An Overview of Coastal Ecosystems and Their Values
1. IntroductionThe Macquarie Dictionary defines the coast as comprising all areas within or neighbouring the foreshore. The length of the coastlines within Australia are:
As would be expected along a coastline of this length, there is considerable
variation of landform types.
Source: Resource Assessment Commission (1993)
Forming as they do the interface between land and ocean, many - though not all - coastal ecosystems possess very high biological diversity and productivity. Although these ecosystems are highly variable, they are both highly inter-related and highly interdependent and they all integrate to form greater coastal landscapes. Thus, their protection and conservation should not be considered individually, but rather as part of an overall coastal management approach.
While conservation of certain coastal ecosystems is addressed by relevant State Government agencies, it is neither possible, nor appropriate, to include all relevant areas into systems of State parks and reserves. Local government must therefore also take some responsibility in regard to the conservation of such ecosystems via non-reserve conservation management.
Even for those ecosystems which are already protected by State parks or reserves, or which fall beyond Local Government boundaries, local planners must still consider the influences of any adjoining land-uses under their control.
These guidelines provide a list of important coastal ecosystem types, whose presence must be taken into account by local governments during planning processes. The list also provides a brief outline of values associated with each ecosystem and key management considerations.
The ecological processes which shape and drive the structure and function of each of the coastal ecosystems, not only maintain these as recognizable and functional coastal systems, but also link these ecosystems. Thus, an apparently minor change in one of these processes such as groundwater flow or tidal inundation may change one ecosystem into another.
Because of the overriding importance of hydrological processes in defining the functional limits of these ecosystems, three broad biophysical settings for coastal ecosystems are recognized; those which are (A) rarely, if ever, flooded (Shores); (B) periodically flooded or waterlogged (Coastal Wetlands); and (C) usually tidally submerged (Inshore Marine).
Each of these biophysical settings is characterized by a suite of coastal ecosystems which reflect the various dominant ecological processes. The biophysical settings and their associated coastal ecosystems covered by these guidelines include:
Each of these biophysical settings and their commonly associated coastal ecosystems are described below.
2. Characteristics And Values Of Coastal Ecosystems
This biophysical setting may include Sandy Beaches, Spits and Frontal Dunes, Hind Dunes, Beach Ridges, Mobile Sand Sheets and Cays. The coastal ecosystems generally associated with these settings vary considerably along the coastline depending on the rainfall, exposure or stability, and the age or maturation of the sandmass.
Sand spits and sandy beaches support no permanent vegetation although they may provide suitable habitats for invertebrates. These ecosystems are characterized by low fertility sandy sediments with a low water-holding capacity, considerable wind-pruning and salt-spray as well as frequent sand remobilisation.
The primary dunes, generally more protected from wind and spray, may support shrubs or woodlands These ecosystems are usually characterized by low nutrient status but the development of organic soil horizons has increased the water-holding capacity of the soil.
1.2 Hind Dunes
In the higher rainfall regions of the tropics, stable hind dunes generally support mixed rainforest. These dunal rainforest ecosystems are characterized by deep and well developed soils having a high organic content and nutrient status as well as good water-holding capacity. Where the rainfall is less abundant or the dunes are low in nutrient status, Eucalyptus open-forests or low-open forests occur.
1.3 Beach Ridges
Apart from heath vegetation which generally dominates beach ridges low microphyll vine forest may occur on beach ridges in the more subtropical parts of Australia.
1.4 Mobile Sand Sheets
Mobile dunes and sandsheets provide a harsh environment for plant life and only a few, highly specialized plants can grow. Plants of this habitat must be tolerant of or resistant to sand blasting and occasional sand burial, salt spray, water deprivation and shifting substrates.
Because of the lack of permanent vegetation, large sand sheets may serve as groundwater recharge areas, where rainfall infiltrates the sandmass and forms part of the regional groundwater aquifer.
Cays are small islands consisting of sand or coral shingle
which has been piled up to above high-water mark on a limestone base
by the combined action of currents and waves. Low-growing grasses and
herbs are usually the first colonising plants which are able to survive
on these low nutrient substrates with a poor water-holding capacity
while subjected to strong, salt-laden winds. Once the sand is somewhat
stabilised by these pioneer species, shrubs and small trees may then
become established. Those cays with a well-developed vegetation invariably
have, and depend on, a freshwater aquifer within the cay. This essential
store of water is replenished during the wet season and serves as the
water supply to the vegetation during the dry season.
Sandy Coasts: Values and Management Considerations
Sandy Coasts comprise an important habitat for numerous, often specially adapted species including rare or threatened plants and animals. Many of these plant communities are slow growing and individual plants may be extremely old. All of these ecosystems are effective sand binders and therefore enhance coastal stability against wind and water erosion. Virtually all of these ecosystems have high scenic and recreational amenity and form an important component of the Australian lifestyle. In addition, some of the more extensive sandmasses (whether vegetated or not) have a regional significance as groundwater recharge areas.
Some of these ecosystems are susceptible to nutrient enrichment and to frequent fires. Both of these events can significantly change the species composition, allowing opportunistic species and exotic weeds to invade. Similarly, breaking the canopy of these ecosystems (e.g. by clearing, burning, grazing or access tracks) may allow a remobilisation of the underlying sandmass, leading to wind or water erosion.
In terms of other habitat values, the above-tide areas of beaches and dunes are important roosting and nesting areas for waders and a number of other shorebirds. Frequent disturbance of shorebirds at their high tide roosts can lead to unnecessary flight and severely drain their energy reserves. This may be critical for the smaller species, which use energy at a higher rate and need to feed for long periods while sand and mud flats are exposed.
Disturbances of all descriptions, from beach vehicles and dogs to major reclamation works, pose a threat to beach or cay nesting birds. As a consequence, some of these species are becoming rare and endangered.
In many localities, foreshore ecosystems are also vital
nesting sites for marine turtles. Physical disturbance or obstructions
such as construction of training walls, jetties, or pipelines will all
have serious impacts on the success of nesting. Other factors such as
the levels of light pollution from landward sources, or predation from
feral or domestic animals, may significantly impair the survival rate
Summary: Sandy Coasts
Sandy Coasts are sensitive to:
Control measures may include:
High bluffs and rocky headlands are mainly found in south-eastern
Australia. Many headlands and bluffs support mixed grasslands, particularly
where soils are shallow. Thickets of shrubs or trees may occur in
these grasslands. Where soils are better developed or in higher rainfall
areas, Araucarian vine forest/thicket may develop.
Rocky Coasts: Values and Management Considerations
These ecosystems have very high scenic and recreational amenity value which is susceptible to inappropriate development and intense visitation. In addition, these ecosystems are susceptible to fires and grazing because of their shallow, often skeletal, soils with low water-holding capacity. Where trees occur, these are often severely wind-pruned and slow growing as a result of exposure to salt-laden winds. Management considerations for these areas include site hardening where access might be facilitated by formed tracks and viewing areas but where the remaining areas have limited access.
Summary: Rocky Coasts Values
Rocky Coasts are sensitive to:
Control measures may include:
B. Coastal Wetlands
Coastal wetlands include lands permanently, periodically or temporarily under water or waterlogged with sufficient frequency and/or duration to affect the biota and/or the soils.
Coastal wetlands may be subdivided into non-tidal wetlands and tidal wetlands to distinguish periodically flooded or waterlogged ecosystems that are salt-tolerant from those that are not.
Increasingly, artificial wetlands are being used for wastewater treatment or for other management objectives such as flood control or water supply. Despite their artificiality, constructed wetlands also have some habitat values which need to be recognized and integrated into the overall management of these wetlands.
This setting includes Freshwater Streams and Streambanks, Swamp Forests and Woodlands, and Ephemeral and Dune Lakes.
3.1 Freshwater Streams and Streambanks
Although the majority of coastal waterways are estuarine in nature, their upper reaches are often characterised by aquatic and streambank plants that are basically freshwater species with limited salt tolerance.
Streambank vegetation plays a role in stabilising riverbanks, intercepting lateral groundwater flows and in nutrient removal. The overhanging canopies, particularly of small streams, provide shade and cooling to the stream. Leaf litter from streambank vegetation is a significant external input into such streams and supports a range of microbial and invertebrate food webs.
Being generally relatively narrow and linear, streambank vegetation is particularly susceptible to changes in adjacent landuse, physical disturbance and fire, exotic weed invasion as well as changes in the quality and quantity of streamflow or groundwater. Nevertheless, many habitat values remain in slightly disturbed ecosystems, while those which have suffered major disturbances need to be rehabilitated to restore their full ecological values.
Consequently, the protection of such streams and their streambank vegetation is vital for a continuation of their functioning and for the unique suites of plant and animal species which inhabit them. Many of the freshwater fish of these instream areas are important forage species for migratory fish, birds and mammals.
In addition, the limit of freshwater aquatic and streambank vegetation generally marks the brackish interchange between freshwater upstream reaches and saline downstream reaches. Upstream areas are important feeding and breeding habitat for many estuarine and marine fish and invertebrates, as well as amphibians, birds and mammals. Freshwater vegetation also provides a source of food for numerous waterbirds and waders. The adults and juveniles of many fish and crustacean species migrate between the fresh and brackish water areas. This movement is aided by the presence of aquatic vegetation.
3.2 Swamp Forests and Woodlands
Swamp forests generally consist of relatively few species of trees. They are highly tolerant of extended periods of waterlogging which induce root oxygen stresses. While many plants can tolerate short periods of root anoxia, plants must have specialised physiological or biochemical mechanisms to survive during the extended periods of anoxia common in seasonally waterlogged areas.
The species diversity of these ecosystems is limited because of the absence of such specialised mechanisms in most species. Even though limited in terms of species number, swamp forests can form exceedingly dense and productive stands. Where waterlogging occurs for shorter periods, swamp woodlands occur with extensive grassy or sedge understoreys.
Swamp forests provide considerable outputs of organic matter which support microbial and invertebrate food webs. Much of this litter can accumulate and, in so doing, adsorbs nutrients such as nitrogen and phosphorus. By these mechanisms, swamp forests improve water quality, provide a rich source of organic carbon and form buffers between the hinterland and coastal waters.
A number of mammal species inhabit swamp forests in Eastern Australia, including the rare Xeromys myoides (False Water Rat), the Melomys burtoni (Grassland Melomys) and many insectivorous bats. Numerous birds and reptiles also inhabit swamp forests and woodlands. Certain birds and bats are highly dependent on swamp forests and woodlands as over-wintering sites.
3.3 Ephemeral and Dune Lakes
Ephemeral lakes are temporary water bodies created by overflow from the main drainage channels. Because ephemeral (temporary) lakes are only intermittently filled, their waters experience extreme physical and chemical fluctuations. This does not necessarily mean that they are devoid of fauna. Species richness amongst macro-invertebrate have been found to be extremely high in such lakes, often with considerable species overlap existing between permanent and temporary water bodies. Ephemeral water bodies may therefore provide important feeding sites for vertebrates, particularly waders, and form an integral part of the ecology of the coastline as a whole.
The geomorphology of dune lakes is diverse but they are confined to siliceous sands. They can occur in deflation hollows, in swales (mainly on the older inner barrier dunes), as backbarrier lagoons, or enclosed within bedrock spurs. Some are perched above the watertable on accumulated humic material, while others are water table windows. Few dune lakes have connection with the sea. For those lakes close to high water line, heavy rains and flooding can lead to overflow from the lake and may lead to semi-permanent connections. Such coastal lagoons have variable salinity. In the great majority of dune lakes, salinity is low and the water is typically acidic and humic and characterized by extremely low levels of total dissolved solids, suspended solids and nutrients.
Non-tidal Wetlands: Values and Management Considerations
Streambank vegetation plays a role in stabilising riverbanks, intercepting lateral groundwater flows and in nutrient removal, while leaf litter from streambank vegetation supports a range of microbial and invertebrate food webs. Consequently, the protection of such streams and their streambank vegetation is vital for a continuation of their functioning and for the unique suites of plant and animal species which inhabit them. In addition, the adults and juveniles of many fish and crustacean species migrate between the fresh and brackish water areas, a process which is aided by the presence of aquatic vegetation. Streambank vegetation is particularly susceptible to changes in adjacent landuse, physical disturbance and fire, exotic weed invasion as well as changes in the quality and quantity of streamflow or groundwater.
Swamp forests constitute important habitats for rare and endangered species, support microbial and invertebrate food webs and improve water quality by absorbing nutrients and trapping sediments.
Occurring in seasonally waterlogged areas, swamp forests and woodlands are vulnerable to hydrological changes which increase seasonal waterlogging or which lower the groundwater table. Such hydrological changes are associated with infilling, draining, water diversion or saltwater incursion. During droughts or where watertables have been lowered, not only are these ecosystems susceptible to fires, but they are also unable to regenerate from seed. In addition, these ecosystems require high water quality in terms of low total dissolved solids, low nutrient concentrations, generally low pHs and low suspended solids. Declines in water quality, particularly high nutrient or particulate organic loadings, will exacerbate soil anoxia and adversely affect the vegetation.
Ephemeral and dune lakes constitute important habitats for numerous species including rare and threatened ones. They also provide drought refuges for waterbirds including migratory waders. Because of their low photosynthetic production and their reliance on external sources of dissolved organic material, dunes lakes in particular are highly susceptible to pollution, specifically from nutrients. As these nutrients are mainly derived from urban runoff, sewage, agricultural activities or clearing and/or burning within their catchment areas, these activities must be carefully controlled. In addition, because of their simple food webs, dune lakes are susceptible to invasion by exotic plants and animals.
Summary: Non-tidal Wetlands
Non-tidal wetlands are sensitive to:
Control measures may include:
This setting includes Mangroves, Saltmarshes, Mudflats, Sandflats and Sandbars, Seagrass Beds and Shallow Channels
Mangroves are flowering plants (angiosperms) adapted to the interface between land and sea where it is sheltered from high wave action. In such locations, they need to endure a highly dynamic, low oxygen environment, as well as cope with potentially toxic levels of salinity. As few other plant species can survive where mangroves grow, they form a vital connection between land and ocean, and perform many irreplaceable biophysical functions.
Mangroves grow most extensively in muddy sediments, although in sheltered areas they may also grow on sand, peat and coral. They are often distinctly zoned, but may include large stands of only one or two species. As in swamp forests, only those plants with waterlogging tolerance and an ability to deal with salt and soil anoxia can survive in this setting. Consequently, they are ecosystems with relatively low plant diversity.
Despite their limited plant diversity, mangroves play an important role in coastal ecology. They provide organic matter (as litter) to estuaries and channels. The litter is broken down by bacteria and fungi and forms a food source for small invertebrates which, in turn, are fed on by higher carnivores. By this detritus based food web, mangroves provide an important life support function for fish, crustaceans, molluscs and birds. As a result, mangrove habitats are of great commercial importance, due to their function as nursery areas and the juvenile and adult fish, prawn and crab populations they support.
Coastal saltmarshes usually occur on the landward side of mangroves, where inundation occurs only by occasional spring tides. The plants of saltmarshes often occur in distinctive zones, determined by a complex interplay of factors. These include tidal scour on seedlings in the lower limit of the saltmarsh, competition with mangroves for light, soil drainage, salinity gradients and inputs of freshwater.
Fish which inhabit saltmarshes appear to congregate in the deeper tidal channels through the marsh, moving out into shallow areas around high tide. Recent studies have found that over half of the fish species using saltmarsh habitat were of commercial importance. Although these fish are predominantly bottom feeders, they do take some food items of terrestrial origin, such as insects, spiders and lizards.
Saltmarsh vegetation provides important habitat for many insects, including rare species of butterflies. The presence of insects and small vertebrates in saltmarshes attracts many waterbirds.
4.3 Mudflats, Sandflats and Sandbars
Mudflats, sandflats and sandbars are important feeding areas for many coastal species. Mudflats, sandflats and sandbars associated with river mouths are also often areas of spawning aggregations for commercially and recreationally important fish such as whiting and barramundi.
Mudflats, sandflats and sandbars are often highly productive sources of food items such as molluscs, small crustaceans, polychaetes, nematode worms, crabs and shrimps. While the flats are submerged, fish and other aquatic animals feed in these areas. While the mudflat is exposed or water depth is low, waders and other waterbirds move out onto sandflats and mudflats from their high-tide roosts. Different species of birds employ different feeding strategies to forage during the ebb-flood tidal cycle; with smaller species of wader generally needing to feed for longer periods.
A variety of factors influence the number of waders to be found foraging on a particular sand or mudflat. Differences between individual flats and their component areas are likely to be subtle; as are the pReferences of the species utilising them. Factors such as the ratio of shoreline length to surface area of the exposed flat, nutrient input and distance to the nearest high water roost, all affect the species-specific attraction to a particular sand or mudflat. These factors therefore need to be taken into account, where possible, when planning for land-uses adjacent to wetlands or estuaries.
The benthic invertebrates of mudflats, sandflats and sandbars are locally susceptible to over-collection by humans, especially in easily accessible areas. For example, bait collection has locally affected the populations of bivalves (pippies), crustaceans (yabbies) and beachworms in some areas.
Mudflats and sandflats are also important in nutrient cycling. Nutrients are adsorbed to the fine particulates in mudflats and may be retained until taken up by growing algae or seagrasses, or released into the water during flood events. In this way, nutrients stored and released by mudflats can significantly enhance local productivity. Thus, for example, many of the important prawning areas are associated with this nutrient cycling role of mudflats.
4.4 Seagrass Beds
Seagrasses are marine angiosperms which have completely adapted to life in a dynamic, saline and often, constantly submerged environment. Adaptations include modifications to root system (in the form of creeping rhizomes), as well as specialised pollination, seed dispersal, internal gas exchange, water-balance and photosynthetic mechanisms.
Seagrass beds generally occur in the lower intertidal and sub-tidal zones of relatively shallow, sheltered inshore areas. Such areas are typically bays, estuaries and saline lagoons. Seagrass bed substrates are usually soft sediments ranging from sand to fine silt. As one of the major factors influencing distribution of seagrasses is light intensity, depth and turbidity play an important role in defining the local extent of seagrass meadows.
Seagrass beds serve a number of fundamental ecological roles. They are a source of significant amounts of detrital material. Depending on species and location, one hectare of seagrass meadow may produce 3-20 tonnes of dried leaf material per year.
They are a vital linkage in coastal food chains and nutrient cycling, and provide a wide variety of animal habitats. Individual plants provide microhabitats for epibiota (small plant and animals living on the stems, roots and leaves of seagrass), which form the lower tiers of fundamental coastal and estuarine foodchains. The decomposition of seagrass litter is undertaken by vast populations of bacteria and fungi. These are eaten by the small organisms, such as zooplankton and benthic invertebrates which, in turn, form a detrital-based food web.
In addition to supporting detrital food webs, seagrass also forms a direct food source for grazing species. These grazers include: dugong, marine turtles, waterbirds, sea-urchins, amphipods, gastropod snails and herbivorous fish species such as Garfish, Luderick, Rabbitfish and Leatherjackets. Other significant species which utilise these areas include cetaceans such as the Indo-Pacific Humpback Dolphin and Bottlenose Dolphin.
Seagrass beds provide the juveniles of many marine species with shelter and protection from predation. A large proportion of the fish and prawn species of commercial importance spend larval and juvenile stages in seagrass beds. Hence, the maintenance of healthy seagrass beds is of fundamental importance to the success of commercial fisheries.
Variations in dominant species and location impart differing values to different seagrass beds. Studies have shown that the larvae of fish species settle to the bottom of the estuaries at different distances from river mouths. Thus, to preserve the biological diversity of coastally-dependent species, it is necessary to protect a variety of seagrass beds along the coast and at varying distances up estuaries.
Seagrass beds also facilitate substrate stabilisation. The presence of seagrass beds reduces near-bottom currents and water turbulence, thereby facilitating the deposition of suspended sediments. Reduced water movement and root structures limit sediment re-suspension and erosion. Seagrasses also transfer nutrients to estuarine waters by exudation from their leaves.
4.5 Shallow Channels
Near-shore island and estuarine channels usually have relatively soft substrates of sand or mud. While often lacking in large benthic species, these areas are characterized by a rich and diverse benthic infauna of molluscs, crustaceans and polychaetes. They are important feeding grounds for a variety of species which includes cetaceans, waterbirds and commercially important fish and prawn species.
Adults and older juveniles of many commercially important prawn species depend on soft unvegetated sediments, both as physical habitat, and for the associated small molluscs, crustaceans, polychaete worms and other organisms which make up their diet. They are also important nursery habitat for many juvenile fish, which escape predation in these areas by schooling behaviour, use of camouflage or because turbid conditions obscure them from predators.
Open-ocean birds, not normally resident species, may also use inshore channels and estuaries for shelter during rough weather.
Tidal Wetlands: Values and Management Considerations
Once established, mangroves foster the stabilisation and accretion of mudbanks. Mangroves also protect and stabilise the shoreline, act as a barrier to storm inundation and maintain water quality by filtering land-based runoff. They also comprise important habitat for roosting, feeding or sheltering for a large range of species including rare and threatened ones.
As a plant community, mangroves are fairly resilient in that they are tolerant of waterlogging, high soil anoxia and high levels of salinity. Similarly, mangroves tolerate high nutrient and organic loadings. Nevertheless, they are susceptible to altered tidal drainage (such as might be associated with infilling or bundwall construction related to aquaculture), freshwater diversion (e.g. flood mitigation works or barrages) and rapid changes in sediment level resulting from either erosion or accretion. It should also be noted that mangroves are generally slow-growing and any clearing of mangroves, even for temporary purposes, will require considerable time for regrowth to occur.
Saltmarsh areas are most often threatened by land reclamation and other activities that modify the tidal inundation frequency of saltmarsh areas. While the high value of ecosystems such as mangroves and seagrass beds is slowly being accepted, saltmarshes are often still mistakenly assumed to be unproductive and expendable.
However, although not as productive as seagrass or mangrove ecosystems, saltmarshes provide important inputs of organic matter to estuarine food chains and provide important habitats for some rare and endangered species. In addition, they also maintain estuarine water quality by filtering sediment from land-based runoff.
Mudflats, sandflats and sandbars are important feeding and spawning areas for many coastal species. In addition, they support a diverse invertebrate fauna which is the basis of their importance to fish and waders. Mudflats and sandflats are also important in nutrient cycling. Mudflats, sandflats and sandbars are susceptible to changes in sediment supply (deposition and erosion) whether natural or due to coastal modifications. Changes in wave regimes such as associated with seawalls or groynes can lead to erosion or re-location of these ecosystems.
Seagrass beds have a number of ecological roles. They produce significant amounts of organic material which links to coastal food chains, they are important in nutrient cycling, they provide microhabitats for a diverse invertebrate fauna and, by reducing near-bottom currents and turbulence, they facilitate substrate stability.
Seagrass beds are susceptible to many of the contemporary land-use pressures on coasts and estuaries. Point sources of pollution, such as effluent outfalls, may cause excessive algal growths that smother seagrass areas. Dredging, large scale removal of seagrass beds, or their periodic harvesting to clear waterways, can have drastic effects on their biological productivity and continued viability. Other factors likely to limit seagrass growth include turbidity, current speed, water turbulence, sediment instability and salinity variations. Once seagrass beds are lost, they do not necessarily recolonise quickly.
Shallow channels usually have relatively soft substrates
of sand or mud. While large benthic species are generally absent, these
areas are characterized by a rich and diverse benthic infauna of molluscs,
crustaceans and polychaetes. They are important feeding grounds for
a variety of species which includes cetaceans, waterbirds and commercially
important fish and prawn species.
Summary: Tidal Wetlands
Tidal Wetlands are sensitive to:
Control measures may include:
C. Inshore Marine
Coral reefs are amongst the most diverse of all ecosystems. They provide nursery and adult habitat for a great variety of marine species, including many of commercial importance. Fringing reefs are found around many continental islands and along the tropical and sub-tropical mainland. Most fringing reefs are structurally uniform with extensive mudflats enclosed by a short outer slope.
Although species diversity of other invertebrates, algae
and fish are lower than on offshore reefs, fringing reefs form important
habitats for a diverse variety of marine species.
Fringing Reefs: Values and Management Considerations
Adjacent coastal land-use patterns can have very marked
effects on near-shore coral reefs. Many factors, including increased
turbidity, sediment deposition rates and nutrient loadings, can all
have direct adverse effects on corals and consequently on the diverse
assemblages of organisms they support. Because the coral calcification
process can be directly inhibited by phosphates, corals are particularly
susceptible to any increase in phosphate concentrations. Corals are
also very sensitive to thermal pollution, such as that originating from
coastal power stations or other industries. Effects may also be less
direct. For example, it is suspected that increased nutrient loadings
in coastal waters (derived from terrestrial sources) can markedly boost
recruitment of coral predators, such as crown-of-thorns starfish.
Summary: Fringing Reefs
Fringing Reefs are sensitive to:
Control measures may include:
Both temperate and tropical rocky shores support a diverse mix of flora and fauna. The composition of these characteristic assemblages varies with temperature and wave exposure regimes and the various assemblages have been used to provide a biogeographical classification of some coastlines. Generally algae dominate these littoral ecosystems in cooler waters but they decline in importance in the tropics. They provide adult habitat and nursery area for numerous fish and crustacean species.
Many commercially important fish species are associated with such habitats, including Leatherjackets, Blackfish, Yellowfin Bream, Snapper, Tarwhine, Trevally, Yellowtail and Sampson Fish. Recruitment of juvenile fishes to these sites generally involves individuals of a larger average size than those of the same species found in seagrasses, possibly indicating that some earlier development is required in seagrass or other habitats, before they migrate to rocky substrates.
Stands of such seaweeds break the force of waves and provide a strip of quieter water along the foreshore, which is utilised as a sheltering area by many species. The diverse assemblage of bottom-dwelling organisms which inhabit rocky shores provide both juvenile and adult fish with a wide range of food items.
Algal beds also provide many other benefits analogous to seagrass beds (e.g. protective effects on sediments) and are important feeding grounds for rare and threatened species, such as marine turtles. In addition, at low tide, rocky shores expose food items such as crabs, limpets and numerous other invertebrates, which support a variety of wading birds.
Rocky Shores: Values and Management Considerations