Biodiversité Perspectives mondiales

5. Are ecosystems healthy enough to provide resources and essential services?

  • 5.1 How is fishing affecting marine species?
  • 5.2 How are human activities fragmenting forests and inland waters?
  • 5.3 How is freshwater quality changing?

The source document for this Digest states:

FOCAL AREA | Maintaining ecosystem integrity, and the provision of goods and services provided by biodiversity in ecosystems, in support of human well-being

Closely related to the assessment of biodiversity components is that of the integrity of ecosystems and their ability to support human livelihoods. The Millennium Ecosystem Assessment has placed particular emphasis on ecosystem goods and services because these provide the basis for human well-being and the ultimate rationale for maintaining ecosystem health. Although the framework for assessing progress towards the 2010 target includes several indicators that link the integrity of ecosystems to human well-being, only a few have suitably developed methodologies and comprehensive global data to allow for their present use.

Source & ©: CBD  Global Biodiversity Outlook 2 (2006),
Chapter 2: The 2010 Biodiversity Target: Establishing current trends, p. 29

5.1 How is fishing affecting marine species?

The source document for this Digest states:


Oceans cover over 70% of the globe. The primary source of food from the oceans is from capture fisheries. Preferred fish catches consist of large, high value, predatory fishes, such as tuna, cod, sea-bass and swordfishes. The intensification of fishing has led to the decline in these large fishes, which are high up in the food chain (e.g., in the North Atlantic, large fish have declined by two-thirds in the last 50 years). As predators are removed, the relative number of small fish and invertebrates lower on the food chain increases, and the mean trophic level (i.e., the mean position of the catch in the food chain) of fisheries landings, declines. Mean trophic levels, upon which the Marine Trophic Index is based, have consequently declined globally at a rate of approximately 0.1 per decade from the 1970s, when landings peaked and the Marine Trophic Index averaged over 4 in many areas, to approximately 3.5 at the present time. In the North Atlantic the Marine Trophic Index peaked earlier in the 1960s and the decline was more rapid (Figure 2.10). From an average of over 4 historically, the Marine Trophic Index has declined If the global decline in trophic levels continues at this rate, the preferred fish for human consumption (which are between trophic levels of 4 and 3) will become increasingly rare, forcing a shift in fisheries and human consumption patterns to smaller fish and invertebrates. In addition, the resulting shortened food chains leave marine ecosystems increasingly vulnerable to natural- and human-induced stresses, and reduce the overall supply of fish for human consumption.

The Marine Trophic Index can be calculated from existing fish catch data and is therefore a widely applicable indicator of both ecosystem integrity and the sustainable use of living resources. Changes in the Marine Trophic Index have also been mapped (Figure 2.11).

Since 1970, when landings and the Marine Trophic Index peaked, the Index has decreased by an average of 0.005 per year in coastal waters, and by 1.5 times that amount in the North Atlantic. If action were taken to better manage fisheries, declines in the Marine Trophic Index could be halted, as seen in Alaska, where the Index has stabilized with the sound management of most Alaskan fish stocks.

Despite increasing fishing efforts, as evidenced by the increase in average fishing depth from 170 m in 1950 to about 280 m in 2000, landings of marine catch decreased throughout the 1990s.

Source & ©: CBD  Global Biodiversity Outlook 2 (2006),
Chapter 2: The 2010 Biodiversity Target: Establishing current trends, p. 29-30

5.2 How are human activities fragmenting forests and inland waters?

The source document for this Digest states:

HEADLINE INDICATOR Connectivity / fragmentation of ecosystems

In terrestrial and inland water ecosystems, human activities oft en lead to the fragmentation of habitats. Previously contiguous areas are divided into a number of smaller patches that are much more vulnerable to outside influence than large ones and that support smaller populations of species, which are consequently more vulnerable to local extinction. Global information on the status of anthropogenic fragmentation is available for large river systems and forests.

In riverine systems, the creation of impoundments to form reservoirs, either for water storage or to generate hydroelectric power, have significant effects on the hydrology and water quality of the affected river system and its biodiversity, particularly that of migratory species. Catchment-scale impacts of dams on ecosystems stem from inundation, flow manipulation, and fragmentation. Known effects include the destruction of terrestrial ecosystems through inundation, greenhouse gas emission, sedimentation, an upsurge of nutrient release in new reservoirs, substantial changes in land-use patterns and an extensive modification of aquatic communities. A global overview of dam-based impacts assessed fragmentation and flow regulation in 292 large river systems representing 60% of the world’s river runoff. Over half of the large river systems that were assessed are affected by dams, and more than one-third, representing more than 50% of the river basin area, are strongly affected by river fragmentation and flow regulation. Only 12% of the area is unaffected (Figure 2.12).

The great advances in remote sensing techniques in recent years make it much easier than before to monitor the degree of forest fragmentation. The size and connectivity of forests are important in determining the value of any given area of forest in maintaining biodiversity and in its capacity to deliver ecosystem goods and services. Fragmentation is associated with a decrease in patch size and increasing isolation between habitat patches. Also, the size of core areas decreases, and the size of edge areas increases. Figure 2.13 presents a global analysis of forest fragmentation caused by human influence. It shows highly fragmented forests in Europe and parts of Southeast Asia, whereas forests in other continents are less fragmented overall, or fragmentation is more localized.

Source & ©: CBD  Global Biodiversity Outlook 2 (2006),
Chapter 2: The 2010 Biodiversity Target: Establishing current trends, p.30-31

5.3 How is freshwater quality changing?

The source document for this Digest states:

HEADLINE INDICATOR Water quality in aquatic ecosystems

Observations of physical, chemical and/or biological parameters over time indicate that the water quality of inland water bodies and their catchments has changed. The integrity of inland waters is affected by a series of factors, in particular the extraction of fresh water for agricultural, industrial and human consumption, and the physical alteration of the ecosystem, for example through the diversion and canalization of watercourses, the creation of impoundments or drainage. Human activities are also impacting upon the quality of fresh water available, through pollution, increased sedimentation and climate change. Inorganic nitrogen pollution of inland waterways, for example, has more than doubled since 1960 and has increased tenfold in many industrial parts of the world.

Biological oxygen demand (BOD), an indicator of the organic pollution of freshwater, has been analysed over the last three decades using data from 528 stations in 51 countries. While water quality in rivers in Europe, North America, and Latin America and the Caribbean has improved since the 1980s, it has deteriorated over the same period in Africa and in the Asia and Pacific region. Mean BOD concentrations typical of moderately polluted waters (~ 5-7 mg/l) were documented in Europe and Africa in the 1980s and 1990s, but have improved in European rivers to levels typical of light pollution (~ 3-4 mg/l) since 2000 (Figure 2.14). BOD concentrations typical of unpolluted waters (~ 2 mg/l) were documented in North America and in the Asia and Pacific region in the 1990s and in Latin America and the Caribbean since 2000. Very high mean BOD concentrations in Latin America and the Caribbean in the 1990s reflect values observed at several stations that were near pollution point sources, and that were not monitored after 2000.

Many countries have stopped or reduced the monitoring of BOD in freshwater ecosystems in recent years. As such, comparatively few, or no, data were available to assess recent trends in BOD in some regions since 2000. Other water quality variables such as dissolved oxygen and inorganic nitrogen are therefore being evaluated for their utility as indicators of the state of freshwater ecosystems.

Water quality monitoring indicates both major direct threats to the sustainability of inland waters and the effects of unsustainable activities outside that ecosystem. In fact, the health and integrity of inland waters is an excellent indicator of the health of terrestrial ecosystems. It can also indicate the impact of responses to environmental problems, such as successful policy interventions leading to improved water quality. Improving water quality in all regions, both by reducing water pollution and by increasing efforts at water purification, appears to be a tangible, though challenging, contribution to the achievement of the 2010 Biodiversity Target.

Source & ©: CBD  Global Biodiversity Outlook 2 (2006),
Chapter 2: The 2010 Biodiversity Target: Establishing current trends, p.31-32

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