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State of the Marine Environment Report for Australia: The Marine Environment - Technical Annex: 1

Compiled by Leon P. Zann
Great Barrier Reef Marine Park Authority, Townsville Queensland

Ocean Rescue 2000 Program
Department of the Environment, Sport and Territories, Canberra, 1995

ISBN 0 642 17399 0

Marine ecosystems: hard and soft shores

P. G Fairweather* & G. P. Quinn

Graduate school of the Environment
Macquarie University, Ryde, NSW 2109*
and
Department of Ecology and Evolutionary Biology
Monash University, Clayton, Vic. 3168

Introduction

Hard and soft seashores ring our island continent and form the interface between sea and land.

It is beyond the scope of this report to describe in detail all of the research on these habitats. However, we can discuss rocky, sandy and muddy seashores from the viewpoints of recent ecological research, our understanding of how the ecological communities in these habitats function, and how this knowledge is used in environmental decision making. Rocky shores are the main hard substrata of headlands along the open coasts and sometimes within estuaries (Bird 1984). Sandy beaches also characterise many of our open coasts and are extremely important for Australia's recreational beach use. Mudflats and sandy tidal flats exist along the shortest amount of coastline (although they may cover large areas), being defined as any mostly unvegetated soft-sediment shores within moderately calm waters. They may often however, be contiguous with seagrass or mangroves (see below).

In this report we focus on research published in the peer-reviewed literature and exclude wherever possible, unpublished research contained in theses and less accessible reports. We also limit our discussion to those hard and soft shores not considered in other parts of the total report. Our presentation focuses upon intertidal and nearshore habitats, thereby largely excluding discussion on subtidal rocky reefs (see Keough and Butler, this volume). In particular, we do not discuss coral reefs and the habitats of their lagoons (including sandy sediments and beach rock); nor the vegetated parts of soft (especially muddy) shores such as seagrass beds, mangrove forests and saltmarshes. As we emphasise below however, these divisions are artificial from an ecological point of view (Fairweather & Quinn 1993).

The distribution of shore types

A first step in examining the state of the environment of hard and soft shorelines is to understand their extent, distribution and characteristics. Estimates of coastline vary enormously because of the fractal nature of the coasts; the estimate tends to increase as our measuring abilities increase and the measuring step subsequently is decreased. Nevertheless, a number of geographers (eg Galloway & Bahr 1979) have attempted to estimate the extent of different coastline types around Australia. Fairweather (1990a) used these estimates to assess the 'availability' of different habitats for study in the various States (Table 1).

The different sorts of seashores are not evenly distributed around our coastline (Table 1). The geomorphologic reasons for this are complex: shore types depend on a source of substratum (eg parent rock or sediment) and the forces of waves, currents and winds that alter them (Bird 1984). The basic distinction worldwide (Cooke & Doornkamp 1990) is between cliffed coasts and shore platforms on the one hand and depositional coasts and beaches on the other. High energy shores lose sediments as they are transported away by water movement and so erode to parent rock material (if available). Australia's high-cliffed coasts are the prime example of this landform. In contrast, shores of lesser energy are characterised by smaller and smaller particle sizes as the available energy wanes. Thus, sandy shores are subject to less energy (both in water but also wind) than are most rocky coasts, but they have more associated energy than have muddy shores (with the finest sediments). The sand deposited upon beaches is often blown further inland where it forms not only dune systems but also acts as a source of coarser particles for estuarine soft-sediment shores. Tidal flats with muddy or more sandy sediments are found mainly in either shallow and therefore calm embayments (eg gently sloping sea floors where wave energy is minimal) or within estuaries. Under these conditions, the ebb and flow of the tide over large expanses of shallow ground tends to vertically accrete fine sediments. Within estuaries, the bottom is exposed to strong current regimes as the estuary flows but also to a major source of sediment from erosion of the land further up the estuary and river system. Much sediment in estuaries is trapped and consolidated by vegetation, particularly mangroves and saltmarshes (Bird 1984).

The world's coasts have been classified in terms of wave types. According to that classification, the north and south coasts of Australia appear to be dominated (Cooke & Doornkamp 1990) by low energy, small wave regimes, while the west and east coasts have mainly swell waves. West-coast swells typically have more energy than have east-coast swells (Cooke & Doornkamp 1990).

Both tidal flats and saltmarshes are more extensive under macrotidal conditions (Cooke & Doornkamp 1990). Mud accumulates only under very sheltered conditions, whereas sand can be deposited under a variety of conditions (Cooke & Doornkamp 1990), just as it can be transported easily by both water and wind due to its size range of particles. Muddy sediments dominate the north coast of Australia, either under extensive mangrove stands (Table 1) or as wide, nearly flat shores experiencing enormous tidal ranges (eg around Broome on the north-west coast). Sandy beaches are common in all States but along the east and west coasts of the continent swept by current systems like the East Australian Current in the east and the Leeuwin Current in the west, beaches up to 150 km in length are separated by rocky headlands. Rocky coasts are most widespread in the south of our continent, as epitomised by the Great Australian Bight and much of the Tasmanian coastline.

Our understanding of hard and soft shores as ecosystems

The next step in assessing the state of hard and soft shores in Australia is to evaluate Australia's research effort and hence our understanding of the dynamic ecosystems along these shores. Assessing the effectiveness of marine research is difficult because research activity may not correlate with research quality per se. Nonetheless, Fairweather (1988a), (1990a) assessed marine ecology in Australia by reviewing all papers published in the period from 1980 to 1987. He found that 22% of the 729 papers dealt with rocky reefs, 10% with sandy bottoms and 6% with muddy bottoms. Thus, less than 40% of this published output came from research on coastal types which made up more than 65% of our coastline (Tables 1, 2). In contrast to this under-representation are studies of coral reefs (31% of papers, at least 14% of coastline), mangroves (13% and 17%, respectively) and seagrass (16%, proportional extent unknown but small). These data suggest that unvegetated, soft-sediment shores have been under-represented in Australia's recent research output in marine ecology, a trend not unique to Australia (Wilson & Browne 1991).

There is evidence that research is concentrated in some States and institutions within those States. For example, the University of Sydney (see Underwood in press) tends to dominate rocky shore research (Table 3), followed by the universities of Western Australia and Tasmania, and Melbourne and Monash in Victoria. The vast majority of this research has been based in the Sydney region at the Cape Banks Marine Scientific Research Area (see Westoby 1991). Only recently is rocky intertidal research being actively pursued in some States, like Queensland and New South Wales (non-urban areas) (eg Fairweather 1991). The relatively high levels of research on rocky and unvegetated soft shores by universities compared to other institutions (Table 3) probably reflects their different research missions: the non-university institutions have concentrated on fisheries biology and non-experimental approaches to large-scale problems whereas university marine ecologists have more recently focused on field experiments at smaller scales.

Research on hard shores

The biota and their patterns of zonation on many of Australia's rocky shores were described in a classic series of papers in the 1940s, 1950s and early 1960s (Dakin, Bennett & Pope 1948, Bennett & Pope 1953, Endean, Kenny & Stephenson 1956, Womersley & Edmonds 1958, Bennett & Pope 1960). More recently, rocky shores have become a focus for ecological research worldwide. They provide a two-dimensional benthic structure (excluding explicit consideration of the infauna of algal and mussel beds and 'pelagic' organisms in rock pools) and the dominant animals on these shores usually have a hard outer surface (shell or exoskeleton), are either sessile or slow-moving and have life cycles commensurate with either the research careers of ecologists or the funding cycles of research. These attributes make quantifying population dynamics feasible and render rocky shores very amenable to field experimentation (Connell 1972). The main emphasis of field experiments has been on factors controlling the upper and lower limits of the distribution of organisms (ie intertidal zonation) and subsequently how biological and physical factors structure assemblages of species on rocky shores.

With few exceptions (eg Black et al. 1979, Underwood 1975, 1981, review by Underwood in press), there have been no attempts in recent years to quantify distribution patterns of local species, either within or between shores. Despite the recent experimental emphasis in marine ecology, there is still a need to measure the temporal and spatial consistency of zonation patterns. Such measurement rarely has been done, either in Australia or overseas. Similarly, the geographical limits of the ranges of most species on hard or soft shores at the spatial scale of individual rock platforms or tidal flats, and their temporal consistency, are not known - even for common species - except from where individuals have been collected for other purposes (eg environmental impact assessments) or in general terms from early natural history accounts (see references above). For example, there are numerous rocky shore species that have a geographic limit to their distribution along the coast between Melbourne and Sydney (eg Lepsiella vinosa, Morula marginalba, Austromytilus rostratus), yet their precise distributional boundaries are unknown. These boundaries should be resolved by a systematic survey of our coastline (ignoring State boundaries!).

One component of ecological research on rocky shores for which local information is particularly lacking is the ecology of populations and assemblages of algae. There are a number of algal taxonomists in Australia but few ecologically-orientated marine botanists working on rocky shores. The life histories of some algal groups have been extensively studied (eg Clayton & King 1991 - includes some Australian contributions) and patterns of recruitment and small-scale spatial variability of micro- and macroalgae and their interactions with sessile animals have been described for one site in New South Wales (review by Underwood & Kennelly 1990). Much of the available ecological information on macroalgae has come from zoologists examining herbivory (eg May, Bennett & Thompson 1970, Steinberg 1989) or ecologists examining general patterns of community organisation in intertidal and subtidal reefs (review by Underwood & Kennelly 1990). There is an urgent need for research on the population ecology of the common intertidal algae, particularly of those species that provide structural habitat for other biota and/or are susceptible to human disturbance - such as Hormosira banksii ( Brown, Davies & Synnot 1990, Povey & Keough 1991). Such research should attempt to link the available information on life histories ( Clayton & King 1991) with field data on patterns of recruitment, growth and mortality. Extent of dispersal also is not known for most Australian algae. An examination of genetic relationships among algal populations, both within and between shores (as has been done for some species of invertebrates: Ayre 1990) would provide indirect evidence of the amount of exchange between separate populations. Data on dispersal ability are essential to assess the ability of algae to recover from natural and anthropogenic disturbances.

In contrast to algae, our knowledge of the ecology of rocky shore invertebrates is considerable. The population dynamics (ie population structure, population and individual growth rates, mortality and reproductive cycles) of most of the common gastropods of the south-east coast of Australia have been described (reviews by Underwood 1979, in press) but the spatial extent of these studies is very uneven and varies considerably between species - as is the case for most marine research on any continent. For example, some species of limpet (eg Cellana tramoserica) have been studied on shores in New South Wales and Victoria, whereas data on most species are restricted mainly to one shore in New South Walers (ie the Cape Banks Scientific Research Area). Information on other groups (eg polychaetes, non-cirripede crustaceans, echinoderms) is less extensive, although some excellent studies are available ( Underwood in press). There have also been numerous experimental studies in Victoria, Western Australia and particularly Cape Banks (New South Wales), on the processes of intra- and inter-specific competition and predation and their influence on the structure of rocky intertidal assemblages (reviews by Underwood 1985, in press, Underwood & Kennelly 1990). These studies have been important internationally for ecologists' understanding of the processes structuring marine benthic communities ( Underwood & Denley 1984). In particular, the studies have shown that the role and nature of competition among mobile herbivorous gastropods is fundamentally different from that of sessile invertebrates and that spatial and temporal variations in recruitment may be an overriding influence on the zonation patterns of organisms and subsequent community structure on rocky shores. It is crucial for testing the generality of these ideas that studies are commenced in other parts of Australia which are directly comparable to those published from the small number of locations described above. This research has yet to occur.

Patterns and variability in recruitment of marine invertebrates have attracted much research attention in recent years ( Underwood & Fairweather 1989) on both small ( Denley & Underwood 1979, Underwood, Denley & Moran 1983) and large spatial scales ( Caffey 1985). Locally, temporal and spatial patterns of recruitment of barnacles on New South Wales shores have been intensively examined ( Denley & Underwood 1979, Caffey 1985) and these studies have led in turn to experimental studies on processes affecting settlement and post-settlement survival ( Jernakoff 1983, Underwood, Denley & Moran 1983) and their consequences on other species (eg Fairweather 1988b). These Australian studies on barnacles have shown that the high degree of variability in recruitment not only influences the barnacles' population structure but can also determine interactions with the other component species within the habitat. These studies have made a major contribution to a general understanding of the complexities of settlement and recruitment of intertidal organisms. In contrast, we need data on the patterns of recruitment, and their causes, for other species - either sessile (eg mussels on southern shores) or mobile (eg gastropods; but see Quinn 1988) and comparisons of recruitment patterns of species with different capacities for dispersal.

A logical consequence of varying degrees of dispersal is that populations of intertidal animals will show different levels of genetic similarity. There have been a number of Australian studies on gastropods and potentially clonal animals such as anemones, corals and seastars (review by Ayre 1990; also Watts, Johnson & Black 1990), but rocky shore studies have been spatially restricted (primarily to Western Australia). Ayre (1990) indicated that for those species examined, the degree of genetic exchange between sexually reproducing populations is high with no apparent genetic subdivision of populations, although there was considerable fine-scale heterogeneity. Comparing the genetic variability between populations of species with different degrees of dispersal is one important direction for extending this type of research.

There is little information available on vertebrates (fish and birds) that use rocky shores: indeed, we probably know more about the activities of humans as predators on shores near urban centres (see review by Quinn et al., this volume) than we do about fish and birds. Some studies on the population ecology of intertidal gastropods have identified fish and birds as potential predators ( Parry 1982), although others have argued that non-human vertebrate predators are not major influences (eg Underwood 1978 regarding fish on New South Wales shores). Basic, presently unavailable information - such as on the abundances of fish and birds on rocky shores, their patterns of feeding and their diets - would provide a basis from which experimental studies (eg predator exclusion) could be initiated. Research on the trophic links between vertebrates and benthic rocky shore biota is clearly required to resolve the role fish and birds (and humans) play in structuring rocky shore assemblages.

Research on soft shores

There are no cohesive theories about any aspects of the ecology of soft sediment intertidal assemblages ( Posey 1987), largely because of a paucity of experiments investigating the mechanisms controlling the biota ( Hairston 1989, Warwick, Clarke & Gee 1990, Wilson 1990). This situation contrasts with generalisations we can make about rocky shore communities due to the experimental effort put into understanding that habitat. Rocky shores are clearly different habitats from soft-sediments and therefore are likely to have different processes reigning over their ecology ( Hairston 1989). The unique features of soft-sediments shores and their assemblages (see Table 4 for comparison of rocky, sandy and muddy shores) include:

Of the complete Australian literature on marine ecology during eight years of the 1980s, Fairweather (1990a) identified unvegetated soft bottoms as the least studied benthic habitat in the country. Overseas, tidal flats are known to be important because they have high biodiversity ( Warwick 1993), are good indicators of environmental health (due to providing the ecosystem service of improving water quality), their biota are important as food for prawns, fish and birds, and they serve as settlement sites for larvae (these last two factors make them integral to our recreational and commercial fisheries). Scientific information about Australian tidal flats is essential to our understanding of how these habitats function as ecological units, which in turn is used to manage human activities in estuaries. At present, requests for information about how these ecosystems work can be met with only general statements, untested ideas or assertions about overseas concepts untried here. As well as providing much-needed ecological knowledge for environmental decision making, any research on tidal flats will stimulate scientific activity in an ecosystem that has been neglected in this country, more so than on any other benthic marine habitat.

Quantitative surveys of subtidal soft-sediment benthos have been done in Australia (eg Poore & Rainer 1979), including detailed examinations of spatial and temporal variation (Jones 1987, Morrissey et al. 1992). There has also been some quantitative sampling in Australian tidal flat habitats which have described the biotic assemblages present (eg Rainer 1981), although most have been related to the presence of some type of effluent discharge (eg Dorsey 1982). In addition, foreign scientists have recently established research programs here, including sampling on sandy beaches (eg Dexter 1983a, 1983b, 1984, McLachlan & Hesp 1984a, 1984b, McLachlan 1985, Warwick, Clarke & Gee 1990, Dexter 1992). However, there have been few studies which have gone beyond this necessary step of description to examine experimentally the factors responsible for such community structure. With the exception of the large research program of Peterson and Black in Western Australia (see below) and the very recent experimental work of Walters and Moriarty (1993) on microbenthos in seagrass, there has been no research program in temperate Australia using experiments to test our ideas about these ecosystems. This situation is in stark contrast to those in the United States of America (eg Peterson 1977, 1979, Wilson 1990, Woodin 1991), Europe (eg Reise 1985) and South Africa (eg Branch & Pringle 1987) where there is a strong experimental tradition of studying tidal flats. The results from these studies demonstrate that a variety of interactions, including competition and predation, can vary from intense to non-existent and that adult-larval interactions can be important for some species ( Wilson 1990, Woodin 1991).

It is a reflection of the lack of interest in community processes in unvegetated soft sediment habitats in Australia that the only experimental research program mounted in this country was instigated by an overseas ecologist on sabbatical leave in Western Australia (see eg, Peterson & Black 1986, 1987, Black & Peterson 1987, 1988, Peterson & Black 1988a,1988b, 1991, Peterson 1991, 1992). The field work in these studies was based on excellent natural history observations of the assemblages present as well as the ideas and experimental techniques previously employed in the United States of America (eg Peterson 1977, 1979, Peterson & Andre 1980, Peterson 1982). They demonstrated, for example, that food limitation in suspension feeders was possible on tidal flats and that competition for food was often more important than competition for space. This experimental program also revealed that the causes of observed patterns in sizes and shore levels were more complex that was suggested by simple inference from sampling. The program has been extremely productive in terms of published output (cited above) and the increase in our understanding of these neglected ecosystems is likewise immense. So it is clear that experimental techniques successfully used overseas are applicable here and further elaborations of these methodologies overseas (eg Wilson 1990, Woodin 1991) illustrate the opportunity for developing and testing theory appropriate for Australian soft-sediment communities. Besides this program, the only papers using manipulative field experiments on Australian tidal flats have been a spatially confounded predator exclusion study (Kent & Day 1983) and recent meiobenthic manipulations in seagrass (Walters & Moriarty 1993).

Thus, in Australia, soft-sediment research has been neglected in favour of studies on coral reefs, rocky seashores and vegetated habitats within estuaries and it has been slow in moving from purely descriptive studies (ie species lists and zonations schemes) to quantitative or semi-quantitative attempts at description of communities (often linked to depth zonation). We have a sparse understanding of trophic interactions on sandy beaches (egRobertson & Lucas 1983) and hence the flows of energy in soft-sediment ecosystems. There have been few Australian studies that have quantitatively monitored the dynamics of soft-sediment biota through space and time, despite recent work showing that a hypothesis-testing rationale can be applied to sampling studies in these habitats (Warwick, Clarke & Gee 1990, Morrissey et al. 1992, Morrissey et al. 1992).

Linkages among different habitats

A full understanding of these shorelines requires that we acknowledge links among different ecosystems. Fairweather and Quinn (1993) argued that exchanges of water and biota are common between offshore and onshore areas of our oceans, along coasts washed by the same seas and across a variety of habitats. There is evidence that the larvae of intertidal or nearshore animals (eg barnacles, crabs, fish) on the west coasts of the United States of America are transported across the continental shelf to recruitment sites (eg Shanks 1988 and references therein; Farrell, Bracher & Roughgarden 1991, Roughgarden et al. 1991) by oceanographic processes such as upwellings. Similar data on the movement of larvae are lacking for Australia. Input from the terrestrial environment, by run-off from adjacent land or through rivers (and therefore estuaries) can provide nutrients, energy and matter for coastal habitats (Nixon 1980). Again, such information is entirely lacking for Australian shores.

These linkages clearly have important implications for the management of our shores (Fairweather & Quinn 1993), such as integrating management of marine and adjacent terrestrial and freshwater habitats. The unit of management should be at the scale of the catchment, although this has been rarely achieved anywhere in the word, let alone in Australia. The methodology for studying these linkages requires working at a larger scale than is usual for intertidal research. For example, recent advances in remote sensing of water movement may allow us to measure the dispersal of larvae of intertidal biota. In addition, monitoring intertidal populations on a range of shores spread across a geographic region may reveal large scale patterns of recruitment that are consistent on some spatial and temporal scales (eg Peterson & Summerson 1992). These linkages imply that the potential for routinely monitoring intertidal habitats at the scale of individual shores or greater needs to be investigated. For example, aerial photography of intertidal macroalgal, mussel or seagrass beds through time would provide data on changes in these assemblages at a spatial scale relevant to management authorities.

Research needs for environmental issues

Intertidal habitats are the most accessible marine environments to humans (and their wastes) and are therefore undergoing considerable anthropogenic change (Fairweather 1990a), from pollution, reclamation for terrestrial uses, vegetation clearing, harvesting of organisms, exotic species, dredging etc. There is a moderately large amount of recent information on Australia on the methodology for measuring environmental impacts on marine environments (eg recent issues of the Australian Journal of Marina and Freshwater Research Vol. 42(5) 1991 and the Australian Journal of Ecology Vol. 18(1) 1993). In contrast, published applications of these techniques to specific impacts on Australian intertidal habitats are rare. The effects of domestic sewage on rocky shores have been described near at least two cities in south-eastern Australia (Borowitzka 1972, Fairweather 1990b, Brown, Davies & Synnot 1990), with comparable changes in algal assemblages: a reduction in large brown algae (eg kelps, Hormosira banksii) and an increase in filamentous, primarily ephemeral, red and green algae (eg Ulva species) The direct effects of sewage on intertidal invertebrates is unknown. The effects of industrial pollutants have not been examined for many seashores in Australia, except where it is confounded with domestic sewage outfalls. McGuinness' (1990) work on the effects of oil on invertebrates in mangroves and saltmarshes in Botany Bay gives an indication of what experiments may be possible. The detrimental effects of TBT (tributyltin, from antifouling paints) on intertidal gastropods (inducing a debilitating sex change in fames known as 'imposex') are well known overseas and now have been documented here (Wilson, Ahsanullah & Thompsom 1993).

Recreational activity of humans in marine environments is increasing, particularly our use of intertidal habitats (see Quinn et al., this volume). Humans collect plants and animals for food and bait and walk over much of the shore (both hard and soft) during both active extractive activities (eg fishing, collecting ) and more passive recreation (eg sunbaking, swimming). Measurements of the spatial and temporal scales of this type of human activity and experimental studies on its effects should be a research priority of marine ecologists in Australia. For example, recreational fishing is growing as a human activity and a large proportion of anglers obtain their own bait from pumping ghost shrimps or worms from sand flats and collecting algae, crustaceans, gastropods, bivalves and ascidians from rocky shores. These are potentially very pervasive activities because these organisms are removed from their populations. This results in the population's reduced abundance as well as indirect effects in its recruitment and the abundance and recruitment of other species by trophic cascades, habitat facilitation, etc. (Fairweather 1990c). In soft sediments, there are also the detrimental effects of obtaining the animals, which in turn disrupts any layering of the sediment (including grain-size sorting and physicochemical conditions) as well as destroying the homes and bodies of many other burrowing organisms (and so the 'bycatch' is very great) (Quinn et al., this volume).

From a conservation perspective, it is unusual to find, for any shoreline in Australia, a listing of rare species living on it or an estimate of the shoreline's local biodiversity. The biogeographic limits and affinities of particular taxa are better known through the efforts of marine taxonomists, but we lack the extensive knowledge of biotic assemblages on hard and soft shores to allow proper planning for conservation. For example, where along the east coast of Australia should we place reserved areas to maximise the species within them by taking advantage of overlapping biogeographic provinces? We do know that mudflats and (to a lesser extent) sandy habitats are extremely important as feeding grounds for migratory wading birds protected under international treaties (ie Chinese Australian Migratory Birds Treay and the Japanese Australian Migratory Bird Treaty). It is also clear that a number of habitats among these shore types are grossly polluted (such as many urbanised estuarine mudflats) or are regularly disturbed by recreation (eg most sandy or rocky shores near cities).