Tara J. Anderson

Autonomous Underwater Vehicle (AUV) for mapping marine biodiversity in coastal and shelf waters: Implications for marine management

Autonomous Underwater Vehicles (AUVs) have only recently become available as a tool to investigate the biological and physical composition of the seabed utilizing a suite of image capture and high-resolution geophysical tools. In this study we trialled the application of an AUV, integrating AUV image capture with ship-based high resolution multibeam bathymetry, to map benthic habitats and biodiversity in coastal and offshore waters of SE Tasmania. The AUV successfully surveyed a plethora of marine habitats and organisms, including high-relief kelp-dominated rocky reefs to deep mid-shelf reef and sediments that are otherwise difficult to access. To determine the spatial extent of these habitats within a broader-scale context, the AUV surveys were integrated with larger scale multibeam mapping surveys. The data collected using the AUV significantly improved our understanding of the distribution of benthic habitats and marine organisms in this region, with direct application to the management and conservation of these environments. For example, preliminary results identified the distributional extent of an introduced invasive marine pest, the screw-shell Maoricolpeus roseus, which was recorded adjacent to rocky reefs but is now known to also extend in high abundance across the SE shelf. Integrating the AUV data with the largescale mapping data provided the opportunity to quantify the relationships between the biological and physical variables, and to use thise data to develop predictive models of biodiversity across the region. The effectiveness of the AUV as a pioneering tool for undertaking spatially repeatable surveys makes it a highly versatile technique for future use in surveying remote environments, particularly with respect to surveying and monitoring biodiversity in newly established Commonwealth MPAs. It also has application in the context of climate change, the study of invasive species, impacts of fishing activities and determining the relative uniqueness and/or representativeness of these marine environments.

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.

Submerged Reefs and Aeolian Dunes as Inherited Habitats, Point Cloates, Carnarvon Shelf, Western Australia

Publisher Summary The Carnarvon shelf is the northern sector of the Dirk Hartog Shelf that extends 280 km along the central western margin of Australia. Distinctive features of this subtropical carbonate shelf, also known as the Carnarvon Ramp, are the marked decrease in shelf width northwards, from 33 km at Cape Cuvier to 7 km at North West Cape, and an indistinct shelf edge. To landward, smaller ridges up to 1.5 km long and 16 m high are aligned to the north–northeast and are interpreted as relict aeolian dunes. Mounds are less than 5 m high and may also have a subaerial origin. In contrast, the surrounding seafloor is sandy, with relatively low densities of epibenthic organisms. The dune ridges are estimated to be Late Pleistocene in age and their preservation is attributed to cementation of calcareous sands to form aeolianite, prior to the postglacial marine transgression. On the outer shelf, sponges grow on isolated low-profile ridges at ∼85 and 105 m depth and are also interpreted as partially preserved relict shorelines. Geomorphic features were mapped in ArcGIS based on a bathymetric grid and a slope map at 3 m spatial resolution. Nonetheless, the observations presented here show that a strong control on the spatial distribution of key benthic habitats and communities is produced by the occurrence of relict reefs and coastal landforms. These features appear to create the substrate and local oceanographic conditions that link to the ecological processes that determine the distribution of benthic biota on the Carnarvon Shelf.

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.

Habitats and Benthos of a Deep-Sea Marginal Plateau, Lord Howe Rise, Australia

Publisher Summary Lord Howe Rise is a marginal plateau located in the Coral Sea and Tasman Sea, composed mainly of continental fragments that detached from the eastern margin of continental Australia during the late Jurassic and Cretaceous. Lord Howe Rise is an extensive feature of the South Pacific Ocean, spanning ∼2,800 km in latitude (19°S to 43°S) and 450–650 km wide. Geomorphic features in the survey area include ridges, valleys, plateaus, and basins. Smaller superimposed features include peaks, moats, holes, polygonal furrows, scarps, and aprons. The physical structure and biological composition of the seabed were characterized using towed video and sampling of epifaunal and infaunal organisms. These deep-sea environments are dominated by thick, depositional, soft sediments (sandy mud), with local outcrops of volcanic rock and mixed gravel–boulders. Ridge, valley, and plateau environments were moderately bioturbated, but few organisms were directly observed or collected. Volcanic peaks were bathymetrically complex hard-rock structures that supported sparse distributions of suspension feeders (e.g., cold-water corals and glass sponges) and associated epifauna (e.g., crinoids and brittle stars). Isolated outcrops along the sloping edge of one ridge also supported similar assemblages, some with high localized densities of coral-dominated assemblages.

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.