The editors would like to thank the Peel Preservation Group for procuring the funding which enabled this study to occur. The groups enthusiasm about saltmarshes provided the spur to continue in difficult circumstances. This project was funded under the National Estate Grants Program, a Commonwealth-financed grants scheme administered by the Australian Heritage Commission (Federal Government) and the Heritage Council of Western Australia (State Government). This project also received funds from the Gordon Reid Foundation, City of Mandurah, ALCOA, Peel Inlet Management Authority, and Peel Development Commission. Department of Planning and Urban Development and the Department of Transport provided all the aerial photography used in the study.

A special thanks to the volunteer interpreters Richard Segal, Tim Leerey and Frederick Bouckaert without which the aerial photograph component of the study would not have been completed. Richard Segal also contributed extensively in the proof reading of the final report. Thanks also to Nicola Fletcher, Nick Long and Dieter Hodge who assisted in the initial transect establishment; Ross Warmsley, John Watts and Brad Smith for assisting in the fieldwork.

The cartography and secretarial staff within the Environmental Science were also very supportive of the study, in particular Mike Roeger. Mary Quayle provided all colour photography for this study.

Rosalind Murray and Matt Keally participated in the study as part of their Environmental Science Degree providing input into the design and implementation of their component of the study. Ron Glasson's experience and patience was tried on numerous occasions when compiling the aerial mosaics, but still he persevered with a smile. Tom Rose provided valuable support and management details, always stressing the need for the study.

Thanks to Eric Paling for advice on nutrient exchange; Jenny Davis for overseeing the invertebrate study; Alan Rossow for assistance in levelling all the vegetation transects; and the Marine and Freshwater Research Laboratory for analysing water and plant samples.

Thanks to Jason Byrne from the Peel Inlet Management Authority for helpful discussions on environmental planning matters.

Lastly thanks to David Everall for originally suggesting the study.

SUMMARY

The Peel-Harvey saltmarshes are important locally and regionally for some of the following reasons. Firstly, plant and animal material produced within the marsh is exported into the estuary. This material then supports food webs becoming food for fish and crustaceans, so forming a resource base for commercial production and recreational pleasure. Secondly, saltmarshes, like fresh water wetlands, act as 'biological filters’ which remove nutrients and pollutants, preventing these compounds from reaching the estuary waters. Thirdly, the saltmarshes are important areas for the rich array of birds that inhabit the estuary at various times of year. Finally, they provide physical stability to the shores of the Peel-Harvey estuary.

Saltmarshes within the Peel-Harvey estuary are declining both in quality and quantity. The greatest areal loss has occurred outside reserve areas. Reserve areas and those of special interest are showing evidence of decline in quality of samphire cover. Decline in the quality of samphire can further accelerate loss and degradation of vegetation and animal species. The loss of samphire from the Creery wetlands presents a urgent case for management consideration due to the proximity to urban development and development pressures in general and also because this area represents one of the largest remaining contiguous areas of samphire. This should not be interpreted that other areas are less deserving of management consideration but that Creery wetland represents unique opportunities for preservation and conservation and its current land tenure requires urgent management consideration. Its conservation and preservation should be considered a high priority.

Within the saltmarshes of the Peel-Harvey there was a distinct zonation of plant complexes, and trends in the distribution of saltmarsh communities along transects, thought to be related to tidal inundation. There was substantial variation within the results, some of which could be attributed to changing environmental factors as well as inter-species and inter-site differences. Several trends were evident. The biomass was found to be less in winter, while the nutrient concentration was greater and temporal variation was found to be higher in above- ground components of plants. Some differences in species composition and biomass were found to be different to that of previous studies of saltmarshes. This may be due to the different locations, sampling methods, or changed environmental conditions between studies.

The complexes found in the Peel-Harvey display a clear relationship with the percentage of annual tidal inundation received. The link between tidal inundation and communities was not so clear, although some trends were apparent. Other factors indirectly affected by the tide, such as gradient, sediment deposition, soil composition and nutrient availability, may have a greater contribution in determining community distribution. Other forms of inundation such as river flooding and infrequent extremely high tides would also affect the distribution of saltmarsh plants.

It is believed that not only are there likely to be changes in the extent of vegetation complexes with changing water regimes resulting from the Dawesville Channel, there is expected to be different changes affecting most species, and thus communities, within the saltmarsh.

The study of invertebrates of the saltmarshes of the Peel-Harvey revealed a broad range of animals which were related to the location and time of sampling, especially sites 4 (Soldiers Cove), 6 (Murray River delta) and 10 (Harvey River delta) contained substantial richness and abundances.

The impact of the Dawesville Channel upon the saltmarshes and invertebrate assemblages of the Peel-Harvey Estuary is difficult to predict and remains to be determined. It is believed that not only are there likely to be changes in the extent of vegetation complexes with changing water regimes resulting from the Dawesville Channel, there are expected to be different changes affecting most species, and thus communities, within the saltmarsh. No real impacts upon the invertebrate assemblages can be gauged from this study due to the limited timespan over which sampling was undertaken and the lack of previous studies. However, some potential impacts upon the invertebrate distributions and assemblages from the Dawesville Channel are likely due to the altered tidal levels of the Estuary. The implications of this are that tidal ranges will be more variable and more frequent which may alter saltmarsh distributions and hence alter invertebrate distributions. The effects of the tidal patterns is predicted to be greater in the Harvey Estuary where higher invertebrate richness and abundance was recorded.

Other implications include greater ocean/estuarine mixing which will maintain the salinity levels in the estuary more similar to the marine environment for most of the year. This may alter the range of some invertebrate species, especially those who require a fresher aquatic environment. The greater interaction of marine species with estuarine species may also have a significant effect on the food chain, as marine species may out compete estuarine species for food or disrupt ecological niches.

Saltmarshes have been identified as critical to the wellbeing of the estuarine ecosystem in a number of ways. Their most important attributes are that they provide a physical linkage between land and sea, they are a location for a pool of salt tolerant plants and animals thus maintaining biological and habitat diversity and they are critical to ecosystem processes such as productivity and nutrient and organic carbon fluxes. The results of such processes are that they stimulate the fish, birds, aquatic plants and other biota of the whole estuary.

The future role that saltmarshes will play in the Peel-Harvey estuarine system cannot be readily quantified. It will undoubtedly be just as, if not more influential if the eutrophic status of the estuary is reduced, longer term tidal exposure of the estuary's periphery occurs and further losses of significant portions of this habitat occur because of the impacts caused by urban development and human activity.

ABSTRACT

The Peel-Harvey saltmarshes are important locally and regionally, because they support extensive food web and act as a biological filter for the receiving waters. This study was undertaken to examine the ecology and extent of saltmarshes of the Peel-Harvey. The extent and composition of the samphire saltmarshes was investigated over the period of 37 years (from 1957 to 1994), using aerial photography over the whole estuary, and detailed field surveys at ten sites. Saltmarshes within the Peel-Harvey estuary are declining both in quality and quantity. The greatest areal loss has occurred outside reserve areas. The loss of samphire from the Creery wetlands presents an urgent case for management consideration due to the proximity to urban development and development pressures in general and also because this area represents one of the largest remaining contiguous areas of samphire.

The complexes found in the Peel-Harvey display a clear relationship with the percentage of annual tidal inundation received. It is believed that not only are there likely to be changes in the extent of vegetation complexes with changing water regimes resulting from the Dawesville Channel, there is expected to be different changes affecting most species, and thus communities, within the saltmarsh.

The study of invertebrates of the saltmarshes of the Peel-Harvey revealed a broad range of animals. The impact of the Dawesville Channel upon the saltmarshes and invertebrate assemblages of the Peel-Harvey Estuary is difficult to predict and remains to be determined.