Extinction risk assessment of the world’s seagrass species
Highlights
► First assessment of extinction probability of all seagrass species worldwide. ► Extinction assessments of seagrass based on IUCN Red List of Threatened Species criteria. ► Ten of seventy-two species of seagrass at elevated risk of extinction and three species endangered. ► Human impacts in the coastal zone are responsible for most threats to seagrass species. ► Seagrass biodiversity contributes to survival of many imperiled marine species and to ocean health.
Introduction
Seagrasses represent one of the richest and most important coastal habitats in the ocean, supporting a range of keystone and ecologically important marine species from all trophic levels (Orth et al., 2006). They are underwater flowering plants (in the class Monocotyledoneae) that form vast meadows, flowering and seeding under water, having evolved from terrestrial origins and re-entered the sea millions of years ago. Seagrasses alone create an important marine habitat, but are also a component of more complex ecosystems within marine coastal zones, contributing to the health of coral reefs and mangroves, salt marshes and oyster reefs (Dorenbosch et al., 2004, Duke et al., 2007, Heck et al., 2008, Unsworth et al., 2008). Seagrasses have high primary productivity and are a basis of many marine food webs through direct herbivory and the detrital cycle, both within the seagrass beds and as wrack which washes ashore (Hemminga and Duarte, 2000); they provide nutrients (N and P) and organic carbon to other parts of the oceans, including the deep sea, and contribute significantly to carbon sequestration (Suchanek et al., 1985, Duarte et al., 2005). The value of ecosystem services of seagrasses has been estimated at US$34,000 per hectare per year (Costanza et al., 1997, here recalculated to 2010 dollars), greater than many terrestrial and marine habitats. Seagrass habitats also support artisanal fisheries and the livelihoods of millions of people in coastal communities, largely in tropical regions (de la Torre-Castro and Ronnback, 2004, Björk et al., 2008, Unsworth and Cullen, 2010). Seagrass is the primary food of dugong, manatee, and some sea turtles, all of which are threatened themselves (Green and Short, 2003, IUCN, 2010).
The additional ecosystem services that seagrasses provide are many (Orth et al., 2006, Heck et al., 2008). The structure of the leaves acts as a filter, clearing the water of suspended sediments; leaves, roots and rhizomes take up and cycle nutrients. The complex root structure of seagrass beds secures and stabilizes sediments providing essential shoreline protection and reduction of coastal erosion from extreme storm events (Koch, 2001, Björk et al., 2008). Seagrass leaves form a three-dimensional habitat creating shelter for many other marine species. The leaves serve as a surface for attachment for a wide variety of small encrusting algae and animals. These in turn provide an important food source for larger seagrass-associated animals. Seagrasses are a nursery ground for juvenile and larval stages of many commercial, recreational and subsistence fish and shellfish (Watson et al., 1993, Beck et al., 2001, Heck et al., 2003, de la Torre-Castro and Ronnback, 2004).
Synoptic studies to date have examined the distribution, status and trends of seagrass habitat, and have clearly indicated that seagrasses are declining globally (Green and Short, 2003, Orth et al., 2006, Waycott et al., 2009). A synthesis of 215 published studies showed that seagrass habitat disappeared worldwide at a rate of 110 km2 per year between 1980 and 2006 (Waycott et al., 2009). However, the actual status of individual seagrass species themselves has received little attention. For the first time, the likelihood of extinction of the world’s 72 species of seagrass has been determined under the Categories and Criteria of the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species.
Section snippets
IUCN Red List assessment process
The IUCN Red List Categories and Criteria (IUCN, 2010) serve to assess and list extinction risk at the species level (Rodrigues et al., 2006, Mace et al., 2008) using pre-established universal criteria. The IUCN Red List Categories comprise eight levels of extinction risk: Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern and Data Deficient. A species qualifies for one of the three threatened categories (Critically Endangered,
Threatened and near threatened species
Nearly one quarter (15 species, 24%) of all seagrass species that could be assigned a Red List conservation status were threatened (Endangered or Vulnerable) or Near Threatened (Table 1). Specific details and documentation by seagrass species are provided in the IUCN Red List database (IUCN, 2010). Nine species could not be assigned a conservation status due to lack of information, and were designated Data Deficient. Three species were listed as Endangered (Table 2): Phyllospadix japonicus (
Conclusion
One in five seagrass species is now listed as Endangered, Vulnerable, or Near Threatened, having a heightened risk of extinction under the IUCN Red List Criteria. The threatened categories serve to set priority measures for biodiversity conservation. Many seagrass species need further investigation to better understand their risk of extinction as well as their distribution, life history, and recruitment rates, in particular those species in Near Threatened and Data Deficient categories.
Acknowledgements
We thank Tom Haas and the New Hampshire Charitable Foundation for their generous support of SeagrassNet and the IUCN Global Marine Species Assessment through Conservation International. We thank C. Short for editing, and the following scientists for their contributions: G. Abrusci, A. Calladine, G. di Carlo, K. Coates, A. Cuttelot, C. Duarte, J. Fourqurean, J. L. Gaeckle, C. den Hartog, H. Harwell, K. Heck, M. Hoffmann, A. R. Hughes, X. D. Lewis, S. McKenna, R. McManus, S. Olyarnik, S. Sarkis,
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- 1
Address: University of Glasgow, Division of Ecology and Evolutionary Biology, Glasgow G12 8QQ, Scotland.
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Address: Adelphi University, Biology Department, Garden City, NY 11530, USA.
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Address: Universiti Putra Malaysia Bintulu Sarawak Campus, Faculty of Agriculture and Food Sciences, Sarawak, Malaysia.