Coral reefs are often described as biodiversity hotspots. But just how much diversity is there on reefs? Scientists try to understand reef biodiversity through the estimation of extinction rates, discovery rates, and global biodiversity estimates. Today we are going to address extinction rates in marine life and on coral reefs on the path to understanding just how diverse coral reefs are.
Fewer than 20 marine species have been found to be recently extinct 1. That number sounds pretty good when you consider greater than 800 species have been recorded as recently extinct 2. However, these are only species recorded and evaluated by the International Union for Conservation of Nature (IUCN). Now consider this: fewer marine species are described, and evaluated for extinction risk by the IUCN. Recently, IUCN evaluations have increased in marine species- there are now >1,200 marine species listed as threatened by extinction, including Acropora palmata pictured below. Webb and Mindel tried to determine whether marine species were truly less at risk for extinction or merely less evaluated 2. Previous studies argued that many marine species were out of reach of human anthropological influences that were plaguing terrestrial species 3. However while large range and mobility makes evaluation difficult it does not confer the “extinction resistance” suggested. Scientists have discarded previous thought that fish (and others) could find part of the deep blue to escape to and repopulate.
Photo. Healthy Acropora palmata. Added to the IUCN Red list in 2008 as critically endangered. Populations declined due to contagious infection.Range includes Caribbean 5. Credit: Philip Renaud.
In marine research, progress has been restricted by the advancement of technology. Within the last century scientists have gained access to scuba technology and submersibles which have furthered the discovery of anything from entire reef systems to individual species that had never been seen or described. In some cases, the discovery of a new species and the description of a species are far separated events, delayed by insufficient equipment and opportunity. One such species is shown below- Prognathodes basabei was described over 20 years after it was initially seen 4. So while the extinction of known species must be considered, so too must the extinction of unknown species. Once considering the difference in how well studied systems are, the extinction risk of marine and terrestrial species is much closer. For both marine and non-marine, extinction risk appears greater when a greater amount of species have been assessed 2.
Photo. Prognathodes basabei. Named and documented in 2016 in deep water Hawaiian reef. Species originally seen over 20 years ago at >200 ft. Credit: Richard Pyle
With the increasing stress on marine environments and in particular the building stress on coral reefs, researchers expect increased extinction rates 3. As extinction rates surpass speciation rates biodiversity on the reef decreases. Estimating the actual rate of extinction remains a challenge in estimating the total biodiversity present on reefs. The race to find species before they disappear continues.
Check out the IUCN Red list to see what species are endangered.
1 Vermeij, G. (1993) Biogeography of Recently Extinct Marine Species: Implications for Conservation. Conservation Biology 7(2):391-397