Annual phytoplankton and nutrient fluctuations in the Hopkins Estuary, South-West Victoria, Australia

The Hopkins River drains grazing farmland for most of its length. Nutrients and phytoplankton populations in the Hopkins Estuary are strongly affected by the hydrodynamic cycle. The findings of this research show that nutrient and chlorophyll a levels in the Hopkins Estuary are high enough to indicate that future algal problems may occur and that management of nutrients entering its catchment and improvement of river banks are of high importance.

Iridoviruses of copepods: their identification, estuarine ecology and host histopathology

Zooplankton Invertebrate Iridescent viruses (ZoopIIVs: Iridoviridae) were discovered infecting copepods. Assays were developed for monitoring an infectious ZoopIIV; and the virus ultrastructure and host infection sites were described. The pioneering work has advanced research methods and our knowledge of infectious viruses in the zooplankton that provide critical ecosystem services globally

Invertebrate larval dynamics in seasonally closed estuaries

Estuarine benthic assemblages are often numerically dominated by polychaetes. The limits of these populations are determined by larval, and probably to a lesser extent adult movement. A previous study (Newton 1996), indicated that planktonic polychaete larvae were very abundant over the summer months in the Hopkins River; however, the identification and source of these larvae was not known. Defining the extent of a population, and therefore the likelihood of that population recovering following a perturbation, is crucial for effective estuarine management. This study investigated both the likely source of the larvae, (i.e. estuarine or marine) and the extent of larval dispersal within and between estuaries by addressing the following questions: Which taxa produced the planktonic larvae? Are these taxa resident estuarine species? Are the larvae of different taxa evenly distributed within the estuary or do physicochemical parameters or other factors influence their abundance? Are the same larvae found in other estuaries along the coast? and Is there exchange of these larval taxa with the marine environment and other estuaries? Larvae were identified and described by culturing commonly occurring planktonic larvae until adult characteristics appeared. The spionids, Carazziella victoriensis and Prionospio Tatura, numerically dominated the plankton in the Hopkins and the spionid, Orthoprionospio cirriformia was recorded from the Hopkins, Curdies and Gellibrand estuaries. Two spionids, Carazziella sp. and Polydora sp. were identified from tidal waters. Mouth status and physicochemical conditions (salinity, temperature and dissolved oxygen) were monitored in each estuary. Whereas the Merri and Gellibrand estuaries were predominantly stratified over the sampling period, the Curdies was more often well mixed and the Hopkins varied from well mixed to stratified. The duration of mouth opening and hence the opportunity for larval exchange also varied in each estuary. The Merri River was closed for 13.5% of days over the study period, the Gellibrand River for 18.4%, the Hopkins River for 49% and the Curdies River for 71.0%. The distributions of larvae at spatial scales of metres, 100s of metres and kilometres were investigated within a single estuary. While the same larvae, C. victoriensis, P. Tatura and bivalve larvae, were found along the length of the Hopkins estuary the abundances varied at different spatial scales suggesting different processes were influencing the distribution of P. Tatura larvae, and C. victoriensis and bivalve larvae. The distribution of larvae between several estuaries was investigated by monitoring meroplankton at two sites at the mouth of each of the four estuaries approximately monthly (except for winter months). Different meroplanktonic assemblages were found to distinguish each estuary. Further, C. victoriensis and P. Tatura larvae were only recorded in the Hopkins but larvae of the spionid, Orthoprionopio cirriformia were detected in the Hopkins, Curdies and Gellibrand estuaries. The extent of larval exchange with other estuaries and the marine environment was determined by monitoring tidal waters. Settlement trays were also deployed to determine if larvae were moving into estuaries and settling but not recruiting. P. tatura larvae were not detected in the tidal waters of any estuary and while C. victoriensis and O. cirriformia were found in both flood and ebb tides there was no evidence of movement of theses taxa to other estuaries. Larvae of the spionids, Carazziella sp. and Polydora sp., were found in tidal waters of each estuary but were rarely detected in the plankton within the estuaries. Neither species was found as an adult in background cores from any estuary, nor with the exception of a few individuals in the Merri, were they detected in settlement trays in any estuary. I conclude that the source of the larvae of C. victoriensis, P. Tatura and O. cirriformia is estuarine and while C. victoriensis, and O. cirriformia move in and outh of the source estuary in tidal waters there was no evidence for movement to other estuaries. The spionids, Carazziella sp. and Polydora sp were considered to be marine and while they moved in and out of estuaries in tidal waters they did not usually settle in the estuaries. The results of this study are a crucial first step in the development of ecological models to better understand dispersal in seasonally closed estuaries that are typical of southern Australia. This study emphasises the unique physicochemical characteristics and biological assemblages within these estuaries and the need for estuarine management to reflect these differences.

Freshwater influences on hydrology and seagrass dynamics of intermittent estuaries

Over a three-year period, impacts of changed flow regimes in small western-Victorian estuaries with Mediterranean climates were investigated. Ecosystems with artificially increased and reduced freshwater inflows were compared using a whole-system, process-based approach. Studies on such systms are rare despite their vulnerability and ecological importance.

Fish use of flooded margins of an intermittently open estuary

Fish communities in the shallow flooded margins of an intermittently open estuary were examined over an 18 month period. A distinct shift in the fish assemblage occurred when the mouth of the estuary closed and was associated with changes in the hydro-period, food availability and physico-chemical changes in the main channel.

Hydrodynamics, nutrients and algae of Fitzroy and Merri River estuaries

Various physical, biological and chemical attributes were investigated for the Fitzroy and Merri River estuaries. This research found algal communities were most influenced by high nitrogen concentrations at times of low flow. Mangement of nutrients within each catchment is therefore of high importance to reduce the possibility of future blooms.

Spatial and temporal variation of infauna in an Australian estuary

Macroinvertebrates living within the sediments of the Hopkins River estuary were examined during 1997. Differences in the abundance and composition of faunal assemblages were identified between vegetated and unvegetated habitats and between the lower, middle and upper sections of the estuary. The numbers of taxa and individuals present were found to be similar to that of other periodically opened estuaries.

Ecology of fish inhabiting the inter-tidal zone of Swan Bay, Victoria, Australia

Swan Bay is a shallow marine embayment of Port Phillip Bay, just north of Queenscliff, Victoria. It has been part of the Harold Holt Marine Reserves since 1977 and is a seagrass habitat. This study investigated the species of fish present in the inter-tidal zone of Swan Bay, collected information on their ecology, investigated the importance of Swan Bay compared to Port Phillip Bay as a nursery and/or breeding area and compared these results with those of similar seagrsss habitats. Field work was carried out monthly over a two year period, from April 1981 to April 1983, using beach seine nets at Swan Bay and Portarlington. Forty four species of fish were identified from Swan Bay and nineteen from Portarlington. Fish were most abundant during the summer and autumn months when seagrass growth was at a maximum and least abundant during winter due to the absence of seasonal residents and decreased numbers of permanent residents. Swan Bay was found to be an important nursery ground for two commercially-caught species: the Yellow-eye Mullet and the King George Whiting. Juvenile Yellow-eye Mullet were more numerous in Swan Bay than at Portarlington. Smell juvenile King George Whiting were more abundant at Portarlington than in Swan Bay where older juveniles were more numerous. The fish fauna of Swan Bay was found to be similar to western Port but the abundance of species varied. Atherinosome microstoma was the dominant species in terms of abundance and biomass. Diet was found to be different from that reported by Robertson (1979) at Western Port due to the different range of prey items.

Ecology of Powerful Owls (Ninox strenua) in contrasting habitats of the Yarra Valley Corridor, Victoria, Australia

In this research I investigated ecological attributes of Powerful Owls (Ninox strenua) in a continuum of habitats throughout the Yarra Valley corridor of Victoria, Australia. These habitats ranged from a highly urbanized parkland (the Yarra Valley Metropolitan Park) to a relatively undisturbed closed forest (Toolangi State Forest). Different aspects of the owls' ecology were investigated at six sites to determine whether their behaviour changed when they occupied habitats with different levels of urbanization and disturbance. The ecological attributes investigated were habitat utilization and habitat requirements (for both roosting and nesting), adult behaviour (through radio-tracking), juvenile behaviour and dispersal (through radio tracking), diet (through analysing regurgitated food pellets) and breeding success rates. A number of methods were used to capture adult Powerful Owls. These are described and their effectiveness discussed. The types of radio-transmitters and colour bands used for identification of owls are also described. The results showed that Powerful Owls are present and successfully breed in urban and suburban areas and that they can tolerate moderate levels of disturbance. However, Powerful Owls do require sites with high prey densities, roost trees and trees with suitable breeding hollows. In comparison with Powerful Owls living elsewhere in forests, the urban owls displayed higher tolerance levels to disturbance and were less selective in terms of habitat usage and diet. Home range sizes of urban Powerful Owls also appeared much smaller than those of the forest-dwelling Powerful Owls. This is probably due to the high prey densities in the urban areas. The ecology of the Powerful Owl is compared with that of two owl species from North America, the Northern Spotted Owl (Strix occidentalis caurind) and the Great Horned Owl (Bubo virginianus). In particular, I compared the similarities and differences in habitat requirements and breeding successes in different habitats for the three species. Overall, it would appear that urban areas can support Powerful Owls providing some old-growth trees are maintained to provide nest hollows. Implications for the long-term management of Powerful Owls in urban areas are also discussed.

Ecology and control of the southern saltmarsh mosquito, Ochlerotatus Camptorhynchus(Thomson), in Victoria

This study has revealed important ecological attributes of the southern saltmarsh mosquito in Victoria, resulting in an increased understanding of population peaks and their relation to Ross River virus disease and meteorological factors. Together with new information on its larval development, these results have further increased options for its control by local governments and public health authorities.

Coastal responses to estuarine discharge from intermittently open systems

This thesis is the first study to examine the interaction between estuarine discharge and coastal environments, for intermittent estuaries in Victoria. The study examined water quality, bacteria and seaweed communities and the diet of mussels, concluding that estuarine discharge is an important driver for the productivity of nearshore marine environments.

The ecology of the Apalachicola Bay system : an estuarine profile /

Mode of access: Internet.

The ecology of Tijuana Estuary, California : an estuarine profile /

Mode of access: Internet.