Life is a challenge for species that live on intertidal rocky shores! Animals and plants here have to deal with storm waves, dehydration, extreme temperature changes, very salty conditions in evaporating rockpools, and predation. As intertidal reefs are alternately inundated and exposed by the tide, they experience rapid changes in environmental conditions, including swell, temperature, salinity, and exposure to air, causing desiccation stress. Consequently, specialist intertidal species adapted to survive in this extreme environmental variability inhabit these reefs.
You’ll find a characteristic rocky shore community in places where rock is exposed at the shoreline. In Victoria, this habitat is usually found on rocky headlands between Portland and Wilsons Promontory, with some minor occurrences in the far east. Intertidal reefs in Victoria are mostly found around headlands and points and are often isolated from one other by stretches of sandy beach. There is little intertidal reef habitat in the Twofold Bioregion. Although there are some differences in species between the far east, central and western Victorian coasts, the type of rock and degree of exposure to prevailing storm waves are more important factors in determining species than their geographical location.
Caption: Snails are the most abundant marine fauna to be found in shallow intertidal pools. Herbivorous snails scrape microalgae from the rocks 📷 Nicole Mertens
Sheltered headlands in our bays support groups of species different from the ones found on sites battered by the waves of the Southern Ocean. This difference is often reinforced by the characteristics of the underlying rock. Areas of exposed rock in the intertidal zone vary from steep sloping rock faces to relatively flat or gently sloping rock platforms and boulder fields. The basalt along the oceanic side of the Mornington Peninsula, for example, weathers gradually, allowing all sorts of creatures to hide under loose rocks or in crevices and cracks. The granite around Wilsons Promontory, on the other hand, is hard and impermeable, so that only the most tenacious plants and animals are able to survive there. Intertidal reefs on the open coast generally have higher species richness than those in embayments. Mushroom Reef at Flinders, and Honeysuckle Reef near Point Leo, are regarded as supporting the most diverse intertidal reef communities in Victoria.
Larger seaweeds found on Victoria’s intertidal rocky shores include Neptune’s Necklace (Hormosira banksii) and the large and fleshy Bull Kelp (Durvillaea potatorum), which grows on the lower fringes of more exposed rocky shores. Most animals found here are molluscs that graze algae from rock surfaces. Many filter-feeding organisms can also be found, including tube-building worms, sea squirts, mussels and barnacles. Crabs and seastars, hermit crabs and shrimps scavenge in rock pools. Predators include snails, fish, and birds such as the Pacific Gull (Larus pacificus) and Sooty Oystercatcher (Haematopus fuliginosus).
Intertidal reefs often appear bare of algae, but in fact a thin layer of microscopic algae grows directly on the rock surface, and this is an important food source for grazing molluscs. Where macroalgae is present, it is typically dominated by the mat-forming brown alga Neptune’s Necklace. The green alga known as sea lettuces (Ulva spp and Enteromorpha spp) and other small turfing species are also often present. These supply mobile invertebrates with food and a refuge from exposure at low tide.
Gastropod molluscs are the dominant fauna on intertidal reefs. Herbivorous species include the Variegated Limpet (Cellana tramoserica), top shells (Austrocochlea spp) and conniwinks (Bembicium spp). Common predators include the Lineated Cominella (Cominella lineolata) and Murex Snail (Bedevavinosa). Other invertebrates on intertidal reefs include small crustaceans such as barnacles and crabs, the Dwarf Cushion Star (Parvulastra exigua) and the Interdial Tubeworm (Galeolaria caespitosa). Intertidal reefs are important foraging habitats for shorebirds at low tide and for fish at high tide.
Caption: Rocky shores and tide pools along the Victorian coast are easily accessible to many, and with that comes challenges to appropriately care for these places 📷 Nicole Mertens
As far as people are concerned, intertidal reefs are one of the most accessible parts of the marine environment. As such, they have important aesthetic, recreational and historical values. Because of their accessibility, they are also subject to human pressures including collection of animals for fishing bait and food, trampling, and pollution. Conservation of these areas depends on reducing habitat destruction, illegal harvesting, pollution, and physical disturbance. Recreational collection of intertidal organisms was having such an impact that it is now prohibited along much of Victoria’s coast. Exploited species included warreners, abalone, elephant snails, dog winkles, limpets, top shells, crabs and cunjevoi: some of the once-common snails are now rarely seen.
Intertidal reefs are also one of the habitats most at risk from the impacts of climate change. As sea levels rise, many of the species living on intertidal platforms will be trapped between the ocean and developed coastal areas. They will have nowhere to go, as it will take hundreds of years for new platforms to be cut from the cliffs if existing intertidal areas are submerged.
Rocky intertidal shores are protected within parks and reserves along the coast, although the extent and nature of the protection varies. Work is in progress to determine future shoreline reservation and protection needs.