The popularity of Karloo Pools has increased so much over the last summer that it’s not unusual to see dozens of bushwalkers swimming in the main pool. Arriving to find a large crowd last weekend I headed upstream to the less populated section of the creek.
The largest pools are located on the bends in the valley, the change in direction causing the water to scour wider and deeper holes in the creek bed. The straight sections of the creek are shallower, a few centimetres to waist deep. If you’ve brought a mask the shallows offer some of the most interesting viewing, with freshwater eels, small fish such as Australian Smelt and Striped Gudgeon, crayfish and many species of aquatic insects.
On this particular afternoon I was more interested in cooling off after a walk in stifling February heat than snorkelling. I found a patch of smooth creek bed and sat with the warm water lapping my chin. I couldn’t really see into the water, and with drooping hat my view was restricted to the surface of the creek.
The water in Karloo Pools is clear, with just a tinge of the brown tannins that colour any water passing through bushland. Pure the water might be, but the surface film, or meniscus, was anything but empty. Leaves, flowers, fragments of and drowned insects all floated past in a steady stream. Inspecting the flotilla of debris were the hunters of the meniscus, Water Striders and Whirly Gig Beetles.
Both the Water Striders and Whirly Gigs seemed unperturbed by the floating head that had entered their habitat. As long as I kept my head low, nose just above the water, they would come within a few centimetres.
I’ve had very limited success photographing Water Striders and Whirly Gigs. The underwater camera can’t focus quickly enough to track such small and fast subjects. The SLR is faster, however both species tend to skitter away when approached from the land, leading to distant shots of tiny subjects.
A thought bubble erupted and the following day I returned to Karloo with macro lens and external flash on the camera. Gingerly carting a significant proportion of my photographic assets into the creek I found a rocky ledge where I could brace my elbows to hold the camera just above the surface. Soon enough I was surrounded by Water Striders.
Water Striders hold their long legs at a shallow angle that lies on the meniscus without breaking the surface. The meniscus distorts with tiny dimples at each contact point. They move across the surface with a rowing motion. When startled they leap a few centimetres off the surface before heading for cover. Many Water Striders are actually two linked animals. I’ve never been sure whether they are mating or perhaps the female carts the male around until his services are required. Either way it doesn’t seem to impair their speed or appetite for any insects that fall to the water. The striders pierce their prey with a tube like proboscis and suck out the body fluids.
Most of the Water Striders had small red dots on their bodies. There was no consistency in the location of the dots and the number varied from one to four. The variable locations suggested it wasn’t their eggs, and checking afterwards I discovered that they were parasitic mites, the Red Water Mite. Apparently Water Striders are a common host for the larval stage of the mites, along with dragonflies and damselflies.
The Whirly Gigs are an aquatic beetle. They spend most of their time in the meniscus but are also capable divers, disappearing beneath the surface if frightened. Whirly Gigs are truly frenetic, swimming in the swirling loops that give them their name. It is very difficult to capture the fast moving beetles in focus, so I took heaps of images in the hope that one might be acceptably sharp.
A fern reflected against the water caught my eye. Framing it in the viewfinder I realised that a large Water Spider was perched on the fern, front legs resting on the meniscus to detect any passing prey. I’ve seen these spiders at night but not in the middle of the day, when they typically hide in vegetation or underwater.
Whirly Gigs, Water Striders and Water Spiders aren’t alone in hunting prey on the surface of the creek, although they are the true specialists of this niche habitat. Dragonflies and Damselflies prowl the air above the creek line for flying and fallen insects. Both rest on creek bank rocks and vegetation, and even on floating debris. I spotted two species on damselfly, one carrying more of the Red Water Mites.
I’ve spent many hours in and around Sydney’s freshwater creeks. It took a change of perspective to draw my attention to the remarkable wildlife that treads softly enough to hunt on the meniscus.
Odds and Sods