Difference between revisions of "Threats to the coastal zone"

This article provides a review of human activities which put pressure on coastal ecosystems and habitats. It discusses generic modifications to coastal ecosystems in relation to specific human activities and introduces the various threats resulting from poorly managed activities.

Living resources

In this section we will look at how and why ecosystems are at risk, despite the fact that humans are increasingly dependant on resources from the sea, particularly coastal areas.

Mariculture – Aquaculture

Aquaculture is an attempt, through inputs of labour and energy, to improve the yield of useful aquatic organisms by deliberate manipulation of their rates of growth, mortality and reproduction. Most often the word ‘mariculture’ is used to describe extensive cultivations of marine animals and plants where the input of energy (mostly food) is minimal. Fish farming, collecting invertebrates from the shore and molluscs cultivation are typical examples of mariculture. Farming and other marine aquaculture practices influence coastal systems, utilizing land, wetlands and the sea (fish cages or artificial reefs). While most of the finfish production is in freshwater, a growing proportion originates from coastal brackish and marine farming systems, including seaweed, shellfish, and crustaceans. Aquaculture has grown substantially over the past four decades and, in many parts of the world, aquaculture in coastal and marine waters is the only growth sector within marine fisheries.

Environmental problems

With the growth of industrial aquaculture, environmental problems have arisen. However, major achievements have been made in the past decade to cope with many of these environmental problems, including improved site selection criteria, improved husbandry techniques (e.g. better stress management and improved disease control). As there is often a high prevalence of pathogens and diseases in mariculture compared to wild stocks, chemicals may be used to control diseases and pests. Toxic and persistent chemicals, antibiotics and antifouling substances (copper for instance) are often used routinely. Nevertheless, the use of antimicrobials in modern farming systems can now be avoided because of the development of appropriate vaccines for some key diseases.

All types of mariculture are liable to produce excessive amounts of nutrients and deposit organic material in the exploited area. Such inputs contribute to eutrophication. Many of the environmental implications are well known: pre-emption of critical fishery habitats (e.g. mangroves); pollution of estuarine and lagoon waters; excessive exploitation of natural stocks of larvae and juveniles; imports of inferior, sick or non-compatible seed stock; and introduction of exotic species.

Fisheries

Fishing is an important economical activity in the coastal zone. However, the potentially high benefits come with equally high risks of ecological deterioration through over fishing, killing of unwanted by-catch and habitat destruction. The most obvious effect of fishing is removal of fish and shellfish from the ecosystem, but fisheries affect coastal marine ecosystems in many other ways while fish stocks are in turn affected by environmental factors. In general, fisheries can induce different selective pressures, either directly, i.e., through elevated mortality (which is often highly selective) or through ecosystem-level responses, as exploitation affects food availability and predation risk in both target and non-target species. Responses to selection can be observed at two levels. Firstly, at the community level, some species may suffer more from effects of fishing than others; some may even increase in abundance. Responses by species to exploitation are associated with their life histories. In particular, species with late maturation at large size and with low population growth rate tend to undergo more pronounced declines than early-maturing species with rapid growth. Secondly, the phenotypic composition within species may also change. If phenotypic variability has a genetic basis, then fisheries-induced selection can result in evolutionary change in life-history traits influencing sustainable yields, behavioural traits (e.g., gear-avoidance behaviour), and morphological traits.

Impact on fish populations

BOX?:The quantitative impact of fisheries on fish populations is far from being negligible as, for instance, up to 1/3 of the biomass (from 3.5 to 2.5 million tones/year) is taken out from the North Sea, 1/3 being consumed by fish, 1/3 going back to the ecosystem to other predators, through diseases, etc. The removal of fish and shellfish biomass as food for humans may lead to stocks being depleted, some stocks even being on the verge of collapse, i.e. North Sea herring, mackerel and cod. Presently, 50% of haddock present at the start of a year is taken in the same year, but not all species are affected in the same way. Declining species also include slow reproducing animals such as elasmobranches (cartilageneous fish, i.e. Dogfish Scyliorhinus canicula, Rays, Conger eel Conger conger, Allis shad Alosa alosa).

The activity of fishing itself might impact living marine organisms in many ways. The removal of target species leads to changed abundance and altered structure of these populations. Shifts in population structure affect the composition of the ecosystem with a decrease in abundance of larger individuals, a shift in population age as older individuals are removed. Life-history changes, increased growth rates and a lowered age at maturity have been reported in Plaice Pleuronectes platesssa and Cod Gadus morhua in the North Sea. Through selection of animals adapted to modern fishing practices it has been demonstrated that whole populations have changed their genetic composition in response to increase human pressure.

Impact of discard

Because of the influence of market forces (undersized fish, over quota catch which are not appropriate for landing) or just because they are not fit for human consumption, whole organisms (fish & benthos) are thrown back into the sea. It even happens that for high-grading the catch in order to maximise the value of a certain species at a certain time, marketable fish is thrown back overboard to the sea by fishers. Indirect death or injury takes place when fish are in contact with the gear or escape through the mesh. Such post-escapement mortality seems significant but further work is required for assessing its full impact on populations. Such discard of unwanted catch is a food-source made available at an unusual place and time to scavengers and opportunist predators. The impact on ecosystems is comparable to that from the discharge of offal, tissues rejected after fish is cleaned and gutted at sea. Seabirds, notably, are affected through access to a new source of food.

Impact on seabed

In addition to the potential for over-fishing, fishery operations can have a destructive physical impact on the seabed, and affect population levels of non-target species through incidental catch, such problems being of particular significance for cetaceans, sea turtles and seabirds such as albatross, in different parts of the world. All commercial bottom fishing disturbs sea-floor organisms and the seabed, with impacts on both habitats and species. The removal of non-target organisms (by-catch) may impinge on commercial species or of no value to fisheries. The mechanical effects on the sea-floor habitat of trawlers, for example, include changes in the size composition of invertebrates with repercussions on the overall trophic structure of the ecosystem. Modification of the substrate include a possible increase in shell debris and the silt / clay content through resuspension of fine particles of sediment, changing in turn geophysical parameters such as penetration depth and surface roughness. Changes in benthic community composition consist of shifts from larger long-lived species to smaller opportunistic species, depending on the intensity of trawling, the gear used and the background level of disturbance, including pollution.

Impact on marine mammals

Unfortunately, effects of fisheries on marine mammals are not well documented. By-catch of small cetaceans, caught in bottom-set gill-nets, have been reported. Litter dumped or lost from fishing vessels includes fishing gear leading to ‘ghost fishing’ where disposed or lost gear continues fishing for year, entrapping also marine mammals and birds. It is important and urgent to integrate fisheries into coastal zone management, with the aim of ensuring sustainable yields, while protecting vulnerable areas and species of birds and mammals. More research is needed into the long-term impacts of fisheries, and their effect on populations of target and non-target species – indeed, on the entire ecosystem of the coastal zone. Changes in the climate, such as the North Atlantic oscillation (NAO see above) appear to be affecting fish distributions and their spawning patterns (ICES, unpublished reports 1999). These changes are coupled with pollution effects on the fish and bioaccumulation of pollutants (Dethlefsen, 1989; Elliott et al., 1988).

The section on Living resources may be accessed via this link.

Water quality/pollution

Coastal and estuarine ecosystems have been, and still are, heavily influenced by the human species through pollution and habitat loss throughout the world. Examples of environmental issues include the enrichment of enclosed waters with organic matter leading to eutrophication, pollution by chemicals such as oil, and sedimentation due to land-based activities or sea-level rise due to the global change. Over 80% of all marine pollution originates from land-based sources which are primarily industrial, agricultural and urban. Pollution accompanies most kinds of human activities, including offshore oil and gas production and marine oil transportation. The relative contribution of each of these channels into the combined pollution input into the sea will be different for different substances and in different situations. Quantitative estimates of these processes are difficult because of the lack of reliable data and the extreme complexity of biogeochemical cycles, especially at the sea-land and sea-atmosphere interfaces. Point and non-point source pollutions continue globally, resulting in the steady degradation of coastal and marine ecosystems. Indirect (or diffuse) inputs are usually widespread, low-level discharge often likely to result in chronic pollution. In this section, generic sources of pollution and effects (eutrophication, contamination and pollution from industry and agriculture, etc.) are considered. The sensitivity of the coastal zone to watershed impacts is examined in relation to land-derived pollution and water quality.

GESAMP (the United Nations Group of Experts on the Scientific Aspects of Marine Pollution) has given a useful definition of pollution:

Contamination is usually considered to occur when an input of waste from human activities increases the concentration of a substance in seawater, sediments or an animal above the background level for that area or animal, but without any obvious effect.

Agriculture

Emissions and inputs from agriculture are a significant source of pollution to the coastal zone and to the atmosphere throughout the world. The contribution of agriculture to the pollution of coastal ecosystems affects biogeochemical cycles, notably in terms of:

• Discharge of methane and ammonia contributing to the greenhouse effect
• Use of insecticides and other pesticides affecting species, cultivated or not
• Pollution, from use of oil for instance
• Nutrients run-off from silage and slurry-manure, use of fertilizers leading to eutrophication

Eutrophication

((Eutrophication)) results from the increase of nutritional resources to a particular water body and includes the supply of mineral nutrients (nitrogen, phosphorus, silicon, trace elements) as well as organic carbon^[2]. Discharges and emissions from land-based sources (industry, households, traffic, agriculture) provide large inputs of nutrients to coastal waters via rivers, direct discharges, diffuse sources and deposition from the atmosphere. However, eutrophication cannot be defined just in terms of an increase in nutrients concentration, as its manifestations (very often harmful to ecosystems) occur due to the existence of natural conditions, such as high temperatures and calm coastal waters. In the recent past eutrophication has been most pronounced in the developed world, but it has to be expected that it will become more and more important in the developing countries of Asia, Africa and Latin America in the near future (Nixon, 1995).

Additional atmospheric input of inorganic nitrogen has increased significantly to a level where it is already higher than the natural nitrogen supply in the North Atlantic Ocean basin. It is expected that the worldwide production of nitrogen (mainly from fertilizer industry and the burning of fossil fuel) will affect the biogeochemical cycles on a global scale. Unfortunately, the interactive effects of the altering N-cycle on the carbon cycle (including the dynamics of greenhouse gases within both cycles) are poorly understood.

The effects of eutrophication vary from increased growth of phytoplankton, benthos and fish to changed species composition at moderate eutrophication, from blooms of nuisance causing or toxic algae to mass growth of certain species and mortality of others at severe eutrophication, and ultimately to anoxic conditions and mass mortality (fishkills). An algal biomass related phenomenon such as oxygen depletion of the water column and consequent mortality of animals can be prevented by a general reduction of nutrient discharges. At present, mathematical models on ecosystem dynamics are reliable enough to estimate dose-effect relationships. Algal species related harmful effects are less predictable. There is a general consensus that there is a global increase in harmful algal blooms. Also, there are reports which suggest a link between blooms of toxic algae and human activities such as salmon (or fish) farming. Changes in N:P:Si ratios may also cause a shift in species composition. Consequently, alterations in pelagic and benthic communities are to be expected. Which species is stimulated by eutrophication is highly dependent on the local environmental conditions.

Industry

Since most contaminants enter the sea by flows from the surrounding land, in particular via rivers, the highest concentrations are often found in estuaries and coastal areas and thus maximal effects of contaminants on the ecosystem could be expected to occur here. This general picture can be influenced by additional inputs from sources at sea - ships, off-shore platforms - and by inputs via the atmosphere. After entering the sea, contaminants are usually diluted and widely dispersed. However, the adsorption of contaminants to suspended solid material in the sea leads to the occurrence of elevated concentrations in the seabed in areas where this material settles. Areas, which are also close to direct sources of input, are doubly at risk as for estuaries and lagoons. Water quality is affected by toxic substances, which are persistent in the marine environment. These substances are of varying origin and composition, but they are together classed as stable or persistent, and have decisive properties in common. They are not readily degradable, or not at all degradable, toxic to living organisms, and bio-available (living organisms can take them up and accumulate them). The persistence of certain groups of contaminants, recognised as “toxic” in the marine environment, varies. Some of the factors which have an influence include their chemical reactivity, which describes the probability for reactions with other substances, e.g. photochemical reactivity which deals with the probability of reactions initiated by light. Their biological reactivity is dependant upon the probability for different biological systems to modify or metabolise a chemical compound. In turn, the distribution and availability of chemicals in the environment depend on a number of parameters, such as:

• the emission, whether the contaminant is emitted as a gas, a solution, adsorbed on particles or included in a solid matrix, and
• the volatility, influence the distribution of the chemical;
• the lipophilicity depends on the solubility of the chemical in lipids and is one of the factors affecting accumulation in organisms;
• the structure of the molecule influences the stability and the biological availability of the chemical.
• The geographical distribution of pollutants is dependant on partition between different compartments. The following factors can have a significant influence:
• the source pattern, whether it is a point or a diffuse source,
• the wind is essential for a long range transport,
• the precipitations are an important mode of transport from the air to seawater and to sediments,
• the contribution from the watershed and riverine inputs are dependant upon factors such as the geology, the geomorphology, the relief…
• the currents in the sea are dependant on tides, location, exposure…
• the movements of organisms are another transport mode of contaminants.

The bio-concentration or bio-accumulation of contaminants in the tissues of organisms is essential to understand. Bio-accumulation describes the ratio of a compound in the organism and the concentration in the surrounding medium. This factor is a function of the stability of the chemical but also how it will accumulate in the fat of the body, i.e. its lipophilicity. Accumulation presents a risk to consumer organisms, including the human species.

Bio-magnification describes a higher concentration in an organism than in its diet. It is related to the biological availability of contaminants to organisms and to their metabolism and excretion rate. Therefore, identical levels of specific contaminant can have different effects due to the fact that they can be present in different forms with different availability for uptake.

Organic synthetic substances

More than 7,000,000 compounds are known as Persistent Organic Compounds (POCs) and there are almost infinite possibilities to combine new substances. Serious environmental damage is caused by some of these POCs in the sea. Effects take place at metabolic and physiological levels, both in marine vertebrates and invertebrates. The great number of organic substances are due to the numerous possible substituents and substitution patterns. In fact, there are only few dangerous chemicals, and in the marine environment, the acute toxicity of compounds is only relevant after accidental spills. The only important exception to this rule is the bird casualties due to operational spills from ships of lipophilic floating substances and surfactants. The more important effects to focus on from a scientific point of view are caused by chronic exposure to relatively low concentrations and affect reproduction, immunology and carcinogenicity. In common, POCs all have the following characteristics: they are stable and toxic, and share a similar structure. It has emerged that some highly stable organic compounds - chiefly halogenated hydrocarbons - can have serious environmental effects in the sea. Such substances have in common the presence of a halogen in their molecule (chlorine, iodine, fluorine, astatine), have a low polarity ad low water solubility. Aromatic compounds are more reactive and susceptible to chemical and biochemical transformation and include pesticides (chlorinated such as DDT – DDE, Polycyclic Aromatic Hydrocarbons, Hexa Cyclo Hexan, and organometallics such as tributyltin). There are 209 congeners of Poly Chloro Biphenyls, all with different properties. This variety makes both analysis and effect studies complicated. The metabolic pathways of PCB congeners are complex. Though the use of PCB has been prohibited for a long time, emissions from unidentified sites still occur. For example, recirculated waste paper used as raw material for new pulp was discovered downstream a paper mill. It is unclear how organic synthetic organic chemicals affect marine organisms but polychlorinated biphenyls (PCBs), for instance, are frequently found in fish liver, seal blubber, bird eggs, and human fat. Organochlorines have been associated with impaired reproductive ability in seals and whales. For instance, octachlorostyrene (OCSs) have been found in benthic organisms. OCS concentrations can be taken as an indication of incomplete combustion resulting in the accumulation of chlorinated hydrocarbons in marine organisms. Organometallic compounds such as tributyltin have been used extensively as antifouling agents and are now banned in many countries because of its effect known as ‘imposex’. Imposex refers to a change of sexual characteristics in invertebrates, female gastropods growing a penis, for instance. Compounds in alternative antifouling products form a special field of interest, since these compounds are especially applied to display their toxic effects in the marine environment. Their use is expected to increase in the near future due to the total ban on tributyltin-based antifouling chemicals by the ‘International Maritime Organisation’ (IMO) by 2003. It is now well established that there are anthropogenic chemicals released to the environment that can disrupt the endocrine systems of a wide range of wildlife species. The reproductive hormone-receptor systems appear to be especially vulnerable. Indeed, changes in sperm counts, genital tract malformations, infertility, an increased frequency of mammary, prostate and testicular tumours, feminisation of male individuals of diverse vertebrate species and altered reproductive behaviours, have all been reported (Sharpe & Skakkebaek, 1993; Colborn et al., 1996). With regard to environmental management, the problem of endocrine disrupting chemicals is extremely difficult to address. Basic research is required to strengthen the scientific foundation for risk assessment: e.g., baseline studies on endocrine dysfunction across classes of animals to reduce the uncertainty associated with species extrapolations (NSTC, 1996). An extensive list of chemicals which are thought to be capable of disrupting the reproductive endocrine systems of animals has been assembled. They fall into the following categories: Environmental oestrogens (oestrogen receptor mediated) (e.g., methoxychlor, bis¬phenolic compounds); Environmental antioestrogens (e.g., Dioxin, Endosulphan); Environmental antiandrogens (e.g., Vinclozolin, DDE, Kraft mill effluent); Toxicants that reduce steroid hormone levels (e.g., Fenarimol and other fungicides; endosulphan); Toxicants that affect reproduction primarily through effects on the CNS (e.g., dithio¬carbamate pesticides, methanol); and Other toxicants that affect hormonal status (e.g., cadmium, benzidine-based dyes).

Metals

Heavy metals are naturally occurring and do not degrade. They are not particularly toxic as the condensed free elements (except Hg vapour) but they are dangerous to living organisms in the form of cations and when bonded to short chains of atom carbon. In particular cations have a strong affinity for sulphur. For example, sulfhydril groups in enzymes attach themselves to cations or molecules and so the enzyme is blocked. They are a problem in the marine environment because they bio-accumulate in marine organisms and despite measures taken to combat pollution, they are still concentrating year after year. Pollution above background levels in the environment can cause serious effects. For instance, copper is a useful oligoelement bit in excess it affects trophic levels. As a free element, mercury has hundreds of applications, for example in electrical switches. Despite emissions of vapour from the industry have been curtailed, there are still releases from unregulated burning of fuel or wastes. This human source of pollutant is added and its atmospheric inputs rival volcanoes. The ultimate sink for metals and many organic compounds is the sediment. Processes involved include deposition and burial as heavy metals are retained by: adsorption onto the surface of mineral particles complexation by molecules in organic particles precipitation reactions

Radioactive substances

Present day levels of radioactive substances found in coastal waters are the result of natural radioactivity (cosmic rays, earth crust), and possibly released radioactivity due to human activities such as oil exploration and combustion, phosphate production and use, land-based mining, managed discharges from nuclear power and reprocessing facilities, fallout from atmospheric nuclear weapons testing and accidents, medical diagnosis and therapy, and food conservation. The world's oceans have been a sink for radioactive waste from the production of nuclear weapons and electric power since 1944. Radioactive waste enters the ocean from nuclear weapon testing and the resulting atmospheric fallout, the releasing or dumping of wastes from nuclear fuel cycle systems, and nuclear accidents (for example Chernobyl in 1985). Dumping of high-level radioactive waste is no longer permitted in the ocean, but dumping of low-level wastes is still permitted. Low-level waste contains less radioactivity per gram than high-level waste. High-level wastes usually have longer half-lives. For example, one common high-level waste that is produced by spent nuclear fuel has a half-life of 24,100 years.

Oil and gas and offshore installations

Oil is at the heart of the modern economy in providing a cheap source of energy and as a raw material for making plastics, etc. It is a mixture of hydrocarbons and up to 25% non-hydrocarbons such as sulphur, vanadium, and metals... Environmental impacts occur at all stages of oil and gas production and use. They result from prospecting activities (including seismic techniques), physical impact due to the installation of rigs, operational discharges when production starts, accidental and routine spills, and finally combustion. Nihoul & Ducrotoy (1994) have estimated the input of oil to the North Sea, due to the offshore industry, at 29% of the total input of oil. Offshore installations may disturb the environment through the placement of structures on the seabed, which disturb benthic organisms, acoustic disturbances and light emission. An increasing number of installations is currently reaching the end of their productive life and will need to be dismantled or removed throughout the world seas. Overall, coastal ecosystems remain largely affected by direct discharges of oil from offshore activities and illegal discharges from ships. Operational discharges consist of production water and drilling cuttings. Although the amount of oil discharged via production water is increasing as platforms are getting older, cuttings still account for 75% of the oil entering the sea as a result of normal operations. The effects on the marine environment have been extensively studied by national authorities as well as by the industry. Despite uncertainty about possible long-term effects, problems with oiled cuttings (drilling muds) are acknowledged. Effects in the vicinity of platforms are well known , in particular those on the macrobenthic invertebrates, which range from lethal to insignificant, depending on proximity. Spills of oil and the release of chemicals (i.e. lubricants) used during exploitation constitute an important source of chronic pollution to coastal seas. Even if accidental spills represent a relatively small source of oil, they directly affect birds and mammals and have devastative effects on local vulnerable economies. Shipping is a main source of oil slicks (chronic and accidental) showing no downward trend. Combustion of oil is the ultimate stage in the chain of production-use. Polycyclic aromatic hydrocarbons (PAHs) originate from various sources such flaring or engines, including on land. Nevertheless, their major sources are not the rivers but sources in the sea itself from platforms and ships (Laane et al., 1998). PAHs are volatile material which travel well airborne, showing the importance of the atmospheric pathway in the distribution of contaminants. Airborne pollutants are dissolved by rain and some are carried to the coast as dust particles or in solution from the atmosphere. The current knowledge about the dependence of the deposition velocity upon the particle size and about the processes controlling wet deposition fluxes, and the quality and completeness of the emission data are still inadequate for describing the environmental cycle and impact of such pollutants.

Conclusion=

The effects of contaminants on coastal ecosystems are very difficult to assess. In the estimation of possible effects, the actual concentrations are compared with the levels that can cause effects. Results of laboratory experiments give only limited information in relation to the field situation, due to the complexity of natural systems and (in general) the co-occurrence of a multitude of contaminants in the field. Actual changes in the sea are often very difficult to discern from the large variability, which occurs naturally. Measurement of marine pollution using biological indicators provides information on the bio-availability of contaminants and the integration of the effects of multiple exposures and exposure over time. Multiple exposure is the combined action of all chemical contaminants. Even if the contaminants are present at concentrations too low to cause gross harmful effects, they can cause a suite of bio-chemical reactions in marine organisms generally called stress. Amongst the result of prolonged stress is the suppression of the immune system, thus increasing sensitivity towards the impact of infectious agents and parasites. Natural factors such as temperature extremes and fluctuations of salinity or anthropogenic activities, such as fisheries, can aggravate these reactions. A suite of bio-chemical reactions in marine organisms may occur as a response increasing sensitivity towards the impact of infectious agents and parasites.

The section on Water quality/pollution may be accessed via this link.

Land use and coastal defences

Land use and human populations

Some 60% of the world’s human population live close to the coast, within about 100 kilometers of the shore. This means that about 3.5 billion people rely heavily on marine habitats and resources for food, building materials, building sites, and agricultural and recreational areas and use coastal areas as a dumping ground for sewage, garbage, and toxic wastes. This proportion is expected to increase, along with growing urbanization, industrialization, and transportation, putting even greater pressure on the living and non-living resources of the coastal ocean. This section considers physical structures and land use modification in the coastal zone, and anticipated future developments (e.g. off-shore airports, wind-energy parks, land reclamation, etc.), due to an increase in human demography and increased use of coastal areas. The tremendous population increase puts a heavy burden on coastal zone management. The obvious global demand for proper guidelines to cope with these increasing pressures presents the science community with a major challenge, namely to supply scientific information on possible solutions, and on the predicted effects of the different measures. There is a need for systemic studies of the ecosystems associated with large coastal urban agglomerations. Growth in the so-called mega-cities adds to a tendency of people to concentrate in the coastal zone anyway. Clearly, this extends the range of impacts on the marine environment beyond traditional sewage and waste, adding things like increased risk of disasters, excessive noise levels and thermal pollution.

Some of the increases in human population numbers are temporary and are due to migrations. Some of this migration towards the coast is temporary, albeit significant (Cook, 1996). For example, the Mediterranean coastal zone, which has a population of about 130 million, swells to 230 million for most of the summer, increasing transportation and pollution problems.

Coastal industries and constructions

Industrial development has altered, disturbed, and destroyed costal ecosystems, including sensitive habitats. Many important industrial centres are situated on estuaries and in the vicinity of urban areas and ports. Main industrial activities affecting coastal areas include metal smelting and processing, chemical, petrochemical (oil and gas storage and refining), paper mills, vehicle factories, ship building, power plants (coal, oil gas, nuclear energy), and food processing (including fish). Data and energy cables are numerous with similar effects to pipelines which are submerged in the seabed. This creates problems for other users (bottom trawl fisheries, marine aggregate extraction). Construction engineering activities very often cause permanent destruction of habitats or decreases in habitat size and their fragmentation, due to coastal protection, land reclamation, extraction of bottom material, dumping and disposal.

Habitat infilling, in particular of salt marshes and mangroves, has taken place for centuries almost everywhere in estuaries, intertidal bays and inlets throughout the world. The main impacts on coastal ecosystems are disturbance and removal of benthic organisms, damage to sites as spawning areas for fish, alteration of seabed profiles, increase in instability of shallow banks and an increase in erosion. Severe beach erosion is a problem shared by many countries. Threat from industry and tourism infrastructure is still acute even if local and regional management plans help slowing down the rate of construction. The construction of artificial islands is now well developed in Japan and in the Southern North Sea, for instance in the Netherlands for the installation of a future airport. This is a highly political issue. Changes to the shoreline have been extensive in recent decades and threats from rising sea levels and sinking landmasses have required new strategies to be developed. For example, water storage schemes and managed retreat schemes along coastlines have been proposed and enacted as soft-engineering works as environmentally friendly and sustainable methods of dealing with long-term problems.

Dredging and dumping at sea

Dredging mainly causes physical disturbance and may result in the redistribution of contamination through release from the sediment. Contaminants might be resuspended and remobilised from sediments and create new entries in food webs. Any increase in suspended matter will impede growth of filter feeding organisms (bivalves) and alter the burial capacity of benthos. It is well known that changes in substrate quality are synonymous to changes in the structure of benthic communities. The bulk of material eligible for dumping at sea comes from dredging operations from navigation channels, material removed in coastal engineering projects. beach nourishment, and reclamation and coastal marsh preservation. Sewage sludge dumping increases the fallout of organic material and associated contaminants to the seafloor. It can contribute to eutrophication in naturally nutrient rich coastal waters. Marine litter is derived from land-based and marine sources. It is found in large quantities on coastal seabed, floating in the water column and on the shore. It originates from many diverse activities such as shipping, fishing and mariculture or recreation and tourism. About 80% of the material is plastic which is non-degradable and provokes smothering. Entangling and drowning of biota (birds, mammals) may happen and inflict physical injury to animals (turtles) or even an obstruction of digestive system after ingestion of plastic objects. Once in the food-web, plastics release toxic substances. Containers or all sorts (bottles, boxes…) will host alien species and help in the transportation of invasive species.

Freshwater inputs

River runoff and load

Flow of fresh water and contained materials to the coastal zone has been grossly altered by human activities. In some arid regions, such as the Nile (Egypt) and Colorado (Mexico), where freshwater on land is a major resource limiting human activities, discharge has diminished to 10% or less of natural flow. In other regions the issue is management of water, with the seasonal pattern of discharge having been greatly modified. Either water loss or alteration of the seasonality of discharge can have major impact on coastal ecosystems. Human activities have also altered the patterns of sediment discharge. Although increased erosion has occurred associated with human land use (especially agriculture) and has led to increases in sediment delivery, a confounding effect has been increased trapping of sediments in water reservoirs. Thus, some regions experience artificially elevated sediment discharge; others experience severe diminution of discharge. To an ecosystem acclimated to receive a particular level of sediment load, either change can be detrimental. For example, severe erosion without sediment replacement may occur in systems (such as the Colorado River delta) poised to receive high sediment loads. By contrast, ecosystems such as coral reefs are generally acclimated to low sediment discharge, and large amounts of sediments can bury or otherwise damage reefs. Human activities have generally led to an increase discharges of pollutants which affect water quality. Some countries have done better than others in effectively regulating and controlling the discharges.

Groundwater discharge into the coastal zone

Although not as obvious as river discharge, continental ground waters also discharge directly into the sea. Like surface water, groundwater flows down-gradient. Therefore, groundwater flows directly into the ocean wherever a coastal aquifer is connected to the sea. Furthermore, artesian aquifers can extend for considerable distances from shore, underneath the continental shelf. In some cases, these deeper aquifers may have fractures or other breaches in the overlying confining layers, allowing groundwater to flow into the sea.

Recreation and tourism

Coastal areas provide recreation opportunities for local people and for tourists who travel the whole world. Tourism cause pressures on coastal ecosystems by excessive influx of visitors. People movements rely on transportation systems which range from pathways for walkers to landing strips for airports. Such movements at planetary level mean the wandering of pests, construction and building with associated pollution and eutrophication and disposal of litter and other waste in tourist areas. The paradox is that, most often, tourism will disturb and threaten local populations and wildlife and their habitats, which attracted them to the area in the first instance.

Beaches, swimming, recreational boating

Beaches are important areas for tourism. However, the increasing population and welfare push many areas to their sustainable limits, both from a tourist and environmental point of view. In beach tourism there are clear feed back mechanisms, nice beaches attract people, and too many tourists on the beach decrease the attractiveness. Tourism, a major source of income for many coastal communities, can have major effects on coastal environments unless scale and type of activities are controlled. Biodiversity reduction, resource depletion, and human health problems may result from the accumulated environmental effects. Setting maxima to tourist numbers is a proper managerial measure However, once these maxima are really reached, pressure to relax the restrictions increase. Clear definitions of maxima, and scientifically adopted calculation methods are necessary. With the increasing welfare also the recreational boating increases, and in some countries harbours and marinas built primarily for recreational use by small boats may disturb more of the coastal zone than commercial and industrial use. The environmental impacts of marinas and small harbours depend on site location, design, construction methods, and ‘house¬keeping’. Careful site planning can help avoid or minimize many of the impacts.

Ecotourism

Seabirds and marine mammals, particularly cetaceans, offer excellent opportunities for ecotourism in many parts of the world. Seabird colonies and seal rookeries are spectacular and increasingly popular places to visit. In many places around the world, whale watching trips are organized or specific advice is given by tourism organizations as to where and how whales can be observed from headlands and coastal promontories (Taylor, 1988). This rapidly growing interest for ecotourism has been reason for concern (De Groot, 1983; Coultier, 1984; Woehler et al., 1994). Subsequently, codes of ethics and best practice guidelines for ecotourism have been published and most of the major tourism organizations have formally declared to follow such guidelines.

Coastal hazards

The coastlines of many countries face high risks of damage from certain types of natural disasters. The major concern is death and property loss by winds and waters of hurricanes or cyclones. Along many densely populated coastlines, the risks of natural disasters are being increased by population growth and unmanaged development projects, including residential urban development. Coastal natural disasters cut across all economic sectors. Wind or water damage from a cyclone (hurricane), inundation by tsunami, wreckage from an earthquake, or coastal erosion from storms can affect tourism, fishing, port operations, public works, trans¬portation, housing and industry. Tropical cyclones (hurricanes) form over the warm oceans (at least 26 degrees C) mainly over the western parts where no cold currents exist. Apart from the wind and rain, a major impact is from the associated storm surge and storm waves. These have been responsible for major loss of lie particularly in low lying densely populated coastal areas such as Bangladesh or China. Tsunamis are quite a different phenomenon and are associated with sub sea earth movements. However, their speed and height can cause extensive coastal destruction with little warning and some distance from their origin.

Biodiversity – Invasive species

The composition and structure of the fauna, flora and habitats of coastal seas has been changing to an unusual rate in the last few decades, due to changes in the global climate and an increase in human activities. The unusual rapid rate of change, rather than the nature of the change itself, is the reason for the deterioration of many environments; over the last 50 years the rate and extent of this deterioration has been unprecedented, as were the consequences on biological diversity. The term ‘biodiversity’ is used by the Convention on Biological Diversity (1992) to refer to all aspects of variability evident within the living world, including diversity within and between individuals, populations, species, communities, and ecosystems. The term is commonly used loosely to refer to all species and habitats in some given area, or even on the Earth overall. In fact, it relates to environmental attributes, often species or species groups, which can be sampled and whose modification is supposed to reflect a change of biological diversity. What is important is the capacity of ecosystems to fulfil their role within the biosphere. The notion of functional diversity is useful in that it provides insight in the resilience of ecosystems and how changes affect them. There are many causes to losses of marine biodiversity, especially in the coastal waters of industrialized countries. Direct habitat destruction through the erection of engineering and drainage works which disturb the physical integrity of coastal and marine systems is the most drastic as the habitat itself is changed to a point where the ecosystem looses its identity and fulfils a completely different function as before. Poor fisheries management, including the uncontrolled exploitation of corals and molluscs and the by-catch of large numbers of non-target species in fisheries is another important aspect of the detrimental exploitation of marine living resources due to the lack of an integrated approach to coastal zone management, leading to impoverished functioning. As a consequence, the productivity of fisheries and such important ecosystems as mangroves and coral reefs has been depressed, and local human communities are suffering. In general, estuaries and salt marshes, mangrove forests, and sea grass beds near cities and towns are severely degraded worldwide with many species being threaten. The increasingly observed worldwide bleaching of corals could presage massive ecological changes for coral reefs and other marine ecosystems.

Conclusion

Living organisms are an essential link in the turnover of biogeochemical cycles through costal systems. They are themselves vulnerable to rapid changes which take place in the coastal zone due to anthropogenic activities, but changes in the structure of populations of organisms will in turn affect the geochemistry of the habitat, to a point where such cycles might become dysfunctional. The consequences of such changes taking place in costal ecosystems may have consequences at global level leading to an unbalance in fluxes of energy and minerals at the interface between land and sea. The dynamics of such systems are very high and complex meaning that conservation is not just concerned with fixing the coast line to its physical actual limits, fighting erosion and sea-level rise. Because costal systems are alive, they are able to cope with changes of any sorts, but what counts is more the rate of change than the nature of the change. What makes the anthropocene unique is the rapidity of changes inflicted by humans to natural systems. Threats of all sorts from human activities onto ecosystems are now well documented but action remains difficult and uncertain because of a lack of understanding of the scale and of the speed of observed changes. Notably, the variability of natural systems is difficult to include in any political reasoning which relies on the certainty of statements for decision making. Through improving the scientific understanding of the performance of coastal ecosystems in terms of fluxes of energy and matter in relation to human impacts, integrated coastal management should become more able to predict the effects of measures taken and find adapted responses to fast evolving demands from society.

References

See also

Author: Dr Jean-Paul Ducrotoy, University of Hull; EFMS (Eureopean Federation of Marine Science and Technology Societies), 2007. j-p.duc@wanadoo.fr