encyclopedia of ecology || coastal zone management

630 Ecological Engineering | Coastal Zone Management

Further Reading

Bellan-Santini D (1980) Relationship between populations of amphipodsand pollution. Marine Pollution Bulletin 11: 224–227.

Clarke KR and Warwick RM (2001) A further biodiversity indexapplicable to species lists: Variation in taxonomic distinctness.Marine Ecology Progress Series 216: 265–278.

Engle V, Summers JK, and Gaston GR (1994) A benthic index ofenvironmental condition of Gulf of Mexico. Estuaries17(2): 372–384.

Fano EA, Mistri M, and Rossi R (2003) The ecofunctional quality index(EQI): A new tool for assessing lagoonal ecosystem impairment.Estuarine, Coastal and Shelf Science 56: 709–716.

Gomez-Gesteira JL and Dauvin JC (2000) Amphipods are goodbioindicators of the impact of oil spills on soft bottom macrobenthiccommunities. Marine Pollution Bulletin 40(11): 1017–1027.

Hurlbert SH (1971) The nonconcept of species diversity: A critique andalternative parameters. Ecology 52: 577–586.

Orfanidis S, Panayotidis P, and Stamatis N (2001) Ecological evaluationof transitional and coastal waters: A marine benthic macrophytes-based model. Mediterranean Marine Science 2: 45–65.

Roberts RD, Gregory MG, and Foster BA (1998) Developing an efficientmacrofauna monitoring index from an impact study – a dredge spoilexample. Marine Pollution Bulletin 36(3): 231–235.

Rosenberg R, Blomqvist M, Nilsson HC, Cederwall H, and Dimming A(2004) Marine quality assessment by use of benthic species-abundance distribution: A proposed new protocol within theEuropean Union Water Framework Directive. Marine PollutionBulletin 49: 728–739.

Satsmadjis J (1982) Analysis of benthic fauna and measurement ofpollution. Revue Internationale Oceanographie Medicale66–67: 103–107.

Simpson EH (1949) Measurement of diversity. Nature 163: 688.Smith RW, Bergen M, Weisberg SB, et al. (2001) Benthic response

index for assessing infaunal communities on the mainland shelf ofsouthern California. Ecological Applications 11: 1073–1087.

Van Dolah RF, Hyland JL, Holland AF, Rosen JS, and Snoots TR (1999)A benthic index of biological integrity for assessing habitat quality inestuaries of the southeastern USA. Marine Environmental Research48: 269–283.

Warwick RM and Clarke KR (1995) New ‘biodiversity’ measures reveal adecrease in taxonomic distinctness with increasing stress. MarineEcology Progress Series 129: 301–305.

Wollenweider RA, Giovanardi F, Montanari G, and Rinaldi A (1998)Characterisation of the trophic conditions of marine coastal waterswith special reference to the NW Adriatic Sea: Proposal for a trophicscale, turbidity and generalised water quality index. Environmetrics9: 329–357.

Coastal Zone ManagementE Wolanski, James Cook University, Townsville, QLD, Australia

A Newton, Universidade do Algarve, Faro, Portugal

N Rabalais, Louisiana Universities Marine Consortium, Chauvin, LA, USA

C Legrand, University of Kalmar, Kalmar, Sweden

ª 2008 Elsevier B.V. All rights reserved.

The Degradation of Coastal Waters

Ecological Engineering for Eutrophication Management

in Coastal Zones

Dead Zones

Ecological Engineering of Coral Reefs

Conclusions

Further Reading

The Degradation of Coastal Waters

As highlighted in Estuarine Ecohydrology, throughout

the world estuaries have experienced environmental

degradation and present proposed remedial measures

based on engineering and technological fixes have been

unable to restore the ecological processes of a healthy,

robust estuary, and, as such, will not reinstate the full

beneficial functions of the estuary ecosystem.This story of degradation is repeated worldwide also

for coastal zones. The problem is more insidious, and

harder to address, because historically coastal zones

were seen as having essentially infinite capacity to dilute

waste from human activities and because the fisheries

resources were essentially free for all. Yet, just like estu-

aries, coastal waters are also suffering from increasing

eutrophication, increasing turbidity, harmful algae

blooms, fisheries collapse, and an increasing loss of biodi-

versity. At the same time these waters are increasingly

polluted and impacted by hydrocarbons from low-level,

chronic oil spills as well as occasional and often cata-

strophic oil spills. Some of these coastal waters are also

showing signs of impacts by climate change.All these effects have negative socioeconomic impacts

through the loss of income and employment for coastal

communities. They suggest that if these issues are not

Ecological Engineering | Coastal Zone Management 631

addressed, coastal waters will increasingly be degradedand ultimately may suffer the fate of many estuariesworldwide that have become essentially little more thandrains for wastes and channels for navigation (seeEstuarine Ecohydrology). This scenario runs contrary tothe wishes of the human population that, with increasingwealth, demands a high quality of life.

Ecological Engineering for EutrophicationManagement in Coastal Zones

Upwelling zones, which receive infusions of nutrientsfrom deep ocean waters, support some of the most pro-ductive marine ecosystems. However, anthropogeniceutrophication of estuaries and coastal zones has been agrowing problem since the latter half of the twentiethcentury. The main drivers for this have been the increas-ing proportion of the population moving to the coastalzones, an increase in the burning of fossil fuels,the increase in the use of synthetic fertilizers and theincrease in consumption of animal protein, due to theintensive rearing of poultry and pork. Other contributingfactors have been the draining of wetlands and the clear-ing of riparian vegetation. The result of these humanactivities has been a very large increase of the inputs ofcertain plant nutrients, particularly nitrogen and phos-phorus, into aquatic ecosystems. Whereas phosphorus isoften the limiting nutrient in freshwater systems, nitrogenis most often the naturally limiting nutrient in estuarineand coastal systems. Within the estuarine to coastalcontinuum, multiple nutrient limitations occur amongnitrogen, phosphorus, and silica along the salinity gradi-ent and by season.

Nutrients are essential for the algal production thatsupports food webs. However, there are thresholds wherethe load of nutrients to estuarine, coastal, and marinesystems exceeds the capacity for assimilation of nutri-ent-enhanced production, and water-quality degradationoccurs. An imbalance of N and P in combination withsilica leads to shifts in phytoplankton community compo-sition. Impacts can include noxious and toxic algalblooms, increased turbidity with a subsequent loss ofsubmerged aquatic vegetation, oxygen deficiency, disrup-tion of ecosystem functioning, loss of habitat, loss ofbiodiversity, shifts in food webs, and loss of harvestablefisheries.

Rivers play a crucial role in the delivery of nutrientsto the ocean. In the subbasins to the North AtlanticOcean, specifically in the Baltic catchments, and in thewatershed of the Mississippi River, inputs of anthropo-genic nitrogen via rivers far exceed other sources ofnitrogen input – atmospheric deposition, coastal pointsources, and nitrogen fixation. Phosphorus loads, likewise,come mostly from rivers. Direct atmospheric deposition

of nitrogen and phosphorus on estuaries and coastalwaters may contribute as little as 1% to as much as30–40% of the total load. The relative sources of nitrogenand phosphorus loads to the coastal ocean correspond tothe degree of various anthropogenic activities in thewatershed.

The susceptibility of estuaries and coastal waters toeutrophication is largely controlled by the physics ofthese systems such as the geomorphology, the tidalrange, the residence time and flushing rates, and theengineering of river mouths or inlets. Partially enclosedsystems with restricted exchange, for example, lagoons,fjords and large estuaries, such as the Chesapeake Bay,are particularly vulnerable. This is also the case forinland seas, such as the Baltic, the Black, and theAdriatic. Some of the symptoms of eutrophication inestuaries may be partially alleviated by ecological engi-neering measures such as building of treatment ponds,dredging, creating man-made mouths, and wetlandrestoration and creation.

Several indices are under development or beingtested for the evaluation of eutrophication by ecologicalengineers. They are important management tools and,combined with scenarios of different future outlooks,may be used as future prediction tools. A widely usedscreening model is the USA National EstuarineEutrophication Assessment that has been updated intothe ASSETS model. It has been applied in most of theUSA estuaries, and several European and Chinesesystems. Another screening model in widespread use inEurope is the OSPAR Comprehensive Procedure.

Some options for the effective control of point sourcesof nutrients are available to ecological engineers. Theseinclude the construction of urban wastewater treatmentplants or the upgrading of existing plants to tertiary treat-ment. However, the outlook is much bleaker for the controlof diffuse sources such as agricultural runoff and atmo-spheric deposition. The harmonization of presentlyconflicting policies such as agricultural subsidies (thatencourage the excessive use of fertilizers) and environmen-tal policies such as the Clean Water Act (USA) and theWater Framework Directive (EU) may in future helpresolve some of these issues. Certainly, changes in thesocioeconomic situation of countries and regions canhave an effect on eutrophication. The collapse of collectivefarming practices after the breakup of the Soviet Union wasone example of how a change in agriculture can relieve thepressures on coastal ecosystems, in this case the Black Sea.However, changes in life styles in European countries as aresult of admission to the European Union have resulted inan increase in the per capita consumption of animal pro-tein, and this has increased the nitrogen input into theaquatic systems. Similar increases in animal protein con-sumption are presently occurring throughout SoutheastAsia as a result of booming economies.


Aquaculture is another human activity that can both beaffected by eutrophication and can also impact eutrophi-cation. The deterioration of water quality resulting fromeutrophication can have serious repercussions on theaquaculture industry. However, the excessive feeding offish in cage aquaculture can also contribute to the increasein nitrogen inputs into aquatic ecosystems. Conversely,the culture of filter feeding bivalves may significantlygraze algal blooms resulting from the over stimulation ofphytoplankton production. An apparently contradictorysituation of high nitrogen–low chlorophyll may developin such cases. Conversely, the destruction by over-harvesting of natural filter bivalve beds may favoreutrophication. Such is the case of the ChesapeakeBay where the loss of the oyster grounds probably con-tributed to the vulnerability of this large estuary toeutrophication.

Poly-culture practices in Chinese bays effectively usemacro-algae to mop up some of the excessive nutrients aswell as bivalves and abalone as grazers. These can helpcontrol the effects of eutrophication, although the aqua-cultures are still vulnerable to the occurrence of harmfulalgal blooms.

Hypoxia and Anoxia

A common manifestation of eutrophication is hypoxia(dissolved oxygen concentration DO < 2 mg l�1) andanoxia (DO¼ 0), that is, the depletion of dissolved oxy-gen in coastal waters, leading to ‘dead zones’. Whenthe DO is less than a critical value (typically 2 mg l�1),mobile animals such as demersal fish, crabs, and shrimpmigrate away from the area. Resident animals die whenthe DO < 1 mg l�1. Fisheries have collapsed, notably inthe Baltic and Black seas.

Hypoxia occurs naturally in many parts of the world’smarine environments, such as fjords, deep basins, openocean oxygen minimum zones, and oxygen minimumzones associated with upwelling systems. Hypoxic andanoxic waters have existed throughout geologic time,but their occurrence in shallow coastal and estuarineareas is increasing. The severity of hypoxia (either dura-tion, intensity, or size) has increased where hypoxiaoccurred historically, and hypoxia exists now when itdid not occur before. The severity of hypoxia increasedin the northern Gulf of Mexico, primarily since the 1960s.Evidence comes from paleo-indicators in accumulatedsediments, long-term hydrographic data, and scenariosbased on empirical models. The size and frequency ofhypoxia in the Gulf of Mexico have increased as the fluxof nitrate increased, and there is a direct correlationbetween nitrate flux to the Gulf of Mexico from theMississippi River and the mid-summer size of the hypoxiczone.

Aerobic bacteria consume oxygen during decomposi-tion of the excess carbon that sinks from the upper watercolumn to the seabed. There will be a net loss of oxygenin the lower water column, if the consumption rate isfaster than the diffusion of oxygen from surface watersto bottom waters. Hypoxia is more likely when stratifica-tion of the water column occurs and will persist as long asoxygen consumption rates exceed those of resupply.

Some of the largest hypoxic zones are in the coastalareas of the Baltic Sea, the northern Gulf of Mexico, andthe northwestern shelf of the Black Sea (reaching84 000 km2, 22 000 km2, and 40 000 km2 (until recently),respectively). Hypoxia existed on the northwestern BlackSea shelf historically, but anoxic events became morefrequent and widespread in the 1970s and 1980s reachingover areas of the seafloor up to 40 000 km2 in depths of8–40 m. Recent reductions in nutrient loads to the north-western Black Sea resulted in a minimization of thehypoxic zone there. There is also evidence that the sub-oxic zone of the open Black Sea enlarged toward thesurface by about 10 m since 1970. Similar declines inbottom-water-dissolved oxygen have occurred elsewhereas a result of increasing nutrient loads and anthropogeniceutrophication, for example, the northern Adriatic Sea,the Kattegat and Skaggerak, Chesapeake Bay, theGerman Bight and the North Sea, and Long IslandSound. The number of estuaries with hypoxia or anoxiacontinues to rise.

The obvious effects of hypoxia/anoxia include thedisplacement of pelagic organisms and selective loss ofdemersal and benthic organisms. These impacts may beaperiodic if recovery occurs, may occur on a seasonalbasis with differing rates of recovery, or may be perma-nent so that there is a long-term shift in ecosystemstructure and function. As the oxygen concentration fallsfrom saturated or optimal levels toward depletion, a vari-ety of behavioral and physiological impairments affect theanimals that reside in the water column or in the sedi-ments or attached to hard substrates. Hypoxia also affectsoptimal growth rates and reproductive capacity. Mobileanimals, such as shrimp, fish, and some crabs, flee waterswhere the oxygen concentration falls below 2–3 mg l�1.Movements of animals onshore can result in ‘jubilees’where stunned fish and shrimp are easily captured, orresult in massive fish kills. As dissolved oxygen concen-trations continue to fall, less mobile organisms becomestressed and move up out of the sediments, attempting toleave the seabed. As oxygen levels fall from 0.5 mg l�1

toward 0, there is a fairly linear decrease in benthicinfaunal diversity, abundance, and biomass.

Entire taxa may be lost in severely stressed seasonalhypoxic/anoxic zones. Larger, longer-lived burrowinginfauna are replaced by short-lived, smaller surfacedeposit-feeding polychaetes, and certain typical marineinvertebrates are absent from the fauna, for example,


pericaridean crustaceans, bivalves, gastropods, andophiuroids. Increasing oxygen stress for the Skagerrakcoast of western Sweden in semienclosed fjordic areasresulted in declines in the abundance and biomass ofmacroinfauna, particularly mollusks, suspension feeders,and carnivores. These changes in benthic communitiesresult in an impoverished diet for bottom-feeding fish andcrustaceans.

Harmful Algal Blooms

Cultural and natural eutrophication have both contribu-ted to changes in nutrient input to coastal waters, and ledto an overall increase in nutrient availability and analteration in nutrient composition. The first result ofthese changes is often an increase of total algal biomassand shifts in species composition potentially leading tosecondary disturbance such as harmful algal blooms(HABs). HAB species range from marine, brackish tofreshwater organisms and cover a broad range of phylo-genetic types (dinoflagellates, diatoms, raphidophytes,cyanobacteria). Most HAB species form massive bloomsof various colors (red, brown, or green). A few species canproduce potent toxins. These toxins can directly killmarine mammals and transfer through the food chaincausing harm at different levels from plankton to humans.A potential impact of HABs on human health occursthrough the consumption of shellfish that have filteredtoxic phytoplankton from the water or planktivorous fish.All poisoning syndromes are serious and can be fatal.They are named paralytic (PSP), diarrhetic (DSP), neu-rotoxic (NSP), azapiracid (AZP), and amnesic shellfishpoisoning (ASP). All syndromes, except for ASP, arecaused by dinoflagellates. ASP is caused by diatoms, agroup of phytoplankton usually thought to be nontoxic.In tropical and subtropical zones, another human poison-ing syndrome, ciguatera fish poisoning (CFP), is causedby toxic dinoflagellates that grow on substrate in coralreef communities. CFP toxins are transferred from herbi-vorous to carnivorous fish that are commercially valuable.Some algal toxins, brevetoxins, are airborne in sea-spray,causing respiratory distress in coastal population,for example, in the Gulf of Mexico. Cyanobacteria(blue-green algae) naturally bloom in still inland waters,estuaries, and the sea during summer. Some cyanobacteriaproduce potent cyanotoxins (anatoxins, microcystins, andnodularin), which are dangerous and sometimes fatal tolivestock, wildlife, marine animals, and humans. Thesetoxins represent a serious health risk in water bodiesused for recreational and/or as freshwater supplyreservoirs.

Although references to HABs date back to biblicaltimes, the number of toxic events and subsequent eco-nomic losses linked to HABs has increased considerablyin recent years around the world. Many reports point out

an obvious link between pollution and HABs, but thereare also other reasons for the expansion of the HABproblem.

Numerous new bloom events have been discoveredbecause of increased awareness and improved detectionmethodologies (e.g., molecular probes for cell recognition,PCR probes for rDNA specific to genera or species ofHABs, enzyme-linked immunosorbent assays (ELISA),remote sensing data from satellites, qualified observers,and efficient monitoring programs). The global increaseof aquaculture activities and trade of exotic species hasled to improved safety and quality controls that revealedthe presence of HAB species and/or toxins in, for exam-ple, aquaculture pens, and contaminated seafood.Mortality events and toxicity outbreaks in fish or bivalvesresources can no longer go unnoticed. Transport of toxicspecies in ship ballast water undeniably contributes to theincreasingly damaging effect of HABs on fisheries, aqua-culture, human health, tourism, and the marine andbrackish environment. UNEP has recently ranked HABsamong the ten worst threats of invasive species trans-ported in ballast water.

Dispersal of HABs is influenced by oceanic and estuar-ine circulation, river flow combined with currents,upwelling, salinity, nutrients, and specific life-cycles ofvarious HAB species. The apparent increase in toxicdiatoms (Pseudo-nitzschia spp.) off the US and Canadacoast is often coupled to physical forcing (storm, wind,rain, and upwelling) and more rarely to the increase innitrate-N in rivers, for example, from the MississippiRiver. Both nutrients and harmful dinoflagellate taxa areintroduced from upwelling/downwelling areas to estu-aries, coastal bays, or lagoons, for example, the Atlanticcoast of France, Spain, and Portugal, Chesapeake Bay,and the Benguela region. Similar processes are observedfor cyanobacteria in the Gulf of Finland. Physical con-vergence, advection, or accumulation process of oceanicdinoflagellates (Dinophysis, Karenia, and Gymnodinium) inembayments also contribute to the extension of HABs insome areas. Large oceanic current systems transport theN-fixing cyanobacterium Trichodesmium from tropical oli-gotrophic regions to W. Florida waters, enriched withSaharian iron dust, where it blooms. Some HABs havespecific life cycles including resting stages for diatoms(spores), dinoflagellates (cysts), and cyanobacteria(akinetes). These resting stages provide these algae witha competitive advantage over populations that cannotsurvive in poor conditions.

Climatic and hydrological changes affect nutrientdelivery and processing, for example, the input of micro-nutrients and freshwater from rainfall and river flow,flooding after hurricanes, and tropical storms also favorHAB’s growth and persistence. Certain PSP and CFPproducers (dinoflagellates) have increased significantlyunder large-scale changing climatic conditions in


temperate environments (Kattegat, NW Spain, and SWPortugal) and in the Indo-Pacific, respectively. Some ofthese blooms have been linked to the North Atlanticoscillations (NAO) and to El-Nino events that affectlocal climate in wind-driven upwelling systems.

Despite the importance of natural events in algal bloomformation, many examples relate HABs to anthropogenicactivities since World War II. Red tides (dinoflagellates) inAsia, for example, the mouth of the Yangtze Estuary inChina and the Seto Inland Sea in Japan, are related to theparallel increasing population density and nitrogen (N)and (P) loadings. Nutrient-enriched conditions in brackishcoastal bays and estuaries have been correlated with highabundance of diatoms (central California, Louisiana in theUS), dinoflagellates (off the coast of North Carolina – US,Northern Adriatic, Aegean, and Black seas), and haloto-lerant cyanobacteria (Baltic Sea, Brazil, Australia), but thedirect cause of this relationship is not fully understood. Intropical regions, eutrophication of reef communities oftenleads to the overgrowth of macroalgae on corals andhigh coral mortality that favor the bloom of benthicdinoflagellates (CFP producers). Both elevated N andP concentrations and silicon limitation can favor thedominance of HABs, for example, the haptophytePhaeocystis in the North Sea. Declining silica inputto coastal zones and estuaries is often due to dammingof rivers and gives a competitive advantage to marinehaptophytes and dinoflagellates over diatoms. The resi-dence time of the water in freshwater systems is increasedby the construction of the dams. This allows for thedevelopment of freshwater diatom blooms. The silicon-rich frustules of the diatoms are not remineralized asrapidly as organic matter and so dams effectively retainsilicon upstream. The ratio of silicon to nitrogen thereforedecreases, and estuarine and coastal diatoms may haveinsufficient silicon to reproduce. The communitiesof phytoplankton organisms may therefore shift so thatdiatoms are replaced by nonsilicon requiring organismssuch as dinoflagellates and this may significantly alter thefood web.

Many potable water reservoirs are under the pressureof expanding population, and are negatively impacted byboth sediment erosion, reduced water flow and elevatedN and P loading that will stimulate noxious cyanobacter-ial blooms. Similar trends are reported for river systemswith weir pools. Many HABs have characteristic modes ofnutrition from autotrophy to heterotrophy, that is, can useorganic carbon, nitrogen, and phosphorus (mixotrophyand osmotrophy). Recent studies have shown that theincrease in organic nutrients could benefit certain HABs(dinoflagellates and prymnesiophytes). The global nitro-gen-based fertilizer usage has shifted toward urea-basedproducts and is expected to continue. Thus, significantamounts of urea are transported to estuarine and coastalwaters with the potential for increasing eutrophication of

these sensitive areas. Since urea is also one very importantnitrogen substrate for some HAB species, the globalincrease of PSP outbreaks is comparable to the increaseof urea use for 1975–2005. Aquaculture sites are also alarge source of nutrient from animal excreta, rich in Nand P, to coastal sediment. Their contribution to HABformation will depend on the hydrology of the system, forexample, HABs proliferate in calm areas.

Among the natural marine environmental contami-nants that are health risks, HABs are most prominent.However, the relative effects of natural versus anthropo-genic factors on harmful algal blooms cannot yet beresolved.

Dead Zones

Once the consequences of eutrophication are felt incoastal waters, there is little that can be achieved toredress the situation by ecological engineers. The scaleof coastal waters and their open boundaries make man-agement difficult or impossible. Examples of this are thedead zones of hypoxic and anoxic waters in the Gulf ofMexico and the Black Sea. Only the surface waters of theBlack Sea remain oxic and most of this deep basin isnaturally anoxic. Two-thirds of the continental USAagricultural lands drain down the Mississippi into theGulf of Mexico. The runoff of excess fertilizers increasesnutrient inputs and also causes imbalances in the nutrientratio. The plume of the Mississippi can be seen fromsatellite imagery but the effects of the nutrientsare more widespread and can be detected through remotesensing by the high chlorophyll concentrations from thephytoplankton blooms. This excessive production unba-lances the ecosystem. The microbial decomposition of theincreased organic matter depletes the water of oxygenleading to hypoxia and even anoxia. The effect is parti-cularly marked during the summer months when thewaters are warm and saline therefore oxygen is less solu-ble. No effective ecological engineering measures arepossible offshore to counter this effect that in someyears covers a very large area of the Gulf of Mexicoleading to the loss of valuable fisheries. However, thesummer is also the hurricane season in the Gulf ofMexico and the turbulence and mixing caused by largeand frequent storms can at times break up the ‘Dead’ zone.

Ecological Engineering of Coral Reefs

Coral reefs can be severely degraded with much smallerlevels of eutrophication than those needed to impact openwaters. As detailed in Estuarine Ecohydrology, coral reefshave a rich biodiversity and they greatly benefit humanityby building islands and atolls, inhibiting coastal erosion,

Australia

1.

2.0.90.80.70.60.50.40.30.20.1

3.

4.

5.

Figure 1 Location map of the 400-km long central region of the

Great Barrier Reef. Predictions of the coral density in the same

region for (case 1) no human impact, (case 2) present conditionswith land use, (case 3) existing land-use practices and with global

warming in the year 2050 following the IPCC scenario A2, (case 4)

halving of the nutrient and sediment runoff from land-use and

with global warming following the IPPC scenario A2 in the year2050, (case 5) same scenario as for case 4 in the year 2100. The

color bar shows the coral density as a fraction of the hard

substrate area for each of the 261 reefs in the model domain(e.g., 0.3¼30%). Adapted from Wolanski E and De’ath G (2005)

Predicting the present and future human impact on the Great

Barrier Reef. Estuarine, Coastal and Shelf Science 64: 504–508.


and supporting fisheries and tourism. The destruction ofcoastal coral reefs is increasing worldwide (e.g., up to 50%in the last 15 years in some Asian countries). There is notone country in the world that has put in place a sustainablecoral reef management policy because human activities onland are not incorporated in coral reef management poli-cies. The present coral reef strategy principle relies ondrawing a line around selected coral reefs and namingthem marine parks or marine protected areas. Corals andthe fisheries are protected inside that line. It ignores thefact that the land and the coral reef are ecologically con-nected through the rivers. As a result this managementpractice invariably fails where the corals are impacted byrivers that are impacted by human activities in thecatchment.

The health of coral reefs fluctuates naturally in time.Historically, coral reefs have been impacted by naturaldisturbances such as tropical cyclones and river floods.If good water quality prevailed after these occasionaldisturbances, reefs have invariably recovered.Nowadays, coral reefs are subject to direct human impactsfrom land runoff from river catchments impacted byhuman activities; this results in an increase in suspendedsediment and nutrient concentration during the recoveryperiod after a natural disturbance, and from global warm-ing that generates increased bleaching events in summer.Coral reefs are weakened, more frequently diseased, andunable to recover between disturbances; they are thuscommonly slowly dying out from failure to recoverfrom disturbances.

The physical forcings of coastal coral reefs are riverfloods and tropical cyclones that are natural disturbances,and the oceanography that enables the exchange of coralplanulae between reefs. The biological forcing is mainlythe competition for hard substrate space between thecoral and the algae. The recruitment of juvenile coraldecreases with increasing algal cover on the hard sub-strate. Human activities on land increase the suspendedsediment and nutrient load, and thus help the algae. Algaeare preyed upon by herbivorous fish that is preyed uponby carnivorous fish. The harvesting of herbivorous fish bypeople also helps the algae. The coral is preyed upon bythe crown-of-thorns starfish (COTS), whose populationdynamics also appears to be helped by human activitieson land resulting in increased nutrient that promotes theplankton that supports the drifting COTS larvae.Additionally, global warming results in an increased mor-tality of adult corals, or poor health making them moresusceptible to diseases or attacks by borers.

An ecohydrology model was built that incorporates allthese processes. It was applied to the Great Barrier Reefand successfully verified against 20 years of data. Themodel (Figure 1) suggests that the biodiversity of theGreat Barrier Reef is already seriously impacted byhuman activities and may progressively over a period of

tens of years degrade to end up being mainly an algae-covered substrate, such as most degraded coastal reefs inEast Africa, Southeast Asia, and Micronesia. Thus, theGreat Barrier Reef, the largest coral reef ecosystem onEarth, may become another casualty of the lack of recog-nition of the need to adopt ecohydrology as a guidingprinciple in managing human activities. The model sug-gests that much-improved land-use practices will enablesome regions of the Great Barrier Reef to recover, evenwith global warming. However, the model suggests that ifglobal warming proceeds unchecked only biologicaladaptation – about which no information is yet available –may prevent a collapse of the Great Barrier Reef healthby the year 2100.


Conclusions

Coastal waters are increasingly degraded worldwide

through human activities on land. Because coastal waters

have open boundaries to the ocean, there are no simple

local engineering solutions to maintain or restore their

ecosystem health and the ecological services that they

provide. In coastal waters, further applications of ecohy-

drology are the use of macrophytes to enhance the internal

consumption rate, and benthic suspension feeders, such as

bivalve mollusks, sponges, tunicates, and polychaetes, to

filter and pelletize excess nutrients and plankton. As

detailed in Estuary Restoration, attempts to restore coastal

water quality by planning to restore seagrass beds and

coral reefs are bound to fail until the land-use practices

that degraded these habitats in the first place are modified.The only ecologically sustainable management strat-

egy for coastal waters is adopting ecohydrology as the

guiding principle for managing human activities on land

while at the same time protecting fisheries, implementing

a fisheries buy-out program, and using engineering and

technology to treat sewage and storm water. Ecohydrology

science offers a number of solutions, including top-down

and bottom-up ecological manipulation and the creation

and restoration of wetlands to help restore the health of

rivers and estuarine waters. This ecological engineering

approach can be combined with some technological fixes,

such as the creation of freshets and smarter land use.

This necessitates changing present governmental practices

based on political geography or specific activities

(e.g., farming, water resources, fisheries, and urban devel-

opments). Generally, the political geography limits or the

usage units do not coincide with the basin boundaries. The

ecohydrology approach also necessitates a high level of

collaboration among stakeholders in order to develop best

practices. Without these changes, estuaries and coastal

waters will continue to degrade worldwide, despite

local integrated coastal management plans that are

implemented.This solution is easy to preach and a nightmare to

implement, mainly for political and socioeconomic

reasons. Worldwide, the implementation of this science-

based strategy will most likely stall until a political solu-

tion is found to regulate human activities on land. Indeed,

local farmers, fishermen, and urban developers are often

at odds with the imposition of land use, water resources,

and fishery management rules that they claim jeopardize

their ability to earn a living.The coastal water ecosystem modeler is faced with

complex processes and feedback processes between phy-

sics and biology, which often cannot be fully quantified

because the data are inadequate. Models should not be

seen as able to replace reality and the need for field

observations.

See also: Estuarine Ecohydrology; Estuary Restoration.

Further Reading

Anderson DM, Glibert PM, and Burkholder JM (2002) Harmful algalblooms and eutrophication: Nutrient sources, composition andconsequences. Estuaries 25: 704–726.

Boesch DF, Brinsfield R, and Magnien R (2001) Chesapeake Bayeutrophication: Scientific understanding, ecosystem restoration,and challenges for agriculture. Journal of Environmental Quality30: 303–320.

Bricker SB, Clement CG, Pirhalla DE, Orlando SP, and Farrow DRG(1999) National Estuarine Eutrophication Assessment. Effects ofNutrient Enrichment in the Nation’s Estuaries. Silver Spring, MD:National Ocean Service, National Oceanic and AtmosphericAdministration.

Carmichael WW (2001) Health effects of toxin-producing cyanobacteria:‘The CyanoHABs’. Human and Ecological Risk Assessment7(5): 1393–1407.

Cloern JE (2001) Our evolving conceptual model of the coastaleutrophication problem. Marine Ecology Progress Series210: 223–253.

Graneli E, Turner RE, and Jefferson T (2006) Ecology of Harmful Algae.Heidelberg, Germany: Springer.

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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

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