sandy beach ecosystems: vulnerability, resilience and ...

17th NSW Coastal Conference, Wollongong, Australia, 2008;

http://www.coastalconference.com

SANDY BEACH ECOSYSTEMS: VULNERABILITY, RESILIENCE AND MANAGEMENT Jones A1, Schlacher T2, Dugan J3, Lastra M4, Schoeman D5,McLachlan A6, Scapini F6 1

Australian Museum, Sydney, NSW University of the Sunshine Coast, Maroochydore, Qld 3 University of Santa Barbara, California, USA 4 Universidad de Vigo, Vigo, Spain 5 University of KwaZulu-Natal, Durban, South Africa 6 Sultan Qaboos University, Muscat, Oman 7 Universit di Firenze, Firenze, Italy 2

Abstract Sandy beaches support a wide range of species, mostly small and buried. In addition to intrinsic biodiversity values, these species provide bait for humans and food for fish and birds. Moreover, beach ecosystems provide numerous other goods and services. Unfortunately, beaches are subject to the coastal squeeze of rapidly increasing human populations on land and the effects of climate change at sea. These effects include rises in sea level, temperature, storminess and erosion, and falls in pH. The combination of sealevel rise and increased storminess will accelerate erosion that threatens the very existence of beaches, especially in urban areas where protective seawalls may be built. As the seawater becomes more acidic, the many sandy-beach species with calcium carbonate shells may experience shell thinning with serious consequences in a highenergy environment. Consequently, beach ecosystems are highly vulnerable to both climate change and human development and their ecological resilience is in question. It is possible to enhance resilience by appropriate management strategies that are ecosystem based. These include the recognition of beaches as interactive systems dependent on adjacent dunes, estuaries and the sea. For example, beaches depend on coastal rivers for sediment but the damming of rivers and instream sediment extraction has reduced supply. Secondly, dunes provide a sand reservoir that maintains the beach during heavy storms and associated erosion. As well, resilience would be enhanced by developing best practice soft-engineering techniques (eg, beach nourishment), regulating off-road vehicles and providing setbacks so that the sea can migrate inland. Because sealevel rise will cause severe socio-economic-ecological impacts, the involvement of all stakeholders will be necessary. This will include the public acceptance of new paradigms concerning human population size and greenhouse emissions, both of which are underlying factors threatening beaches.

Introduction Sandy beaches form about 50-60% of Earth’s coastline (Bird 1996) and 49% of Australia’s coast (about 8,000 ocean beaches) (Short and McLeod 1996). That these beaches have iconic status and huge socio-economic value is well understood (Batley and Cocks 1992; Blackwell 2003; Klein et al. 2004). Less understood is the fact that they are living 1



ecosystems that provide various services to humans (McLachlan and Brown 2006; Schlacher et al. 2008a; Defeo et al. in press). Moreover, the maintenance of beach biodiversity, ecological processes and services deserve protective management in order to achieve ecologically sustainable development (ESD). Such management is urgent since coastal ecosystems are home to >50% of the world’s human population (UNCED 1992). In Australia, 85% of the population live within 50 km of the coastline, a product of the large and continuing internal migration to the coast (ABS 2006). Consequently, beaches are highly vulnerable to a ‘coastal squeeze’ between burgeoning human populations from the land and the growing effects of climate change from the sea. The former imposes numerous developmental, recreational and pollution pressures on beach ecosystems (Brown and McLachlan 2002, Schlacher et al. 2008a, Defeo et al. in press); the latter provides numerous ecological challenges including beach erosion and water changes involving temperature, pH and circulation (Jones et al. 2007). These factors have the potential to threaten the very existence of sandy beaches and their biota. This paper briefly introduces some aspects of sandy-beach ecology and ecosystem services, discusses the vulnerability of beaches to major pressures and explores the concepts of ecosystem-based management and ecological resilience as components of optimal management for sandy shores.

Sandy-beach ecology Contrary to popular opinion, sandy beaches are not ecological deserts. Hundreds of species occur, many of which are endemic to sandy beaches, but most escape notice by being small and buried (Brown and McLachlan 1990). They include primary-producing microscopic algae (mostly episammic and epipelic diatoms), decomposers (bacteria and fungi) and meiofaunal and macrofaunal invertebrates (mostly nematodes, crustaceans, polychaetes and molluscs). The tiny meiofauna, bacteria, algae and protozoans occupy the interstitial spaces between the sand grains and form a distinct food web. The larger macrofauna are active burrowers with a range of feeding modes. They can be very abundant particularly in dissipative beaches. Individual species such as the amphipod crustaceans Exoediceros fossor (Stimpson 1856) and Exoediceroides maculosus (Sheard 1936) can attain densities exceeding 10,000 ind·m-1 on semi-sheltered beaches in New South Wales (Jones et al. 1991). Beaches with inputs of algae/seagrass wrack support a rich and diverse driftline fauna of crustaceans and insects. Adaptations to the dynamic conditions include mobility, burrowing ability, protective exoskeletons, rhythmic behaviour, orientation mechanisms and behavioural plasticity (Chelazzi and Vannini 1988, Brown 1996, Scapini 2006, Brown and McLachlan 1990, Hacking 1996, Jones et al. 1998). Other beach biota include seabirds and turtles, species that depend on beaches for feeding and/or nesting purposes. Importantly, beaches have functional ecological linkages with adjacent ecosystems such as sand dunes, the surf zone and estuaries (Brown and McLachlan 1990). Sand, organic matter and nutrients are exchanged (Short and Hesp 1982) and some species are shared (Gladstone et al. 2006). Because beaches have no large attached plants, many animal species depend on surf-zone phytoplankton and stranded macrophytes for food (Koop et al. 1982, Colombini and Chelazzi 2003, Dugan et al. 2003). Other ecological links involve life-cycle phenomena. For example, birds and turtles undergo long-distance migrations (Bouchard and Bjorndal 2000), and many beach 2



invertebrates have dispersive oceanic larvae. As well, some fish species feed on beach invertebrates (Du Preez et al. 1990). Such linkages are relevant to the vulnerability and resilience of beach ecosystems and have implications regarding the appropriate spatial scale of management. At between-beach scales, there are ecological differences associated with the degree of wave action and its interaction with grain size and slope of beaches (McLachlan et al. 1993). These physical factors are used to classify beaches into reflective, intermediate and dissipative types (Short and Wright 1984). Exposed, reflective beaches are steep with a narrow swash zone, coarse sand particles, little organic and water content, and waves that break abruptly in the intertidal zone. In contrast, dissipative beaches have waves breaking far from shore. They are flat with a wide swash zone, fine sand with large water content and steeper vertical physico-chemical gradients. They have more species including more soft-bodied species such as polychaete worms, higher total abundance and biomass, and lower fecundity and mortality rates than reflective beaches. In extreme cases, reflective beaches may support no intertidal macrofaunal species at all (McLachlan et al. 1995). Global patterns of species richness are correlated with the Beach Index (McLachlan and Dorvlo 2004), a composite of tide range, beach slope and particle size. Because these patterns are correlated with physical factors rather than biological factors, it is likely that ecological assemblages are “physically controlled” rather than “biologically accommodated” (Brown and McLachlan 1990, Jaramillo and McLachlan 1993). A consequence of physical control is that the loss of any particular species would have little effect on others, unlike biologically-accommodated assemblages where cascading effects may follow the loss of key species (Schiel et al. 2004). Secondly, on physically-controlled beaches, recovery from disturbance by any species is independent of other species. However, the influence of biological factors should not always be discounted, especially on dissipative beaches (Defeo and McLachlan 2005). Consequently, both physical and biological factors play ecological roles on sandy beaches although the relative importance of various factors and mechanisms in explaining distributional patterns is not well established. In fact, Australian sandy beaches are poorly studied by comparison with other coastal habitats (Fairweather 1990). This knowledge deficit hinders attempts to predict the effects of events such as climate change and to recommend management responses

Ecosystem services Ecosystem services are defined as the benefits to humans provided by ecological systems. Unfortunately, these services are nearly always undervalued and coastal services are not fully appreciated (Millenium Ecosystem Assessment 2005). The services provided by sandy beaches were listed by (Defeo et al. in press) as follows:     

sediment storage and transport; wave dissipation and associated buffering against extreme events (storms, tsunamis); dynamic response to sea level rise (within limits); breakdown of organic materials and pollutants; water filtration and purification; 3


        


nutrient mineralization and recycling; water storage in dune aquifers and groundwater discharge through beaches; maintenance of biodiversity and genetic resources; nursery areas for juvenile fishes; nesting sites for turtles, shorebirds and pinniped rookeries; prey resources for birds and terrestrial wildlife; provision of scenic vistas and recreational opportunities; supply of bait and food organisms; and functional links between terrestrial and marine environments in the coastal zone

Pressures and vulnerability Environmental pressures are ultimate (underlying) or proximate (Ehrlich 1968). The latter (for beaches) include recreational activities, the construction of related infrastructure, pollution, construction, ecologically harmful beach management (e.g., mechanical beach grooming) and resource exploitation. The former include human population size, consumption rates and technology. The latter, especially population growth, are encouraged by Government policy. In consequence Australia’s population is due to double in about 50 years years at the current record high rate of increase (ABS 2006). Coastal urban infrastructure and ecosystems are particularly vulnerable to such growth. The following brief comments concerning individual pressures and ecological effects on beaches draw heavily on Brown and McLachlan (2002), Schlacher et al. (2008a), Defeo et al. in press) and Jones et al. (2008), all of which contain more detail.

Climate Change

Climate change is an umbrella term that includes primary changes (higher atmospheric CO2 concentrations and air temperatures), second-order effects (e.g., warmer water with reduced pH), third-order (e.g., sea-level rise and changed hydrology) and lower-order effects (e.g., beach erosion, coastal retreat, biological changes) (Cocks and Crossland 1991). Dunes and beachfronts were listed as “vital areas” that would be lost or experience dysfunction (Cocks and Crossland 1991). Coastal ecological effects have been summarized by Harley et al. (2006). Some beach biological effects may be direct such as the physiological effects of temperature rise and changed rainfall regime; others may be indirect e.g., the effects of oceanic acidification on surf-zone phytoplankton that provide food for some beach species. Yet others may arise from the interaction of factors e.g., sea level rise, storm surges and human activities may combine to exacerbate sand erosion. Of primary concern are the geomorphic adjustments to coasts caused by sea-level rise (Cowell and Thom 1994). Sand will be eroded from the upper beach and deposited on the near-shore bottom, causing the shoreline to recede horizontally at 50 -100 times the vertical sea-level rise. This erosion, accelerated by increased storm surges (Slott et al. 2006) may completely remove the intertidal sandy habitat depending on the management options employed (see below). Also of importance is the predicted reduction of pH. Increased ocean acidity will reduce calcification rates in marine organisms (Feely et al. 2004) with potentially severe effects on mollusc and crustacean species that depend on 4



robust shells for protection against physical abrasion and predation. Rising temperatures will affect the distribution of species unable to acclimate, adapt or migrate. At particular risk are the narrow-range endemics (O’Hara 2002) and the species with limited dispersal abilities e.g. peracarid crustaceans which lack dispersive larval stages. Indirect effects of temperature change may also be important. For example, small increases (~0.6 ºC) in temperature have been associated with major changes in planktonic ecosystems in the North Atlantic (Richardson and Schoeman 2004). Since plankton is essential for suspension-feeding beach species, changes in plankton assemblages may have large effects on these beach species. As well, the semi-terrestrial peracarids and insects will probably be affected both directly and indirectly by changes in water and air temperatures (Marquez et al. 2003).

Nourishment

Since more than 70% of the world’s beaches are eroding (Bird 1996), engineering solutions have become increasingly important. Hard-engineering solutions (such as seawalls, breakwaters and groynes) have been ineffective (Pilkey and Wright 1989) and are now largely supplanted by the soft-engineering approach of beach nourishment (Finkl and Walker 2004). Although more ecologically-friendly than seawalls, nourishment still imposes ecological impacts (Blott and Pye 2004, Goldberg 1988, Nelson 1988, Peterson and Bishop 2005, Speybroeck et al. 2006, see Jones et al. 2008 for an Australian example). Biota can be affected directly via burial or changes to sediment texture and compaction, or indirectly via loss of prey (Bishop et al. 2006, Peterson et al. 2006, Speybroeck et al. 2006). These effects may be compounded by changes in beach slope and the reduction in habitat area (Peterson et al. 2006, Fanini et al. 2007). Nourishment activities can also disturb birds and destroy dune vegetation (Speybroeck et al. 2006). However, nourishment usually imposes a short-term, pulse disturbance (Bender et al. 1984) after which recovery occurs. Recovery often occurs in months rather than years depending on the match of sediment and beach profile to the original conditions (Nelson1988, 1993a, b, Peterson et al. 2000, 2006, Rakocinski et al. 1996). However, the recovery often produces a new fragile ecosystem, less buffered than the natural one against threats (Fanini et al. 2009). Beach species may well be adapted to physical disturbances since these (e.g., storms) are a feature of their evolutionary history (Hall 1994).

Coastal armouring In past decades, beach erosion was usually countered by building seawalls and groynes (Nordstrom 2000, Finkl and Walker 2004). Unfortunately, such hard engineering causes significant habitat changes with consequent ecological impacts (Martin et al. 2005, Bertasi et al. 2007, Sobocinski 2003, Dugan and Hubbard 2006, Dugan et al., in press). Beaches become narrower, reducing habitat for invertebrates, (Dugan and Hubbard 2006, Dugan et al., in press, but see Jaramillo et al. 2002 for an exception). Moreover, armoured beaches accumulate less wrack and debris which is important as food and habitat (Sobocinski 2003, Dugan and Hubbard 2006). By contrast, increased deposition of wrack can occur on some beaches where offshore structures have been placed (Martin et al. 2005). 5



Effects of armouring on vertebrates also occur. For example, the avifauna on armoured Californian beaches was depauperate compared with unarmoured beaches (Dugan and Hubbard 2006, Dugan et al. in press). Further, the loss of dry-sand, upper-beach zones following armouring prevents nesting by turtles. In extreme circumstances, seawalls can lead to the total loss of the intertidal habitat as in the ‘jersification’ of the coast, a reference to the absence of beaches in New Jersey where societal assets have been extensively protected by seawalls.

Recreation

As beach recreation intensifies (De Ruyck et al. 1997, Caffyn and Jobbins 2003, Fanini et al. 2006), management is designed to optimise recreational and economic outcomes. This often involves maintaining the beach and its qualities via nourishment (Speybroeck et al. 2006) or beach grooming (Llewellyn and Shackley 1996, Dugan et al. 2003). Other issues involve dunes. These are sometimes flattened to construct tourism infrastructure (Nordstrom 2000) and their vegetation can be damaged by human trampling (Liddle and Grieg-Smith 1975). Trampling may also affect some intertidal invertebrates (Moffett et al. 1998, Weslawski et al. 2000a, Fanini et al. 2005, Veloso et al. 2006, but see Jaramillo et al. 1996). Other taxa sensitive to recreation include shorebirds and turtles. For example, human activities modify the feeding and reproductive behaviour of shorebirds (Burger 1991, 1994, Lord et al. 2001, Verhulst et al. 2001). Another growing recreation issue involves off-road vehicles (ORVs). They can disturb intertidal sand surfaces and embryonic foredunes (Anders and Leatherman 1987, Kutiel et al. 1999, Priskin 2003, Schlacher and Thompson in press), destroy dune vegetation (Luckenbach and Bury 1983, Rickard et al. 1994, Groom et al. 2007), crush invertebrates (van der Merwe and van der Merwe 1991, Schlacher et al. 2007, 2008b) and disturb turtles and shorebirds (Hosier et al. 1981, Buick and Paton 1989, Williams et al. 2004).

Beach Grooming

Grooming is used to remove wrack and litter by raking and sieving the sand (Kinzelman et al. 2003). Unfortunately, grooming also removes propagules of dune plants and disturbs resident organisms and the sand surface, thereby increasing erosion by wind. As well, there are reductions in the wrack-dwelling macroinvertebrate assemblages (e.g. Griffiths and Stenton-Dozey 1981, Griffiths et al. 1983, Stenton-Dozey and Griffiths 1983, McLachlan 1985, McGwynne et al. 1988, Inglis 1989, Dugan et al. 2003, Colombini and Chelazzi 2003, de la Huz et al. 2005). Such reductions have flow-on effects on shorebird abundance (Tarr and Tarr 1987, Hubbard and Dugan 2003, Dugan et al. 2003) and the heavy grooming equipment can destroy the eggs and young of shorebirds, turtles and fish (Martin et al. 2006).

Development in general

Beach systems undergo progressive development as human coastal populations grow and infrastructure expands (Nordstrom 2000). Dunes are often removed, reducing the 6



sediment reservoirs and habitat resilience that are important in times of erosion. Attempts to redress erosion involve armouring and/or nourishment and fences to re-build dunes. Such strategies will be tested by sea-level rise and larger storm surges. Exacerbating this issue has been the damming of coastal rivers and the instream extraction of sand, processes that reduce the supply to beaches (Awosika et al. 1993, Innocenti and Pranzini 1993). Development has also brought buildings. These can affect sediment transport and introduce artificial light to the beach environment, a factor that can disrupt the movement of turtle hatchlings from the nests to the shoreline and increase the risk of predation (Verheijen and Wildschut 1973). Also the daily feeding migrations and orientation of nocturnal arthropods can be disturbed by artificial lights (Nardi et al. 2003).

Finally, development and burgeoning human populations have increased the demand for fresh water. Where this is sourced from coastal aquifers, the water table can fall with consequences for the dune ecosystem and the intertidal beach. Marine water may enter in the aquifers with negative effects on the dune and back-dune vegetation (Teobaldelli et al.2004). Other impacts include subsidence and increased rates of beach loss (Inman et al. 1991, Bondesan et al. 1995, Nicholls and Leatherman 1996). Other pressures include pollution, exploitation, mining and biological invasions. All of these have documented effects on beach ecosystems (McLachlan and Brown 2006, Schlacher et al. 2008a, and Defeo et al. in press) but are not addressed here due to space constraints. Clearly coasts are subject to a range of pressures acting individually and in combination. Urban sandy beaches are particularly vulnerable since their very existence will be in question as seas rise (Cowell et al. 2006). Moreover, some of the most serious pressures will grow, especially those associated with climate change and human population growth. Concern about the former is such that the Australian Government Department of Climate Change is assessing coastal vulnerability to climate change (Wilks 2008).

Management for resilience In Australia, coastal management is subject to government legislation such as the Commonwealth Coastal Policy 1995 and the New South Wales Coastal Policy 1979 amended 1997. Although there are aims to protect the coast and property and provide for recreation (James 2000b), “effective goals for beach management are yet to be thought out and clearly articulated in Australia” James (2000a p. 149). Such goal setting is rapidly growing more important as the effects of climate change are felt. Specific goals that integrate the interacting natural, socio-cultural and management systems (James 2000b) and that apply to both human utility and conservation are required. It is now common practice to provide strategic guidance through a vision statement. A suggested vision statement for beaches is: Beaches are maintained in a near-pristine state supporting fully diverse functioning ecosystems and sustainable low-impact human uses. This vision may not apply to heavily-used urban beaches, but for most other beaches it is consistent with ESD objectives for ecosystems i.e., the protection of 7



biodiversity and ecological processes. It also serves both ecocentric and anthropocentric ethics since the economic, recreational and aesthetic values of most beaches to humans derive largely from their natural state. If society desires to maintain beaches in near-pristine condition, the ecological concept of resilience becomes paramount. Resilience of ecosytems comprises two components, the ability to resist pressures without substantial change and the ability to return to a natural state following ecological impacts (i.e., recovery). Resilience is enhanced by the presence of all species of the natural community, genetic diversity within species (i.e., minimum viable populations), multiple examples of each habitat type, the availability of colonists to enable recovery and, of course, the absence of unusual stresses/disturbances. Of particular concern are the press disturbances (Bender et al. 1984). These are persistent (e.g., chronic pollution) and may preclude recovery. Less threatening are the short-term pulse disturbances from which recovery is theoretically possible even if the immediate impact may be large. Also, the spatial scale is important. A small-scale disturbance may have small effects and fast recovery (Fanini et al. 2005) while large-scale disturbances are more serious and possible irreversible. Questions that underly management for resilience are:  will systems resist pressures?  if not are the impacts acceptable?  if not will the system recover in an acceptable time frame?  will systems slowly degrade or shift to an alternative state? These questions require both scientific and social input, the latter being necessary to establish desired goals and the limits of acceptable change (Oliver 1995). In order to promote resilience, several principles apply. First, all the important pressures must be identified and addressed. Although many proximate pressures receive attention (e.g., pollution, dune maintenance), in Australia, population and economic growth are not considered threatening processes. Rather, both are actively promoted despite being ecologically unsustainable. For example, the past Prime Minister, John Howard said “the idea that we can address climate-change matters successfully at the expense of economic growth is not only unrealistic but also unacceptable” (reported in Breusch 2006). But growth imposes both short-term pressures on coastal systems and fuels long-term pressures such as climate change. Until ecological sustainability achieves primacy over growth as a societal goal and there is a commitment to ecological sustainability as core business, environmental decline will continue. Secondly, to maintain ecosystem resilience, management strategies must be ecosystem based. Ecosystem-based management (EBM) considers the entire ecosystem including humans. It integrates human activities and knowledge of ecosystem structure, function and interconnectedness within and among systems at various scales in space and time. It recognises the interdependence among ecological, social, economic and institutional perspectives, considers cumulative effects, promotes adaptive management and applies the precautionary principle. A key goal of EBM is to sustain the ability of ecosystems to deliver all ecosystem services rather than the current preoccupation with the short-term provision of a single service. (McLeod et al. 2005). Third, management requires substantial scientific knowledge of the ecosystem in question, its coupling with socio-economic systems, and the operation of EBM to be effective. Unfortunately, beach ecology is poorly developed (Fairweather 1990) and the EBM approach is in its infancy (McLeod and Leslie 2008). Consequently, definitive 8



management strategies await testing but some suggestions regarding beach resilience can be made. A crucial aspect of beach resilience concerns the integrity of the sediment budget. Unfortunately, this has been impaired by human effects on beach-dune systems (Tomlinson 2002, Alonso and Cabrera 2002, Sherman et al. 2002). Given this, the fact of existing erosion and the certainty of future erosive pressures from sea-level rise and increased storminess, the very survival of some beaches is in question. Adaptive measures to protect beaches include the vegetation and stabilisation of dunes, maintenance of sediment supply and the provision of buffer zones. As well, managed retreat strategies (rolling easements or setbacks that allow the landward migration of the coastline) have been adopted by several countries including Australia (see e.g., the State Coastal Planning Policy of Western Australia 2003). But all these strategies have their limitations. For example, although dune management is a prime management tool (Tomlinson 2002), it would only retard the retreat of the coast. Further, setbacks involving buyouts would be extremely expensive and socially unacceptable in urban areas. Here, society may protect assets via engineering solutions such as large-scale beach nourishment and/or the construction of sea walls. Unfortunately, the latter would probably cause the total loss of the beach (Finkl and Walker 2004) and would thus fail as an ecological management strategy. Moreover, seawalls may only provide short-term protection of societal assets. In the long term “our coastal communities may have to rethink their location and may be forced to consider a retreat from the beach” (Tomlinson 2002). Nourishment is more attractive than armouring for both economic and conservation purposes since it can maintain beach habitat in a semi-natural. General management recommendations (Speybroeck et al. 2006) include:  importing sediments and creating beach profiles that match the original beach conditions as closely as possible;  the avoidance of sediment compaction;  careful timing of operations to minimise biotic impacts and enhance recovery;  the selection of locally-appropriate techniques;  the implementation of several small projects rather than a single large project;  interspersion of nourished beach sections with unaffected areas; and  repeated application of sediment in shallow layers (