G’day everyone. Over the last year I was privileged enough to study the ecophysiology of the fish at Edgbaston Reserve for my honours project at uni. Below is a little summary of my impressions of Edgy and my work. Let me say, what a year, what a project, what a place!
Edgbaston Reserve, hidden in the Queensland outback, is an amazing place crammed full of unique life. Like many semi-arid areas, the reserve seems somewhat desolate during the dry times, but in truth you just need to know how to look because there's fascinating life on this reserve everywhere.
I spent some time there during the dry season in October 2019 and during the wet season in February and March 2020. During the dry time, there were kangaroos around my swag in the morning, frogs in the toilet, kites and galahs overhead, brown snakes on the move and a mind blowing community of little critters year round in the ancient springs.
During the wet season, life explodes, making the reserve seem comparatively quiet during the dry season.
The land greened up and there was a boom of plants, mammals, reptiles, amphibians, birds and mosquitoes the size of B-52s.
The handling capabilities of the car and all terrain vehicle were tested avoiding the hundreds of burrowing frogs that had appeared.
Burrowing frogs are wicked and in many ways symbolic of their land. They retreat to the ground during the dry times in stasis drawing down on their reserves while cocooned in soil as hard as concrete or constantly digging to escape the dry front in the soil. When the rain comes and softens the soil, there's a mad dash to break free, feed, mate, spawn and for the new generation metamorphose before the good time ends and they must go back underground.
They were pretty amazing, but I also saw a 6-foot long black-headed python that had just shed (breathtaking), planigales, earless dragons, scorpions, emus and so much more.
Some of the insects and plants I saw still don’t have a name, just a handwave at their place on the evolutionary tree. Edgbaston is home to numerous threatened and vulnerable species, some famous and some unknown. Two of Edgbaston’s celebrities are the endemic fish the Red-finned Blue-eye and the Edgbaston Goby, who happen to be two of the focal species of my honours year.
When I first heard of fish that evolved in the outback, it seemed counterintuitive. But it helps to understand the long journey through time that Edgbaston documents.
The escarpment of the Aramac range that edges Edgbaston once part of the shore of Australia’s inland sea and you can find shells forever preserved in stone in the red dust of the reserve.
When Australia broke from the other continents and drifted north, our inland sea dried up and our aquatic life had to find refugia in soon to be arid landscapes. At Edgbaston, you will find snails, yabbies, crabs, shrimp, fish and more living in alkaline water (>pH7).
When the rains come and the land floods, the springs are often connected and historically this allows for colonisation of new springs and the maintenance of genetic diversity. Unfortunately, these flood events have also provided a foothold for the invasive Eastern mosquito fish to get into the last stronghold of the endemic fish.
There was a noticeable decline of the endemic fish on the property before Bush Heritage acquired it but through the efforts of staff and volunteers, these species have been preserved.
The largest threat to these endemic fish is the Eastern mosquito fish. The main techniques for protecting the endemics include translocation of endemic fish to new springs, fencing of endemic occupied springs and eradication of the mosquito fish.
The fish have all been studied before, to varying degrees, but there's a gap in our knowledge that I attempted to fill in my honours year, which can be broken into three parts.
Part 1: understanding their environment
If you look at large bodies of water like lakes, the physiochemistry of the water is relatively stable and while things such as temperature or pH change seasonally, there aren’t normally dramatic changes over very short time periods.
These gradual seasonal changes are normally slow enough that the species living in the water can slowly adjust as sudden changes can be lethal. Edgbaston springs are nothing like that. They fluctuate so much!
The most consistent area of the springs is around the vent, where ancient water from the Great Artesian Basin bubbles up alkaline, devoid of oxygen at approximately 24°C.
Once in the spring, the physiochemistry fluctuate massively across both time and the spring itself, far more than what most fish are ever exposed to.
I measured the temperature, dissolved oxygen, conductivity and pH of the springs and saw large changes both seasonally and over 24 hours. Part of this is because of how shallow they are. My sense of depth changed rapidly working in these springs – I saw baby gobies in water only millimetres deep and depths greater than 300mm felt like the Mariana’s trench of arid springs.
As the sun baked the ground during the day, the springs changed depth and size. As water evaporated, the dissolved minerals in the waters join the salt crusts (trona) already edging the springs.
I saw water temperatures as high as 48°C and pH ranged from pH7- pH9.83. They were nearly devoid of oxygen at night and hyper saturated during the day. In the space of 24 hours, the springs have been recorded fluctuating as much as 27°C and are known to be close to freezing in winter. For many species, these sort of extreme values and fluctuation would be lethal!
Part 2: understanding how the fish use their environment
Big fluctuations or unfavourable conditions can be stressful for an organism. Humans find 20°C a lot less stressful than 0°C, but at least we have internal heat. Fish don’t and they are constantly at the mercy of the environment they live in and their performance can easily be impaired by the environment.
Many species will move to areas where the conditions aren’t as stressful. Considering how much the Edgbaston springs vary over a day, I was curious to see where each species were more likely to be found.
The Red-finned Blue-eye were hard to find consistently and it was difficult to pinpoint any conditions under which they were truly prevalent, though they seem to prefer clear deep sections but will occupy only the upper 10-40mm of the water column.
The goby were normally found in cool and deep sections, often with high pH and oxygen levels, though I did see them in extremely shallow water even at the heat of day.
The mosquito fish were unfortunately the most commonly found species, and were typically seen in deep sections, when water was warm, close to neutral and low in oxygen. If these were the conditions that each species preferred, then I’d assume because these are the conditions that are the least stressful for them. But I can’t say these are preferences, there’s not enough data and testing for that, and I believe it likely that interactions with other species plays a part in where each species is found.
The Eastern mosquito fish and Edgbaston goby are each highly aggressive species. I did see mosquito fish and goby together, but only in sections deep enough for the species to stratify. The Red-finned Blue-eye seemed to coexist well with the goby even in shallow water, but never with mosquito fish.
Mosquito fish are known for choosing habitat that is the least stressful for them, and it’s possible that their large numbers and aggressive nature against the comparatively weaker Red-finned Blue-eye might force the endemic species out of favourable habitat, into stressful areas that are very alkaline and thermally variable or extreme.
This extra stress could reduce their ability to forage, breed and ultimately compete against the invasive fish. The extent of this effect would depend on the tolerances of the species involved, and any adaptations they have evolved for these springs, which leads us to part 3.
Part 3: adaptations of fish to their alkaline environment
These springs are challenging for many reasons, but the alkaline pH is particularly difficult because it can affect the ability of fish to excrete waste. Where we excrete our waste as urea, most fish excrete their waste as ammonia.
In other environments with similar pH conditions to the Edgbaston springs, fish have developed a myriad of adaptations to survive. I was expecting something similar in the Edgbaston fish as well, but the data I collected suggested that wasn’t the case. It seems the Edgbaston fish are very tolerant of alkaline conditions but figuring out the exact way they do this will require further investigation.
Looking back on my trips to Edgy from the big smoke, I feel unbelievably privileged and humbled to be able to experience a slice of this amazing place.
I don’t miss the mosquitoes or the flies caught between my eyelashes when I blink, but memories of everything else, like frogs hiding in my equipment to beers at sunset and makeshift picnics between floodwaters, has left a mark on me.
I remember after a particularly long night of surveys I had watched the sun rise over a spring and it was magic. Watching the stars from the top of my car, the sickle moon highlighted the edges of the clouds and it was like watching the stars from below the ocean and the springs looked infinitely deep.
When the sun rose, the clouds began to burn and the land was painted pink and gold. It’s impossible to witness something as beautiful as that and not feel connected to the land.
Going back to the city, it can be disheartening when you see how disconnected many people are to the world they live in. People seem to focus on their lives in concrete jungles and dream of the life they see through their phones. For me, this highlights the importance of places like Edgbaston.
Without the important work of organisations like Bush Heritage, by the time people look up from their phones and appreciate the world, we could lose these beautiful species and places.
I think we need more people to understand how weird, wacky and wonderful our fauna and flora are.
Our land has amazing life that is unbelievably precious, unique and sometimes downright bizarre. Through research and hard work, we can learn more about how these species have adapted to the conditions in this land, what their greatest threats are and how we can help them best.
Maybe, with a lot of hard work and a bit of luck, we may turn the tide for many species and hold them back from extinction.