The ecology and palaeoecology of Chironomidae in fresh, saline, and estuarine habitats in eastern Australia - towards an understanding of the past and future

Abstract

The late Quaternary period (40 ka BP), encompassing the Last Glacial Maximum (21 to 18 ka BP), Little Ice Age (~3 ka BP), and period of heaviest anthropogenic impact following European settlement is explored in terms of the palaeoecological and ecological assembly of eastern Australian aquatic Chironomidae (Insecta: Diptera: non-biting midges) species relative abundance distribution patterns in fresh and estuarine habitats. Transitional spatiotemporal gradients were employed to examine larval assemblage patterns, dynamics and processes by locating all study sites at climatic or estuarine ecotones. The southeastern Australian coastal sites included the Clyde River, Curalo Lagoon, W om boyne, Termeil, Meroo, and Werriga Lakes while the fresh lakes included tropical Lake Euramoo and temperate Lake Selina. At the Clyde River, chironomid larval assemblages had non-random distribution patterns that were strongly structured by the estuarine gradient and with minimal seasonal response and a robust diversity of around 44 species. The lagoons and coastal lakes had depauperate species assemblage dynamics that were strongly affected by extremes in salinity and sediment disturbance associated with flood events or breaches by the sea with some influence from ENSO phenomena and anthropogenic impact. Recurrent subfossil assemblages were associated with taphonomic influences whilst recurrent live larval assemblage compositions were attributed to environmental conditions extreme for most aquatic insects. These assemblage patterns and dynamics from the estuarine ecotones were in contrast to those observed at the climatic ecotones of the freshwater lakes. Highly coordinated assemblage patterns were observed at lake Euramoo and these were attributed to a broadly tolerant larval chironomid fauna mostly persisting in swampy lake margins from 6,000 yr B.P. to the present where habitats were minimally affected by shifting lake level and temperature. At Lake Selina, assemblage patterns were much more dynamic and responsive to climatic changes associated with shifts in water level and temperature between 40,000 to 3,000 yr B.P.; however these lentic assemblages were also more strongly influenced by lotic environments. The underlying assembly processes responsible for the observed patterns and dynamics of the larval chironomid assemblages are complex. This means that allogenic, autogenic, and uniformitarian theories are difficult to adequately and independently test. Nevertheless it is clear that the assembly processes acting over the past 40,000 years are highly unlikely to be different to those operating today and there is minimal support for the activity of autogenic processes operating amongst the chironomid assemblages studied in eastern Australia. This may have resulted from the scales of observation chosen and effects from time-averaging on subfossil assemblages because these were observed to have important effects. Other important factors included the definition of boundaries between microhabitats in the ecological surveys and between zones for subfossil assemblages. This strongly influences the perception of equilibrium and stasis that are closely tied with the assessment of the strength and coordination of ecological interaction. Show more