According to a recent paper to be published in the journal Proceedings of the Royal Society B: Biological Sciences, scientists have described four out of five of the world's marine fishes.
The study by Camilo Mora, Derek Tittensor and Ransom Myers of Dalhousie University used about 2.1 million records for marine fishes in the Ocean Biogeographical Information System (OBIS) as a basis for modelling the completeness of taxonomic inventories across a range of spatial resolutions (3"36) on a global scale.
The authors found that based on the OBIS data, there are 15716 marine fish species currently described, and that about 4084 species (21%) await description.
Most undescribed fish in deeper waterThe authors state that the proportion of species remaining to be described is greater in the open and deep ocean (i.e. bathypelagic, bathydemersal and demersal habitats) and smaller in shallower and coastal areas (i.e. reef and benthopelagic habitats).
These variations in the completeness of inventories among habitats probably reflect variations in the accessibility and facilities available to sample those habitats.
For instance, the bathydemersal region, one of the most inaccessible and deepest marine environments, has the lowest census completeness. In contrast, shallower reef habitats are the most complete of all inventoried habitats...Pelagic fish species have also been well inventoried...which has previously been attributed to the large body size of most species in this environment and their ease of capture...
The completeness of the taxonomic censuses to be highly scale dependent: at broad 36 resolution, taxonomic inventories in 24% of the world's oceans are more than 80% complete.
This contrasts with only 1.8% for an identical level of completeness at a finer 3 resolution.
SamplingThe authors also found an uneven distribution of incompleteness in space, with the coastal regions of a few developed countries or territories more completely sampled than the high seas, and tropical regions having the lowest completeness of taxonomic inventories despite their diversity.
According to the authors, even though significant efforts have been made in the taxonomy and in indexing the biology and distribution of marine fishes, ...our results indicate that these enormous efforts fall short for describing the worldwide diversity and distribution of marine fishes with reasonable accuracy, particularly at smaller spatial scales.
Fishes are one of the most intensively studied marine taxonomic groups, suggesting that the situation may well be worse among other marine taxa. This scarcity of data occurs nearly 250 years since species first started to be described according to the Linnaean system of classification.
Given that current projections on biodiversity change and the extent of human threats predict major biodiversity losses within the next half of a century...many species may be lost without us ever knowing they existed.
The precarious nature of existing data also highlights potential flaws in the accuracy of existing patterns.
Our spurious knowledge about the current distribution of marine fish species also raises concern upon the effectiveness of existing conservation efforts aimed at protecting biodiversity and upon the future quantification of human-driven extinctions.
With biodiversity increasingly being threatened by human-related activities, the uncertainty arising from incomplete data is a problem needing to be rapidly addressed...
For more information, see the paper: Mora, C, DP Tittensor and RA Myers (2007) The completeness of taxonomic inventories for describing the global diversity and distribution of marine fishes. Proceedings of the Royal Society B: Biological Sciences. doi:10.1098/rspb.2007.1315