Ecology and Geology of the Queensland Coast
(was MangroveCreatures - see post index below)
Thursday 23 November 2017
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.
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