A considerable percentage of marine species are unidentified. The ocean may be home to one million or more species, with 230,000 so far described by science. The age of discovery continues, with the rate of description of new marine species higher than ever, suggesting that most will be discovered by the end of this century. The importance of species diversity for marine ecosystem functioning is well known. It is therefore important to know which species live where, why, in what abundance, and how these factors are changing through time.

This webpage describes what is currently known about marine species. The information comes from the world’s largest marine biodiversity database, the Ocean Biogeographic Information System (OBIS). The work provides a ‘baseline’ to work from, and considers three aspects of the management of marine species. The taxonomic status looks at how well defined the organisms have been classified, the biogeographic status considers the distribution of the species and ecosystems in geographic space and geological time and their conservation status defines how well protected the species will be into the future.

Biodiversity monitoring has increased globally since the 1950s, with daily averages of 120 sampling events and 1 800 observations in OBIS. Despite this, 98.7% of the ocean volume can still be regarded as severely under-sampled and all we know of 62% of all marine species might be based on a single record. Assessments of completeness based on species richness estimator models confirm that many species remain to be sampled in most parts of the world’s oceans.

Our knowledge of species richness is more than 80% complete for only 1.5% of all marine regions. For over 50% of the ocean, however, no reliable estimate could be calculated. Even in highly-sampled regions such as Europe, there are still many spots with over 30% undiscovered or unreported species. When restricted to fish, completeness scores are higher globally, particularly in coastal areas, but not in open waters.

Understanding where species occur is a necessary first step towards identifying areas of high richness, endemicity (where species are limited to a particular region), or threat. It is therefore essential for effective conservation planning. For those areas with sufficient data, several biodiversity indices agree that South-East Asia, the South-West Pacific, the Gulf of Mexico and the Caribbean Sea are notably rich in biodiversity.

According to the Red List of the International Union for Conservation of Nature, 17% of marine species assessed are considered to be threatened with extinction and 20 marine species are extinct. Plotting the numbers in OBIS shows the areas of greatest importance to threatened species. These include the Caribbean and Atlantic Coast of the USA, waters between Eastern Africa and Madagascar, and the Indo-Pacific. However, considering how little we know of rare species, true rates of threat in marine species may be substantially higher, and spatially more distributed, than current estimates suggest. In addition, OBIS lists almost 500 species that have more than 10 observations but have not been recorded at all in the last 50 years.

Monitoring ocean biodiversity is expensive and requires highly skilled people. Very few marine regions or taxonomic groups have benefitted from long-term monitoring programs, hence our stocktaking remains far from complete. Publishing existing biodiversity data into open data repositories such as OBIS provides the most cost-effective means to address this shortfall. It is hoped that momentum in this direction can be maintained, alongside new efforts to discover and document the diversity and distribution of life in the ocean. In addition, it is recommend that focused efforts are needed to monitor the abundance of key species at all trophic levels, potentially as part of a global initiative such as the Global Ocean Observing System.

Hulbert Biodiversity index (ES50) based on OBIS

1-27

27-38

38-42

42-44

44-46

46-48

48-50

The ES50 represents the expected number of species in a random sample of 50 records. Biodiversity rich hot spots are located in South-East Asia, South-West Pacific, the Gulf of Mexico and the Caribbean Sea.

Distribution of threatened species in OBIS based on IUCN Red List categories (EN, CR, VU)

1-11

11-22

22-33

33-44

44-57

57-73

73-117

Areas of areas of greatest importance to species known to be threatened according the the Red list of IUCN and distribution data from OBIS. The highest number of species threatened to extinction are located in the Caribbean and Atlantic Coast of the USA, waters between Eastern Africa and Madagascar, and the Indo-Pacific (notably around Australia).