Non-indigenous species

Potential impact of slugs and snails on native grasslands (2004)

K. Holland, M. McDonnell and N. Williams

Given that no native molluscs are known from open grasslands in Australia, exotic slugs and snails represent a potential threat to grassland plant communities that is commonly overlooked. In 2004, Kelly Holland completeed an Honours project, working with Mark McDonnell and Nick Williams, investigating the potential impact of invasive slugs and snails on native grasslands.

Molluscs were surveyed across a range of native grassland sites, including those surrounded by urban areas of Melbourne, and in agricultural districts of western Victoria. This revealed a range of exotic slugs and snails that have invaded native vegetation, with 5 slug species and 3 snail species observed. The most commonly encountered species was the brown field slug (Deroceras panormitanum). Some sites also supported high densities of the vineyard snail (Cernuella virgata). There was a clear difference between urban and rural sites, with significantly higher mollusc abundance in urban areas. This suggests that native grasslands may be more at risk from exotic molluscs as the landscape surrounding sites becomes increasingly urbanised. There was also a negative relationship between mollusc abundance and fire frequency. Site management, including appropriate fire regimes, may help to control mollusc populations.

The palatability of a range of native grassland plants was investigated for the black-keeled slug (Milax gagates) using laboratory feeding trials. The slugs consumed a wide variety of plants, and highly palatable species came from a range of plant families. Variable glycine (Glycine tabacina) was a particular favourite, meaning that slugs may preferentially graze legumes. Other highly palatable species included daisies, such as the endangered button wrinklewort (Rutidosis leptorrhynchoides), and some lilies e.g., small vanilla lily (Arthropodium minus).

It remains to be seen what impact exotic slugs and snails are having on native grassland communities. Despite this, they could be limiting plant recruitment, particularly of palatable native forbs. Molluscs are known for targeting young seedlings, and will also feed underground on roots and seeds that are just beginning to germinate. If you are concerned about slugs and snails look for evidence such as chewed leaves, silvery trails or empty shells. During the day molluscs can often be found sheltering under cover such as rocks or logs.

Spread of non-indigenous plants

B. Hamilton and M. McDonnell

As part of a research partnership program with Parks Victoria, students and staff at ARCUE examined the ecology of Spartina anglica in south-eastern Victoria. Spartina anglica is an introduced threatening weed that has the ability to spread rapidly choking estuaries and bays and causing sediment accretion, channelization and altered hydrology. An assessment of the threat that Spartina poses to the mudflats of the Bass River region of Western Port Bay was conducted by determining the identity of the species, its current distribution and potential distribution. Spartina anglica has spread approximately 3 km either side of the mouth of the Bass River. A transplantation experiment indicated that S. anglica is capable of surviving to distances of at least 500 m from the upper edge of the mudflats, out onto the open mudflats of Western Port Bay. These data were shared with Parks Victoria to facilitate the management and control of this weed species in Victoria.