Eelgrass, a species of valuable seagrass

Eelgrass –Zostera marina – is a seagrass. Seagrasses grow in shallow waters along coasts. Seagrass beds represent, some say, the third most valuable ecosystem, after estuaries and wetlands. Seagrasses also support a most endearing, but vulnerable mammal, the Dugong or Sea Cow (Dugong dugon).

Most people are aware of marine organisms conquering dry land in the course of evolution, with the fish going on land and developing legs out of fins the most popular image. Hundred million years ago, terrestrial grasses did it the other way around. From land they went back to the sea. This happened three more times, involving different species, resulting today in a number of marine flowering plants that are grouped together as seagrasses. ‘Seagrass’ is not a taxonomic term, but denotes an ecological group: plants that share the same characteristic of spending their whole life – including flowering, fruiting, and germination – under water. That sets them apart from all other marine plants.

Zostera marina
a marine flowering plant

Taxonomy of Z. marina

Zostera marina is such a seagrass. It is widespread, occurring along the shores of northern America, Europe and Asia, all in northern latitudes. Other Zostera species (there are sixteen) occur also in southern latitudes, and the genus Zostera is circumglobal, except for Latin America and on the western side of the African continent.

Zostera marina (illustration downloaded from

Because of its widespread distribution, the species is richly endowed with names. In English it is known as eelgrass, common eelgrass, narrow-leaved eelgrass, seawrack, or seagrass. Other vernacular names (listed in the World Register of Marine Species) include Обикновена морска трева (Bulgarian); groot zeegras, gewoon zeegras (Dutch); zostère (French); ზღვის ბალახი (Georgian); gemeines Seegras, echtes Seegras (German); smalålegras, ålegras (Norwegian); zostera morska (Polish); miliúrach, milfhéarach, miléarach chaol,miléarach (Scottish Gaelic); smal bandtång, bandtång (Swedish); gwellt-y-gamlas culddail (Welsh). A partially overlapping list in he Encyclopedia of Life records 33 common names.

Z. marina can be found in bays, lagoons, estuaries, and on beaches. Its leaves can grow up to over a meter. It anchors itself with a root system that spreads out, a rhizome. It reproduces sexually and produces fruit, called a nutlet. It can also reproduce vegetatively by sprouting from its rhizome. In this way it can form a meadow-like colony on the seabed, called a clonal colony or genet: a group of genetically identical individuals. Research (Borum, Jens (2004)) found for one such meadow that it was (genetically) 3,000 years old.

It looks like grass, it functions like grass

Z. marina lives up to its common names like seagrass, eelgrass, or the Dutch zeegras. Growing in the sea, it looks like grass with its long leaves. It is not a grass though. Seagrasses belong to four families in the order Alismatales, whereas grasses belong to one family, Poaceae, in the order Poales. Z. marina is however, like terrestrial grass, an important source of food for various species. Chief among them are birds, such as Brant Geese (Branta bernicla), Canada Geese (B. canadensis), Widgeon and Black Ducks (Anas spp.), and Redhead (Aythya americana). But Green Sea Turtles (Chelonia mydas) for instance, graze it too, as do some isopods (crustaceans that include for instance wood lice) and snails. Occasionally caterpillars of the grass moth Dolicharthria punctalis feed on it. The populations of Z. marina in Izembek Lagoon, Alaska, United States and Laguna Ojo de Liebre, Baja California, Mexico, may be the largest Z. marina systems in the world, and are also the primary staging grounds for migratory waterfowl. (Green EP and Short FT, 2003.)

The ecological and socioeconomic value is even greater because of the species that are associated with Z. marina systems and include for instance the Pacific Herring, (juvenile) Atlantic Cod, the Blue Mussel, the alga Entocladia perforans, the Isopod Idotea chelipes, and the sea urchin Paracentrotus lividus.

Humans eat lots of grasses: wheat, oats, rye, rice, corn or maize – these are all grasses. So it’s not a surprise that Z. marina as a grasslike plant was used for food too. People from the Seri tribe of the coast of Sonora, Mexico, ate the rhizomes and leaf-bases, or dried it into cakes for winter food. The plant played such a significant role apparently, that the Seri language has many words related to eelgrass and eelgrass-harvesting. And, as Wikipedia notes furthermore, the month of April is called xnoois ihaat iizax, which means the month when the Eelgrass seed is mature. Eelgrass was also an important source of food for natives of British Columbia and up to today still represents an important cultural value (Green EP and Short FT, 2003).

But it’s good for packing and stuffing too, and even protection from the sea …

Like wheat that produces straw – used for beds, animal fodder, floor cover and more – so Z. marina was used for more than food alone: as packing material (still practiced), as stuffing in mattresses and cushions, as housing insulation, and as thatching material for roofs (Denmark). Wikipedia gives as modern use the production of biomass energy. The Dutch protected themselves by constructing dykes along the former Zuiderzee (now IJssel Lake) from Eelgrass. It used to be a major source of income of residents of the island of Wieringen (from “Wier”, dutch for algae and by which they referred to Eelgrass). When the Zuiderzee was closed and became a freshwater lake (1932), Eelgrass largely disappeared, which was a great loss for the residents in that area.

How many seagrass species are there?

That depends on which species one considers a seagrass. True seagrasses are considered those that are purely marine, occurring only in sea water. That group has twelve genera and some 58 species according to Wikipedia. McCoy ED and Heck KL (1976) in Green EP and Short FT (2003) give a number of 59, but also caution that

… the actual number of seagrass species is a matter of debate, depending in part on their proximity to the marine environment and on the level of discrimination in physical taxonomy and genetics.

Zostera marina belongs to the true seagrasses. There are also plants that are like seagrasses, but occur in brackish water and inland, and some can also grow in marine surroundings.

Widgeon grass

Ruppia maritima or Widgeon grass is such a seagrass-like species, which belongs to the Ruppiaceae, one of three seagrass-like families. R. maritima is, like Z. marina, distributed worldwide. The plant has wide salinity tolerance and occurs in fresh water, brackish water, marine environments, and in hyper-saline conditions, such as land-locked freshwater lakes where salts have been accumulating. Some treat the plant also as a seagrass.

This species has, like Eelgrass, a wealth of common names. Aside from Widegeon grass, it is also known in English as Beaked Tasselweed. Examples of names in other langugages include a/o Snavelruppia (Dutch), småhavgras (Norwegian), Rupia morska (Polish), Scothóga mara (Scotch Gaelic), Hårnating (Swedish), and Tusw arfor (Welsh).


Taxonomy of Wdgeon grass (Ruppia maritima)
Ruppia maritima (Original book source: Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz 1885, Gera, Germany Permission granted to use under GFDL by Kurt Stueber. Source: Downloaded from Wikipedia 06 mar 2015.)

Widgeon grass is grazed by geese, ducks and swans, among them widgeons, ducks of the genus Anas, which explains its name. Green EP and Short FT (2003) mention R. maritima meadows in the Patos Lagoon near the city of Rio Grande, Rio Grande do Sul, covering an area of 120 km2. These meadows are complex habitats and sustain local fisheries

… providing substrate, refuge, nursery and feeding grounds. Associated drift algae can also be locally abundant alternative habitats. Pink shrimp (ca 2800 metric tons landed annually in the region) and the blue crab (ca 1400 tons), found foraging in the seagrass, are important local artisanal fishery resources. Whitemouth croaker (ca 7500 tons) and mullet (ca 2300 tons) also use the Ruppia beds as nursery or foraging grounds. The stout razorclam (Tagelus plebius) is another commercially important species. Predators such as the bottlenose dolphin are common (31-100 individuals within the lagoon system) in the Patos Lagoon and feed principally on whitemouthed croaker which is found in the Ruppia beds.

The Maryland Department of Natural Resources describes it as one of the more valuable waterfowl food sources, and that all parts of the plant have nutritional value. Fish also eat the plant, and they then help the plant to disperse since they transport its fruits inside their guts, as do the birds that eat it. The plant also releases its fruit directly in the water.

R. maritima is considered to have a high economic value in the USA since it supports many animal species that are important in commerce and sport. Wetland restoration often begins with the recovery and protection of R. maritima, and its ecological importance is further increased because of its wide range tolerance of salinity.

The Maryland Department of Natural Resources mentions that it is often found growing together with Z. marina. That may be so for that part of the USA, but Z. marina and R. maritima have otherwise quite distinct separate distributions:

Post 007-On Zostera marina and seagrass-Fig 05-Distribution of seagrass, Zostera marina, Ruppia maritima-1867 by 700
Range of Zostera marina and Ruppia maritima, and the overall distribution of true seagrasses. (Spatial data: International Union for Conservation of Nature (IUCN). In IUCN 2014. IUCN Red List of Threatened Species. Version 2014.3. Downloaded on 06 February 2015.) - Click to enlarge

Eelgrass in decline

The IUCN lists R. maritima as Least Concern, but notes that its taxonomy is confused, and therefore its actual range not certain. The IUCN lists Z. marina as Least Concern too, but also notes that there is large scale decline in part of its range due to wasting disease and pollutions threats, areas where it is stable, and areas where it has disappeared completely. Dredging and trawling, as well as harvesting of scallops and mussels, and aquaculture and coastal development in general, damage eelgrass beds as well, or cause it to disappear completely.

Does the decline matter?

Z. marina can form beds on its own, as well as mixed with other sea grasses or seagrass-like plants like R. maritima. In its range, Z. marina is often the dominant species in a sea grass bed. Seagrass beds consist of a variety of seagrass species variously distributed along the coasts of continents the world over. The map below shows the distribution of species richness of seagrass beds. It is clear that in the Asian tropics seagrass systems can be very rich with communities that have up to 15 different species.

Post 007-On Zostera marina and seagrass-Fig 06-Map of seagrass species richness distribution-WCMC-015-SeagrassRichness2003
Global distribution of seagrass species richness. (Created by UNEP World Conservation Monitoring Centre in collaboration with Dr Frederick T. Short (University of New Hampshire, USA). (UNEP-WCMC, Short FT (2003). Global seagrass species richness. In Supplement to: Green and Short (2003). Cambridge (UK): UNEP World Conservation Monitoring Centre. URL:

Seagrass systems

(Summarised from Green EP and Short FT, 2003.)
Coastal systems are crucial for the life of other species, many of which have a socioeconomic role in human societies. Seagrass communities are

… an important but under-rated resource for coastal people. Physically they protect coastlines from the erosive impact of waves and tides, chemically they play a key role in nutrient cycles for fisheries, and biologically they provide habitat for fish, shellfish and priority ecotourism icons like the dugong, manatee and green turtle.

Seagrasses form an integral part of highly complex ecosystems. Seagrasses themselves are significant primary producers: using sunlight as a source of energy, they produce lots of organic matter. This productivity is increased by other primary producers, such as algae. This plant material forms an important part of many food chains. The three-dimensional structure of seagrass systems provides a/o shelter and cover for other species, binds sediments and can influence currents. All this result in many species being associated with such systems. Some species cannot live in places other than seagrasses, other species rely on them for shorter or longer part of their life. Seagrass systems form therefore a prerequisite for a high level of biodiversity along the coast where they occur. For instance, in Florida, USA, 113 species of algal epiphytes (algae that live on other plants) were recorded associated with seagrass systems. Other numbers include 450 of algal epiphytes, 248 arthropods, 197 mollusks, 171 polychaetes, and 15 echinoderms in New South Wales, Australia. In Florida 100 species of fish were reported, and 30 species of crustaceans. Species that depend exclusively on seagrass systems range from epiphytic algae to manatees and dugong.

Fourteen functions and values of seagrass ecosystems are distinguished in the report, including primary production (which renders them a critical source of food for many species, and which is exported to adjacent ecosystems), nutrient and contaminant filtration (improving water quality), oxygen production (supporting water quality improvement), nutrient regeneration and recycling (efficient nutrient recycling supports overall ecosystem productivity), wave and energy dampening (reducing erosion and turbidity and increasing sedimentation), and carbon sequestration (important for reducing the increase of CO2 levels that fuels climate change).

Seagrass and algae beds are considered the third most valuable ecosystem globally. Waycott, Michelle et al. (2009) put the value of seagrass systems at 1.9 trillion USD per year in the form of nutrient cycling. The importance of seagrass systems for carbon management is highlighted too on various other places (e.g. here, here, and here). Green EP and Short FT (2003) put it in this perspective (literature references removed):

The role of the worlds oceans in removing carbon dioxide from the atmosphere is still being investigated and remains poorly understood. It appears that biological processes in the surface layers of the world’s oceans are one of the few mechanisms actively removing carbon dioxide from the global carbon cycle. Within these processes, seagrasses clearly have a minor role to play, although their high productivity gives them a disproportionate influence on primary productivity in the global oceans on a unit area basis, and they typically produce considerably more organic carbon than the seagrass ecosystem requires. Any removal of carbon either through binding of organic material into the sediments or export into the deep waters off the continental shelf represents effective removal of carbon dioxide from the ocean-atmosphere system which could play some role in the amelioration of climate change impacts.

So, yes, the decline does matter …

Many of the species thus associated with and depending on seagrass systems form important sources of food and income for human communities. Coastal communities benefit furthermore from these systems through protection from for instance coastal erosion and storm surges.

Where people used Zostera marina for food and other purposes and such is no longer the case, the direct impact of a decline in Z. marina is perhaps no longer significant. However, both Zostera marina and Ruppia maritima constitute sources of food for many species of birds and fish that are important to human populations, and, as the above describes, both species are an essential part of the system that they and other seagrasses form. The systems as a whole are of great importance, even where a single species might not be of direct importance for humans, and these systems cannot exist without the individual species of seagrass that form the backbone and basis of a complex, interdependent array of hundreds of different species of a large spectrum of taxonomic groups.

Sadly, seagrasses as habitats are in decline too. Waycott, Michelle et al. (2009), assessed 215 different studies and found

… that seagrasses have been disappearing at a rate of 110 km2 yr-1 since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879.

They note furthermore that rates of decline have accelerated from 0.9% per year before 1940 to 7% per year since 1990. They produced a geographic overview of gains and losses, but note that

Major gaps in information exist for West Africa, northeast South America, and the northwest Pacific area of the United States, where seagrasses are typically restricted in distribution. However, the largest data gap exists in the tropical Indo-Pacific region (from East Africa to Hawaii), where seagrasses are widespread and abundant. Seagrasses in this region perform vital ecosystem services for local human populations, support numerous elements of local economies (8), and are food for endangered species such as dugong and green turtle (22). Furthermore, this region has the highest number of seagrass species, including several endemic species (22).

Red dominates ….. (Source: Waycott, Michelle et al., 2009) - Click to enlarge

Dugong and managetees

Among the animals that rely to a greater or lesser degree on seagrass beds are a group of marine mammals, the manatees and Dugong. Of these, the Dugong or Dugong dugon is probably the most well known. Also known as sea cow, the Dugong occurs along the northern shores of the Australian continent, the shores of south and south-east Asia, the Indian subcontinent, the middle east, and the west side of the African continent, as well as northwards along the coast of Vietnam and Japan.

Taxonomy of the Dugong
The Dugong

The Dugong relies heavily on seagrasses. It uses it for food, and it finds shelter there. Manatees, Trichechusspp., belong to the same order of Sirenia. ForT. manatus seagrasses are an important staple. T. senegalensis relies more on herbaceous food and grasses, among which Ruppia spp. Living in the Amazon basin, T. inunguis does not have use for seagrasses.

The distribution of these four species, illustrated in the map below, is striking. They all four live in the tropics and subtropics, but their ranges do not overlap, except for where T. inunguis and T. manatus meet at the mouth of the Amazon.

Post 007-On Zostera marina and seagrass-Fig.10-Distribution of seagrass, manatees, dugong-1930 by 700
Map showing the distribution of Dugong dugon, Trichechus manatus, T. senegalensis, and T. inunguis. (Spatial data: International Union for Conservation of Nature (IUCN). IUCN 2014. IUCN Red List of Threatened Species. Version 2014.3. Downloaded 06 february 2015.) - Click to enlarge

Vulnerable species and seagrass destruction

(Summarised from Marsh, Helene et al., 2002)
The Dugong is listed by the IUCN as a vulnerable species. The animal is believed to be represented by relict populations: the populations were more numerous and more widespread in historical times. Populations are now separated by large areas where its numbers have been greatly reduced or where it no longer exists. Its range is now fragmented. Dugongs are seagrass specialists and need seagrass beds to survive and reproduce. Where seagrass beds are destroyed, the Dugong disappears. Other causes of the decline of Dugongs are accidental entangling in mesh nets and traps for fishing; hunting for meat, oil, and medicament; and being struck by boats. Destruction of seagrass beds can be extensive. Mining and trawling destroy seagrass directly. Dredging, land clearing and land reclamation cause disturbances: an increase of sedimentation and turbidity, which lead to degradation of seagrass extent, density and productivity through smothering and lack of light. Extreme weather events such as cyclones / typhoons and floods can lead to losses of hundreds of square kilometers of seagrass. Such losses are thought to be mostly caused by sedimentation increase and/or an increase in epiphytes due to an enrichment in nutrients. It is not always possible to separate natural and man-made causes of seagrass loss. Risks exist also in the runoff of herbicides from agricultural lands, specifically sugarcane production areas that areadjacent to seagrass beds.

The Smithsonian identifies runoff from land as the most important cause of seagrass disappearance. Both Zostera marina and Ruppia maritima are classified as Least Concern. Seagrass beds as a system are not classified in such a way, but clearly, the system is under pressure, even if species are still only Least Concerned. The decline of seagrass beds impacts directly on people’s livelihoods (all sorts of fisheries) and ultimately national economies.


Various initiatives try to address the decline. As noted above, information gaps exist on seagrass. One project that aims to help close those gaps is Seagrasswatch, a ‘global scientific, non-destructive, seagrass assessment and monitoring program’. Now active in 17 countries, with an additional nine participating countries, it aims to;

… raise awareness on the condition and trend of nearshore seagrass ecosystems and provide an early warning of major coastal environment changes. The Seagrass-Watch program has a simple philosophy of involving those who are concerned, and involves collaboration/partnerships between community, qualified scientists and the data users (environment management agencies).

Other initiatives work in the field on actual management. In Madagascar for instance are several projects that aim to halt the decline by establishing community managed areas along the coast. These projects also address the value that coastal systems (mangroves, seagrass) have for halting the increase of CO2
in the atmosphere, and therefore for minimising the rise of global temperatures and the impacts of subsequent climate change.

A project like the Blue Carbon Project focuses on offsetting emissions by conserving ocean vegetation. It describes ‘identifying effective, efficient and politically acceptable approaches to reduce the atmospheric concentration of CO2 as one of society’s most pressing goals’. It formulates as the blue carbon solution:

One of the most promising new ideas to reduce atmospheric CO2 and limit global climate change is to do so by conserving mangroves, seagrasses and salt marsh grasses. Such coastal vegetation, dubbed “blue carbon”, sequesters carbon far more effectively (up to 100 times faster) and more permanently than terrestrial forests. Carbon is stored in peat below coastal vegetation habitats as they accrete vertically. Because the sediment beneath these habitats is typically anoxic, organic carbon is not broken down and released by microbes. Coastal vegetation also continues to sequester carbon for thousands of years in contrast to forest, where soils can become carbon-saturated relatively quickly. Therefore, carbon offsets based on the protection and restoration of coastal vegetation could be far more cost effective than current approaches focused on trees. Furthermore, there would be enormous ad-on benefits to fisheries, tourism and in limiting coastal erosion from the conservation of blue carbon.

International agreements

The Dugong migrates. It can travel substantial distances and crosses international borders when doing so. The Convention on the Conservation of Migratory Species of Wild Animals or CMS “aims to conserve terrestrial, aquatic and avian migratory species throughout their range”. With 120 countries as parties as of May 2014 a number of mammals, birds, insects, fish and reptiles that migrate and cross international borders, are subject to specific conservation attention under the CMS. The Dugong is covered by this convention.

The CMS works a/o with Memoranda of Understanding. One such is the Memorandum of Understanding on the Conservation and Management of Dugongs and their Habitats throughout their Range or Dugong MoU. While seagrasses themselves are not subject of any specific international agreement, in the range of the Dugong they get special attention, since they are the primary habitat of Dugongs. One instrument of the Dugong MoU is the Conservation and Management Plan for the Dugong MoU. According to that plan, countries will work on activities such as identifying, assessing and evaluating threats to Dugong populations and develop measures to address these threats. Another activity is that countries will reduce to the greatest extent practicable the incidental capture and mortality of dugongs in the course of fishing activities. Countries will also identify and map areas of important Dugong habitat such as seagrass beds. The problem is of course that many countries that harbour Dugong and seagrasses often lack the necessary resources, be they financial, technical, institutional or human resource wise.

A new project of the Global Environment Facility (GEF) is about to start, the Enhancing The Conservation Effectiveness of Seagrass Ecosystems Supporting Globally Significant Populations of Dugongs Across the Indian and Pacific Ocean Basins project. This Dugong and Seagrass Conservation project(as the short title goes) is developed in the context of the Dugong MoU, will work through a number of national projects that focus on protection, policies, awareness, inventories and other topics. A project like this addresses also the resource issues mentioned above. This specific project also aims to achieve greater regional coordination and integration, something that species and systems that cross international borders and are marine clearly need. It aims also to help address the information gaps on seagrasses.

Will it be enough?

There are of course many more projects that work on Dugongs, manatees or seagrass systems or coastal environments in general. For the time being, losses appear greater then areas or populations that are preserved. The question can also be asked whether it is more important to conserve the Dugong or seagrass beds. I personally think that seagrasses as a system are more important to conserve (a mix of preserving and using them wisely), than Dugong. In the end, seagrass systems sustain coastal communities more than the Dugong as a single species. The Dugong, however, is more pattable than seagrasses can ever be. Dugongs are therefore seen as more effective conservation ambassadors and is indeed used as a vehicle as in the Dugong MoU of the CMS.

An important factor in conservation success will be whether countries will realize the socio-economic importance of seagrass beds. Lots of people adhere to the idea that conservation is a luxury, and nature protection should be paid for by a robust economy. In such thinking, harbour development, for instance, trumps seagrass (or coral, or mangrove) preservation, as trade is seen as a greater contributor to the economy than those ecosystems. Economic policies should however realize and acknowledge that the economy is based on healty natural systems. As long as policy and decision makers think the other way around, conservation and preservation will be in the losing seat.

And, as always, climate change is as yet the scary unpredictable factor, the full impact of which on coastal systems is not yet known. One factor is coastal depth. Seagrasses grow in shallow waters. The more seas rise, the more seagrass beds may come under great stress due to lack of light. Seagrass system survival may then depend on the speed with which they are capable (and allowed) to colonise new areas opened up by shorelines creeping inland to make up for areas that have grown too deep to sustain them. The threat of climate change and sea level rise is mentioned on several places in Green EP and Short FT (2003), but they also note that in some places, coral reefs may replace seagrasses. Whether that will happen, depends of course also on how well coral reefs will weather climate change effects. Factors such as temperature and acidity will affect both seagrass and coral species in various degrees, where corals are specifically sensitive to changes in acidity. The next question is then, if certain seagrass species are capable of successful adaptation, which of the species now associated with seagrass ecosystems will likewise be capable of adapting?



Borum, Jens, Carlos M Duarte, Tina M Greve, and Dorte Krause-Jensen. (2004). European Seagrasses: An Introduction to Monitoring and Management. M&MS Project.

Green EP, Short FT (2003). World atlas of seagrasses. Prepared by UNEP World Conservation Monitoring Centre. Berkeley (California, USA): University of California. 332 pp. URL:

Marsh, Helene, Helen Penrose, Carole Erose, and Joanna Hugues (2002). Dugong : Status Report and Action Plans for Countries and Territories. Nairobi, Kenya: United Nations Environment Programme, 2002.

McCoy ED and Heck KL (1976) Biogeography of corals, seagrasses and mangroves: An alternative to the center of origin concept. Sys Zool 25:201-210. In: Green EP, Short FT (2003). World atlas of seagrasses. Prepared by UNEP World Conservation Monitoring Centre. Berkeley (California, USA): University of California. 332 pp. URL:

Waycott, Michelle, Carlos M Duarte, Tim J B Carruthers, Robert J Orth, William C Dennison, Suzanne Olyarnik, Ainsley Calladine, and others. “Accelerating Loss of Seagrasses Across the Globe Threatens Coastal Ecosystems.” Proceedings of the National Academy of Sciences of the United States of America 106, no. 30 (2009): doi:10.1073/pnas.0905620106. Online accessible via

Online sources

Wikipedia entries:

IUCN Red List information:

Zostera marina:

Ruppia maritima:

Dugong dugon:

Trichechus inunguis:

Trichechus manatus:

Trichechus senegalensis:

Catalogue of Life:

Zostera marina:

Ruppia maritima:

Dugong dugon:

World Register of Marine Species (WoRMS):

Zostera marina:

Ruppia maritima:

Encyclopedia of Life:

Zostera marina:

Ruppia maritima:

Convention of Migratory Species of Wild Animals (CMS):

CMS general:

CMS Dugong information:

CMS Dugong MoU:


Dep. of Nat. Res. of Maryland, USA, on Ruppia maritima:

The GEF Dugong and Seagrass Conservation project:

The Oak – Its durability will be tested

The Oak, a symbol of old for strength and durability, stirring the imagination throughout the ages, beloved, and of economic importance, will not escape climate change. Its strength and durability will be severely tested, but its diversity may be its rescue
Drawing of Oak leavs and fruit: Walter Hood Fitch - Illustrations of the British Flora (1924) - Permission granted to use under GFDL by Kurt Stueber. Source: - Permission is granted to copy, distribute and/or modify this image under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”. Obtained via:

The Oak – Stirring the imagination

At times tall, with a lush foliage, at times crooked and gnarled especially on windswept places in for instance coastal areas, the Oak – Quercus robur – is one of Europe’s most well-known and beloved trees. Occurring throughout Europe, present also in localities of North Africa, and up to Central Asia and Asia Minor, the Oak has stirred people’s imagination throughout the ages. It can stand magnificently alone, or grow in forests, and can become 30 meters high. The tree is a symbol of strength and endurance, which is also reflected in its scientific name, robur, which means strenght or force. The Oak is also one of the trees often occurring in folk tales and fairy tales. As such, the Oak has played its role in countries’ and cultures’ fortunes. Many countries and regions have chosen the Oak as a national tree, including Serbia, Cyprus, England, Estonia, France, Germany, Moldova, Romania, Latvia, Lithuania, Poland, the United States, Wales, Galicia and Bulgaria. Oak leaves and branches were frequently used as symbols on coat of arms, coins and the like, but also as wreaths during festivities, and as decoration or ornamentation of houses or cars. The Oak featured also prominently in the German romantic period in paintings and novels. And it has it’s share of medicinal uses. The importance of the Oak for people is reflected in the word “oak”. As the Online Etymology Dictionary writes:

oak (n.)
Old English ac “oak tree,” from Proto-Germanic *aiks (cognates: Old Norse eik, Old Saxon and Old Frisian ek, Middle Dutch eike, Dutch eik, Old High German eih, German Eiche), of uncertain origin with no certain cognates outside Germanic.
The usual Indo-European base for “oak” (*deru-) has become Modern English tree (n.); likewise in Greek and Celtic words for “oak” are from the Indo-European root for “tree,” probably reflecting the importance of the oak to ancient Indo-Europeans. The Old Norse form was eik, but as there were no oaks in Iceland the word came to be used there for “tree” in general. Used in Biblical translations to render Hebrew elah (probably usually “terebinth tree”) and four other words.

Distribution map of Quercus robur. Published here for educational purposes with permission of EUFORGEN as stated on the their website

The Sacred Oak

Not only nations took to the Oak. Whole cultures regarded the Oak reverently. For the Celts the Oak was a sacred tree; the Druids of the Celts climbed into the trees and cut the mistletoe, and each acorn possessed the soul of a fairy. For Germanic people the Oak was a symbol of the god Donar, a tree representing thunder and lightning, probably because it appears to be more frequently hit by lightning than other trees. Explanations given for that include the Oak’s high amount of starch, which is a good conductor; it’s deep root system; and the fact that the Oak often grows where there are crossing underground water currents. The Greeks associated the Oak with Zeus, and the Romans associated the Oak with Jupiter and dedicated it to the god Pan: the tree brought fertility. But for both Greek and Romans, the Oak was also the sacred tree of the goddess Rhea, resp. Diana. The Dryads were in that Oak cult the nymphs of the Oak. Slavic people revered the god Percula by means of the Oak.

These cultural and religious beliefs have largely disappeared. One important actor in that process was Saint Bonifacius. As the biography by Willibald will have it, Bonifacius cut down the sacred Oak of Donar in Geismar, in present-day Germany, in 723, precisely to prove that the Oak did not have divine powers, or at least that the wrath of distressed gods would not follow. As a result, many germanic people converted to christianity. This event is regarded by many as a key point in the christinanization of north-western Europe. Perhaps it can also be regarded as the starting point of losing respect for the Oak and perhaps the forest in general. Europe (excluding the Russian Federation) is, after all, by now one of the poorest continents in terms of forest. (FAO. 2010.)

Witnesses of history

We are all witnesses of history, just as even shortlived creatures like mosquitos are, or even amoebae, be it that one single amoeba does not have much chance to live through a memorable event. Oaks though would be marvellous for that, as they are long-lived. This tree can live up to 500 years, and such a specimen, the Kroezeboom (website in Dutch), lives in the Netherlands (in Overijssel). But both Great Brittain (in Bowthorpe) and France (in Bretagne) have specimens thought be 1,000 years old, Denmark (in Jaegerspris) has one between 1,000 and 1,400 years old, and an Oak in Erle, Germany is estimated to be 1,500 years old. This Oak is probably the oldest Oak in Europe. Such old trees could tell a lot. But an oak shares with amoebae that we can’t hear from an Oak what happened in, say, 1753. Things Oaks, and other trees, can tell us about is for instance the climate, by examining the growth rings, unless such old trees have already hollowed out from the inside out. However, we would have to cut it down to do that, and that would be a shame. Better to rely on trees that have already died off and are, for instance, preserved in peat. Trees are therefore not only of value to us alive, but also when dead.

The Bowthorpe Oak. Note: The featured photo is of the thousand year old Bowthorpe Oak in Great Brittain. This image was taken from the Geograph project collection. See this photograph's page on the Geograph website for the photographer's contact details. The copyright on this image is owned by Robin Jones and is licensed for reuse under the Creative Commons Attribution-ShareAlike 2.0 license
The 1500 old year Oak et Erle, Germany Downloaded from, under creative common license. Photo by Pal Meir

What about using the Oak for when you’re hungry or sick ?

The Oak is not the best of food sources for us. The acorn contains quite some nourishment that would benefit us, but it is indigestable. On the other hand, ground acorns were used as a coffee substitute, and to make some kind of bread. Otherwise acorns were more suitable for feeding pigs. Even if not really edible, a good crop of acorns was seen as a sign that the harvest would be good.

Medicinally the Oak has much more to offer. I quote from Plants For A Future:

The oak tree has a long history of medicinal use. It is anti-inflammatory, antiseptic, astringent, decongestant, haemostatic and tonic. The bark is the part of the plant that is most commonly used, though other parts such as the galls, seeds and seed cups are also sometimes used. A decoction of the bark is useful in the treatment of chronic diarrhoea, dysentery, intermittent fevers, haemorrhages etc. Externally, it is used to bathe wounds, skin eruptions, sweaty feet, piles etc. It is also used as a vaginal douche for genital inflammations and discharge, and also as a wash for throat and mouth infections. The bark is harvested from branches 5 – 12 years old, and is dried for later use. Any galls produced on the tree are strongly astringent and can be used in the treatment of haemorrhages, chronic diarrhoea, dysentery etc. The plant is used in Bach flower remedies – the keywords for prescribing it are ‘Despondency’, ‘Despair, but never ceasing effort’. A homeopathic remedy is made from the bark. It is used in the treatment of disorders of the spleen and gall bladder. The German Commission E Monographs, a therapeutic guide to herbal medicine, approve Quercus robur Pedunculate Oak for coughs/bronchitis, diarrhoea, inflammation of mouth and pharynx, inflammation of the skin.

(Numbered references to sources removed to improve readibility.)

The Economy of the Oak

Throughout the ages, the Oak has contributed greatly to the economy of countries. Its wood has graced buildings and made great ships possible. Oak wood is strong and is very resistant to insect and fungal attack, as it has a high tannin contents. It is still used for furniture, floors, timber frame buildings, and veneer production. The tannins that make the Oak so suitable for furniture and buidlings, render barrels made from Oak very suitable for storing wines and sprits, as do other compounds from the wood. Oak wood imparts colour, taste and aroma, and does that even more so if charred. The use of Oak for barrels to produce alcoholic drinks continues until today, and oak wood chips are used for smoking a/o fish, meat and cheeses. It’s not only Q. robur that is used in these fashions. Japanese Oak is used in making drums, the bark of the Cork Oak is used to produce wine stoppers, and Northern Red Oak in North America is the most prized of the red oak group for lumber. I didn’t find an economic valuation of the Oak expressed in a monetary value. But the integration of the Oak in the economy can be imagined by the uses listed by the ecocrop database maintained by the FAO:

The Oak’s value

So, the Oak is important to us in spiritual sense, in medical sense, practically in construction, furniture, and for food and beverages, as well as, because of all the previous, in economic sense. What else does it do? The answer to that would be ecological. The relations that the Oak has as a species with lots of other species are numerous indeed. If we stretch the application of the term “ecological” to include the spiritual value it has for us – and surely stretching the term to that is more defensible than the use of the term “ecosystem” to describe related digital gadgets as in ‘the Apple ecosystem’ – then for that aspect alone the Oak is of tremendous value, given the role it has played, and to an extent continues to play, in defining the cultural – if not political – heritage of countries.

Using ‘ecological’ in the more conventional way, the Oak plays an outsized role. This tree can be considered the heart of the forest system:

A mature oak tree, standing a hundred feet tall, provides lodging, and often board as well, for more different kinds of animals than any other European tree. Thirty species of birds, forty-five different bugs and over two hundred species of moth have been collected from oaks. Each part of the tree has its own particular lodgers.

This phrase – quoted on several websites – stems from David Attenborough, one of the great, if not the greatest, popularizers of natural history in the old-fashioned sense: going out and looking at and observing in nature. (Attenborough, David. 1995.)

Among those birds are for instance the Eurasian Jay (Garrulus glandarius) who counts the acorn among it’s food sources. Birds such as the Great-spotted Woodpecker (Dendrocopos major), or the Eurasian Nuthatch (Sitta europaea) live from insects that live on and in the Oak’s bark. As for mammals, one would expect a mammal like the the European Red Squirrel (Sciurus vulgaris) to rely on the Oak too. However it does not: it cannot digest acorns, and relies on other fruits instead, notably the hazelnut, the fruit from the hazel tree (Corylus avellana). The Eastern Grey Squirrel (Sciurus carolinensis) from North America, introduced to Great Brittain and Italy, can more easily digest acorns, and this is considered one of the factors that allows this squirrel to outcompete the European Red Squirrel. Mice however, do eat acorns, when they are fallen on the ground. Birds like the Rook (Corvus frugilegus) and Wood Pigeon (Columba palumbus) also eat fallen acorns.

Numerous insect species live on the leaves, the buds and the bark, and in the acorns. Well-known are gall wasps. These wasps secrete chemicals which induce the Oak leaf to grow around the egg or larva and protect these. The best known is the Common Oak Gall Wasp (Cynips quercusfolii) wich produces spherical galls of about 2 cm on the underside of the Oak leaf. Some of these galls can be brightly colored. Other insects, such as the Green Oak Moth (Tortrix viridana) relies on Oak leaves when it is a larva. The larva eats the leaf, then rolls up in an Oak leaf. It transforms into a pupa, which in turn produces the adult moth.

Numerous fungi find a place on the Oak too, and on dead leaves that are fallen on the ground. An exampe is the Edible Beefsteak Fungus (Fistulina hepatica). The leaves on the grounds also feed many invertebrates. The Oak has symbiotic relationships too: associations between the Oak and another species that benefit both. An example is the Orange Oak Bolete (Leccinum quercinum). The fungus gets sugars from the Oak. The Oak is helped by nutrients that the fungus extracts from the soil.

The Encyclopedia of Life records forty-nine different species of gall-wesps, moths, and parasitic or half-parasitic fungi and plants. Aside from this, the Oak provides a place to grow for numerous lichens and mosses, and also higher plants, such as the Mistletoe (Viscum album). The Mistletoe is half-parasitic: it has both green leaves that provides it with energy, and it is rooted in the Oak to extract nutrients that it otherwise would get if it would be rooted in the soil.

And that’s when the Oak is still alive. When it is dead and decaying, many different fungi live from it and help break the wood down so that the tree eventually returns to the soil. It’s not just fungi that benefit from a decaying Oak tree. Such a tree provides roosting sites, for example for owls, and hibernation sites for bats.

To all this we should add the organisms that rely on the Oak indirectly, for instance mice that eat fallen acorns and fall prey to hunting
owls. The Oak then is at the heart of a complex web of relations of food and shelter.

Whereas the Oak provides so much for other organisms, the tree relies in turn for its continued existence on other organisms. Most of its fruit, the acorns, are eaten or rot away. It relies on jays or squirrels that bury acorns and then forget some, or die before they can eat them, to successfully sprout new Oaks. Of course, humans can do that too, so, is it necessary to ensure the presence of those animals that do seed dispersal? One study concludes that the replacement costs of one pair of jays for seeding or planting is 4,900 USD or 22,500 USD respectively. (Hougner, Cajsa, et al. 2006.) Not only the Oak is valuabe, the biodiversity it supports and which in turn helps the Oak, is that too.

Will the King of the forest be beaten by Climate Change?

That is a question to which the definite answer is not yet found, and we will probably only find out definitely in the course of time with the ongoing pressures of climate change growing more intense. That said, research has been undertaken to investigate this, but of course, it is very difficult to give definite answers, since that would require laboratory and/or field experiments to be done. While laboratory experiments can be conceived with planting acorns and observing young Oaks under controlled conditions, given the longevity of the tree that is expressed in hundreds of years, it is virtually impossible to say something sensible on basis of direct observations and predict in this way how Oaks will react and what one can best do. In fact, one study concludes reports age-dependent reactions to changes in climate: young trees react differently than older trees. (Rozas, Vicente. 2005.)

This research as so many others of this kind, relies on studying tree-ring growth patterns in relation to various environmental conditions that change over time, specifically climatic conditions. Other studies look at genetics and historical changes (measured in thousands of years). One such study emphasizes the importance of diversity in existing Oak populations in the reaction to climate change. The study “… predicts that substantial evolutionary shifts can be expected in a limited number of generations due to the high level of genetic diversity in oaks, and that gene flow will be an important driver of adaptive evolution.” (Kremer, Antoine. 2010.)
The study continues with the advice to enhance the adaptive potential of local populations by mixing local stocks with seeds or seedlings from other sources during regeneration.

Biodiversity and climate change

In a previous post I referred to the inclusion of genetic diversity in the concept of biodiversity. Studies like the above emphasize how important diversity is to increase the chances of survival for species in the face of climate change. The study referenced above refers to the genetic diversity that exists in Oak populations. The number of subspecies for Q. robur listed in the Catalogue of Life suggests that the Oak is indeed quite diverse. The species is not even agreed upon by everyone.

One article observes that a number of different Oak species are distinguished which by others are assigned to eitehr Q. robur or Q. petraea. It then continues with the observation that the distinction between Q. robur and Q. petraea as species is questionable, since they are interfertile, and these species are by some regarded as ecotypes or subspecies within one composite species of Q. robur. (Gömöry, Dušan, et al. 2001.)

Based on the apparent diversity of the mighty Oak – Quercus robur – perhaps we can be optimistic that its variability that makes it hard to pin down as a species, lets it survive the challenges of climate change.


In the text above, many sources are not directly indicated to improve readibility. Below follows a list of various sources from which I took information.

Referenced documentation

Attenborough, David. The Private Life of Plants: A Natural History of Plant Behaviour. 1995. London, BBC books.

Hougner, Cajsa, Johan Colding, and Tore Söderqvist.Economic Valuation of a Seed Dispersal Service in the Stockholm National Urban Park, Sweden. Ecological Economics 59, no. 3 (2006): 364-374.

FAO. Global Forest Resources Assessment 2010 : Main Report. 2010. Rome: Food and Agriculture Organization of the United Nations.

Gömöry, Dušan, Igor Yakovlev, Petar Zhelev, Jarmila Jedináková, and Ladislav Paule. Genetic Differentiation of Oak Populations Within the Quercus Robur/Quercus Petraea Complex in Central and Eastern Europe. Heredity 86, no. 5 (2001): 557-563.

Kremer, Antoine. Evolutionary Responses of European Oaks to Climate Change. Ir. For 67 (2010): 53-65.

Rozas, Vicente. Dendrochronology of Pedunculate Oak (Quercus Robur L.) in An Old-growth Pollarded Woodland in Northern Spain: Tree-ring Growth Responses to Climate. Annals of forest Science 62, no. 3 (2005): 209-218.