Waterbirds species - native

Impact of Camphor laurel by Ms Judy Davies (honours thesis summary)

The article "Invasive and toxic camphor laurel: a potential threat to native Australian Birds" concentrates on terrestrial birds. However, it is likely that the known effect of C.camphora on macroinvertebrates will also affect the water bird populations that form part of the aquatic food chain. The breakdown of leaf litter is a source of energy in the river system and this is achieved by different functional feeding groups of invertebrates each of which have a different role and are found in different stages in the river between the source and the mouth (Vannote et al., 1980). In the upper reaches of a river, the main source of leaf litter is from the riparian zone where it accumulates amongst retention structures such as woody debris, roots or small boulders in the stream bed. Bacterial (Boulton and Brock, 1999) and fungal (Canhoto and Graca, 1999) microbes colonise the litter, producing enzymes to break down the cellulose in the cell walls. This enables the initial break down of the leaf by a group of invertebrates known as shredders who dominate these low order streams (Prochazka et al., 1991). The shredders convert large organic substrates to smaller particles that become a food source for another functional feeding group - the collectors (Cummins et al., 1989). This process provides the trophic link between the upper reaches and the lower sectors of a river (Graca et al., 2001), the feeding and breeding grounds for many water birds.

Fungal colonisation can be deterred by the presence of terpenes (Canhoto and Graca, 1999). Shredders have selective feeding habits in that they prefer leaves that are not tough, have a high nutrient content and do not contain compounds that act as a chemical defence against predation (Graca, et al.,2001). If the riparian zone is dominated by C. camphora, the main source of litter in the stream will be the leaves from that species, which are relatively tough and contain certain terpenes such as camphor and a - pinene. Camphor is used as a basic ingredient for insect repellent and a -pinene for insecticide (Brown, 1997). Shredders do not necessarily prefer native tree species to exotic tree species; the over-riding factor being the intrinsic properties of the leaf (Graca et al., 2001). Therefore, in these streams the supply of suitable food for shredders will either be lacking or be limited to species of litter being transported from upstream. Suitable food is essential for the survivorship of any animal and it has been found that in the streams where there is an infestation of C. camphora in the riparian zone, the abundance of shredders is low (Davies, 2004). In these streams the decomposition rate is compromised because of the low abundance of the shredding functional feeding group. There are also low dissolved oxygen levels due to the rotting vegetation, which has not been broken down into smaller particles.

The low abundance of the shredding functional feeding group and the low dissolved oxygen levels can result in an overall decrease in the health of an upland stream and this will have an effect on the habitats in the lower reaches of that river system where the larger invertebrates and vertebrates, such as water birds, are found.

References
Boulton, A. J. and Brock, M. (1999). Australian Freshwater Ecology Processes and Management. Gleneagles Publishing, Glen Osmond, South Australia.
Brown, W. H. (1997) An introduction to Organic Chemistry. Saunders College Publishing. Sydney Canhoto, C., and Graca, M. (1999). Leaf barriers to fungal colonisation and shredders (Tipula lateralis) consumption of decomposing Eucalpytus globulus. Microbial Ecology 37 163 - 177
Cummins, K. W., Wilzbach, M. A., Gates, D. M., Perry, J. B. and Taliaferro, W. B. (1989) Shredders and riparian vegetation. Leaf litter that falls into streams influences communities of stream invertebrates. Bioscience 39 (1) 24-31
Davies, J.N. (2004. Is Cinnamomum camphora (camphor laurel) detrimental to the macroinvertebrates in the rivers of northern New South Wales? Honours Thesis, Ecosystem Management Department, University of New England
Graca, M.A.S., Cressa, C., Gessner, M.O., Feio, M. J., Callies, K. A. and Barrios, C. (2001). Food quality, Feeding preferences. Survival and growth of shredders from temperate and tropical streams Freshwater Biology 46 (7) , 947-958
Prochazka, K., Stewart, B.A., and Davies, B.R., (1991. Leaf litter retention and its implications for shredder distribution in two headwater streams. Archive Hydrobiologia 120 (30) 315-68
Vannote, R.L, Minshall, G.W., Cummins W.K., Sedell, J.R., and Gushing C.E. (1980). The river continuum concept. The Canadian Journal of Fisheries and Aquatic Sciences 37 130-137

Email: Joe Friend