Elsevier

Biological Conservation

Volume 144, Issue 7, July 2011, Pages 1961-1971
Biological Conservation

Extinction risk assessment of the world’s seagrass species

https://doi.org/10.1016/j.biocon.2011.04.010Get rights and content

Abstract

Seagrasses, a functional group of marine flowering plants rooted in the world’s coastal oceans, support marine food webs and provide essential habitat for many coastal species, playing a critical role in the equilibrium of coastal ecosystems and human livelihoods. For the first time, the probability of extinction is determined for the world’s seagrass species under the Categories and Criteria of the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species. Several studies have indicated that seagrass habitat is declining worldwide. Our focus is to determine the risk of extinction for individual seagrass species, a 4-year process involving seagrass experts internationally, compilation of data on species’ status, populations, and distribution, and review of the biology and ecology of each of the world’s seagrass species. Ten seagrass species are at elevated risk of extinction (14% of all seagrass species), with three species qualifying as Endangered. Seagrass species loss and degradation of seagrass biodiversity will have serious repercussions for marine biodiversity and the human populations that depend upon the resources and ecosystem services that seagrasses provide.

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,

References (65)

  • F.T. Short et al.

    Global seagrass distribution and diversity: a bioregional model

    Journal of Experimental Marine Biology and Ecology

    (2007)
  • N.M. Smith et al.

    Canopy structure and pollination biology of the seagrasses Posidonia australis and P. Sinuosa (Posidoneaceae)

    Aquatic Botany

    (2002)
  • D.A. Willette et al.

    The distribution and expansion of the invasive seagrass Halophila stipulacea in Dominica, West Indies with a preliminary report from St. Lucia

    Aquatic Botany

    (2009)
  • S.L. Williams

    Introduced species in seagrass ecosystems: status and concerns

    Journal of Experimental Marine Biology and Ecology

    (2007)
  • K. Aioi et al.

    The seagrasses of Japan

  • S.O. Bandeira et al.

    The seagrasses of Mozambique and Southeastern Africa

  • M.W. Beck

    The identification, conservation, and management of estuarine and marine nurseries for fish and invertebrates

    BioScience

    (2001)
  • M. Björk et al.

    Managing Seagrasses for Resilience to Climate Change

    (2008)
  • D.M. Burdick et al.

    The effects of boat docks on eelgrass beds in coastal waters of Massachusetts

    Environmental Management

    (1999)
  • S.H.M. Butchart et al.

    Using Red List Indices to measure progress towards the 2010 target and beyond

    Philosophical Transactions of the Royal Society B

    (2005)
  • Campagna, C., Short, F.T., Polidoro, B.A., McManus, R., Collette, B., Pilcher, N.J., Sadovy, Y., Stuart, S., Carpenter,...
  • K.E. Carpenter

    One third of reef-building corals face elevated extinction risk from climate change and local impacts

    Science

    (2008)
  • R. Costanza

    The value of the world’s ecosystem services and natural capital

    Nature

    (1997)
  • W.F. de Boer

    Seagrass-sediment interactions, positive feedbacks and critical thresholds for occurrence. a review

    Hydrobiologia

    (2007)
  • P.C. de Grammont et al.

    An evaluation of threatened species categorization systems used on the American continent

    Conservation Biology

    (2006)
  • C. den Hartog

    New seagrasses from Pacific Central America

    Pacific Naturalist

    (1960)
  • W.C. Dennison et al.

    Assessing water quality with submersed aquatic vegetation

    BioScience

    (1993)
  • C.M. Duarte et al.

    Major role of marine vegetation on the oceanic carbon cycle

    Biogeosciences

    (2005)
  • C.M. Duarte et al.

    Seagrass ecosystems: their global status and prospects

  • N.C. Duke

    A world without mangroves

    Science

    (2007)
  • K.L. Heck et al.

    Effects of nutrient enrichment and large predator removal on seagrass nursery habitats: an experimental assessment

    Limnology and Oceanography

    (2000)
  • Cited by (608)

    View all citing articles on Scopus
    1

    Address: University of Glasgow, Division of Ecology and Evolutionary Biology, Glasgow G12 8QQ, Scotland.

    2

    Address: Adelphi University, Biology Department, Garden City, NY 11530, USA.

    3

    Address: Universiti Putra Malaysia Bintulu Sarawak Campus, Faculty of Agriculture and Food Sciences, Sarawak, Malaysia.

    View full text