Number of marine species

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Description of marine species

Based on the World Register of Marine Species (WoRMS), there are currently (2022 census) about 242,000 known and described marine species living in the world's oceans. Marine biota continue to be discovered and named at a current average of 2,332 new species per year. The time span between the collection of the first specimen of a new species in the field and its formal description is on average 13.5 years (the so-called 'shelf life'). However, it is possible that up to 25% of the newly described species will ultimately turn out to be identical to previously described species, meaning that roughly only 1,750 of the 2,332 new marine species described annually represent real new discoveries (Bouchet et al., 2023[1]).

Estimates of the total number of known and unknown marine species vary between 0.3 million and 2.2 million (Costello et al., 2012[2]; Appeltans et al., 2012[3]; Mora et al., 2011[4]). Projections of the magnitude of total biodiversity (terrestrial and marine) of the planet range from 9 to 390 million eukaryotic species (Mora et al., 2011[4]; Larsen et al., 2017[5]).

The reason for the huge range in the estimated number of species is the lack of information on the diversity of some of the smaller organisms on Earth. For example, in the ocean, there is a plenty of information on marine mammals (seals, whales, dolphins, porpoises) and fish, while only recently are scientists beginning to understand the extreme diversity present in micro-organisms such as bacteria and phytoplankton. Microscopic organisms (e.g., mesopsammon, parasites, picophytoplankton) require special laboratory techniques for isolation, preparation, sometimes also cultivation, and study. Moreover, there are still limitations to sampling new species in the world’s oceans. Access to the deep sea has been possible for 150 years from specially equipped vessels, but the discovery and exploration of vent ecosystems only started 50 years ago at the onset of manned research submersibles. Only 7.0% of the new species come from deeper than 1,000 m[1]. In Europe alone it is estimated that there are 41,000 - 56,000 species present of which 5,000 - 20,000 have yet to be identified.

Census of Marine Life

The Census of Marine Life was an international project spanning 10 years that recorded the diversity, distribution, and abundance of life in the ocean. More than 2,700 scientists from 80 nations contributed to the Census. The results of their research, which included 540 marine expeditions, were reported at The Royal Society, London, in October 2010.

During the Census, scientists found and formally described more than 1,200 new marine species, with thousands more awaiting formal descriptions. They further discovered and mapped areas in the ocean where marine species congregate, and documented long-term and widespread declines in marine life as well as species resilience and recovery. [6]

Progress in the Census of Marine Life

The publicly accessible online World Register of Marine Species (WoRMS) founded in 2007 has greatly facilitated access to knowledge on the already known species by a much broader public of professional and non-professional scientists from throughout the world. There have never been so many authors involved in new species descriptions. A significant part of the taxonomic workforce in fact comprises retired professionals and citizen scientists. A citizen scientist is not necessarily someone without training in science but, like a retired professional, he/she is someone who is not paid to do research and publish scientific papers. In the case of marine molluscs, 57% of the 6,656 species described in 2000–2014 were described by 'amateurs'[1].

However, taxonomic studies are facing several bottlenecks of scientific, economic, sociological and regulatory nature (Bouchet, 2006[7]):

  • The comparison of specimens of a potentially new species with closely related known species is problematic because only a small portion of the known marine species (less than 20%) are currently (2022) registered with a genetic barcode.
  • High costs prevent citizen taxonomists and retired professionals from publishing in open-access journals and retrieving information from scientific publications under restricted access.
  • The focus of many research funding programmes on fundamental science or on questions of high societal relevance is a complicating factor for obtaining funding for taxonomic studies.
  • Taxonomic field work in Exclusive Economic Zones is hampered by the Convention on Biological Diversity (CBD, 1994) and the Nagayo protocol ('Access to Genetic Resources and the Fair and Equitable Sharing of Benefits Arising from their Utilization', 2014), due to the regulatory obligation to request permits from host countries. In many cases permit applications have to specify the species and number of specimens to be collected, which is of course impossible for the exploration of still unknown marine species.

Related articles

Species extinction
Measurements of biodiversity

External links

Wikipedia article Census of marine life
Census Highlights report 2007/2008


  1. 1.0 1.1 1.2 Bouchet, P., Decock, W., Lonneville, B., Vanhoorne, B. and Vandepitte, L. 2023. Marine biodiversity discovery: the metrics of new species descriptions. Front. Mar. Sci. 10: 929989
  2. Costello, M. J., Wilson, S. and Houlding, B. 2012. Predicting total global species richness using rates of species description and estimates of taxonomic effort. Syst. Biol. 61: 871–883
  3. Appeltans, W. et al. 2012. The Magnitude of Global Marine Species Diversity. Current Biology 22: 2189-2202
  4. 4.0 4.1 Mora, C., Tittensor, D. P., Adl, S., Simpson, A. G. B. and Worm, B. 2011. How many species are there on earth and in the ocean? PloS Biol. 9 (8), e1001127
  5. Larsen, B. B., Miller, E. C., Rhodes, M. K. and Wiens, J. J. 2017. Inordinate fondness multiplied and redistributed: the number of species on earth and the new pie of life. Q. Rev. Biol. 92: 229–265
  7. Bouchet, P. 2006. The magnitude of marine biodiversity, in: Duarte, C. (Ed.) The exploration of marine biodiversity: scientific and technological challenges. pp. 31-62

The main author of this article is Philippe Bouchet
Please note that others may also have edited the contents of this article.

Citation: Philippe Bouchet (2024): Number of marine species. Available from [accessed on 17-07-2024]