Aquatic invertebrates and waterbirds of wetlands and rivers of the southern Carnarvon Basin, Western Australia

Abstract

-Fifty-six sites, representing 53 wetlands, were surveyed in the southern Carnarvon Basin in 1994 and 1995 with the aim of documenting the waterbird and aquatic invertebrate fauna of the region. Most sites were surveyed in both winter and summer, although some contained water only one occasion. Altogether 57 waterbird species were recorded, with 29 292 waterbirds of 25 species on Lake MacLeod in October 1994. River pools were shown to be relatively important for waterbirds, while many freshwater claypans were little used.At least 492 species of aquatic invertebrate were collected. The invertebrate fauna was characterized by the low frequency with which taxa occurred: a third of the species were collected at a single site on only one occasion. Patterns of occurrence were not strongly seasonal. Many undescribed species were found and many range extensions were. recorded, reflecting lack of previous aquatic invertebrate work in the region. The level of regional endemicity could not be assessed adequately, although it is probably comparatively low. In terms of their invertebrate fauna, five types of wetlands were distinguished: river pools, rock pools and larger flowing streams; seeps, springs and smaller creeks; freshwater claypans; birridas; and Lake MacLeod. Environmental factors to which invertebrates appeared to respond were ratio of calcium/ alkalinity, total dissolved solids, turbidity, colour, flow, longitude and nutrients, although some factors were inter-correlated.Additional surveys should find extra species of waterbird and, more particularly, aquatic invertebrate using wetlands of the southern Carnarvon Basin. For many invertebrates, occurrences are too sparse for effective protection of species within a nature reserve system and other mechanisms will be required to ensure their conservation. Comparison of site classifications based on waterbird, aquatic invertebrate and plant data showed patterns among sites identified using one element of the biota did not reflect patterns shown by other elements. This suggests that, until further work has identified an element that reflects the whole wetland community, as many biotic elements as possible should be surveyed.

Some gaps in the reserve system of the southern Carnarvon Basin, Western Australia

“…Drier 'crabhole' swamps, saline pans east of Shark Bay and some large swamps on Mardathuna Station are examples of physiognomically distinctive wetlands that were poorly sampled or not sampled at all (Halse et al, 2000). Thus, wetland reserve selection was adversely affected by lack of rainfall in parts of the study area.…”

“…Singleton taxa were removed from the data-set for each biotic element, but sites with only one species were retained. The sites were classified into seven groups in terms of their aquatic invertebrate, waterbird and floristic attributes Halse et al, 2000) but all three classifications had different partition structures.…”

“…No geographical interpretation of compositional gradients in each of the wetland communities was attempted because wetland composition related to local topographic, edaphic and/or temporal factors, rather than to altitudinal and climatic gradients Halse et al, 2000). Reserve recommendations are based on the wetland site classification groups.…”

“…In the longterm, most claypans probably provide habitat for the same pool of invertebrate species, so claypans have been treated as a homogeneous group for the purposes of conservation. Nevertheless, there was more variation within the claypan community than existed between some other groups, and a large pool of patchily distributed species (see Figure 6 in Halse et al, 2000). Because of this variation, four claypans are recommended as typical of sites suitable for reservation: CB54, CB75a, CB70b and CB75b.…”

“…The patterns are summarised by Halse et al (2000) and Gibson et al (2000a) for wetland communities, and by McKenzie et al (2000a) for terrestrial communities. This paper should not be used without prior reference to all three of these publications.…”