Responses of billabong rotifer communities to inundation

Responses of billabong rotifer communities to inundation


Billabongs are remnants of past river meanders along Australia’s low gradient floodplains. They are similar in morphology and formation to oxbows elsewhere, but their ecology reflects a unique evolutionary time-scale. The Murray-Darling river system, for example, occupied its present drainage basin 60 million years ago in Gondwana. For millions of years, as Australia moved north, the low-gradient rivers meandered back and forth across their floodplains – billabongs formed and re-formed. In this ancient and highly stable river system, extant billabongs may have occupied the same position for thousands of years. They have been subjected to variations of climate, from tropical to arid, but have not been scoured by glaciation. During periods of aridity billabongs may have provided refugia and foci of speciation, and a source of colonizing biota when the climate became wetter.

As part of a long-term study of microfaunal ecology in billabongs, we report here on the species composition and population dynamics of the resident rotifer community in a River Murray billabong pre- and post-flooding in summer 1990. The significance of microfaunal community responses is then considered in relation to the billabong ecosystem, particularly in the context of floodplain food webs.

Daily plankton collections were taken from a billabong of the River Murray for two weeks prior to inundation in March1990 and continued for ten days after flooding. Quantitative responses of the plankton community and the component species were analysed against measured environmental variables and between species. Rotifers and copepod nauplii were the predominant net plankton (> 53 μm). Significant negative or positive responses to inundation were detected for most common taxa of 63 rotifer species recorded. A four-fold dilution from intrusion of river water masked rapid population increases. Opportunistic responses to inundation appear to be a survival strategy in the highly unpredictable billabong environment.

Lor-Wai Tan & Russell J. Shiel

Murray-Darling Freshwater Research Centre P.O. Box 921 Albury, NSW 2640, Australia

Hydrobiologia 255/256: 361-369, 1993.

J. J. Gilbert, E. Lukens & M. R. Miracle (eds), Rotifer Symposium VI.

© 1993 Kluwer Academic Publishers. Printed in Belgium.

What is limnology

What is limnology

Limnology comes from the Greek words limnos meaning lake and logos for knowledge. So limnology is the study of the biological, chemical, and physical features of lakes and other bodies of fresh water bodies that may be still or flowing.

Why should we care

Limnology is the science of understanding the composition of freshwater ecosystems and how these ecosystems interact with each other. Primarily, limnology studies how organisms enter into and leave freshwater ecosystems.

Limnologists use various methods, including testing of aquatic organisms for their physiological and biochemical functions (fish and invertebrates), and observation of natural processes (evolution, reproduction, and morphogenesis) to better grasp how aquatic ecosystems work. In addition, limnologists learn about freshwater ecosystems through students or clients who work with nature research projects.

Most freshwater ecosystems are described in the scientific literature as being comprised of many different types of organisms (bottom-up approaches), but limnologists can also learn more about a specific ecology by studying natural systems. Natural and natural-derived resources are combined into matrices called trophic webs. These webs show the food chains and interactions between organisms.

The bacteria of the phytoplankton are responsible for the formation of plant and animal cells (bacteria comprise about 99% of all cellular life), as well as the synthesis of vitamins in the plants and animals. The plants and animals that feed on the phytoplankton will include microorganisms (single-celled algae) that consume the phytoplankton. These organisms act as a sort of fertilizer on the soil, allowing for additional growth of other organisms. Food and fertilizer take a variety of forms in nature, all of which are important to limnologists.

Different ecology allows for different trophic (feeding and consuming) relationships. At the base of the trophic web is the phytoplankton, which include bacteria, archaeabacteria, and fungi. At the base of the trophic web are microplankton, or bottom feeders. Other organisms such as zooplankton are also intricately involved in supporting the trophic web.

Some limnologists who specialize in identifying these micro invertebrates are known as aquatic micro invertebrate taxonomists. Taxonomists use dissecting, light and even scanning electron microscopes to identify these zooplankton some of which are only micrometers in length.

Limnology and Environmental Impact

There is a great need for limnology services worldwide. Limnologists are often involved in studying environmental change of large water bodies such as lakes and wetlands are vital habitats for mollusks, birds, and mammals. We believe the world can be a better place if limnology is more widely studied; areas of study include remaining corals being threatened due to warming temperatures and acidifying oceans, salinity issues related to freshwater expansion, freshwater productivity, introduction of invasive alien species, and bioaccumulation of pollutants in freshwater systems. Decay of natural forest products during the warming process causes nutrient overload in watersheds and threatens biodiversity.

Limnology is often called the study of “fresh” water. The study of Limnology is important because it can lead to a better understanding of the world around us and how it affects our daily lives. While we often think of water, as the world’s most important resource, we are not the only ones who need it for survival and the study of Limnology provides the solution to some of these problems. The biggest possible negative impact on our world is from the lack of fresh water. Without this resource, life as we know it would cease.

Freshwater eocsystem
River Murray lock