soft-sediment habitats adjacent to coral reefs.

Including biogeochemical factors and a temporal component in benthic habitat maps: influences on infaunal diversity in a temperate embayment

Mapping of benthic habitats seldom considers biogeochemical variables or changes across time. We aimed to: (i) develop winter and summer benthic habitat maps for a sandy embayment; and (ii) compare the effectiveness of various maps for differentiating infauna. Patch types (internally homogeneous areas of seafloor) were constructed using combinations of abiotic parameters and are presented in sediment-based, biogeochemistry-based and combined sediment–biogeochemistry-based habitat maps. August and February surveys were undertaken in Jervis Bay, NSW, Australia, to collect samples for physical (% mud, sorting, % carbonate), biogeochemical (chlorophyll a, sulfur, sediment metabolism, bioavailable elements) and infaunal analyses. Boosted decision tree and cokriging models generated spatially continuous data layers. Habitat maps were made from classified layers using geographic information system (GIS) overlays and were interpreted from a biophysical-process perspective. Biogeochemistry and % mud varied spatially and temporally, even in visually homogeneous sediments. Species turnover across patch types was important for diversity; the utility of habitat maps for differentiating biological communities varied across months. Diversity patterns were broadly related to reactive carbon and redox, which varied temporally. Inclusion of biogeochemical factors and time in habitat maps provides a better framework for differentiating species and interpreting biodiversity patterns than once-off studies based solely on sedimentology or video-analysis.