The estuarine macrobenthos of the Calliope River and Auckland Creek, Queensland

Quantitative benthic sampling in the Calliope River and Auckland Creek has been conducted at approximately 3 monthly intervals since November 1974 at 11 transects, each with 5 stations (55 sites). In September 1976 power generation commenced, using the estuary for thermal discharge. The data to August 1976 - the 'pre-thermal' situation - are intended to serve as the baseline for comparison with the 'post-thermal' situation. The 'pre-thermal' data are analysed here. A total of 263 taxa were found comprising 15 species of seagrasses and algae, 75 species of polychaetes, 51 species of molluscs, 91 species of crustaceans and 30 species belonging to other phyla. Of these species, those represented by less than 5 individuals, and those occurring in less than 2 sites or times, were not considered further. The remaining 72 species (representing 88.7% of all individuals collected) were classified into site-, time-, and species-groups using the 'Bray-Curtis' dissimilarity measure, followed by group-average sorting. Nine site-groups were accepted; these showed good topographic coherence and they could be characterized by their depths, substrate types, and position in the river. Classification into species-groups showed that many species were scattered throughout various sites, and on the basis of the pseudo-F test, only 39 species conformed to the site groups. Species classification using species-occurrences within the already established site-groups, gave 14 species-groups which characterize by their absence or presence, the various site-groups. Classification into time-groups showed that intertime dissimilarities are high, indicating that either sampling times were too distantly spaced, or alternately that seasonal differences overlie a non-seasonal trend. Cyclical analysis of summated species data identified a non-cyclic and a cyclic component with a period of approximately 12 months. A recolonization model has been proposed to describe these data; it is postulated that the intense flooding of December/January 1974 led to the removal of the benthos and that species reappearance was more or less linear over a period of 29 months, while the number of individuals of all species increased logarithmically. When compansons with the 'post-thermal' fauna are made, it will be essential to allow for this recovery when assessing the thermal effects.