Survey of the macroalgae of Gwydir/Border Rivers Catchment, northern New South Wales

A project undertaken at the Royal Botanic Gardens Sydney and supervised by Tim Entwisle and Stephen Skinner

The western two-thirds of New South Wales has a drainage system dominated by the Murray-Darling Rivers system and the many tributaries that flow into the Darling. There are both riverine systems and semipermanent lacustrine systems, with a smaller number of artesian fed waterholes. For many years the phytoplankton of inland rivers and associated man-made reservoirs has been monitored, particularly by the former Department of Land and Water Conservation (now part of DIPNR). The macroalgae, mostly metaphyton (raft formers that often begin life on the bottom) and periphyton (attached to snags and aquatic vegetation) have been frequently overlooked in that monitoring. Attached and benthic species become established, compete for space and resources, multiply and reproduce, face senescence and reestablishment in a circumscribed area, unlike the more mobile plankton. The floristics of macroalgae in riverine systems provides the opportunity to establish a long term perspective on the fluctuations in the health of the river system.
Preliminary results.

We visited 84 sites throughout the catchment and collected 166 samples within which we found plenty of different algae, and a number of Charophytes. While cyanobacteria were frequently encountered, and there were samples where the filamentous diatoms Melosira varians and a Synedra species were numerous, the greatest variety was encountered among the Chlorophyta. The water net Hydrodictyon reticulatum and an inland species of Baitweed, Enteromorpha sp., were both collected once, while members of the orders Cladophorales, Chaetophorales, Oedogoniales and particularly Zygnematales were found throughout. Many of these records extend the range of species in New South Wales, and Australia. A number appear to be new to science.

Some notable finds:

  • Basicladia ramulosa Ducker is the Australian representative that gives ‘moss-back’ turtles their moss. We came across a moss-back snake necked turtle near Copeton Dam (Fig. 3).
  • Quite a number of the Zygnematales, Spirogyra and its relatives, were fertile, and this should help us to map the local distribution of species. Among the taxa found were several new records for Australia, and at least one new species, a Zygnemopsis. Zygnemopsis species are similar to Zygnema species and have two star-like chloroplasts in each cell of their filaments but have the gametangial cells filled with laminated pectin after the zygospore matures. This Zygnemopsis has a box-like zygospore with cups at the corners and thrives in the Dumaresq River (Fig. 4).
  • Sirogonium sticticum (Eng. Bot.) Kütz., a close relative of Spirogyra, was collected in two of the water bodies in the inland delta: it has previously been reported in Australia from coastal areas and the Great Dividing Range in Australia.
  • As in other parts of the world, the riverine floras were notable for the number and variety of the Zygnematales, and the presence of Cladophora species (Fig. 5) and Stigeoclonium species, while the associated, usually still water, habitats were notable for the range of species of Oedogonium and Bulbochaete. As determinations proceed, we hope to be able to produce a reliable species list for the Catchment, which will be useful to compare with other catchment areas on the western fall of the Great Dividing Range as these catchments are surveyed.
Captions to Figures

Figure 1. Thorndale Bridge, a typical waterhole in the inland delta, with Spirogyra rafts and balls of Nostoc.

Figure 2. The Severn River at Wells Crossing.

Figure3. Moss-back snake neck tortoise covered in Basicladia ramulosa.

Figure 4. Azolla pinnata with yellow rafts of Zygnemopsis sp. nov., Dumaresq River at Mingoola.

Figure 5. Nostoc pruniforme on the rock and Cladophora glomerata streamers, Moredun Creek.

 
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