Scientists may be trained to think laterally and experiment with different substances, but chemistry graduate, Jessica Veliscek Carolan, was still surprised to find herself covered in flour making pasta for yabbies in a controlled study at ANSTO.
The study is being conducted by ANSTO's Institute for Environmental Research (IER) in an effort to give field workers more accurate information on the time it takes for small animals, such as yabbies, to come into equilibrium with a new diet following a major environmental event, such as a flood. Pasta was used as a measurement tool, and the early results show that it takes around two months for the animals to adapt.
A range of highly-sensitive isotopic and nuclear techniques are used to provide unique information about the best methods of managing freshwater ecosystems, including rivers.
"One of the main techniques used to understand how yabbies, and therefore other animals, react to a new diet, is to measure their stable isotope signature. This is the ratio of heavy to light stable isotopes of a particular element in a sample compared to a standard," explained Jessica.
"Stable isotope signatures vary or change in response to physical, chemical and biological processes because less energy is required to move or react to the lighter isotope than the heavier one. This change is known as isotope fractionation," she said.
"For example, when an animal eats something and begins digestion, the lighter isotopes will be preferentially digested because it is easier to digest than the heavier one. The undigested content will contain a higher ratio of the heavier isotope than the food that was originally consumed, and is therefore termed 'enriched'."
The isotopic signature of living creatures may be a reflection of what they eat, but the effects of variables such as sex, age, metabolism and time on isotopic fractionation between diet and animal tissues is not well understood, which is where this research plays a key role.
"Since different foods have different isotopic signatures, if the yabby's food changes, so does its signature. But this takes time. The aim of our study, therefore, is to establish exactly how much time," said Jessica, who worked under the guidance of Aquatic Ecosystem scientist, John Twining, in coordinating the study - and wrangling the yabbies.
While fish have been used in previous studies, yabbies are ideal to study because they are one of the hardiest and most widespread species of freshwater crayfish in Australia. They are adapted to a wide range of temperatures and eat virtually anything, from decaying plant matter to meat.
The yabbies were purchased from a commercial supplier and placed in the IER's aquariums, located on ANSTO's site, south of Sydney. As Jessica soon found out, the yabby's species name - Cherax Destructor relates not only to its burrowing abilities (which can make it highly destructive to dams), but its aggressive and territorial nature.
"As soon as we placed the yabbies in the aquariums they started fighting. We had to put a whole lot of measures in place to ensure that there was sufficient distance between them," said Jessica, who gained entry to ANSTO's Graduate Development program after receiving a degree in Science (Adv) (Hons) with a major in Chemistry from Sydney University.
The task of finding out what they liked to eat wasn't a problem; given half a chance, the yabby will eat anything, including its companions. The challenge was finding a robust, and measurable, food source enriched with Nitrogen 15 and Carbon 13. These are the heavy isotopes used to measure the time it takes for the yabby's isotopic signature to reflect its changed diet.
Initially the team used commercial fish food, but this did not have an isotopic signature significantly different to what the yabbies had been eating in the field. So, the team decided to develop their own recipe, and Jessica soon found herself up to her elbows in flour making pasta enriched with Blood & Bone.
"Coming from university, I found it pretty amusing to be standing in a professional lab making pasta, drying it out and cutting it into bite-size pieces for the yabbies to eat," she said, with good humour.
To their surprise, the Blood & Bone did not significantly increase the 15N and 13C content, so the focus then shifted to worms, which were fed cabbage that had been soaked in enriched isotopes, and the aquatic plant Egeria densa, which had enriched isotopes added to the surrounding water. Both the worms and the E. densa were found to be greatly enriched and so were dried, ground and added to the pasta.
To measure the fractionation between yabby tissue and what they eat, as well as to determine the timescale over which yabbies reflect a changed diet, tissue from the yabby's tail was sampled several times over four months. The samples were dried and ground with a pestle and mortar before being sent to a laboratory with an Isotope Ratio Mass Spectrometry (IRMS) instrument, which measured the proportions of the less frequently occurring but heavier isotopes 15N and 13C.
These tests revealed that it takes around two months for yabby tissue to reflect a new diet, which is longer than current assumptions.
"The benefit of this research is that, scientists in the field have a better understanding of the results they are getting," explained Jessica. "Currently a lot of assumptions are made to interpret field data so the laboratory experiments help to prove whether those assumptions are valid. This research could impact the time-line in terms of how long people wait, after an event, to go out and collect samples."
While the research is providing indicative data, there is still work to be done.
"Once we know how long it takes for an animal to reach equilibrium with its diet, we then need to look at what happens if you dramatically change the signature of the food. Will the yabby take as long to change its signature? Also, how do factors such as sex, age, season, temperature and feeding rates influence the rate of change or biokinetics," Jessica said.
"This kind of research represents just a couple of pieces in a very big puzzle. However, it does contribute to understanding how food webs in ecosystems work, and how to best manage our valuable resources," she concluded.
Published: 17/09/2009