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

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.

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