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The Ocean Health Index evaluates the condition or population status of ‘marine species’ to calculate Status and Trend scores for the Biodiversity (Species) and Sense of Place (Iconic Species) goals. Data are only available for a small fraction of the species that live in the ocean for the following reasons.

Oceans cover 70% of the Earth’s surface and include more than 98% of the biosphere, or space where life exists. They are home to numerous life forms, including plants, vertebrate and invertebrate animals, and microorganisms, but the actual number of species they contain remains unknown. Of approximately 1,868,000 species known globally, about 15% are marine (Carpenter et al. 2011).

Scientists with the Census of Marine Life project reported that approximately 230,000 marine species have been identified to date, and estimated that at least three new marine species remain to be found for every one already known. Researchers discovered an average of 1,650 new marine species each year between 2002 and 2006 (COML 2010).

Mora et al. (2011), predicted that ten times as many species remain to be found. They estimated the number of species on land and in the ocean based upon analysis of the taxonomy (classification) of the ~1.2 million species that have been scientifically described globally. Their analysis predicts that ~8.7 million species exist globally (~2.2 million are marine), and indicates that 86% of the species on land and 91% of species in the ocean remain to be discovered and described. They calculated that describing them all would require 1,200 years, 303,000 taxonomists and approximately US $364 billion (Mora et al. 2011).

Marine species face increasing risks of extinction caused by changing climate, ocean acidification, overexploitation, habitat loss due to development, pollution, and invasions by alien species. Approximately 15% of the species evaluated to date by the International Union for the Conservation of Nature and Natural Resources (IUCN) or Global Marine Species Assessment (GMSA) have an elevated risk of extinction and are classified as Critically Endangered, Endangered or Vulnerable to extinction.

Risks for Extinction are particularly high in some groups.

For example, data in Carpenter et al. (2011) and Polidoro et al. (2009) indicate that:

•      One-quarter of the world’s primary habitat producing species, such as reef-building 
        corals, mangroves and seagrasses, are at elevated risk of extinction.

•      More than one-quarter of seabirds are threatened.

•      17% of sharks and 12% of grouper species are listed as critically endangered, 
        endangered or vulnerable to extinction.

IUCN Risk of Extinction Assessment

The Risk of Extinction assessment, which began in 1973, is coordinated by the International Union for the Conservation of Nature and Natural Resources (IUCN) and Global Marine Species Assessment (GMSA). Assessments are carried out by Specialist Groups, and the resulting information is assembled by IUCN as the Red List.

There are many taxonomic groups of organisms, each consisting of many species. Each assessment requires a great deal of data and usually requires considerable time. Information often remains incomplete even for groups that have been assessed.  For example, even though all known species of sharks and rays have been assessed, 47% are ‘data deficient’, the IUCN term indicating that there is not enough information available to determine risk category or population trend.

In order to increase the number of marine species that are assessed, IUCN, Conservation International and Old Dominion University initiated the Global Marine Species Assessment (GMSA) in 2006, with the goal of completing IUCN Red List assessments for 20,000 marine species by 2012. Working with IUCN Specialist Groups, GMSA has completed assessments of all of the world’s known species of sharks and rays, groupers, and reef-building corals (Polidoro et al. 2008). 

IUCN Red List Categories

After completing a risk of extinction assessment, the IUCN determines whether or not a species qualifies for a particular threat category by deciding if it meets the threshold for that category in one of five criteria. Critically Endangered species face an extremely high risk of extinction in the wild. The other threatened categories – Endangered and Vulnerable – refer to species that are either at a very high, or high, risk of extinction in the wild.  Both the risks of extinction and the population trends for species within a region are used in calculating the region's goal scores for Sense of Place (Iconic Species) and Biodiversity (Species).   

The IUCN Red List Categories include eight levels of extinction risk:

•      Extinct (EX)

•      Extinct in the Wild (EW)

•      Critically Endangered (CR)

•      Endangered (EN)

•      Vulnerable (VU)

•      Near Threatened (NT)

•      Least Concern (LC)

•      Data Deficient (DD)

For more information, please see our IUCN Risk Assessment Page.

What Is An Iconic Species?

Not every marine species is an iconic species.

Iconic species are animals or plants which are important to cultural identity as shown by their involvement in traditional activities such as local ethnic or religious practices and/or which are locally or more broadly recognized for their existence and aesthetic values. Species important exclusively for economic reasons are not included, but economic importance does not disqualify species that are also culturally significant. Examples of iconic species include polar bears, sea turtles, and sharks.

Marine species can be iconic not only to people who live close to and interact with them, but also to people who live far away from them and may never see them in person. Deriving a sense of value from the existence of a species is not limited to geographic location.

To learn more about iconic species, please visit our Iconic Species Page.

How Was It Measured?

The Ocean Health Index uses information for all marine species included in the IUCN Red List. The main taxonomic groups included are: habitat forming corals, mangroves, seagrasses, sea snakes, marine mammals, seabirds, marine turtles, angelfish, butterfly fish, groupers, wrasses, parrotfish, hagfish, and tuna and billfishes. Seabird data are also obtained from Birdlife International and NatureServe (2012).  For the 2013 Ocean Health Index, assessments were available for a total of 8,173 marine species. As of 2015 GMSA increased that number to more than 13,000.  The growing number of assessments has raised the percentage of marine species on the Red List from less than 1% in 2001 to 13%.  

Larger samples will be available in the future, but it will require decades to prepare complete assessments for every relevant group, and additional time will be necessary to assemble information on newly discovered species. Owing to the large gaps in knowledge concerning most of the ocean’s species, measures used in the Ocean Health Index and other assessments will need to rely on incomplete samples for some time to come.   

The Ocean Health Index evaluates the risk of extinction and population trend of marine species to calculate Status and Trend scores for the Biodiversity (Species) and Sense of Place (Iconic Species) goals. 

Sense of Place: Iconic Species
For Sense of Place, only iconic species were considered. There are no official country-level lists of iconic species, so a list was put together by using the World Wildlife Fund’s global and regional lists for Priority Species (especially important to people for their health, livelihoods, and/or culture) and Flagship Species (‘charismatic’ and/or well-known). 

Status for each region was calculated as the percentage of its iconic species in each IUCN threat category. Each species present within a region is represented by the weight assigned for its threat category. Six of the IUCN's threat categories are used, with corresponding weights as follows: EX=0.0, CR=0.2, EN=0.4, VU=0.6, NT=0.8, LC= 1.0.  The sum of the weights divided by the number of species gives the average risk category for Iconic species within the region, which is used as its status score. 

Trend is calculated with information from the IUCN on population status by giving scores of 0.5 (increasing population), 0.0 (stable), and -0.5 (decreasing population) to each species in the region, then designating the average of those scores as the trend.

Biodiversity: Species
Status and trend were calculated in the same way as for Iconic Species, but using all species within a region that were assessed by IUCN. Data on species distributions and threat categories are taken from the IUCN Global Marine Assessment results. Where neither IUCN nor BirdLife International distributions are available, distributions are determined with data from AquaMaps. 

What Are The Impacts?


The oceans comprise many diverse and complex ecosystems. In general, ecosystems with more biological diversity tend to have greater resilience (i.e. the ability of the system to withstand pressures).

Some ecosystems depend upon certain key species for optimal function and productivity. For example, Sea Otters play a key role in helping kelp forests flourish by preying on sea urchins that have the potential to denude significant areas of forest if left unchecked.


Over a billion people rely on fish and seafood as a daily source of protein. About half of that protein now comes from ocean and inland fisheries and the other half from freshwater and marine aquaculture. Fish consumption is especially high in coastal regions and in small island states.


Directly and indirectly, the depletion of marine species affects the livelihoods and income of hundreds of millions of people worldwide, including about 200 million people dependent on fisheries. Worldwide, 45 million people fish for a living and are threatened by overfishing. Population depletion of marine species also can affect important economic sectors such as tourism and recreation.

Get More Information

Census of Marine Life (COML)

This 10 year project ended in 2010, but left a legacy of discoveries, data and publications about marine species. All that information is publicly available at the link below. 

Global Marine Species Assessment (GMSA)

The GMSA project evaluates the global status for all marine vertebrate species, plants, and select invertebrates in order to determine the risk of extinction according to the IUCN Red List Categories and Criteria.


Mora, C., D.P. Tittensor, S. Adl, A.G.B. Simpson and B. Worm. (2011). How many species are there on earth and in the ocean? PLoS Biol 9, e1001127.

Palumbi, S. R. et al. (2008). Managing for ocean biodiversity to sustain marine ecosystem services. Frontiers in Ecology and the Environment 7, 204–211.

Shao, K.-T. (2009). Marine biodiversity and fishery sustainability. Asia Pac J Clin Nutr 18, 527–531.

Stone, Gregory. et al. Oceans: Heart of Our Blue Planet - A CEMEX Book with amazing photographs and written by top marine scientists - Conservation International.

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