You know that you are at the Mid Tide Level on rocky ocean shores in south-eastern Australia in the Eastern Warm Temperate Zone, when you find two other kinds of barnacle. One is the scaly, but flattened Rosette Barnacle, Tetraclitella purpurascens, that prefers hidden surfaces away from the force of the waves, and the Rose-coloured Barnacle, Tesseropora rosea, that loves to have the full force of the waves smashing against it. Bennett and Dakin refer to this level as the Barnacle Zone in their books on "Australian Seashores".
The Rosette Barnacle, Tetraclitella purpurascens, is grey in colour with a rough scaly appearance. It prefers protected and semi-protected areas on rock faces, in crevices and under boulders sheltered away from the direct force of the waves.
While the Rose-coloured Barnacle, Tesseropora rosea, prefers to live on exposed coasts where wave action is moderate or strong, often fully exposed to raging surf. Like all barnacles, it feeds on plankton using basket-like feeding arms called cirri.
Two of the most widespread mollusc (shell fish) of the intertidal zone are the abundant Variegated Limpet, Cellana tramoserica, and the also abundant Zebra Top Shell, Austrocochlea porcata. On southern shores its close relative the Ribbed Top Shell, Austrocochlea constricta, takes its place in being the most abundant.
The Variegated Limpet, Cellana tramoserica, is one of our most common shells. It is very variable in colour and may be pink, grey, yellow, or orange, with darker stripes or mottling. In New South Wales individuals seem to be more brightly coloured than along southern shores.
Variegated Limpets may also be squat, or very high. It is difficult to believe that all forms of this limpet belong to the one species. Walk across a shore and look at all the different forms of the Variegated Limpet.
Another group of molluscs with very limpet-like shells are the Siphon Shells. They don't have gills, but have a region in the mantle cavity which acts like a lung. In other words, they are air breathers, and are related to the common Garden Snail, and slugs. Along south-eastern Australia the most common forms are the Denticulated Siphon Shell, Siphonaria denticulata and the Corded Siphon Shell, Siphonaria funiculata.
Is there a pattern to where the various forms of limpets and false limpets are found?
Are the flatter limpets of one species found somewhere, while the tall ones of the same species are found somewhere else?
What environmental factors might be influencing the limpet's and false limpet's shape?
Can you think of reasons why there are many colour patterns in any species? Look carefully to see what you can observe.
Five other gastropod molluscs of the rocky seashore are the Striped-mouth Conniwink, the Black Nerite, the Zebra Top Shell and its close relations the Ribbed Top Shell and the Wavy Top Shell.
With the Stripe-mouthed Conniwink, Bembicium nanum, the shell is usually more wide than high with a distinct ridge, called the keel, just above the flattened base. It is found in the upper tide levels of exposed rock platforms. The shape of the shell is conical, hence the common name "Coney-wink" or Conniwink.
Another abundant mollusc is the Black Nerite, Nerita atramentosa. It lives on and under rocks and in crevices at mid- to high-tide levels. This distinctive mollusc may often be found in shallow gutters or depressions where remnant wet areas remain after a falling tide.
Compare the Conniwink with the Zebra Top Shell, Austrocochlea porcata, whose shell is more globe-shaped and not flattened at the base. You may notice that different Zebra Top Shells have bands which are quite variable in width. The bands are caused by something which is in the algae that they eat and doesn't want. So they excrete the chemical into their shell. The Zebra Top Shell is a herbivore, which means its eats plants (microscopic algae = seaweeds). You can see its characteristic "tracks" in shallow pools as it grazes its way through the thin coating of algae.
The southern representative of this group is the Ribbed Top Shell, Austrocochlea constricta. Until very recently, this species was grouped with A. porcata. Is is a more unicolour shelled mollusc with deeper ribbing on the shell.
Another Top Shell found along south-eastern Australian shores is the Wavy Top Shell, Austrocochlea concamerata. Sometimes found high on the shore, it prefers sheltered locations underneath boulders and in crevices.
We now find our first chiton, the well-named Snake-skinned Chiton, Chiton pelliserpentis. It can be distinguished by the snake-skin like scales and colour pattern of the surrounding girdle.
The highest occurring anemone is the Waratah Anemone, Actinia tenebrosa. It may be found in protected areas, often under ledges away from the sun. Its deep red colour is characteristic. It is found throughout southern Australia and is very common in places. This anemone broods its young, which may be seen in the column just before ejection.
The Sand Anemone, Oulactis muscosa, may be found in sand-filled cracks in the rocks where it obscures itself by adhering to sand grains and pieces of shall. It is always found on a sand covered area with only its tentacles and oral disk visible. The column is usually off-white, with rows of darker spots. The tentacles are usually grey-white.
Neptune's Necklace, Hormosira banksii, is a very common to abundant brown algae found in moist depressions and gutters at mid tide level. It is sometimes so abundant that it carpets large areas.
If you look in a pool where Neptune's Necklace is growing, you may see filaments or clumps of another almost formless hairy algae clinging onto the necklace's bubbles. This is Ectocarpus, Ectocarpus siliculosus.
We are now at the Low Tide Level on our walk down a rocky ocean shore in the Eastern Warm Temperate Zone found in south-eastern Australia.
Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. New Holland, Sydney.
Edgar, G.J. (1997) Australian Marine Life: the plants and animals of temperate waters. Reed Books, Kew.
Jones, D. & Morgan, G. (1994) A Field Guide to Crustaceans of Australian Waters. Reed, Chatswood.
Quinn, G.P., Wescott, G.C. & Synnot, R.N. (1992) Life on the Rocky Shores of South-Eastern Australia: an illustrated field guide. Victorian National Parks Association, Melbourne.
Marine Research Group of Victoria (1984) Coastal Invertebrates of Victoria: an atlas of selected species. Museum of Victoria, Melbourne.
Macpherson, J.H. & Gabriel, C.J. (1962) Marine Molluscs of Victoria. Melbourne University Press & The National Museum of Victoria.
Shepherd, S.A. & Thomas, I.M. (1982) Marine Invertebrates of Victoria, Pt. 1. South Australian Government Printer, Adelaide.
Underwood, A.J. & Chapman, M.G. (1993) Seashores: a beachcomber's guide. New South Wales University Press, Sydney.
Wilson, B.R. & Gillett, K. (1979) A field guide to Australian Shells: Prosobranch Gastropods. A.H. & A.W. Reed, Sydney.
Womersley, H.B.S. (1987) The Marine Benthic Flora of Southern Australia. pt. 1 , South Australian Government Printer, Adelaide.