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Ecological Engineering | Coastal Zone Restoration 637

Van Dolah FM (2000) Diversity of marine and freshwater algal toxins.In: Botana LM (ed.) Seafood and Freshwater Toxins: Pharmacology,Physiology, and Detection, pp. 19–43. New York: Dekker.

Wolanski E (2001) Oceanographic Processes of Coral Reefs: Physicaland Biological Links in the Great Barrier Reef. Boca Raton: CRCPress.

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Wolanski E and De’ath G (2005) Predicting the present and futurehuman impact on the Great Barrier Reef. Estuarine, Coastal andShelf Science 64: 504–508.

Wolanski E, Richmond R, McCook L, and Sweatman H (2003) Mud,marine snow and coral reefs. American Scientist 91: 44–51.

Coastal Zone RestorationC B Craft and J Bertram, Indiana University, Bloomington, IN, USA

S Broome, North Carolina State University, Raleigh, NC, USA

ª 2008 Elsevier B.V. All rights reserved.

Introduction

Dune Restoration

Tidal Wetland Restoration

Further Reading

Introduction

Coastal dunes and tidal wetlands are found at the inter-face between land and sea. They are dynamic ecosystemsand serve as the first line of defense against the sea,buffering wind, waves, storm tides, and rising sea level.The physical environment of dunes and tidal wetlands isharsh. Both are exposed to wind and wave action and saltthough they differ in availability of water. Dunes arewater-limited as the unsaturated sandy soils have lowwater holding capacity that favors establishment ofdrought-tolerant vegetation. In tidal wetlands, the soilsare saturated during tidal inundation, creating anaerobicsoil conditions that favor colonization by hydrophytic(flood-tolerant) vegetation.

Dune Restoration

Coastal dunes are a natural feature of sandy shorelinesand are present in most temperate regions. They areamong the most dynamic landforms, shifting withthe winds and storm tides. Dunes are part of the near-shore environment that change seasonally and with episo-dic storms. They serve as reservoirs of sand to re-nourishthe beach during storms as erosion of sand transports itoffshore where it is deposited on sand bars to be returnedgradually by the tides. Formation of dunes requires asource of sand, usually carried from the beach by onshorewinds, and vegetation to catch sand and stabilize it.

Dunes are stressful environments characterized byblowing sand that abrades vegetation, salt spray, highsoil temperatures, low water holding capacity and low

nutrients, especially nitrogen (N). Historically, manydunes were deforested for timber then used for grazing.Today, they are under stress from shoreline developmentand overbuilding of the coastal fringe. Development ofthe shore often leaves no room for dunes to migrateinland, as occurs when sea level rises. The combinationof ever-changing environmental conditions and urbanencroachment makes coastal dunes a globally endangeredecosystem.

The Dune Community

Dune vegetation consists of distinct plant communities,pioneer, scrub, and forest zones, that occur along a gradi-ent of increasing distance from the sea and increasing age(Figure 1). The pioneer zone occurs on the upper beachor foredune area, closest to the sea. Vegetation consists of afew species of grasses, sedges, and forbs that are able towithstand salt spray, sandblast, burial by sand, temperatureextremes, drought, episodic flooding with salt water andlow nutrient (N) availability (Table 1). Pioneer speciesinclude dune initiators and dune builders. Dune initiatorsare annuals such as sea rocket, Cakile maritima, which iswidely distributed throughout the world, sea purslane(Sesuvium spp.), and other species. Dune initiatorsare important for trapping seeds of dune builders. Dunebuilders consist of perennials such as American beachgrass (Ammophila breviligulata), European beach grass ormarram grass (A. arenaria), European dunegrass (Elymus

arenarius), and American dunegrass (Elymus mollis) in coolclimates, and sea oats (Uniola paniculata) and bitterpanicum (Panicum amarum) in warm climates.Saltmeadow cordgrass, Spartina patens, also is common in

Table 1 Environmental constraints on establishment of coastal dune and tidal wetland vegetation

Constraints Dune Tidal marsh/mangrove

Physical Inadequate water/drought Excess water/anoxiaSalt spray Salinity

Wind/sand abrasion Excess wave action

Excessive soil temperature Excessive soil temperature

Nutritional Inadequate N, (P) Inadequate N, (P)Acid sulfate soils

Disturbance Foot/vehicular traffic

Grazing/herbivory Grazing/herbivory

Colonization Excessive tidal energy

Disease Fungal pathogens, scale insects

See text for an explanation of the various constraints.

Sea Foredune zone(Swale)

Shrubzone Forest

zone

Figure 1 Vegetation of the coastal dunes from the sea inland to the forest.

638 Ecological Engineering | Coastal Zone Restoration

the foredune zone where it is found on low, moist sites

where exposure to salt is greater. Once dune initiators and

dune builders become established, secondary invaders such

as Abrona, Ambrosia, Artemesia, Croton, Carex, Carpobrotus,

Euphorbia, Erigeron, Festuca, Fimibristylis, Hydrocotyle, Ipomoea,

Lathyrus, Lupinus, Schizachyrium, Solidago, Spartina, and

Sporobolus colonize the pioneer zone.The shrub zone lies immediately behind the foredune

zone and consists of secondary dunes and low-lying areas,

swales, and flats, between them. In addition to pioneer

species, the shrub zone is colonized by woody vegetation

that stabilizes dunes. The shrub zone receives less salt

spray and fresh sand relative to the foredune zone.

Nitrogen supply also is low. In the shrub zone, woody

shrubs and trees are stunted by salt spray and wind. Along

the US Atlantic coast, seashore elder, Iva imbricata, is

important in the shrub zone. It is highly adaptable and

tolerates saltwater, salt spray, sandblast, and sand accu-

mulation. Seashore elder grows in foredunes, swales,

maritime forests, and upper fringes of the salt marsh.

Growth of pioneer species is poor in the shrub zone

relative to the foredune zone. Shrub species do well

though and they are important in stabilizing sand and

initiating soil development. The decline of vigor and

growth of pioneer species in the shrub zone is thought

to be linked to reduced sand accumulation that supplies

mineral nutrients, especially phosphorus (P).

The forest zone is the oldest and most stable dunecommunity. It forms only after substantial time passesand soil formation begins. Considerable protection fromsalt spray and flooding is needed for the forest zone todevelop. Once dunes are stabilized and pioneer and shrubcommunities develop, trees may be planted to acceleratesuccession. However, trees are not planted in the fore-dune or shrub zones near the sea because salt sprayinhibits their growth. Also, trees shade out pioneer andshrub species and inhibit regeneration of these speciesfollowing a severe disturbance such as disease outbreak,insect outbreak, or fire.

Limiting Factors for Establishment

Establishment of dunes requires a supply of sand andvegetation to catch and stabilize it. Sand is supplied byonshore winds that pick it up from the beach and carry itinland where it is intercepted by vegetation. Sand istransported mostly by saltation, bounced along as theimpact of moving grains dislodges other grains, and bysurface creep. Sand fences often are erected to trap sandand initiate dune building. Fences may be built usingwooden pickets, boards, bamboo, reeds, fabric, or othermaterials such as branches that deflect and slow the wind.Guidelines for using fences include (1) use fences of40–50% porosity as they are most efficient in trapping

(a)

(b)


sand, (2) install fences parallel to the shoreline, and (3) asingle row of fence is suitable at lower wind speed butdouble fences may be needed at higher wind speed. As thedune builds, continued sand trapping and dune growth isfacilitated by installing additional fences atop the originalfence as it becomes buried. Other sources of sand for dunebuilding include dredged material pumped onto thebeach and sand pushed up by bulldozers.

The dune environment is harsh. The sandy soils holdlittle water and are low in nutrients, especially N. Dunevegetation responds favorably to fertilizer additions, espe-cially N with a lesser response to P. Because of its fragilenature, it is essential to keep existing dunes and duneplantings free of vehicular and foot traffic (Table 1). Insome regions, grazers, rabbits in Europe, nutria inLouisiana (USA), may graze on dune vegetation, reducingplant cover (Table 1). In Europe, where dunes were affor-ested centuries ago, grazers such as sheep and rabbits areimportant for maintaining early-successional vegetation.

Figure 2 (a) Installation of a sand fence for dune restoration in

January 1978. (b) The same site in October 1981.

Restoration and Ecosystem Development

Restoration of coastal dunes has been widely used aroundthe world, including Europe, North America, SouthAfrica, New Zealand, and elsewhere to help stabilizebeaches and barrier islands.

In Europe, coastal dunes have been used for centuriesfor low-intensity agriculture (e.g., grazing). In the nine-teenth-century pine trees, Pinus maritima, P. mugo, andother trees were planted along the coast of France fordune stabilization and silviculture. With increasing urbanencroachment and fragmentation in the twentieth cen-tury, public awareness of the importance of dunes forshoreline defense, habitat for nature and esthetics led tointerest in restoring these ecosystems.

In Europe, where trees were planted for silviculture,early dune restoration efforts involved cutting down thetrees and shrubs to promote conditions favorable forpioneer vegetation. The first, scientifically based restora-tion efforts involved planting European beach grass,American beach grass, and other pioneer vegetation toidentify suitable species for use in dune plantings. In the1960s, experimental plantings were established along theUS Atlantic coast. Different sources of sand were testedand different species, including American beach grass,were planted to determine their geographic range andenvironmental requirements. On the Pacific coast, similarexperiments were underway evaluating European beachgrass.

Frequently, dunes are established too close to thebeach which does not allow for the natural ebb and flowof sand between the dune, beach, and offshore sand bar.Along the US Atlantic coast, it is recommended thatdunes be placed at least 100 m from mean high water toavoid dune erosion during storms. Once a site is selected,

a sand fence is installed to catch and perennial vegetation

is planted to stabilize and hold the sand in place

(Figure 2a). Plant stems and leaves increase surface

roughness that decreases wind velocity near the ground

and interferes with sand movement, and roots that hold

sand in place. Over time, a healthy dune community

develops (Figure 2b). Vegetation is planted early in the

growing season to avoid high soil temperatures that occur

later and to give plants the full growing season to colonize

the site.Dune vegetation is N-limited and sometimes

P-limited. N–P–K fertilizer (30–10–0) is applied at the

rate of 23 kg ha�1 (50 lb acre�1) 2–3 months after planting

to promote plant growth. Do not fertilize at the time of

planting as the fertilizer will leach from the soil. Rather,

once the root system begins to develop, fertilizer is

applied in three applications (69 kg ha�1 total) spread

out over the growing season.Several pioneer species should be planted as multi-

species plantings generally outperform monoculture


plantings. Beach grass traps sand and accumulates it faster

than other species. Beach grass also migrates faster toward

the ocean than other species such as sea oats and bitter

panicum, but it is susceptible to disease and insect pro-

blems (Table 1). Infestations by insects and pathogens are

less of a problem in cool temperate climates as opposed to

warm climates. In North Carolina (USA) American beach

grass is attacked by a scale insect (Eriococcus carolinae) and

a fungal pathogen (Marasmius). Woody vegetation, which

is common on older dunes, is not planted in the foredune

area because it does not grow well. Rather, shrubs and

trees will colonize the site as succession proceeds, assum-

ing environmental conditions are stable (i.e., the sea is not

encroaching).Monitoring studies indicate that multispecies plant-

ings are most successful in accumulating sand, building

dunes, and providing good plant cover. On Ocracoke

Island (North Carolina, USA), 10 years after planting a

mixture of American beach grass and sea oats, sea oats

dominated the zone where sand was no longer accumu-

lating. On the active sand-accumulating zone toward the

beach, beach grass was dominant. Long-term monitoring

of restored dunes on the Brittany Coast of France

revealed that, after 10 years, fixed (nonmigrating)

dunes had been reestablished but plant species diversity

was lower than in mature dunes. In North Carolina, 20

years after installing a sand fence and planting with

American beach grass, a 3 m high dune developed that

had built 30–40 m seaward (Figure 3). After 10 years,

species richness averaged three species m�2 with a total

of nine species observed on the planted site. After 20

years, species richness doubled to 6.2 species m�2 and

15 species were counted. Over time, American beach

grass decreased in importance as it was replaced by

later-successional vegetation, S. patens, and woody vege-

tation, red cedar (Juniperus virginiana), wax myrtle

(Myrica cerifera), and silverling (Baccharis halimifolia).

0

0

1

2

3

4

5

6

10 20 30 40 50Distance (m)

Ele

vatio

n (m

, MS

L)

Plantedarea

19661970

1975 (2.9 species m–2, 9 species total)1985 (5.9 species m–2, 15 species total)

60 70 80 90 100

Figure 3 Change in dune profile characteristics and plant

species composition 4, 10, and 20 years after dune restoration

along the North Carolina (USA) coast.

Tidal Wetland Restoration

Tidal wetlands consist of salt marshes, found mostly intemperate regions, and mangroves, found in tropical andsubtropical regions. Marshes are dominated by grasses,notably the genus Spartina, rushes (Juncus, Schoenoplectus),sedges, forbs, and shrubs. Mangroves, salt- and flood-tolerant trees, and shrubs that inhabit the intertidalzone, are dominated by the genera Rhizophora, Avicennia,Laguncularia, Conocarpus, Sonneratia, and others. Similar todunes, tidal marshes were used for centuries for grazingand for mangroves, for silviculture, and for gatheringfirewood. In Europe, the United States, and elsewhere,levees were constructed around tidal marshes to isolatethem from the sea for agriculture. Like dunes, today tidalmarshes and mangroves exist in a fragile environmentsqueezed by human encroachment.

Tidal Marsh and Mangrove Communities

Vegetation of tidal wetlands often grows in distinct zonesdetermined by tidal inundation and salinity. Marsh vege-tation often is separated into ‘low’ and ‘high’ marsh basedon the frequency of tidal inundation. Smooth cordgrass,Spartina alterniflora, of the US Atlantic coast, forms mono-typic stands in the low marsh, where inundation by theastronomical tides occurs twice daily. Other species ofSpartina (i.e., S. foliosa on the US Pacific coast, S. townsendii

in Europe, S. anglica (the fertile form of S. townsendii) inChina) and some forbs (e.g., Halimione portulacoides) domi-nate the low marsh in other parts of the world. A differentassemblage of species grows at higher elevations, in thehigh marsh. In the US, needlerush (Juncus roemerianus),saltmeadow cordgrass (S. patens), and salt grass (Distichlis

spicata) grow in the high marsh. Puccinellia maritima iscommon in the high marshes of Western Europe.

Tidal wetland vegetation varies with the salinity oftidal floodwaters. Salinity, mostly sodium chloride, stres-ses plants by altering osmotic potential that interfereswith water and nutrient (N) uptake. High marsh vegeta-tion generally is less tolerant of salinity than Spartina andgrows better at higher elevations in the marsh and in areasfarther away from the ocean, where salinity is diluted byfreshwater. In arid and semiarid regions where precipita-tion is low and evaporation is high, salinity of floodwatersmay exceed that of seawater, which is 35 parts per thou-sand (ppt). In these regions, salt-tolerant halophytes suchas glasswort (Salicornia spp.), saltwort (Batis spp.), andothers (Borrichia, Suaeda, Distichlis) dominate. Vegetationgrows slowly and cover is sparse in these salt-stressedtidal wetlands.

Similar to marshes, mangrove vegetation grows inzones related to hydroperiod and salinity. In theWestern Hemisphere, red mangrove (Rhizophora mangle)


grows closest to the water’s edge while black mangrove(Avicennia germinans), white mangrove (Laguncularia race-

mosa), and buttonwood (Conocarpus erectus) grow furtherinland. Salt marsh vegetation, including Spartina,Distichlis, Batis maritima, Sporobolus virginicus, and others,often is found growing with mangroves.

Limiting Factors for Establishment

Successful establishment of tidal wetland vegetationrequires recreating or restoring hydrology and salinity,as well as other factors (soils, nutrients) that favor marshand mangrove vegetation (Table 1). Reestablishing theappropriate hydroperiod, the depth, duration and fre-quency of inundation, is critical for successfulestablishment of vegetation. Restoring hydroperiod iseasier in tidal wetlands than in inland wetlands becausethe astronomical tides provide for predictable and fre-quent inundation. In the intertidal zone, a narrowelevation range exists where vegetation can be success-fully established and the width of this zone will depend onslope of the land and tide range. A large tidal range andgentle slope (1–3%) will produce the maximum amountof potentially restorable marsh area (Figure 4a). Lowmarsh vegetation such as Spartina alterniflora grows atelevations between mean sea level and mean high water.Above mean high water, inundation is less frequent and‘high’ marsh vegetation such as S. patens, Distichlis spicata,

(a)

(c)

Figure 4 Tidal marsh restoration on (a) dredge spoil and (b) graded

marsh 7 years after restoration.

and Juncus roemerianus grow between mean high water

and the mean spring high tide line. Where tidal inunda-

tion is less predictable or where tide range is small, small

differences in elevation produce distinctly different plant

communities. In North Carolina (USA), four different

species grew in distinct zones, all within an elevation

range of less than 30 cm. Thus, it is critical to understand

the hydroperiod requirements of different species so they

can be planted in the appropriate elevation zones.Determining the appropriate salinity regime also is

critical for successful establishment of tidal wetland vege-

tation. Smooth cordgrass and red mangrove grow well in

areas regularly inundated by a mixture of freshwater and

seawater, in the range of 20–30 ppt. Other species are less

tolerant of salinity and should be established in areas

where salinity is lower, from fresh (0 ppt) to brackish

(15–20 ppt) salinities.Soil properties also determine whether tidal marsh

vegetation becomes established or not. Nitrogen, in par-

ticular, limits growth of Spartina and other vegetation so

N additions usually are needed to jumpstart the plant

community. On sites that are planted, success is best

achieved when N is added in slow-release form directly

into the planting hole. Sufficient phosphorus (P) is

brought in by tidal inundation so that P additions usually

are not necessary.Wetlands created on upland or terrestrial soils pose

significant problems. Grading the site to intertidal

(b)

(d)

upland soil, (c) the redge spoil marsh, and (d) the graded upland


elevations exposes subsurface soils (Figure 4b) with highbulk density that impedes rooting. Subsoils also containessentially no organic matter and N. In some situations,grading exposes acid sulfate soils (Table 1) with low pH(2–3) and high ferrous iron (Fe2þ) concentrations that killvegetation. In addition to N, establishment of vegetationon graded upland soils requires additions of lime to raisethe pH and P to counteract the high Fe content thatimmobilizes P. Because of the problems involved withcreating wetlands on upland soils, emphasis today is onrestoring degraded wetlands back to health rather thancreating entirely new ones. Other advantages of restoringtidal wetlands, rather than creating entirely new ones, isthat restored sites contained wetland vegetation and soilsin the past so the restoration effort begins with soils thatcontain some relic organic matter, N and, possibly, viableseeds.

On sites such as dredge spoil, where no vegetationexisted and no seed bank is present, vegetation needs tobe planted. Similar to dune vegetation, marsh and man-grove vegetation should be planted early in the growingseason, before soil temperatures get too high. Seeding orsowing rhizome fragments usually is ineffective becausetidal inundation disperses the seeds and fragments fromthe site. This is especially problematic on sites with a longfetch that enables large wind-generated waves whoseenergy translates onto the site and may uproot evenplanted vegetation (Table 1). Herbivory by geese, nutria(Myocastor coypus), and muskrats (Ondatra zybethicus) thatgraze on aboveground biomass also may hinder establish-ment of vegetation in tidal wetlands.

Table 2 Estimated rate of development of wetland-dependent

functions following saltwater marsh creation

Time required to achieveequivalence to naturalmarshes

Hydrologic functions

Energy dissipation 1–3 years

Sediment stabilization 3–5 years

Biogeochemical functionsSediment, P retention 1–3 years

Carbon, N sequestration 3–5 years

Microbial processes 5–15 yearsSoil formation 10’s to 100’s of years

Ecological functions

Primary production 3–5 yearsSecondary production

Benthic invertebrates 10–20 years

Finfish, shellfish 2–15 years

Water fowl and wading birds 1–3 yearsSongbirds 10–15 years

Restoration and Ecosystem Development

Large-scale efforts to restore tidal wetlands began in thelast century as marsh and mangrove vegetation wasplanted throughout the world to control coastal erosionand reclaim land. Documented accounts of large (9000 ha)mangrove plantings date from the late 1800s. Cordgrass,Spartina townsendii, was transplanted extensively inEurope in the 1920s and 1930s to slow coastal erosion,reduce channel siltation, and to reclaim land for agricul-ture. From the 1930s to the 1960s, S. townsendii andsmooth cordgrass, Spartina alterniflora, were planted inAustralia, New Zealand, the United States, and Chinafor the same reasons.

One of the first systematic efforts to create and restoretidal wetlands was initiated by the United States ArmyCorps of Engineers (COE) in the 1960s and it was focusedon creating salt marshes using dredged material. TheCOE began planting smooth cordgrass on materialdredged from navigable waterways to stabilize dredgedmaterial by establishing vegetation (Figure 4c). Thetechnique proved successful and, in the 1970s, S. alterni-

flora was successfully used to stabilize eroding estuarine

shorelines. In the 1980s, salt and brackish water were

created and restored to mitigate or replace wetlands lost

to mineral extraction, highway and pipeline construction,

dredging activities, oil spills, and coastal development

(Figure 4d). Most of these wetlands were created using

dredged material or graded upland sites or by restoring

hydrology to diked marshes. Restoration usually involves

removing dikes, levees, or tide gates to restore tidal inun-

dation to promote growth of marsh vegetation and initiate

wetland soil formation. In the northeastern US, restora-

tion frequently involves removing tidal gates that were

installed, in some cases 100 years ago, to exclude tidal

inundation and reduce flooding of coastal communities.

Once the tide gates are removed, tidal inundation and

salinity are reintroduced and S. alterniflora gradually

replaced freshwater wetland vegetation.Successful restoration of hydroperiod and vegetation

does not ensure immediate recreation of wetland func-

tions on the site though. Created and restored tidal

wetlands are young relative to older, mature, wetlands

and some time must pass before ecological functions such

as productivity, biogeochemical cycles, and habitat

develop to levels found in older natural wetlands. Many

wetland functions depend on establishment of a produc-

tive plant community with good spatial coverage.

Emergent vegetation is important for dissipating energy

from waves and for stabilizing sediments, and good cover-

age usually develops within 3–5 years following planting

(Table 2, Figures 5a and 5b). Woody vegetation such as

mangroves takes longer to form good coverage. Also,

mangroves are susceptible to attack by fungal pathogens

and the isopod, Sphaeroma, which may slow the restoration

effort.

1600(a)

(b)

1400

1200

1000

800

600

400

200

0

4000

3000

2000

1000

0

1 5 10 15 25Year after establishment

1 5

Natural marsh biomass during 22 yearperiod of record

Natural marsh biomass during 22 year period of record

10 15 25Year after establishment

Abo

vegr

ound

bio

mas

s (g

m–2

)B

elow

grou

nd b

iom

ass

(g m

–2)

Figure 5 Development of above- and belowground biomassstocks over time on a constructed Spartina alterniflora marsh in

North Carolina (USA). Reprinted from Craft C, Reader J, Sacco

JN, and Broome SW (1999) Twenty-five years of ecosystem

development of constructed Spartina alterniflora (Loisel)marshes. Ecological Applications 9: 1405–1419, with permission

from the Ecological Society of America.


Biogeochemical functions such as sediment deposition,carbon sequestration, N and P accumulation in soil, and

microbial N fixation also develop within 3–5 years.Heterotrophic microbial processes (decomposition,methanogenesis, and denitrification) and soil inverte-

brates are strongly linked to soil organic matter sosufficient organic matter must accumulate to supportthese processes, usually about 5–15 years (Table 2). Soil

formation takes longer to develop, on the order of tens tohundreds of years.

Animal use of created and restored wetlands dependson their ability to disperse to and colonize the site.Invertebrates with planktonic (free-swimming) larvaereadily disperse to the site whereas invertebrates thatlack planktonic larvae take much longer to colonize.

Oligochaetes, a major component of the salt marshbenthic invertebrate community, lack planktonic larvae

and several decades elapsed before these organisms colo-nize the site. Fish and birds readily use created andrestored wetlands once hydrology is restored and vegeta-tion covers the site (Table 2). Fish use is enhanced bymaximizing the amount of edge between vegetation andopen water. Waterfowl use of created and restored wet-lands is enhanced by increasing the proportion of openwater, up to about 50% of the area. Songbird use increaseswith amount of woody shrubs which takes longer todevelop than herbaceous vegetation.

Ecosystem development of tidal wetlands is acceler-ated by addition of fertilizer N and seasoned organicmatter that jumpstart plant growth and heterotrophicactivity. Amending soils with organic matter, however,is costly and time consuming and generally is notemployed for most projects.

In recent years, large-scale restoration of tidal marsheshas been undertaken for mitigation of natural resourcedamages. In Delaware Bay (USA), Public Service Electricand Gas developed a large-scale estuarine enhancementproject to mitigate for loss of finfish caused by entrain-ment in power plant cooling water. As part of theenhancement effort, tidal inundation was restored to1800 ha of diked salt hay (Spartina patens) marsh to createnew habitat to enhance fisheries production in theestuary.

In the Mississippi River delta (USA), tidal wetlands arerestored to combat wetland loss attributed to naturalsubsidence and anthropogenic factors that exacerbate it.Enacted by the US Congress in 1990, the Coastal WetlandPlanning, Protection, and Restoration Act (CWPPRA)was designed to protect, restore, and create tidal wetlandsby freshwater and sediment diversion from theMississippi River and by beneficial use of dredged materi-al. CWPPRA spends about 40 million USD annually tosupport wetland restoration in the delta. In 1997, a long-term plan, Coast 2050, was developed to combat wetlandloss in the region. The goal of Coast 2050, which has yetto be implemented, is to restore more than 10 000 km2 ofcoastal wetlands over the next 50 years, with a price tag of14 billion USD.

See also: Dunes; Mangrove Wetlands; Wetland Models.

Further Reading

Broome SW (1988) Tidal salt marsh restoration. Aquatic Botany32: 1–22.

Craft C, Reader J, Sacco JN, and Broome SW (1999) Twenty-five yearsof ecosystem development of constructed Spartina alterniflora(Loisel) marshes. Ecological Applications 9: 1405–1419.

Craft CB, Megonigal JP, Broome SW, et al. (2003) The pace ofecosystem development of constructed Spartina alternifloramarshes. Ecological Applications 13: 1417–1432.

Houston JA, Edmonson SE, and Rooney PJ (eds.) (2001) Coastal DuneManagement: Shared Experience of European ConservationPractice. Liverpool, UK: Liverpool University Press.

644 General Ecology | Coevolution

Kaly UL and Jones GP (1998) Mangrove restoration: A potential tool forcoastal management in tropical developing countries. Ambio27: 656–661.

Leatherman SP (1982) Barrier Island Handbook. College Park, MD:University of Maryland.

Lewis RR (1982) Creation and Restoration of Coastal PlantCommunities. Boca Raton, FL: CRC Press.

Minello TJ and Webb JW, Jr. (1997) Use of natural and created Spartinaalterniflora salt marshes by fishery species and other aquatic fauna inGalveston Bay, Texas, USA. Marine Ecology – Progress Series151: 165–179.

Mitsch WJ and Gosselink JG (2000) Wetlands. New York: Wiley.Roze F and Lemauviel S (2004) Sand dune restoration in North Brittany,

France: A 10-year monitoring study. Restoration Ecology 12: 29–35.

Thayer GW (ed.) (1992) Restoring the Nation’s Marine Environments.College Park, MD: Maryland Sea Grant.

Van der Muelen F, Junerius PD, and Visser JH (eds.) (1980)Perspectives in Coastal Dune Management. The Hague: SPBAcademic Publishing.

Weinstein MP and Kreeger DA (eds.) (2000) Concepts andControversies in Tidal Marsh Ecology. Dordrecht: Kluwer AcademicPublishers.

Woodhouse WW, Jr. (1978) Dune Building and Stabilizationwith Vegetation. Special Report 3. Fort Belvoir, Virginia: USArmy Corps of Engineers, Coastal Engineering Research Center.

Zedler JB (ed.) (2001) Handbook for Restoring Tidal Wetlands. BocaRaton, FL: CRC Press.

CoevolutionR B Langerhans, Harvard University, Cambridge, MA, USA

ª 2008 Elsevier B.V. All rights reserved.

Introduction

The Basics of Coevolution

Coevolution Drives Diversification

Further Reading

Introduction

What Is Coevolution?

All organismal populations experience multiple selectivepressures deriving from varied aspects of their environ-ment. In addition to abiotic features (e.g., climate), this‘environment’ is often comprised of many other organisms.Thus, most populations evolve in response to interactionswith other species. While the abiotic components ofthe environment cannot evolve in response to organisms,the biotic components can – and this phenomenon hasplayed an integral role in the evolution of phenotypicdiversity. Coevolution is reciprocal evolutionary changebetween interacting species driven by natural selection.That is, each player in a coevolutionary relationshipevolves adaptations in response to its interaction withthe other player(s). Although this general concept hasbeen around since Darwin, the term ‘coevolution’ wascoined by Paul Ehrlich and Peter Raven in a classic articlein 1964, ‘‘Butterflies and plants: A study in coevolution.’’Since then, the field of research examining coevolutionhas blossomed into a large-scale research program.

The Broad Importance of Coevolution

Coevolution is undisputed as one of the most importantprocesses shaping biodiversity. The importance of

coevolution goes far beyond the classic examples, suchas predator–prey coevolutionary arms races, figs and figwasps, yuccas and yucca moths, ants and acacias, andfungal farming by several taxa. Coevolution’s influencespans all subdisciplines within ecology and evolutionarybiology. Indeed, a large extent of the historical andongoing patterns of phenotypic evolution and speciesdiversification is the product of coevolution. Coevolutioncan stem from numerous types of species interactions thatare commonplace on this planet, such as interspecificcompetition for resources, predator–prey interactions,host–parasite interactions, plant–herbivore interactions,and flower–pollinator interactions. Even the eukaryoticcell originated from a symbiotic relationship where oneof the species evolved into the organelles we now callmitochondria. A similar scenario is responsible for theformation of chloroplasts, and thus the origin of plants.Most vertebrate and invertebrate species rely heavily oncoevolved symbionts residing within their digestive systemor other special organs to allow proper digestion andgrowth. Coral reefs, and the communities they support,depend largely on coevolved symbioses betweencorals and zooanthellae, as well as interactions with othercorals and algae-feeding fish. The symbiotic organisms,lichens, are critically important during primary successionin terrestrial ecosystems. Even the colonization of land byplants was facilitated by mutualistic interactions with

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