Miniature sand flat wildlife looks like a tiny African savanna

Imagine taking a photo of the most featureless and lifeless-looking patch of bare muddy sand in a tropical estuary and the photo revealing that even this place was seething with life.  In fact the place was full of creatures that were just too small to be seen when I was standing up.  The video below shows a swarm of springtails (Collembola).  It reminds me of the great migratory herds of Africa seen from an aircraft. A single sand fly near the centre of the frame provides an indication of scale.

I filmed the swarm at about four in the afternoon, in the cooler, cloud-shaded conditions when springtails had emerged after the heat of the day and were were swarming.  Scientific literature reports that springtails are one of the most common organisms on earth and that densities of 100 000 per square metre are common.  As these springtails are on the surface even during the middle of a summer day, I suspect that their yellow colouration is related to protection from UV rays  In some of the photos below, these animals are so small, even with high magnification, they are hard to see so please click on the photos to enlarge.

A muddy sand flat between a creek and the beach

Filming set-up, a compact camera with a screw-on close-up lens

The original photo, each yellow or brown fleck is a springtail

Springtail tracks and holes can be seen in fine mud even when the creatures are hiding

Insect predators were also zipping around on the muddy surface. Large yellow and black striped hover flies fly at high speed just above the surface and probably catch sand flies. Rove beetles, which look like tiny earwigs seem to be the most abundant and roam over the surface and into and out of holes. Caterpillar-like beetle larvae that were considerably larger than the rove beetles were also occasionally seen. Tiny bugs, which are as small as some species of sand fly were also present. In truth it is difficult to know for certain which of these insects are predators as most groups have both predators and herbivores.

A tiny fly (robber fly?) that hunts by sight

Rove beetles often make chambers under stuck down mangrove leaves

A sand fly-sized bug, which runs across the surface at speed

In hot dry weather, a good place to find tiny animals is under a mangrove leave that has become stuck to the surface of the mud or under loose flakes of algae. Sometimes a full ecosystem of predators and prey can be found under a single leaf. On close inspection, there is a rove beetle and hundreds of blue-green springtails in the photo below, all of which were under a leaf.

Rove beetle and blue-green springtails

Some of these insects are not be restricted to the sheltered waters of a small tidal estuary. I have also found the rove beetles on open sandy beaches near the high tide line and on exposed sand flats where the blue soldier crabs march. 

Sand flats at Yule Point

Beetle tracks under the sand, near the work of a sand bubbler crab

A rove beetle beside a sand ball

It is beyond question that these creatures are present in vast numbers but are they ecologically important? Juvenile predatory fish such as whiting seek the shallow waters where these tiny insects live. Sand fly larvae are also predators and I wonder if springtails are their main dietary item. Certainly, the tiny fauna would consume algae and help to prevent purification of surfaces with excessive algal slime. More research needed.

Big hairy yellow stripe hermit crabs seem to graze algae and not hunt for springtails.