Can we recreate or restore intertidal habitats for shorebirds? PHILIP W. ATKINSON British Trust for Ornithology,The Nunnery, Thetford,Norfolk IP24 2PU, UK, e-maih phil.atkinson @bto. org Atkinson,P.W. 2003. Can we recreateor restoreintertidal habitats for shorebirds?Wader StudyGroup Bull. 100: 67-72. Lossof intertidalhabitat to developmentcontinues apace. Coupled with the long-termeffects of climatechange therewill be an increasingneed to createnew areasof intertidalhabitats if shorebirdpopulations and flyways areto be effectivelyconserved. Habitat restoration and creation efforts in the US, Europeand Japan have shown that creatingsalt marshis often a hit or miss affair as new sitestend to supportdifferent communities and a differentrange of ecologicalfunctions to surroundingareas. Creating mudflats often meets with a higherdegree of successif sedimentsupply is sufficientas benthicinvertebrates and shorebirdscolonise relatively quickly. Sitesin higherenergy environments tend to reachequilibrium quicker than lower energyenvironments. Many restorationsites tend to be small and thus factors,such as enclosure,tend to impact on the birds that use the sites.Not only do thefactors controlling the restoration need to be betterunderstood so that high quality habitats canbe producedbut alsothe impactsof creatingnew habitatson shorebirdsat the populationlevel. This will requirea muchbetter understanding of flyways,migration strategies and other factors controlling populations at a large scale. INTRODUCTION many countrieswhere this hasbeen an issue,there has been an acceptancethat lossof habitatswill needto be compen- One of the greatestthreats facing shorebirds has been the loss satedfor by the restorationor creationof new habitats. or degradationof breeding,staging and winteringhabitats. Many countriesnow have a policy of compensatingfor This has been global in extent and there is probably not a lost wetland habitats. The compensationwill vary in re- flyway that has not been affected by large-scaleloss and sponseto eachparticular situation, e.g. compensationfor a deterioration of wetland habitat. Total wetland loss world- the lossof an areathrough development will be very differ- wide has .been estimated at 50% of those that have been in ent to the strategyused to mitigatethe widespreadeffects of existencesince 1900 (Dugan 1993, OECD 1996). In north- changingclimatic conditions and accelerating sea-level rise. em countriesmuch of thisloss took place during the first half Compensationfor loss of a particularsite usually involves of thetwentieth century but during the latter part, tropical and the creation of a new site elsewhere. Solutions to sea-level sub-tropicalwetlands were increasinglybeing degradedor rise will necessarilyinclude a larger scale approachwhich lost, predominantlythrough conversion to agriculturaluse, will include a mix of maintaining current sea defences which is the major causeof wetland loss worldwide. By throughsoft or hard engineeringtechniques, abandonment 1985, it was estimated that 56-65% of wetlands had been or managedrealignment, i.e. takingback sea walls andcreat- drainedfor intensiveagriculture in Europeand North America, ing intertidalhabitats (Dixon et al. 1998).There is hugepoten- 27% in Asia, 6% in South America and 2% in Africa, a total tial to replace lost areas and create valuable habitat for of 26% lossto agricultureworldwide (OECD 1996). These waterbirds. figures mostly refer to freshwaterhabitats and the global The sciencebehind the restorationand creationof many coastalwetland resourceis generallypoorly known. How- terrestrialhabitats is well advanced.However, intertidal habi- ever, changeswithin thesehabitats (including tidal flats, salt tats posespecial problems for restorationbecause they are marshes,sea grass beds, mangroves, saline lagoons, shingle topographicallyand ecologicallycomplex and they support banks and transitional brackish-water habitats) have been many speciesof animals, some of which require specific everybit aslarge asfreshwater habitats. In the United King- habitatsand linkagesto other terrestrialor marine habitats. dom, 23% of estuaries and 50% of salt marshes have been Moreoverthey exist and evolve within dynamiccoastal set- drained since Roman times (Davidson et al. 1991, Moser et tings,subject to changingtidal levels,salinities and long term al. 1996). mechanicalprocesses that are associatedwith sea-levelrise Added to this continuinganthropogenic loss will be the andclimate change (Atkinson et al. 2001). Often thesecom- creeping effects of changing environmental conditions plexities are ignored and there is a tendencyfor created throughclimate changeand rising sea levels. As a result, coastalhabitats to lack the diversityseen in naturalareas and managersof estuarineand open shorehabitats, which sup- supportonly generalistspecies. Also, created sites rarely portimportant populations of waterbirds(defined here as any follow expectedpaths and the stablestates that are reached speciesdependent on wetlandhabitats at any time duringits often differ from what was expected,despite multi-million lifecycle),will facenew challengesto mitigatethe effectsof dollar investments(Zedler & Callaway 1999), leadingto the both direct habitat loss and thesechanging environmental conclusionthat the currentstate of restorationtheory applied conditions.The responseto thesechanges will differ, but in to coastalhabitats does not necessarilylead to predictability. 67 Bulletin100April2003 68 Wader Study Group Bulletin To effectivelymitigate this loss,there is a greatdeal to in the Wadden Sea. Although only a fraction of the area learn,not only aboutthe processesunderlying coastal habi- presentabout 2,000 yearsago, theseintertidal habitats are tat restoration or creation, but also those that control the still the largestcontiguous area of salt marshin Europe,and shorebirdpopulations that many of theseareas will be created the Wadden Sea is Europe'slargest intertidal wetland cov- for. The purposeof thispaper is to assessthe stateof know- eringsome 8,000 km 2. However,in the50 yearsto 1987, ledgeabout creating or restoringsalt marshes and tidal flats 33% of the areawas lost to embankments(Dugan 1993) and for shorebirds,and to ask what we need to know to be better new marshes formed in front of the new sea walls. Within equippedto predictthe outcomes of creationand restoration The Netherlands, there are over 17,000 ha of man-made salt effortson shorebirdpopulations. As mostresearch has been marshes,created specifically for flood defence purposes carded out on thesetwo habitats,this paper concentrateson rather than for any other environmentalbenefit (Esselink them.However, it mustbe acknowledgedthat much needs to 1998).This policyis changingand salt marshes on theNorth be doneto addressthe issuesof creatingand restoring other Seacoasts of Germany,Belgium, The Netherlandsand Den- intertidal habitatssuch as mangrovesand sea grassbeds mark,which are of high conservationimportance because of whichare alsoimportant for waterbirds(e.g. Field 1968). the large concentrationsof wintering,passage and breeding waterfowl that they support,are now increasinglybeing CURRENT STATE OF COASTAL WETLAND managedfor natureconservation purposes (Esselink 2000). RESTORATION SCIENCE Again little hasbeen published in the peer-reviewedlitera- ture althoughthe createdmarshes at Sieperdain The Neth- The scienceof restoringcoastal habitats has been developed erlandsare a notableexception (Castelijns et al. 1997, Eert- in the United States for three decades and there is now a mann et al. 2002). substantialand growingbody of literaturecovering the ex- Elsewherein the world,Japan has led the way in creating pertisethat has been acquired there on the creationand re- tidal mudflatsand, according to the EnvironmentAgency of storation of wetlands. Of most relevance to this review, are Japan,37 coveringapproximately 900 ha were createdbe- those studies that have focussed on efforts to create and re- tween 1973 and 1998 (WAVE 2001a,b). This is small com- storetidal wetlands(e.g. Broomeet al. (1988), Zedleret al. paredto the lossof nearly4,000 ha (42% to reclamation) (1988) & Zedler (1996)), despitethe fact thatmany of them over the sametime period(WAVE 2001a,b).The total area have concentratedon physicalfeatures with only limited of tidal flats in Japanis 51,443 ha (EnvironmentAgency of monitoringof plants,fish andinvertebrates. This hasculmi- Japan1997). Six of thenewly created mudflats were directed natedin the productionof practicalhandbooks for the re- towardscreating areas for birds,but there are few accessi- storationof tidal wetlands(e.g. Zedler 2001). A recentspe- ble data with which to assess success. cial issueof WetlandsEcology and Managementfocused Researchhas therefore been geographically rather limited uponthe beneficial use of dredgematerial for therestoration andfocussed on particularhabitats or ecosystems.One of the of US salt marshesand mudflats (Streever 2000). Unvege- largestissues, rarely tackled in moststudies, has been a de- tated mudflats are not classed as wetlands under S.404 of the tailed assessmentof the physical,temporal and biological US Clean Water Act and thus intertidal habitat creation work factorsthat determinethe resultinghabitats and communi- in the US has focussed on the creation of salt marshes. As a ties and how theserelate to the rangeof variationfound in consequence,mudflat creation schemes in theUS haveusu- naturalareas. Most studieshave simply describedthe bio- ally beenmotivated by a desireto