sábado, 25 de febrero de 2012


By Hugo Guntram von Österreich und von Toskana*
February 22, 2012

The oldest living organism on planet Earth is a seagrass growing on the floor of the Mediterranean Sea. This marine angiosperm is known scientifically as Posidonia oceanica (Posidoniaceae) (Fig. 1). It is a slow-growing plant that reproduces asexually, covering hundreds of kilometers. It also produces flowers and fruits called sea olives.

Figure 1. Photograph of meadows of Posidonia oceanica. Pictures (a) illustrates the individual shoots, (b) shows the largest clones (15 km). Source: PLos ONE. Photograph by M. San Félix. doi:10.1371/journal.pone.0030454.g002

A group of scientists from France, Portugal, Spain and Australia have studied the genetics, demography and model-based calculations of Posidonia oceanica on 1544 sampling units from a total of 40 locations across the Mediterranean Sea. 

Their findings indicate that the clones of this Mediterranean seagrass species are most likely at least 100,000 years old. This age estimate is far higher than the oldest record held by the Tasmanian plant (Lomatia tasmanica, Proteaceae), a clone of an endangered shrub found in south-western Tasmania and considered to be at least 43,600 yars old.

Seagrasses form vast meadows and are very important in marine ecosystems. These aquatic plants are keystone species in marine habitats. They sustain an abundant biodiversity. A great variety of animal and plant species find shelter and food in a seagrass bed. Moreover, seagrass meadows are important barriers that protect the beach against seawave erosion  (Video 1).

                                               Video 1. Seagrass beds (Posidonia oceanica).

Unfortunately, seagrasses are experiencing a worldwide decline (Video 2) due to water contamination and urban development along the shores. Fishing with towing gear, although illegal but done nevertheless, has a negative impact on these seagrass meadows as well.

                                                        Video 2. Seagrass global trends.

As always, man (Homo sapiens) is at the epicenter of the destruction, be it directly or indirectly, of these plants that have survive for thousands of years. The seagrasses may no longer be able to adapt to the global climate change and the pollution caused by man´s activities.

In the Mediterranean Sea, man by accident introduced the alga Caulerpa taxifolia in 1984. This tropical alga is having a devastating impact on the Posidonia oceanica ecosystem. When Caulerpa taxifolia invades the seagrass meadows the biodiversity is reduced. This alga produces toxins which make it unpalatable to the native fauna. So far the coasts of France and Italy are the most affected by this invasive alga.

But despite the bleak prospects for these important marine plants, not all hope is lost. There are people trying to reverse the situation.

Considering the importance ot seagrass meadows for the marine ecosystems, The Nature Conservancy, the Seaside Heritage Seagrass Community Program, scientists from the University of Virginia and the Virginia Institute of Marine Science and hundreds of volunteers have been working hard in a seagrass restoration project in Virginia´s coastal bays in the United States . It is considered the largest seagrass project in the world (Video 3).

                                                    Video 3. Virginia seagrass restoration.

The project with eelgrass (Zostera marina), another species of marine angiosperm, has proven successful (Video 4). Researchers at the University of Virginia and the Virginia Institute of Marine Science and volunteers have been seeding (over 26 million seeds) barren stretches of bay bottom since 1998 and monitoring the growth and spreading of the eelgrass. Now there are 17 square kilometers carpeted with healthy seagrass meadows.

                                     Video 4. World´s largest successful seagrass restoration project. 

We´re changing the environment of these bays back to what it was when it was  a very healthy thriving system 80 years ago, so it´s an exciting change”, expressed Dr. Karen McGlathery, one of the scientist involved in the project.

The new meadows of restored eelgrass are already providing a habitat for a variety of marine species, including fish, crabs, shrimps, scallops and other mollusks. 


Arnaud-Haond S, Duarte CM, Díaz-Almela E, Marbà N, Sintes T & Serrão (2012). Implications of Extreme Life Span in Clonal Organisms: Millenary Clones in Meadows of the Threatened Seagrass Posidonia oceanica. Plos ONE, 7 (2): 1-10.

Jensen HS, McGlathery KJ, Marino R & Howarth RW (1998). Forms and availability of sediment phosphorus in carbonate sand of Bermuda seagrass beds. Limnol. Oceanogr., 43 (5): 799-810.

Long MH, McGlathery KJ, Zieman JC & Berg P (2008). The role of organic acid exudates in liberating phosphorus from seagrass-vegetated carbonate sediments. Limnol. Oceanogr., 53 (6): 2616-2626.

Lynch AJJ, Barnes RW, Cambecèdes J, & Vaiilancourt RE (1998). Genetic Evidence that Lomatia tasmanica (Proteaceae) Is an Ancient Clone. Austr. J. Bot., 46: 25-33.

Orth R, Moore K Neikirk B, Marion S & Wilcox D (2009). Restoration of Seagrasses in Virginia Seaside Bays, Year 6 (Oct. 1, 2007, to Dec. 31, 2008) and Summary. FY 2007 Task 10.01. Final Report. Virginia Coastal Zone Management Program, 28 p.

Seaside Heritage Seagrass Community Restoration Program (2011). Volunteers needed  fot the Largest Seagrass Restoration in the World. South Bay off Oyster, Virginia. 1 p. (Poster)

Virginia Seaside Heritage Program (2010). Accomplishments Report 2002-2009. Virginia Coastal Zone Management Program, 13 p.

*Hugo Guntram von Österreich und von Toskana (PhD, DVM) is member of the Union of Concerned Scientists (UCS) of the United States of America.

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