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The World's Seagrass Species: On the Road to Potential Extinction?
Short, F.T., Polidoro, B., Livingstone, S.R., Carpenter, K.E., Bandeira, S., Bujang, J.S., Calumpong, H.P., Carruthers, T.J.B., Coles, R.G., Dennison, W.C., Erftemeijer, P.L.A., Fortes, M.D., Freeman, A.S., Jagtap, T.G., Kamal, A.H.M., Kendrick, G.A., Kenworthy, W.J., La Nafie, Y.A., Nasution, I.M., Orth, R.J., Prathep, A., Sanciangco, J.C., van Tussenbroek, B., Vergara, S.G., Waycott, M. and Zieman, J.C. 2011. Extinction risk assessment of the world's seagrass species. Biological Conservation 144: 1961-1971.

The authors write that "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." In addition, they say that they 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," citing the work of Dorenbosch et al. (2004), Duke et al. (2007), Heck et al. (2008) and Unsworth et al. (2008).

What was done
"For the first time," in the words of Short et al., "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," which effort they describe as "a four-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."

What was learned
The twenty-six seagrass experts -- hailing from eleven different countries -- determined that ten seagrass species (comprising 14% of all seagrass species) are at elevated risk of extinction, with three other species qualifying as Endangered. But what is the cause of the problem? Is it CO2-induced global warming and ocean acidification? Not much is said about these two villains; but the international team of experts name a number of others, including suspended sediments and siltation (Dennison et al., 1993; de Boer, 2007), coastal construction, land reclamation, shoreline hardening, and dredging (Erftemeijer and Lewis, 2006), damaging fisheries practices such as trawling and aquaculture (Pergent-Martini et al., 2006), mechanical damage from boats, boat moorings and docks (Burdick and Short, 1999; Kenworthy et al., 2002), introduced species (Williams, 2007) that compete for space and resources (Heck et al., 2000) and certain diseases (Rasmussen, 1997). Thus, they conclude that "the most common threat to seagrasses is human activity," particularly that of the type which is responsible for most of the threats listed above.

What it means
Short et al. state that these "localized impacts to seagrass species will decrease their survival capacity in the face of global threats," such as "the effects of global climate change." Thus, it is only logical to conclude that if these localized impacts of human activity could somehow be dramatically reduced, there would be a correspondingly dramatic improvement in the ability of seagrasses to withstand the threats of anthropogenic-induced global warming and ocean acidification.

Burdick, D.M. and Short, F.T. 1999. The effects of boat docks on eelgrass beds in coastal waters of Massachusetts. Environmental Management 23: 231-240.

de Boer, W.F. 2007. Seagrass-sediment interactions, positive feedbacks and critical thresholds for occurrence: a review. Hydrobiologia 591: 5-24.

Dennison, W.C., Orth, R.J., Moore, K.A., Stevenson, J.C., Carter, V., Kollar, S., Bergstrom, P.W. and Batiuk, R.A. 1993. Assessing water quality with submersed aquatic vegetation. BioScience 43: 86-94.

Dorenbosch, M., van Riel, M.C., Nagelkerken, I. and van der Velde, G. 2004. The relationship of reef fish densities to the proximity of mangrove and seagrass nurseries. Estuarine and Coastal Shelf Science 60: 37-48.

Duke, N.C., Meynecke, J.-O., Dittmann, S., Ellison, A.M., Anger, K., Berger, U., Cannicci, S., Diele, K., Ewel, K.C., Field, C.D., Koedam, N., Lee, S.Y., Marchand, C., Nordhaus, I., Dahdouh-Guebas, F. 2007. A world without mangroves. Science 317: 41-42.

Erftemeijer, P.L.A. and Lewis, R.R.R. 2006. Environmental impacts of dredging on seagrasses: a review. Marine Pollution Bulletin 52: 1553-1572.

Heck, K.L., Carruthers, T.J., Duarte, C.M., Hughes, A.R., Kendrick, G.A., Orth, R.J. and Williams, S.L. 2008. Trophic transfers from seagrass meadows subsidize diverse marine and terrestrial consumers. Ecosystems 11: 1198-1210.

Heck, K.L., Pennock, J., Valentine, J., Coen, L. and Sklenar, S.S. 2000. Effects of nutrient enrichment and large predator removal on seagrass nursery habitats: an experimental assessment. Limnology and Oceanography 45: 1041-1057.

Kenworthy, W.J., Fonseca, M.S., Whitfield, P.E. and Hammerstrom, K.K. 2002. Analysis of seagrass recovery in experimental excavations and propeller-scar disturbances in the Florida Keys National Marine Sanctuary. Journal of Coastal Research 37: 75-85.

Pergent-Martini, C., Boudouresque, C.F., Pasqualini, V. and Pergent, G. 2006. Impact of fish farming facilities on Posidonia oceanica meadows: a review. Marine Ecology 27: 310-319.

Rasmussen, E. 1977. The wasting disease of eelgrass (Zostera marina) and its effects on environmental factors and fauna. In: McRoy, C.P. and Helfferich, C. (Eds.). Seagrass Ecosystems. Marcel Dekker Inc., New York, New York, USA, pp. 1-51.

Unsworth, R.K.F., DeLeon, P.S., Garrard, S.L., Jompa, J., Smith, D.J. and Bell, J.J. 2008. High connectivity of Indo-Pacific seagrass fish assemblages with mangrove and coral reef habitats. Marine Ecology Progress Series 353: 213-224.

Williams, S.L. 2007. Introduced species in seagrass ecosystems: status and concerns. Journal of Experimental Marine Biology and Ecology 350: 89-110.

Reviewed 14 September 2011