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Thursday, February 09, 2012
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Components of biodiversity


Sustainable Use


Threats to biodiversity


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Indicator Facts

Focal Area: Status and trends of the components of biodiversity

Headline Indictor: Trends in the extent of selected biomes, ecosystems, and habitats

Key Indicator Partners:

Data Available: Global time series (Mangroves: 1980 onwards, with regional and national variations; Seagrasses: 1930s onwards), Regional case studies (Coral reefs: 1980s onwards)

Development Status: Ready for global and national use

Reason for indicator

Habitat modification and/or destruction is considered to be one of the main drivers of biodiversity loss. Trend analysis on the global extent of different biomes, ecosystems and habitat-types is an essential component of understanding the status and trends of biodiversity as a whole. Data on these trends is also essential for assessing and modelling the status of threatened species or populations. This indicator assesses global trends in mangroves, seagrass beds and coral reefs, some of the most threatened systems in terms of habitat degradation. These ecosystems are also amongst the most productive in the world, providing fundamental ecosystem services (e.g. food, building materials, nutrient cycling, carbon sequestration) at local, national and global levels. The extent of marine habitats indicator not only addresses the degree of change in extent of these highly important systems, but also the time period and rates of change, which can be critical in determining appropriate actions.

Status

The indicator is unique in that many habitat types can, or will be assessed globally and continuously using remote (satellite) sensing techniques. However time-series satellite data is currently patchy and/or not available for some habitats, and therefore data used in the indicator are derived from a combination of both satellite observations and ground based monitoring.

Mangroves:

Mangrove extent data has been excised from the FAO Forest Resource Assessments (FRAs), which has generated mangrove extent data from 900 national and sub-national data sets for the period 1980-2005.

Seagrass beds:

Trends in global seagrass losses have been derived from a comprehensive assessment of seagrass data available from 215 studies between 1879-2006.

Coral reefs:

Obtaining quantitative global data for coral reefs currently poses significant difficulties, however trends in coral extent (measured by changes observed in percent cover of live coral) are available for the Indo-Pacific and Caribbean regions.

Indicator scale

Data can be aggregated or disaggregated to examine trends at the global, regional, and national (sub-national) levels.

The Indicator

 

Extent of Mangrove and Seagrass, and Coral Condition

Source: Adapted with permission from Butchart et al. 2010

 

How to Interpret the Indicator

A downward trend represents a reduction in habitat extent. Given the key roles these habitats play in facilitating entire ecosystem functioning, trends can be seen as a sentinel of wider changes in adjacent systems. As such, declines are a significant indicator of the rate of biodiversity loss, where the steeper the slope of the trending line, the faster the rate of decline. Conversely, a constant or increasing trending line implies biodiversity loss has been halted or reversed. However, it is important to complement trends from this indicator with other data to establish whether the change in habitat extent will result in a positive or negative change for biodiversity.

Current Storyline

Mangroves:

‘The FAO estimates that approximately 20% or 36,000 km2 of the world’s mangroves have been lost between 1980 and 2005. The amount of mangrove forest area that has been lost is disturbingly high, however the rate at which mangroves are declining seems to have reduced more recently, falling from an average of 1,870 km2 (or-1.10%) per year during the 1980s, to 1,185 km2 (-0.75%) in the 1990s, to 1,020 km2 (-0.67%) between 2000-2005.

This represents a 45% reduction in the annual rate of loss.’

Seagrass beds:

‘A comprehensive assessment of global seagrass losses conducted on data from between 1879 and 2006 estimated that 29% of the known, measured area of seagrass beds had disappeared, equating to a global figure of 51,000 km2. The rate of decline is high (median = 0.9% per year) and has been accelerating since 1980 averaging greater than 5%, or 110 km2 of seagrass meadow lost per year.’

Coral reefs:

‘It is thought that coral reefs have suffered a significant global decline in biodiversity since the 1970s or earlier, with coral cover in the Indo-Pacific and Caribbean regions falling by almost half during the 1980s before stabilizing but not recovering to earlier levels. There are also indications that both reef structure and the proportion of reefs with living coral has declined which has had further ramifications on levels of reef-associated biodiversity.’

National Use
This indicator is primarily formed from national and sub-regional data and as a result this indicator can be produced at the national and regional levels. The on-going challenge for further development of this indicator at all levels is for national monitoring programmes to implement systematic or complementary methodology for data collection, and to incorporate geographical regions that have been poorly surveyed in the past. For more information on interpreting trends and producing national indicators of marine habitat extent contact Megan Tierney at UNEP-WCMC Megan.Tierney@unep-wcmc.org).
Future development

Work will continue to find potential sources of data for this indicator, specifically concentrating on ecosystems for which this indicator is not yet in development. Work will also be conducted to establish sources of satellite observation data that can provide temporal trends in the future. As part of the FRA 2010, countries have been asked to provide data on area of mangroves. UNEP-WCMC and other organizations such as NASA are currently updating the global coral reef layer using multiple sources of data. It is hoped that this project will be completed in the near future.

Indicator publications: Mangroves
Indicator Publications: Seagrasses
 TitleDescription
Accelerating loss of seagrasses across the globe threatens coastal ecosystems (2009) Journal Article: Waycott, M., et al. 2009. Proceedings National Academy of Sciences 106, 12377-12381
World Atlas of Seagrasses (UNEP-WCMC 2003)English
Indicator Publications: Coral reefs
 TitleDescription
Flattening of Caribbean coral reefs: region-wide declines in architectural complexity (2009)Journal Article: Alvarez-Filip, L. et al. 2009. Proceedings of the Royal Society Biological Sciences B 276, 3019-3025
Recent region-wide declines in Caribbean reef fish abundance (2009)Journal Article: Paddack, M. J. 2009. Current Biology 19, 590-595
Regional decline of coral cover in the Indo-Pacific: timing, extent, and sub-regional comparisons (2007)Journal Article: Bruno, J., Selig, E. R. 2007. PLoS One 2, e711
World Atlas of Coral Reefs (Multiple Authors 2001)English
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Photo credits:
Congo rainforest with mist ©World resources institute; reef from above ©SF Brit; Sunset over mangroves ©Laura Tidwell

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