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The bimodal wave climate of the semi-protected shallow Gulf St Vincent in South Australia has been analyzed through a forty-year (1980-2020) wave hindcast and an investigation into the climatic drivers of wave climate anomalies is presented. The sea and swell partitions of the wave climate were modelled independently as well as using an integrated model with both partitions represented. The wave hindcast was validated against two wave buoys located off the coast of Adelaide’s metropolitan beaches and key wave parameter anomalies were calculated across the gulf. Teleconnections were investigated, and the Southern Annular Mode is found to have the strongest correlations to wave parameter anomalies while the Southern Oscillation Index and the Dipole Mode Index fluctuations are found to correlate seasonally with wave parameter anomalies. Projected future trends of these climate drivers from literature have been related to the teleconnections found in this study to inform future trends of bimodal wave conditions in the gulf. The Southern Annular Mode is projected to trend positive which will reduce wave height and the westerly component of waves in the gulf, while the Southern Oscillation Index is projected to become more variable in the future which will lead to more extreme winter and spring wave conditions. An understanding of these trends allows coastal managers to pre-emptively manage the impacts of waves on the coastline at a seasonal to annual basis and provides insight into future wave conditions beyond these time periods.

The previously reported rapid spread of mangroves at Port Gawler on the northeastern shore of Gulf St Vincent, South Australia has continued. This is a tidal-dominated coastline where reduced incoming tidal currents have led to increased sedimentation on the tidal flat and the development of an area of samphire and mangroves that have split the tidal flat in two. We predict that the remaining sections of the tidal flat will eventually become a mature mangrove forest, although human activity may delay this process. [ABSTRACT FROM AUTHOR]

Plastic pollution is fast becoming one of the most prominent contamination issues facing the marine environment. Microplastics are a major subset of plastic waste now present in all global oceans, with their numbers standing only to increase. This study applies a coupled hydrodynamic model and Lagrangian particle-tracking model to predict and simulate microplastic transport in South Australian waters. Virtual particles representing microplastics were released daily for 365 days from two major freshwater input sources along the coastline of Adelaide, Australia. These particles entered the Gulf St Vincent and were tracked over two model years using LTRANS software. The model identified general gulf circulation as circular, clockwise, with net southward particle transport from particle release sites. A potential accumulation zone associated with a local eddy was identified. Concentrations of particles that passed through local marine parks were also calculated in response to the potential concerns they pose in vulnerable protected areas. • A dual hydrodynamic model and particle-tracking model approach was implemented. • Microplastic trajectories originating from coastal freshwater input sources were modelled. • Microplastic density maps identified a potential accumulation zone in the Gulf St Vincent. • Particles entering marine park boundaries in the Gulf St Vincent were determined. [ABSTRACT FROM AUTHOR]

Little is known about the ecology and behavior of southern Australian bottlenose dolphins ( Tursiops sp.). This hinders assessment of their conservation status and informed decision-making concerning their management. We used boat-based surveys and photo-identification data to investigate site fidelity, residency patterns, and the abundance of southern Australian bottlenose dolphins in Adelaide's coastal waters. Sighting rates and site fidelity varied amongst individuals, and agglomerative hierarchical cluster analysis led to the categorization of individuals into one of three groups: occasional visitors, seasonal residents, or year-round residents. Lagged identification rates indicated that these dolphins used the study area regularly from year to year following a model of emigration and reimmigration. Abundance estimates obtained from multisample closed capture-recapture models ranged from 95 individuals ( SE ± 45.20) in winter 2013 to 239 ( SE ± 54.91) in summer 2014. The varying levels of site fidelity and residency, and the relatively high number of dolphins found throughout the study area highlights the Adelaide metropolitan coast as an important habitat for bottlenose dolphins. As these dolphins also appear to spend considerable time outside the study area, future research, conservation, and management efforts on this population must take into account anthropogenic activities within Adelaide's coastal waters and their adjacencies. [ABSTRACT FROM AUTHOR]

Urbanised coastlines are affected by cumulative impacts from a variety of anthropogenic stressors, but spatial information on the distribution of these stressors at the local scale is scarce, hindering the ability of managers to prioritise mitigation options. This work investigated the spatial footprint of land-based nitrogen discharges to a metropolitan coastline and assessed the potential role of this stressor alone on seagrass dynamics at the scale of the ecosystem. The macroalga Caulocystis cephalornithos was used as a time-integrative sampler of nitrogen in the water column over 202 sites monitored across an area of ∼800 km 2 . The stable isotopic signature of nitrogen in tissues (δ 15 N) was used to map plumes of anthropogenic origin. The surface area of these plumes was found to be proportional to nitrogen loads from land. The largest plume was associated with discharges from an industrialised estuary and a wastewater treatment plant, where a monthly nitrogen load in excess of 110 tonnes affected an area >80 km 2 . The location and size of the plumes changed with seasons as a result of wind forcing and rainfall/wastewater reuse. The location of the plumes was compared to published seagrass distribution obtained from video transects. Dense seagrass meadows only occurred in areas unimpacted by plumes throughout the year, mostly in shallow (<5 m) regions for Amphibolis antarctica , and deeper (5–10 m) for Posidonia sp., possibly as a result of this species higher tolerance of low light conditions. This higher tolerance might also explain why Posidonia sp. is observed to preferentially recolonise areas of previous loss in the region. While a decrease in the spatial footprint of nutrient plumes has created conditions for natural seagrass recolonisation in some areas, it did not halt seagrass loss in others, suggesting the influence of additional stressors such as wave dynamics and light attenuation due to turbid/coloured stormwater. [ABSTRACT FROM AUTHOR]

The northeastern shore of Gulf St Vincent, South Australia is a mesotidal, low-wave-energy coastline, characterised by tidal-dominated bioclastic carbonate sedimentation. Distinctive assemblages of subtidal, intertidal and supratidal marine plants and invertebrate animals have resulted in well defined, adjacent bio- and litho-facies that lie parallel to each other across broad areas of coastal sedimentation. At Port Gawler, the intertidal zone is bounded by a landward high-tide beach and a subtidal Posidonia australis seagrass meadow seaward. Thirty years ago, within the immediate study area, this intertidal zone comprised an inner sandflat and an outer muddy seagrass meadow dominated by Zostera muelleri, the two areas separated by a shallow tidal distributary. Avicennia marina is a species of mangrove that has colonised much of the protected, tidal-dominated coasts of South Australia. Propagules of this tree readily take root in intertidal mud, with a natural ecological succession of Z. muelleri followed by A. marina. Over the time of observation, juvenile mangroves have progressively colonised a narrow zone along the landward side of the muddy seagrass meadow; they appear unable to colonise a sandy substrate. Juveniles advanced rapidly southward from mature woodland in the north towards equally mature woodland in the south. From the initial tap root, juvenile plants send out radial roots from which project, snorkel-like, an array of vertical pneumatophores. Redistributed algal, seagrass and other organic flotsam collect around these vertically protruding pneumatophores, promoting accumulation of organic sediment. Within the newly forming mangrove woodland, there has been pronounced sediment aggradation of >0.5 m, greatly altering the dynamics of tidal flow. Tidal flow is now largely constrained to a channel between the mature southern woodland and that formed most recently. Higher velocity flows through this channel have exhumed populations of infaunal bivalves, and floodtide and ebbtide deltas of coarse bioclastic sediments are a consequence. The aggraded sediment of the new woodland shelters the area landward. Consequently, more muddy sediments are now covering what was formerly bare sandflat, thus providing new areas for mangrove colonisation. Migration of mangroves towards the high-tide beach is inevitable and will be limited only by their need for regular flushing of accumulated salt from their roots by seawater at high tide. Thus, A. marina drives rapid geomorphic change in the tidal-dominated coasts of the South Australian gulfs. In similar coastal areas of southeast Asia, where intertidal muddy sediments predominate, this species appears to be an ideal candidate for reforestation projects. Juvenile plants should grow successfully and rapidly, so preparing coastal environments for the establishment of more ecologically diverse mangrove communities. [ABSTRACT FROM AUTHOR]

Abstract: The input of groundwater-borne nutrients to Adelaide''s (South Australia) coastal zone is not well known but could contribute to the ongoing decline of seagrass in the area. As a component of the Adelaide Coastal Waters Study (ACWS), the potential for using the radium quartet (223Ra, 224Ra, 226Ra and 228Ra) and 222Rn to evaluate submarine groundwater discharge (SGD) was evaluated. Potential isotopic signatures for SGD were assessed by sampling groundwater from three regional aquifers potentially contributing SGD to the ACWS area. In addition, intertidal groundwater was sampled at two sand beach sites. In general, the regional groundwaters were enriched in long-lived Ra isotopes (226Ra and 228Ra) and in 222Rn relative to intertidal groundwater. Radium activity (but not 222Rn activity) was positively correlated to salinity in groundwater from one of the regional aquifers and in intertidal groundwater. Radium isotope ratios (223Ra/226Ra, 224Ra/226Ra and 228Ra/226Ra) were less variable than individual Ra isotope activities within potential SGD sources. Recirculated seawater (estimated from the intertidal groundwater samples with seawater-like salinities) also had distinctly higher Ra isotope ratios than the regional groundwaters. The activities for all radioisotopes were relatively low in seawater. The activity of the short-lived 223Ra and 224Ra were highest at the shoreline and declined exponentially with distance offshore. In contrast, 228Ra and 226Ra activities had a weak linear declining trend with distance offshore. Rn-222 activity was at or near background in all seawater samples. The pattern of enrichment in short-lived Ra isotopes and the lack of 222Rn in seawater suggest that seawater recirculation is the main contributor to SGD in the ACWS area. Preliminary modeling of the offshore flux of 228Ra and 226Ra suggest that the SGD flux to the ACWS area ranges between 0.2 and 3·10−3 m3 (m of shoreline)−1 s−1. [Copyright &y& Elsevier]

Gulf St Vincent is one of a pair of elongate, triangular, shallow water embayments into the southern coast of continental Australia. From the southern floor of this embayment, within a shallow basin-like depression where present-day water depth is about 40 m, vibracore SV23 recovered c. 4 m of late Quaternary sediments. The uppermost 1.5 m of this core comprises postglacial (Holocene) marine deposits; six radiocarbon ages for the interval 64–130 cm downcore are all around 10 000 cal. yr BP, while two for 18–24 cm are several thousand years younger. Radiocarbon analysis of an oyster shell at 154 cm yielded a minimum age of c. 37 000 cal. yr BP. Well-preserved benthic foraminifera are abundant in all the recovered sediments. The early phase of Holocene marine sedimentation in Gulf St Vincent was marked by the development of a marginal marine, perhaps lacustrine to estuarine environment, as signified by the presence of oogonia, gypsum crystals and the foraminifera Miliolinella labiosa and Elphidium cf. articulatum. Development of seagrass meadows followed; these were inhabited by Nubecularia lucifuga and Discorbis dimidiatus. As the marine transgression proceeded, the environment remained somewhat restricted, as indicated by Ammonia beccarii, but numbers of this species declined giving way to Massilina milletti as conditions began to resemble those of the modern Gulf St Vincent. Culmination of the transgression provided the conditions necessary for the dominance of Ammobaculites reophaciformis and Flintina triquetra. A. reophaciformis and F. triquetra therefore record the final episode of the transgression and transition to the modern, deeper water environment. At several lower horizons they also occur as conspicuous spikes, equivalent to their modern abundance. These spikes, which coincide with equivalent decreased numbers of A. beccarii, are interpreted to represent downward bioturbation of the overlying deeper water sediment. [ABSTRACT FROM AUTHOR]

In Gulf St Vincent, Australia, the salinity of the head waters can exceed 42 in summer when evaporation is maximum and the rainfall is minimal. A depth-integrated implicit finite difference model is extended to simulate the summer–autumn evolution of salinity, temperature, and density distributions, with climatological evaporation, rainfall, air temperature, and wind stress as inputs. Advection of salt and heat by the density- and wind-driven circulation is modelled by the Quick scheme, whereas horizontal mixing by tidal circulation is parameterised by a dispersion coefficient related to the oscillatory vertical shear. Simulated distributions and seasonal variations compare well with available observations, which feature the flow of highly saline water along the eastern side of the gulf, while the western side is bathed by less saline shelf water. Model results show that, despite the increasing salinity gradients in summer, opposing temperature gradients can stifle the shelfward density currents in the southern parts of the region. Autumn cooling intensifies these density currents so that at the end of the season the flushing of highly saline water, accumulated in the gulf throughout the summer, is enhanced. It was found that the variability in the general circulation brought about by the directional variability in the prevailing winds is an important factor in maintaining the observed salinity distributions in the region. [Copyright &y& Elsevier]