There are a variety of different habitats along the Victorian coastline, each home to unique and diverse marine flora and fauna. Listed below are examples of some of these habitats:
- Victoria has a diverse range of wetlands including saltmarshes, mangroves, and floodplain billabongs.
- A wide range of threatened plants and animals depend on healthy wetlands for their survival. They provide refuge and critical habitat for a range of species - for example, tens of thousands of migratory birds (some weighing less than 30 grams) travel from the Northern Hemisphere to our coastal wetlands each year.
- These wetlands also help in moderating floods and erosion by holding and slowly releasing large volumes of water. As well, they are vital in stabilising shorelines, maintaining water flows, and purifying waterways by filtering sediments and recycling nutrients.
- Eleven of Victoria’s wetlands are so important that they are internationally recognised under the Ramsar Convention on Wetlands. Victoria’s Ramsar sites are home to as many as 1,300 species of native plants and 450 of native animals, including more than 100 species of waterbirds. The Westernport Ramsar site contains three of Victoria’s 13 marine national parks.
- We need to appreciate that wetlands are fragile systems. Victoria’s wetlands are increasingly popular as tourist destinations - for example the Gippsland Lakes continue to attract large numbers of visitors and offer a range of recreational opportunities. Our coastal wetlands are also at risk from altered water regimes, increased salination, pollution from catchment activities, the introduction of pest plants and animals, unsustainable land uses, inappropriate fire regimes and incompatible recreational activities.
- Victoria has lost more than 37% of its wetland areas to activities such as land clearing and draining since European settlement. 90% of this loss has occurred on private land. We need to work very hard to protect our remaining wetlands before they are lost forever.
What can you do?
- Support the creation of marine national parks and sanctuaries that protect wetland habitats.
- Help monitor the health of coastal wetlands through programs such as Estuary Watch and Coastcare.
- Become involved in stream protection programs for those streams that drain into costal wetlands.
- Watch for developments that might impact on local wetland areas, e.g. inappropriate urban, recreational and agricultural development.
- Develop community displays highlighting the importance of wetland habitats.
- Estuaries are places where rivers meet the sea. Semi-enclosed bodies of coastal water where fresh and saltwater meet, they can encompass bays, inlets, river mouths, mudflats, wetlands, mangroves, salt marshes and reed beds (NCR).
- Estuaries may be permanently or periodically open to the sea, with salinity that varies from almost fresh to very saline. Environmental condition may be stable over long periods of time or change frequently or rapidly. Estuaries are, therefore, complex and highly variable environments that often appear to be unpredictable (EPA).
- The coastline of Victoria has some 123 bays, inlets and estuaries, varying in water area from about 2,000 km2 to 1 km2 (Coastlinks). Victoria’s three largest embayments (Port Phillip Bay, Western Port and Gippsland Lakes) can also be thought of as estuaries (EPA).
- In marine embayments, environmental conditions are marine and relatively stable. The communities are made up of inshore coastal species. Many estuaries flow into marine embayments. In some estuarine environments environmental conditions can vary on an hourly time-scale with the tides, and seasonally with rainfall and long-term chaotic changes associated with unusual rainfall patterns. Unique communities that can survive in these highly variable environments have developed (MV).
- Discharges from upstream catchment areas meet the ebb and flood of tidal discharges in estuaries, and the aquatic flora and fauna of freshwater regimes also meet their marine counterparts there. Hence estuary habitats are subject to influences from both marine and riverine environments. These include saltwater and freshwater input, sedimentation, tides and periodic flooding.
- Victoria’s estuaries contain a wide variety of sheltered habitats, including intertidal and subtidal reef, channels, seagrass, Ruppia, mangroves and saltmarshes. They are dominated by intertidal sandflats and mudflats, and subtidal sediment beds (NCR).
- These varied habitats of Victoria’s estuaries are associated with diverse and productive communities of aquatic invertebrates that live buried in the sand. Estuary mud and sand flats are important feeding grounds for local and migratory shorebirds, and nurseries for ecologically, recreationally and commercially important fish such as Australian Salmon Arripis trutta, King George Whiting Sillaginodes punctata, and Bream Acanthopagrus butcheri (NCR).
Unusual features of south-eastern Australian estuaries
- Worldwide, there is generally freshwater input at the head of an estuary. As this water flows through the estuary, it is mixed with seawater carried into the mouth with the incoming tide. The tidal outflow exceeds the inflow so that there is a net movement of water through the estuary. However, most south-eastern Australian estuaries do not fit this model. Many have sand barriers across their mouths, which cut off or restrict the inflow of seawater for periods of months to several years. Also, under conditions of hot weather and low rainfall, in south-eastern Australia evaporation of water from the estuary may be similar to the freshwater input. Under these conditions, salt concentrations in parts of the estuary are similar to that of seawater, or even slightly higher. Evaporation rates in south-eastern Australian estuaries never greatly exceed the freshwater input – the situation which produces the hypersaline estuaries of north-western Australia.
Estuarine species - Benthic Burrowers
- Estuaries are home to a variety of animals and plants. The benthic (sea floor) community is made up of animals living in the sediments of the estuarine floor. The diversity and abundance of the benthos indicates the overall health of the estuarine ecosystem (MV).
- What are benthic macrofauna? Benthic animals are those associated with the bottom of seas, rivers, lakes, etc. A large proportion of the biodiversity of estuarine habitats is found in the benthic community. Many of the worms, shrimps, snails and bivalves that live there are important food sources for fish and birds.
- Unlike fish and plankton which can move up and down in the water column, benthic animals live in what is essentially a two-dimensional environment. Concentrations of fish and plankton form and disperse in response to tides and weather. But because of their reduced mobility, benthic communities do not change very much in response to tides or weather.
- Benthic species live in an environment where concentrations of pollutants are likely to occur. Many benthic animals can only recolonise an area by larvae settling, so cannot recolonise until the next breeding season. Often mobile animals will move back into the area only slowly. Short-term pollution events are therefore detectable in the benthic community for a long time.
- Chemical changes associated with the change from freshwater to saltwater in estuaries cause dissolved materials transported down rivers into the estuary to flocculate (collect together in a loose aggregation). The flow of water in estuaries is slower than in rivers, so the flocculant material and suspended particles can settle out of the water into the sediments. These processes allow pollutants to reach greater concentrations in the sediments than in the water. Because of their close association with the sediment, benthic organisms are affected by pollutants before animals in the water column. The benthic community can therefore be the first organisms to show weakening environmental health in an estuary.
Threats to Victorian estuaries
- Estuaries are highly productive coastal environments, providing habitat for a wide variety of fish and invertebrates (crabs, prawns and oysters) of ecological, commercial and recreational importance. They also supply food to many resident and migrant birds.
- The plants and animals in an estuarine community depend on the physical and chemical environment. Managing the estuary to maintain a healthy environment requires maintaining the physical and chemical environments in the range normally experienced by the natural community.
- Estuaries are used by the Victorian population for transport, commercial and recreational pursuits. Many of our major estuaries have cities located on or near them. Many Victorians participate in fishing and other water sports based on estuaries. As a result, the health of our estuaries has a high profile in Victoria. However, we currently have no way of assessing whether the overall health of our estuaries is improving, being maintained or deteriorating (MV).
- Since estuaries are at the bottom end of catchments, they are subject to all the impacts on the catchment. Estuaries are often the most popular and heavily used portions of a river reach, and can be used for boating access, fresh water, fertile land for agriculture, and fish and shellfish catches (Estuaries Network). As many catchments in Victoria are degraded, most estuaries are at risk. Few would be considered to be in a natural or near-natural condition (EPA).
- Victorian estuaries are under pressure from urbanisation, farming, modified stream flows and drought. Because they are downstream from catchment activities, estuaries are especially vulnerable to the cumulative effect of human activities (Estuaries Network).
- There is probably no other natural ecosystem as vulnerable to human activities downstream than an estuary, so integrated management along the entire watercourse is extremely important (Estuaries Network).
What can you do?
- Support the creation of marine national parks and reserves that protect estuarine habitats.
- Help monitor the health of estuarine areas through programs such as Estuary Watch and Coastcare.
- Become involved in stream protection programs for those streams that drain into estuaries or marine areas.
- Watch for developments that might impact on the health of your catchment area e.g. aquaculture / marine farming operations, stormwater outlets, and development.
- Develop community displays highlighting the impact of catchment activities on estuarine and marine habitats.
- 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 can generally 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 (DSE). 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 (NCR). 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 (DSE).
- 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 (NCR).
- 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 and the large and fleshy Bull Kelp, 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 and Sooty Oystercatcher (DSE).
- 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, Hormosira banksii. The green alga Sea Lettuce (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 limpet Cellana tramoserica, top shells Austrocochlea spp and conniwinks Bembicium spp. Common predators include the whelk Cominella lineolata and murex Lepsiella vinosa. Other invertebrates on intertidal reefs include small crustaceans such as barnacles and crabs, the seastar Parvulastra exigua and tubeworm Galeolaria caespitosa. Intertidal reefs are important foraging habitats for shorebirds at low tide and for fish at high tide.
- As far as people are concerned, intertidal reefs are one of the most accessible parts of the marine environment, and consequently 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 (NCR). Conservation of these areas depends on controlling 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.
Open water habitats (Pelagic)
- Pelagic (open ocean) species are those that are found in open ocean waters, rather than in waters close to shore or inland.
- Away from the shoreline, Victoria’s deeper open waters support plankton, sea jellies, squid, large mammals including fur seals, Bottle-nosed Dolphins and Southern Right Whales, seabirds such as gannets, petrels and Little Penguins, and fish including pilchards, anchovies, Silver Trevally, Barracoota and Jack Mackerel.
- Pelagic fauna may gather together (aggregate) for different reasons. Many pelagic fishes school as a means of protection against predators. Aggregation may also occur because many individuals are attracted to a particularly favourable habitat. For example, Orange Roughy Hoplostethus atlanticus aggregate around seamounts, pinnacles and canyons as they seek out habitats with particular hydrologic profiles. Southern Right Whales migrate from the Antarctic to Victorian waters and gather together in preferred nursery areas along the western Victorian coast to give birth and nurse calves.
- Seabirds, predatory fishes and marine mammals all congregate in areas were there is a reliable food supply, such as the upwellings (see below). The Bonney coast of western Victoria is one of only 13 known areas of frequent aggregation for Blue Whales Balaenoptera musculus.
- The aggregation of pelagic species, for whatever reason, also creates opportunities for courtship and breeding in normally scattered species. For example, Blue Whales which have congregated along the Bonney coast to feed have also been seen courting each other. Species that gather together are often more vulnerable to recreational and commercial fishing pressures, diseases and localised environmental disturbances.
- The quality of pelagic waters also has a direct influence on the health of nearshore waters and other marine habitats. The marine national parks along Victoria’s open coast waters therefore extend to the state limit of three nautical miles (or 5.5 km) and protect pelagic waters.
Plankton and nekton
- The water column in Victorian marine waters is a habitat for plankton and for pelagic animals including fish and sharks (nekton). This habitat is obviously present throughout the Victorian marine environment, but it is considerably different along different environmental gradients.
- The temperature of marine and coastal waters fluctuates seasonally. There are greater temperature ranges in bays and estuaries, as the smaller bodies of water are more quickly heated and cooled. Ocean temperature is influenced by currents and upwellings. The east of the state is influenced by the warmer East Australia Current, whereas the Otway and Central bioregions are influenced by the temperate South Australia Current and Northern Bass Strait waters. The Flinders bioregion is under the influence of the South Australia Current, East Australia Current, Northern Bass Strait and cold subantarctic surface waters
- Other important environmental gradients include greater wave action in shallower waters and greater turbidity closer to shore. In bays and estuaries, the habitat is highly influenced by nutrient runoff, suspended matter and freshwater inputs from rivers and other drainages.
- Plankton are a major source of food for benthic (bottom-dwelling) invertebrates and nekton. They also play a key role in the carbon, nitrogen and other nutrient cycling in marine systems. The photosynthesising fraction of plankton, phytoplankton, is highly productive. In Port Phillip Bay it is responsible for at least two-thirds of primary production.
- Diatoms and dinoflagellates are the dominant type of phytoplankton. The abundance of phytoplankton communities in Victoria varies depending on the season, with peaks during summer and lowest concentrations during winter. This is probably because temperatures are higher in the summer and more light tends to be available, while factors limit abundance during colder months.
- Phytoplankton abundance is also limited by the availability of nutrients, particularly nitrogen. Concentrations of phytoplankton are often highest in estuaries and river mouths, where there is greater input of nutrient from terrestrial runoff.
- Phytoplankton are preyed on by zooplankton (small floating animals). Zooplankton include a wide variety of organisms, including amoeboids, crustaceans, jellyfish, invertebrate larvae and fish larvae. Crustaceans, particularly copepods and cladocerans, make up a large proportion of the zooplankton in Port Phillip. The composition of the zooplankton, similar to that of phytoplankton, shows some influence of seasonality.
- In Victoria, active-swimming pelagic organisms, nekton, are predominantly fishes and cephalopods, but also include marine mammals, penguins and crustaceans (e.g. krill). Nekton play an important role in the trophic pathways of Victorian marine ecosystems. They facilitate the transfer of energy from plankton, through the food web, to higher order organisms; for example plankton are a food source for small nektonic species which in turn are prey for other predators.
- High abundances of nekton are often associated areas of high phytoplankton productivity, such as upwellings. In Victoria, nektonic fishes and cephalopods support significant recreational and commercial fisheries. Marine mammals also have high scientific, social, historical and tourism value.
- Between November and April, along the Bonney Coast in the Otway bioregion, an oceanographic process called ocean upwelling occurs. Seasonal prevailing winds drive warm, nutrient-depleted surface water away from the coast. This draws deeper, colder water to the surface to replace it. The deep water is nutrient-rich, and as it reaches sunlit surface waters it promotes high productivity of phytoplankton. These phytoplankton are the base of a highly productive food chain that sustains a high biomass of zooplankton and nekton, including krill and commercially important pelagic fishes such as tuna, sardines and anchovies.
- The krill and small fishes are an important food source for pelagic sharks, and seabirds and fur seals during the summer breeding season, and also support the significant population of Blue Whales along the Bonney coast.
- Victoria is surrounded by a magnificent stretch of beaches and coastal sand flats, and sandy plains are a common feature beneath the surface of Victoria’s coastal waters. These undulating sandscapes might at first seem to be desert-like expanses with no visible sign of life and for a long time sandy habitats were considered biological deserts and they are one of the least studied marine habitats in Australia. They can be harsh environments which few animals or plants can tolerate, except for the occasional shrimp-like sea crustaceans. This is especially true on high-energy ocean beaches where crashing waves and strong currents make it very difficult for plants and animals to attach to the constantly shifting sediment.
- Because the sediment in sandy habitats is fairly unstable and is shifted by water currents plant life such as seaweeds and seagrasses are unable to establish themselves. This instability and the lack of shelter also mean that few large vertebrate animals live here permanently. Instead, animals tend to be small and burrow into the sand or live in the tiny spaces between sand grains.
- Grain size is a good indicator of wave energy. Large grains are deposited by stronger currents whereas fine-grained sediments indicate quieter water. Grain size is an important determinant of whether animals can burrow in or not.
- The stark appearance of sandy habitats is deceptive. The ripples lining a sandy seafloor may look bare and empty, but they can be rich and plentiful in animals. If you look closely, you’ll find them alive with a rich and abundant assortment of organisms.
- Healthy sands and sediments usually have small animals living under the surface (called infauna) including worms, crustaceans and bivalves such as pipis. Small animals living on the surface are called epifauna. These are important food items for many fish, crabs, rays and sharks that forage over the sand so their presence is vital to healthy, functioning food chains.
- Many species have adapted to living in sandy habitats with great success, on and under the surface of the sand. Other microscopic animals have even colonized individual sand grains. A square metre of sand can yield several thousand organisms and hundreds of species.
- Many transient animals such as fish and stingrays pass over sandy plains, while other more permanent residents such as flounders and crabs use their sandy coloured bodies as camouflage to blend into the soft sea floor.
- Sandy habitats in the cool waters of Victoria are ‘species packed’, yielding unique and bizarre species many of which have not even been named. Sheltered inlets with fine sand and many nutrients can support communities of 300,000 per sq. m, such as the intertidal population near the Werribee treatment plant in Victoria. Parts of Victoria’s east coast have been identified as the most biologically diverse shallow-water marine environments in the world. The Ninety Mile Beach, to the west of Lakes Entrance, is Victoria’s most extensive stretch of sandy seafloor habitat, and home to spider crabs, sea anemones, sand skaters and stingrays. Up to 800 species have been recorded in a 10 square metre area on the sandy seafloor from Lake Tyers to Cape Conran and one square metre of sand from the subtidal area off Ninety Mile Beach can contain 6,000 individuals.
- Animals living in the sand such as scallops, prawns and worms are essential prey for many fin fish, skates and rays. A scattering of large rocks, shells and rubble provides anchorage for plants and non-mobile animals like sponges. The Ninety Mile Beach Marine National Park protects a small section of this habitat.
- Few people are aware of the importance of soft sediment habitats in nutrient cycling in the marine environment. Microscopic algae growing on sediments play an important role in controlling nutrients. In Port Phillip Bay, for example, mats of minute algae take up nitrogen produced from the Werribee treatment plant and other sources to create carbon, a rich food source for many small animals, and keep the water clean. This delicate system could be permanently damaged by decreasing light levels, for instance through dredging, or by overloading the amount of nitrogen put into the Bay.
- Water currents and waves sculpt sands along the bottom into soft peaks and troughs like miniature submerged mountains. Variation in the size and type of sand grains, the force of currents and waves and depth all combine to create different habitats which support different species of animals.
- Sand can range from coarse, shelly rubble to fine silty sediment. Coarse sediments are more unstable and difficult to burrow into. They tend to have more animals living on top of the sand or buried deep down. Fine silty sands in sheltered inlets are more compact and therefore provide a more stable environment and contain more animals (and sometimes plants) in the upper layer than course sand.
- As few plants grow in sandy habitats, much of the food present comes in from the sea and land. Dissolved nutrient in the water, drift algae and dead animals are brought in by the sea, while insects and plant litter come from the land.
Creatures in sandy habitats
- Many people are familiar with some of the more noticeable creatures that live in sandy environments in the surf zone and just past the breaking waves – fish such as flathead and flounder, creatures in shells including pipis, and swimming and burrowing crabs.
- Gastropod snails are also common, ploughing through the sand like small bulldozers. Many of them have richly patterned shells and brightly coloured bodies. Bivalve molluscs such as cockles and commercially harvested scallops lie partially buried in the sediment. Occasionally scallops make comical attempts at swimming. By rapidly clapping their two shells together they are able to propel themselves through the water and escape the clutches of potential predators such as sandy octopus.
- The remaining organisms are far more abundant but rarely seen, either because they live under the surface, or because they are very small. Invertebrate animals that live and feed beneath the surface of the sand are called infauna. Other animals that are fixed in the sediment but feed above the sand surface, or that are mobile and move about on top of the sand, are called epifauna.
- Crustaceans, the most abundant animals in sandy habitats, include shrimp-like sea fleas (amphipods) and sea lice (isopods). Sea lice have flattened bodies, many with spade-shaped tails adapted for digging and swimming. Slender-bodied sea fleas slide easily between sand grains and propel themselves through the water with a flick of their tails. Some are hunters, others are foragers and feed on rotting plant material that has washed in.
- This drift algae is a very important source of food for many of the animals that live in sandy habitats, as plant life in these areas is generally restricted to microscopic algae and fungi attached to sand grains. Tiny worms and copepod crustaceans less than one mm long live between the sand grains and graze on microscopic organisms attached to sediment particles.
- Many worms are also present in Victoria’s sandflats. These include thin narrow ribbon worms, which slide between the sand grains, and segmented bristle worms which roam around on top of the sand in search of prey. Other worms stay permanently fixed in tubes in the sand with only their mouthparts extending into the water to capture food. Many fish love to make a meal of the tubes and pipi siphons which emerge from the sand. These sand dwelling animals are also collected for bait by fishers.
- Sea cucumbers and burrowing worms are the earthworms of the sea and aerate the sand by digging it out to make their tunnels, or by swallowing it to extract the food it contains. Many these species produce mucus which acts like glue and binds the sand together. The tubes of various worms are often tough and densely packed which helps stabilize the sand and enables other animals to attach themselves.
- Large many-armed sea stars roam around sandy plains, while heart urchins, close relatives of sea urchins, bury themselves in the sand, visible only by a few hairs poking out. Delicate brittle stars reach large numbers. Soft-bodied anemones are less common because the fragments of shell which they need to cling onto are scarce.
- Shrimps, prawns, juvenile crabs, gobies and young flounder may use sheltered sandy areas as nursery grounds and eat large numbers of the small invertebrates living in the sand. Delicate animals such pink and orange sea pens are found in deeper waters scattered amongst stalked sea tulip (ascidians), sponges and feather-like hydroids.
- Some of the biggest animals are large fish such as flounders, rays and stingarees (a close relative of rays) which forage along sand and mudflats. Sole and greenback flounder capture animals moving on top of the sand and also unearth soft-bodied and shelled organisms from the sediment.
- Many small fish such as sardines and sprats dart about in the water above the sand and intermingle with hardyheads and silversides, toadfish and King George whiting. Sand whiting forage on the bottom, feasting on worms, small crabs and ghost shrimps. Flatheads are common and voracious predators, eating small fish and a wide variety of crustaceans such as prawns. Many fish species in sandy habitats, including sand whiting and flatheads, are important to recreational and commercial fishers.
- Crabs, birds and octopus are other important predators.
- A few sand species such as the giant marine worm can grow up to two metres long, but most permanent residents in sandy habitats are less than a centimetre in diameter so that they can fit between the sand grains.
Threats to sandy plains
- There have not been many studies of the biological communities in Victoria’s sandy habitats so their ecological importance is not fully understood. There is a similar lack of knowledge about how these communities react to severe disturbance such as sand and scallop dredging, or sources of pollution such as oil spills, sewage discharge, agricultural herbicides and toxic wastes.
- Because there is often very little growing on bare sand or sediments it is difficult to assess the health of these habitats visually. Scientists usually have to take sand samples (cores) and analyse the types and abundance of animals in these habitats, as well as determining their chemical and physical properties.
- Pollutants including petrochemicals and heavy metals such as lead and cadmium have a major impact on sandflat habitats in Victoria. Sediments can act as sinks for many pollutants such as oil and heavy metals, contaminants which can accumulate in the sand over time.
- Deposit feeders including many worms and sea cucumbers swallow the sediments and so ingest these toxins, and these animals are then eaten by predators such as fish. The pollutants which accumulate in tissues can make shellfish and other marine species unsafe to eat, for both fish and humans. If contaminated sand is stirred up, these chemicals can be released into the water where they may be taken up by filter feeding animals such as tube worms, sponges and sea squirts.
- Excessive nutrients, for example off Werribee sewage plant, may affect sand communities by killing off sensitive species and causing a population boom in other more resilient species, or creating plankton or bacterial blooms. Introduced marine pests such as the North Pacific seastar, Asterias amurensis can have a huge impact on sandy seafloor communities as they are voracious predators of shell fish and other invertebrates. Other threats include bait collection of animals, such as pipis, which can have a serious effect on local populations if large numbers of animals are removed.
- Dredging (eg. for scallops or sand) is another highly destructive process that involves the removal of a deep layer of sand, fatally damaging the delicate organisms in its path. Sand is often dredged off the seafloor for use in construction and to replace sand being eroded from urban beaches.
- Although scallop dredging has been phased out of Victoria’s bays, dredging along the Victorian coast continues unchecked. These physically destructive processes can kill resident animals, modify the habitat and re-suspend toxins that may be lying in the sediments.
- Sponges, sea squirts, sea pens and other invertebrate animals often attach themselves to shells, rubble and small rocks in the sand. Because these animals are relatively soft, and cannot move, they can be seriously damaged and killed by dredging. Communities which have been subjected to intense and repeated dredging take a long time to recover and may never return to their original condition.
- We know so little of the biological communities inhabiting sandy sea floors and researchers continue to uncover new species with each investigation. They are considered diverse communities which are good indicators of environmental health, yet they remain poorly understood. Even with our limited knowledge it is clear that the submerged sands around Victoria are unique environments which deserve our protection.
What can you do?
- You can help conserve sandy areas by supporting the creation of marine national parks and reserves that protect these habitats.
- Sand is one of the raw materials from which glass is manufactured – ideally pure white silica sand. Unfortunately, sand mining is a destructive process in marine and coastal environments. Recycling glass is one way to take the pressure off the natural resource.
- For further information concerning sandy plains and conservation initiatives to protect them, contact:
The Victorian National Parks Association
Phone: 9347 5188
Seagrass meadows and estuary grass
- A healthy bed of dense, green seagrass, busy with animals and fish swimming above, is an incredible sight.
- Seagrasses are flowering plants that grow underwater in coastal marine and estuarine environments. They are generally only found in shallow, well-lit water in the shelter of bays and inlets, and often form dense meadows which resemble the lush, green grasslands that grow on land. On a warm, sunny day in clear water you can actually see the bubbles of oxygen rising up out of the seagrass leaves.
- Seagrasses disperse seeds and grow from horizontal rhizomes (a horizontal, usually underground, stem that often sends out roots and shoots from its nodes). Some species also occur in shallow, sheltered areas along the open coast.
- Seagrasses have terrestrial (land based) ancestors and have only returned to the sea in recent evolutionary history. Like flowering plants on land they produce flowers and seeds but these are small and difficult to see in many species. Most seagrass species produce flowers in autumn or summer. Pollen from the flowers is released into the water and carried to flowers on other plants where pollination occurs. Seeds or fruits are produced which then develop into a new plant. In the warmer months seagrasses propagate by sending out rhizomes which give rise to new shoots and to more rhizomes. A single seed can therefore give rise to a large area of genetically uniform shoots connected by a network of rhizomes.
- In Victoria, the main types of seagrass are eelgrasses (Heterozostera tasmanica, Heterozostera nigricaulis and Zostera muelleri), sea-nymph (Amphibolis antarctica), paddlegrass (Halophila australis) and strapweed (Posidonia australis). Eelgrasses and Amphibolis are the most common.
- The eelgrass Zostera muelleri grows on sheltered intertidal mudflats. The two Heterozostera eelgrasses grow on subtidal sediments: Heterozostera nigricaulis mostly in bays and estuaries, and H. tasmanica in sheltered coastal waters. Amphibolis antarctica grows on moderately exposed sand and sand covered reefs. It is not known to occur east of Wilsons Promontory.
- Halophila australis is most common on sheltered sands and Posidonia australis is only found on sheltered subtidal sediments in Corner Inlet and Nooramunga, where it forms extensive beds. Estuary grass Ruppia megacarpa are related to true seagrass and often considered similar habitat. Ruppia occurs in shallow estuaries, coastal lagoons and salt lakes.
- Seagrass communities are very important in maintaining ecological processes, including primary productivity, nutrient cycling, food web pathways and provision of habitat. They supply gases and nutrients that are an essential part of marine food webs, hold sediments together and provide habitats for adult and young fish and other animals.
- Seagrasses are anchored in silty or sandy substrates by an extensive underground network of fibrous stems (rhizomes) and roots that stabilise the sediment. Leaves or blades extending up from the base act as a baffle, slowing the surrounding water flow. This allows sediment to accumulate around them and helps prevent erosion.
- Seagrass roots absorb nutrients, but unlike land plants they do not take up water. To cope with living in oxygen-poor mud, seagrasses have evolved air canals that carry oxygen from the leaves to the buried rhizomes and roots. Nutrients and gases are also absorbed across the leaf surface.
- Seagrasses create important structure in soft sediment habitats, and are highly productive components of the marine ecosystem. They form a surface where algae and sessile (non-moving) invertebrates can attach themselves, and a sanctuary for mobile invertebrates. Seagrass beds are primary habitat for many syngnathids, including pipefishes, seahorses and seadragons, which are species of conservation significance.
- In addition, seagrasses are important nurseries for many ecologically, commercially and recreationally important fishes, including king george whiting (Sillaginodes punctata), southern sea garfish (Hyporhamphus melanochir) and bream (Acanthopagrus butcheri). They are also important breeding and feeding grounds for large numbers of fish and invertebrate species and play an important role in nutrient cycling and the food web of inshore coastal areas.
- Seagrasses meadows spread across thousands of hectares in southern Australia’s temperate waters. However, there have been dramatic declines in seagrass habitat in recent decades, both globally and within Victoria. There is no clear single cause of this decline and it is most likely to be a combination of many factors. It is vital for the creatures that depend either directly or indirectly on the plants, for shelter, food or reproduction, that seagrass habitats remain intact.
Animals and plants in the seagrass community
- Seagrass meadows are alive with animal activity and are habitats for many plant and animal species. A diverse range of fish from fiddler rays to delicately coloured pipefish moves through the meadows, while sedentary invertebrate animals such as stalked sea squirts (ascidians) and large razor clams attach themselves in the sediment.
- Small plants and animals live on stems or leaves and amongst the rhizomes (‘roots’). These are known as epiphytes and epifauna and include bacteria, micro-algae, small macro-algae and encrusting animals such as delicate, yellow sponges and sea mosses (bryozoans).
- Small fish and crabs graze on these encrusting organisms and may also forage on small animals living in small patches of sediment at the base of plants. Live seagrass itself is a minor source of food for animals that live in seagrass communities but forms a major part of the diet of some animals such as black swans.
- Seagrasses actively produce small amounts of nutrients required by other coastal plants and animals. Dead seagrass is also an important source of nutrients for many animals like bacteria, marine worms and crustaceans. Large amounts of decaying seagrass provide nutrients that are recycled through the food chain. Dead and broken leaves washed up on the shore provide a valuable food source and habitat for small crustaceans such as sandhoppers and various micro-organisms.
- Small crustaceans live in seagrass meadows and include species of seed shrimps, sea fleas, sea lice, small pebble crabs and pea crabs. Segmented worms (polychaetes) crawl over seagrass leaves in search of food, or else fix themselves in permanent tubes. Sea snails of different kinds and soft-bodied sea hares are also common. Many-armed sea stars, prickly sea urchins and sea cucumbers are abundant.
- Sedentary animals such as sponges, sea squirts and anemones are distributed in patches throughout seagrass beds. Delicate filter-feeding pearl oysters and solitary anemones attach themselves to leaves. Larger predators include octopus, squid, fish, seabirds and crabs.
- Seagrass meadows are important because they provide refuge and shelter for many organisms from physical threats such as predators and wave action. They act as nursery grounds for the young of a range species, many of which are commercially important, including snapper, bream and garfish, western crayfish and shrimps.
Threats to seagrass communities
- There are 60 seagrass species in the world, and 16 of them are found only in temperate Australian waters. Seagrass meadows are nursery grounds for many species including snapper, shrimp and bream, and are extremely important to the overall health of marine ecosystems and to commercial and recreational fisheries.
- Seagrasses are very sensitive to human disturbance caused by sewage outfalls, heavy metal pollution, agricultural runoff and other activities. There is also concern that netting by commercial fishers could change the structure of seagrass areas by trimming the tops from the seagrass blades. This could lead to a denser seagrass stand, reduce light penetration and change the population structures of invertebrates that feed on the seagrass.
- Seagrass meadows are regarded as important indicators of the health of the marine environment. Unfortunately there has been an extensive decline in seagrasses around the coastline of temperate Australia in the last 20 years. In some areas seagrasses have completely disappeared and in many cases scientists have been unable to determine the exact cause. They are very slow to recover from disturbance, if at all, as shown by the 85% loss of the once-extensive seagrass beds of Western Port Bay. The parks at Western Port and Corner Inlet protect seagrass meadows. Corner Inlet is the stronghold of the broadleaf seagrass Posidonia.
- Like all plants, seagrasses need sunlight to photosynthesise and survive. One square metre of seagrass can generate up to 10 litres of oxygen per day via photosynthesis. Seagrasses naturally have a small amount of other organisms (epiphytes and epifauna) living on their leaves. Increased nutrient levels in the surrounding water can cause epiphytic algae to bloom and smother seagrass blades, preventing enough sunlight from reaching the leaves.
- Nutrients can enter marine systems from sewage works, stormwater, aquaculture or agricultural fertiliser and septic tank run off and seepage. More particles in the water can also lower light penetration. Sources of suspended particles can include topsoil from forestry or agricultural operations, industrial and mining discharges, coastal engineering works and dredging.
- Seagrass species vary in their susceptibility to disturbance. For example some 90% of Heterozostera (eelgrass) plants have disappeared from Western Port Bay while the amount of Amphibolis (wireweed) hasn’t changed much. A common characteristic of all seagrass species, however, is that they are very slow to recover from any sort of disturbance, and some species may never return to their original state. The extent of seagrass recovery depends on the resilience of the species and the scale and nature of the disturbance. While smaller areas can be recolonised, larger areas prove more difficult. Rapid colonisers such as Zostera are also far more likely to recover than slow colonising Posidonia.
- The loss of seagrass can release sediment that was once held together by their roots and rhizomes. This causes erosion and a suspension of solids in the water, and stops as much light from reaching the rest of the seagrass plants. Erosion can also result in a build-up of sediment on beaches. Valuable fish nursery areas and habitat may also be destroyed which impacts on commercial and recreational fisheries.
- Loss of seagrass can happen over a wide area or be restricted to specific sites. Small scale disturbance is caused by boat propellers and anchors (which frequently rip out clumps of seagrass), dredging, spoil dumping and feeding by plant-eating animals like swans. Heavy metals, pesticides and other chemical pollutants cause more widespread damage, killing plants or interfering with their capacity to grow and reproduce.
- Some scientists have suggested that increased sea temperatures, associated with a build up of greeenhouse gases in the atmosphere, may be partly responsible for the decline. Dieback may also be the result of a depletion in the Earth’s ozone layer, resulting in an increase in harmful UV rays, which cause seagrass ‘sun burn’ and death. Natural disturbances such severe storms and floods also take their toll.
- It is natural for some algae, sponge or other encrusting life form to grow on seagrass blades. When there is only a small amount of this growth (called epiphytes) this is not a problem, but too much can smother and kill seagrass. Harmful algal growth is often caused by a high level of nutrients in the water – often coming from farms, households, drains and human and animal excrement.
- Also, if the surrounding water becomes murky and blocks available sunlight then seagrasses can weaken and die. This murkiness is often caused by dirt and sand floating in the water and again is often caused by actions happening on land – like building roads and chopping down trees, or by coastal dredging.
- Chemical pollution from land and marine sources also harms seagrass. In Western Port there was an 85% decline in the total seagrass cover between 1974 and 1984. A combination of human activities is believed to be responsible for the loss. Generally seagrass takes a long time to grow back after it has been damaged which is also why it is so important to protect and restore existing areas.
Conservation and management
- A large number of research projects are currently being undertaken to determine the cause and extent of seagrass decline, however, the picture is far from clear. In many cases the source of disturbance cannot be identified, although it is likely that direct and indirect effects associated with human activities are to blame. Scientists have employed aerial and satellite images which give an accurate picture of the extent of seagrass and show whether seagrass beds are changing.
- While it is possible to track the loss of seagrass cover, halting and reversing the decline has proved far more difficult. Attempts to replant damaged seagrass beds in various parts of the world have met with little success. While Posidonia australis and Halophila decipiens are catagorised as rare in Victoria, there are few laws or projects in Victoria aimed specifically at protecting seagrasses.
What can you do?
- Support the creation of marine national parks and reserves that protect seagrass habitats.
- Help monitor the health of seagrass areas through programs such as Reef Watch, Coastcare and Sea Search
- Become involved in stream protection programs for those streams that drain into marine areas with seagrass communities.
- Watch for developments that might impact on local seagrass areas e.g. aquaculture / marine farming operations, stormwater outlets, and dredging operations.
- Develop community displays highlighting the importance of seagrass habitats.
Where to see Seagrass Meadows
- Seagrass meadows are sometimes visible from piers and jetties in the shallow, sheltered waters of bays and inlets. Snorkelling over these meadows is possible in some locations and is a great way to experience seagrass communities.
- West Coast: Portland Bay, Port Campbell Bay, Peterborough
- Central Coast: Flinders Pier in Westernport Bay, Newhaven on Phillip Island, off Williamstown beach, Port Phillip Bay.
- East Coast: Corner Inlet