{"id":7848,"date":"2018-03-08T10:19:09","date_gmt":"2018-03-08T09:19:09","guid":{"rendered":"https:\/\/game-csic.com?p=7848\/"},"modified":"2018-03-09T11:44:44","modified_gmt":"2018-03-09T10:44:44","slug":"descubriendo-la-posidonia-oceanica","status":"publish","type":"post","link":"https:\/\/game-csic.com\/en\/descubriendo-la-posidonia-oceanica\/","title":{"rendered":"Discovering Posidonia oceanica"},"content":{"rendered":"
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D\u00edaz-Almela,<\/a>Elena. Post-Doc at the Centre for Advanced Studies of Blanes (CEAB-CSIC) in the Aquatic Macrophyte Ecology group (GAME)<\/h4>\n\n\t\t<\/div>\n\t<\/div>\n
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\n\t\t\t\n\t\t<\/div>\n\t<\/div>\nPosidonia oceanica<\/em> It is one of the largest marine plants on the planet. It is perennial, with a woody rhizome that ends in a cluster of green, strap-shaped leaves with smooth edges and parallel veins. These can exceed one metre in length. (Fig.1)<\/p>\n
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Fig.1. Floor plan of Posidonia oceanica<\/em>, showing a horizontal stem, two vertical ones, the roots, and an inflorescence. Also shown is a detail of the hermaphrodite flower with empty anthers, and another detail of the ripe fruit, called the \"sea olive\". Author: Jordi Corbera, extracted from the book \"Seagrass Meadows and Marine Forests of Andalusia\".<\/figcaption><\/figure>\n

The petiole and the leaf blade are flattened. The younger leaves are located in the centre of the shoot, as that is the position of the apical meristem, which, when dividing, produces leaves alternately to the left and right.<\/p>\n

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Fig. 2. Detail of a Posidonia apex showing the scales that cover the rhizome, which are formed from the hardened petioles of the leaves. Author: Carlos M. Duarte<\/figcaption><\/figure>\n

As the plant produces a permanent mark (node) at the junction of the rhizome with the base of each leaf, this allows the reconstruction of the plant's past growth, similar to the growth rings of trees (Fig. 3).<\/p>\n

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Fig.3. Nodes or insertion marks of the leaves on the bare rhizome of a vertical bundle of Posidonia oceanica. Internode No. 1 is the most recent, and No. 9 the oldest. Author: Elena D\u00edaz Almela.<\/figcaption><\/figure>\n

Posidonia<\/em> It has clonal growth, where the repeating unit is the clump or shoot, consisting of a clump of leaves, a rhizome, and at least one root.<\/p>\n

There are horizontal growth shoots, also called apices, which colonise the substrate, dividing several times a year, and growing annually between 1 and 10 cm. Their internodes can measure more than 1 centimetre.<\/p>\n

But most shoots grow vertically. Seeking the light, they avoid being buried. Vertical shoots, with internodes of 1 or 2 millimetres (Fig. 2), usually do not grow more than 1 cm per year, except when reacting to intense burial, in which case they can grow up to 4 cm per year.<\/p>\n

The plant compensates for its very slow growth with incredibly long-lived shoots, which can exceed 60 years. This, combined with the size of some clones, suggests that each plant as a whole can live for centuries or millennia, and some estimate between tens and hundreds of thousands of years, making it the longest-lived known species on the planet.<\/p>\n

The accumulation of sediments and the slow vertical growth of the plant cause the meadow of Posidonia<\/em> It rises over millennia, forming a kind of reef called a \"mata\" (Fig. 4), with very interesting environmental properties, as we shall see.<\/p>\n

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Fig. 4. Formation of the Posidonia meadow through the combination of sedimentation and vertical growth of the plant. Extracted from the educational guide \"Posidonia in your hands\".<\/figcaption><\/figure>\n

The shoots remain interconnected by the rhizome over several metres, exchanging nutrients and sugars. When uprooted, they have some chance of dispersing, taking root, and starting a new plant, colonising other locations (Fig. 4).<\/p>\n

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Fig. 5. Vegetative fragment of Posidonia with 2 horizontal shoots, which has naturally rooted on the seabed. Author: Elena D\u00edaz Almela.<\/figcaption><\/figure>\n

Although Posidonia oceanica<\/em> It reproduces mainly vegetatively, but it is also capable of sexual reproduction. Some years, in autumn, the meadows bloom. The shoots produce green inflorescences, composed of spikelets with hermaphrodite flowers (with ovary and stamens) and male flowers (stamens only, Fig. 5).<\/p>\n

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Fig. 6. Inflorescence of Posidonia oceanica with the central spikelet fully open. One flower is releasing pollen. Author: Roland Graille.<\/figcaption><\/figure>\n

The pollen of marine plants is adapted to water and is dispersed by currents. The pollen of Posidonia<\/em> It is elongated and flexible, and it sticks to the female stigma as soon as it comes into contact with it (Fig. 7).<\/p>\n

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Fig. 7. Filiform pollen grains of Posidonia oceanica adhered to the stigma of a hermaphrodite flower. Author: Elena D\u00edaz Almela.<\/figcaption><\/figure>\n

The fruit of Posidonia oceanica<\/em> It has a single seed and resembles an olive. That is why they are called \"sea olives\" (Fig. 8.a and 8.b).<\/p>\n

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Fig. 8. a) Sea olive, still attached to the plant, peeking out among the leaves of Posidonia. Author: Elena D\u00edaz Almela.<\/figcaption><\/figure>\n
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Fig. 8 .b) Open sea olive, showing the mature seed. Author: Elena D\u00edaz Almela. Upon detaching from the infructescence, the fruit floats for hours or days, adrift (Fig. 9).<\/figcaption><\/figure>\n
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Fig. 9. Exceptional accumulation of drifting sea olives in June 2003 in the Balearic Islands. Author: Elvira \u00c1lvarez<\/figcaption><\/figure>\n

When the seed is mature and germinated, the fruit splits open, dropping it to the ground. It takes root and grows if the conditions are suitable (Fig. 10).<\/p>\n

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Fig. 10. Posidonia seed on the seabed. Author: Elena D\u00edaz Almela.<\/figcaption><\/figure>\n<\/div>","protected":false},"excerpt":{"rendered":"

Posidonia oceanica is one of the largest marine plants on the planet. It is perennial, with a woody rhizome that ends in a cluster of green, ribbon-like leaves with smooth edges and parallel veins. These can exceed one metre in length. (Fig.1) The petiole and the leaf blade are flattened. The leaves more\u2026<\/p>","protected":false},"author":2,"featured_media":7864,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[105],"tags":[],"post_series":[],"class_list":["post-7848","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog","entry","has-media"],"_links":{"self":[{"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/posts\/7848","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/comments?post=7848"}],"version-history":[{"count":10,"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/posts\/7848\/revisions"}],"predecessor-version":[{"id":7878,"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/posts\/7848\/revisions\/7878"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/media\/7864"}],"wp:attachment":[{"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/media?parent=7848"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/categories?post=7848"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/tags?post=7848"},{"taxonomy":"post_series","embeddable":true,"href":"https:\/\/game-csic.com\/en\/wp-json\/wp\/v2\/post_series?post=7848"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}