Sand/Mud flats

I‘ve started my involvement in the project by trying just to have a few dives with some easygoing and curious people, take some photos, learn and have fun. I‘ve tried to take pictures of anything that looked a bit odd, then tried to make sense of it from the limited reference sources that I have handy. Basically, it turns out that every picture tells a story. So here‘s a bit if a first installment of ?holiday snaps‘. Inshore sandy and sediment covered habitats are very common in Australia and cover more area than reefs. Most sand and mud dwelling animals rely on food that has washed down from coastal areas, like decomposing leaf litter, algae, and other dead animals. These coastal and estuarine areas can sometimes be very productive. A location near a sheltered muddy estuary can be about 100 times more productive than an area of clean sand along an exposed ocean coastline. This food washing away from the coast is spread around on tidal currents, and may eventually collect in certain areas where the current along the seabed is disturbed. This disturbance can be caused even by a small object a few centimeters big, like a sponge, or even a hole in the sand made by a browsing stingray. This means that while life can be very rich out on the sand and mud way from the shore, it is often patchy. Every buried shell or stone provides a holdfast for life. In the above photo an isolated sponge has made a tenuous home on a buried object, approx 7-8M off the beach. The sediments Page 38 collect behind this obstruction and the sponge in turn attracts worms and bivalve molluscs (shells). Most of the life on the sandy and muddy bottom consists of very small creatures like bacteria or single-celled plants that feed on the nutrients washed into the ocean. These small creatures in turn become food for any larger animals that are adapted to take advantage of life on the mud, but life for these bigger animals isn‘t easy. The sand and mud will move about after big storms so its hard for fixed bottom-dwelling animals like sponges to establish themselves. In approx 7M close to the reef near the Primrose Sands shop, strong winds seem to have exposed some buried animals. Out in the daylight this cockle appears not to have the strength to re-bury itself. It is a delicious treat for someone. Probably dying, its smell has attracted a couple of scavenging snails (on the left centre of the picture). A larger animal that might move about freely during the day on a reef will find the sand and mud plains too barren to hide from predators. It is very hard for a bigger animal to bury down into the sand and hide. If an animal buries itself too deeply, the supply of oxygen can be poor in the lower levels, so they often can‘t hide for long. Some animals like worms and shells have adapted to this kind of life and they thrive in great numbers out on the sediments. They have changed their body shapes, or evolved special features like long breathing tubes. This allows them to bury themselves easily and hide for long periods. Animals that have adapted in this way are now much safer than their reef relatives and are more likely to die of old age. A marine flatworm, about 25cm long, out during the daylight hours and one would think an easy meal for a fish? Perhaps its poisonous to eat, any ideas readers? Rather than burying themselves, larger animals like stingrays have evolved special camouflage, or venomous spines to protect them against predators. In about 9 metres off the beach at the mouth of the bay, the bottom was particularly rich in nutrients. Lots of small seaweed clumps can be found and the bottom was showing signs of plenty of activity from patrolling rays. A harmless Whitley‘s Skate was seen carrying a marine leech on its back. Page 39 Marine leeches are poorly studied and little is known about them, but they seem to pick on rays in particular. Surprised in the low vis, I saw a 2m wide Smooth Stingray with its venomous tail spine reared up defensively ?Steve Irwin style‘. It moved off quickly, only because I couldn‘t get out of the way faster. Animals like the octopus have changed their habits or camouflage to be less vulnerable to predators out in the open. Some come out of hiding only during the night like octopus. This little dumpling squid is perfectly adapted and able to adjust its colour to the seaweed cover that is available. This one was seen in 7.5 M off the beach, hiding among the green seaweed clumps. Its usual to see 2-3 smallish flathead every dive. They are heavily fished in the area. Flathead are suspected predators upon juvenile Spotted Handfish. Divers and fishermen only encounter the stuff that is big enough to be seen with the naked eye called ?megafauna?, and then usually only the relatively small number of animals that can be seen on the surface during the daytime. That‘s just some of the things seen on one dive during the day. Night time, well that‘s a whole different story.