Walking on the Edge – Rock Platforms

As far as rocks go, you have to love sandstone. Our beautiful sandstone bedrock in NSW gives us our majestic historic buildings, our stunning red-yellow cliffs and our sandy beaches. At the interface where land meets sea, it also gives us a fascinating and sometimes dangerous formation – the rock platform.

Rock platforms are formed when waves erode the base of cliffs over time. This leads to notch caves which may eventually collapse, leaving behind a flat section at the base of the cliff. Wave energy then passes over the platform, leading to gradual erosion from above. This gives rock platforms their characteristic surface complexity, which provides a home for a wide diversity of marine life.

nerita-atramentosa

Nerita atramentosa; black nerites, sheltering on sandstone in Narrabeen Head Aquatic Reserve

Rock platforms are a tough place to live. As tides rise and fall twice each day, organisms are in turn exposed to the baking sun and submerged under water. Wave action threatens to rip plants and animals from the rock, and predatory pressure comes from above, in the form of birds, as well as below, from fish and invertebrates. Yet there are many organisms that manage to live in the rocky intertidal zone, including barnacles, anemones, crabs, sea urchins, sea stars, chitons, sea hares, sea snails, colonial worms, sea squirts and algae.

It’s best to explore rock platforms as a slow nature walk. Go too fast and you’ll miss most of the marine life, as animals are typically small and secreted in crevices, pools and shady overhangs. You can easily spend a couple of hours exploring a single rock platform. Avoid turning over rocks as this can disturb the marine life, but if you’re careful you can lift the occasional rock to see underneath so long as you replace it exactly as you found it. Be careful where you tread, staying on sand and bare rock wherever possible.

marine-snail-cluster

Marine snail cluster, Bateau Bay – Shelly Beach

Always check weather forecasts before doing a rock platform walk, as big seas and high winds can be dangerous. Time your walk for low tide, and as a rough guide don’t proceed with the walk if seas are over 2 metres high or 10 seconds period, or winds over 20 knots. Each rock platform is different, so when you arrive check the local conditions in any case. If there is any form of swell passing over the platform, stay back and always stay facing the water so you can see what’s coming.

A few particular items of equipment will make a difference to your rock platform walk. Bring a guidebook or identification sheets so you can appreciate the animals you find. Bring sun and wind protection of course, and wear shoes that can get wet – I prefer non-leather soft-soled sandals. And yes, bring your camera – I regularly take my DSLR with me to get macro shots of molluscs, wide angles of the platform and telephoto shots of seabirds. I also take a water resistant compact camera which is great to put in rock pools for underwater close-ups of critters.

spenglers-trito-in-wrack

Spengler’s triton in wrack, Bateau Bay

There are too many rock platforms in NSW to list them all here; in Sydney alone there are interesting rock platforms at North Narrabeen, Long Reef, Bluefish Point, Shark Point and Shelly Beach (Cronulla). Several of Sydney’s Aquatic Reserves protect invertebrates in the intertidal area; of course always check the signs. Outside of Sydney, if you are near a Marine Park, check out the literature, for example there are several rock platforms highlighted in Batemans and Solitary Islands Marine Parks.

Depending on the time of year, keep an eye out for whales, dolphins and seals too – on a recent walk in the Royal National Park we saw all three. The land-sea interface might be “on the edge” for us humans, but it’s abundant with other forms of life.

See more photos of rock platforms in Narrabeen Head and Bateau Bay by Marine Explorer.

 

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