we continue to walk down a rocky ocean shore in south-eastern Australia,
known as the Eastern Warm Temperate Zone, we now approach the region
of the low tide level. This region is uncovered from between two hours to
half an hour each low tide cycle.
So the creatures and algae of these low tidal levels spend a lot of their time being battered by waves and the debris that the water carries, and not much time being dried out by the sun.
Is the marine environment as harsh as the intertidal environment ?
Decide on what questions you want to explore, and then research and discuss the issues that you think are important.
Predatory molluscs, such as whelks, as well as fish, birds, carnivorous seastars, etc. are common here. They roam over the shores seeking out stationary or slow-moving prey.
In eastern Australia, the zone-forming organism that tells us that we are at the low tide level is the "Sydney Coral", Galeolaria caespitosa. Many think that the limy worm-tubes are a form of coral, but the thick white encrustation is made up of the intertwined tubes of countless thousand worms.
Here we find two species of barnacle, which are really crustaceans, related to crabs, prawns and lobsters, although they certainly don't look like it.
The Surf Barnacle, Catophragmus polymerus, prefers situations where there is a very rough, exposed situation on coasts subjected to high wave energy. The scaly pattern of the plates is distinctive.
There are two very large barnacles at this low tide level. The most common is the Giant Rock Barnacle, Balanus nigrescens. It may grow to 3 cm. high and has a distinctive blue-coloured mantle inside the feeding plates. Its close relative, and similar looking Imperial Barnacle, Balanus imperialis, has a purple coloured mantle.
We also find a number of molluscs at the low tide levels. Because of the strong wave action, they need adaptations to allow them to remain here.
What sorts of adaptations do the different groups of animals (molluscs, crabs, and barnacles) need to be able to remain in this wave washed habitat ?
We also find the Variegated Limpet, Cellana tramoserica commonly at this low tide level as well. But because of the stronger wave action, these individuals are often taller, more rugged, more eroded and colourless that the same species of limpet higher on the shore. In fact the forms look so different, they do appear to be separate species. This is called variation, or variability.
Another common chiton is the Spiculed Chiton, Acanthopleura gaimardi. It is distinguished by its black and brown banded girdle, with numerous, short blunt spines. This species is only found in the tidal region.
One of the most dangerous animals (for the other creatures living there) is the small Mulberry Whelk, Morula marginalba. It is also known as the Black Oyster Borer, and is hated by Oyster Farmers in estuaries. It roams over a wide range of shore levels and cannot be considered as a zone indicator.
Another group of molluscs are the False, or Keyhole Limpets. One common species is the Black Keyhole Limpet, Amblychilepas nigrita, which has a body much larger than its shell. The gills poke through the hole in the top of the shell. The animal may be pinkish, fawn, light brown or grey in colour.
What features are we looking for when we wish to nominate a particular species as a zone indicator ?
Some researchers have based their whole zonation pattern on these zone indicator species. Read any books by John Dakin or Isobel Bennett for more information. See Bennett, I. (1987) W.J. Dakin's classic study: Australian Seashores. Angus & Robertson.
A small sea star which might be overlooked, because it prefers to hide under bounders in shallow rook pools is the Small Green Sea Star, Patriella exigua.
The Common Eight-Armed Seastar, Patriella calcar, is probably the most colourful creature along south-eastern Australian rocky ocean shores. Its colour may range from red, brown, green, blue, mauve, orange, grey, cream, white and black or mixtures of all.
The Eleven-armed Seastar, Coscinasterias calamaria, is a large grey-coloured sea star with uneven length arms, many undergoing regeneration.
Why would some creatures have so many color patterns so that every one looks different, while others have very similar colour patterns with almost no variation between individuals?
We are now at the region around which the lowest tide levels reach. This is the Low Fringe Level which you may visit to investigate the creatures and algae that live there.
Bennett, I. (1987) W.J. Dakin's classic study: Australian Seashores. Angus & Robertson, Sydney.
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.