Seaweed

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Seaweed
Kelp grass (Cymodocea nodosa)

Kelp grass ( Cymodocea nodosa )

Systematics
Class : Bedecktsamer (Magnoliopsida)
Monocots
Order : Frog-spoon-like (Alismatales)
Family : Cymodoceaceae
Genre : Cymodocea
Type : Seaweed
Scientific name
Cymodocea nodosa
( Ucria ) Ash.

The kelp grass ( Cymodocea nodosa ) is a seaweed from the genus Cymodocea in the plant family Cymodoceaceae .

Seaweed grass is an important habitat for seahorses .

Common names

English-language common names are Lesser Neptune Grass or Seahorse Grass .

Description and ecology

Vegetative characteristics

The seaweed grass is a perennial herbaceous plant that grows on the seabed ( submerged ) . The creeping shoot axis (a rhizome ) lies within the soil substrate, normally only the grass-like leaves are freely visible . These are in bundles of two to five. They are divided into a short leaf sheath enveloping the shoot, a short ligule at the transition to the blade and a long, free, ribbon-shaped leaf blade. This is between 10 and 45 centimeters long and 2 to 4 millimeters wide and is similar to that of the common seagrass Zostera marina . Each has seven to nine parallel leaf veins , their tips are blunt with very small two or three-pointed teeth. Discarded leaves leave behind circular leaf scars on the vertical shoot made up of numerous nodes with very short internodes. The very short above-ground shoot forms only the tip of a short (vertical) rhizome that grows vertically upwards and extends from long, horizontally (horizontally) running monopodial white to pink-colored creeping shoots with about 1 to 6 centimeters long internodes ; at the node sits next to these short vertical sections of the rhizome, each with only one strongly branched root that can be up to 35 centimeters long. The creeping, horizontal rhizomes achieve growth rates of several meters per year, which makes the species an effective pioneer plant that can easily conquer and colonize previously free habitats.

Generative characteristics

Cymodocea nodosa rarely flowers. It then blooms between May and August. Cymodocea nodosa is dioeciously separated ( dioecious ); male and female flowers sit individually on different plant specimens. The inconspicuous flowers, without a flower cover, do not differ in structure from those of other species of the genus Cymodocea , they are pollinated by currents of water. The male flower is stalked ansitz with two ends at the same height anthers . The female is sitting or very short stalks with two free ovary , each with a short style , the long two scars is divided.

Two approximately lenticular fruits are formed in each case. The fruit is laterally compressed and semicircular in outline, with three parallel ribs and a short, terminal beak. It is 8 millimeters long and 6 millimeters wide with a thickness of 1.5 millimeters.

Of Cymodocea nodosa are diploid and tetraploid clans, also side by side in the same habitat , above. The number of chromosomes is 2n = 14 and 2n = 28.

Differentiation to other seagrass species

Cymodocea nodosa can be distinguished from the three other European seagrass species (plus the neophyte Halophila stipulacea ) by the long horizontal and short vertical rhizomes that are absent from the otherwise similar genus Posidonia . in addition, the fruits are noticeably larger than those of the Zostera species.

Occurrence

Cymodocea nodosa is common throughout the Mediterranean . The distribution area extends into the Atlantic Ocean and extends north to southern Portugal ( Parque Natural da Ria Formosa ) and south to Madeira , the Canary Islands and Cape Verde Islands as well as the coasts of the African countries Mauritania and Senegal .

A Cymodocea nodosa - sea ​​grass meadow , for example, borders directly on the new sandy beach of St. George's Bay ( Paceville , San Giljan ) on Malta .

In the western Mediterranean, Cymodocea nodosa usually grows in shallow water at depths of a few cm to 2.5 m, but it can also occur at depths of 30 to 40 m. As a rule, the plant grows in sheltered places on sandy substrate . In the eastern Mediterranean seaweed is often found in small, sandy zones that form in crevices or small hollows on flat rocks. Occasionally the seaweed there is accompanied by the Caulerpa species Caulerpa prolifera , which can make up up to 20% of the plant cover. In addition to pure seaweed meadows, the species can also occur together with Neptune grass in the Mediterranean . In Israel , the stocks are subject to large seasonal and year-to-year fluctuations. Occasionally the seaweed meadows disappear completely in order to subsequently renew themselves from the seed stocks in the sediment. The plant can survive moderate disturbance.

natural reserve

Seagrass meadows with seaweed are protected habitat types according to OSPAR for the European north-east Atlantic and according to the Bern Convention for the Mediterranean ( EUNIS habitat type A5.53131). The stocks are declining, for example between 15 and 80 percent of the previously documented stocks in the Bay of Cadiz have been lost. The seagrass meadows are threatened by water pollution, but above all by mechanical disturbances in the populated sandbanks. When disturbed, it is often replaced by opportunistic species such as the neophytic alga Caulerpa taxifolia . But the species itself is not considered threatened with extinction in the Red List of IUCN has classified it as uncritical ( "least concern").

Systematics

The first publication of this species took place in 1793 under the name ( Basionym ) Zostera nodosa , by the botanist and Franciscan priest Placido Michele Aurifici, known under his religious name Bernardino da Ucria. The new combination to form Cymodocea nodosa was carried out by Paul Friedrich August Ascherson in 1870 . The type species of the genus Cymodocea Cymodocea aequorea K.D.Koenig is now considered a synonym of Cymodocea nodosa .

Cymodocea nodosa is the only European species of the genus Cymodocea . According to genetic data from Petersen et al. In 2014 the genus is not monophyletic . Accordingly, the species Cymodocea nodosa forms a clade with its sister species Cymodocea rotundata , whose sister group is common to the other species and genera of the family Cymodoceaceae with the exception of Halodule . The necessary taxonomic adaptation, either splitting up the previous genus or combining it with the others, has not yet been carried out.

Fossils

Fossil finds that could be assigned to the species Cymodocea nodosa are from the Eocene of the Paris basin (with two other seagrass species) and the Pliocene of the Italian Po Valley, here also finds of fossil fruits of the species. This indicates a great age both of the species and of the sea grass in general.

Individual evidence

  1. ↑ a b c d Cymodocea nodosa in the IUCN 2016-3 Red List of Threatened Species . Posted by: FT Short et al. , 2007. Retrieved May 5, 2017.
  2. ↑ a b c d Jens Borum, Tina M. Greve: The four European seagrass species. Chaper 1 in: Jens Borum, Carlos M. Duarte, Dorte Krause-Jensen, Tina M. Greve (editors): European seagrasses: an introduction to monitoring and management. EU project Monitoring and Managing of European Seagrasses (M&MS), EVK3-CT-2000-00044, Report. September 2004, ISBN 87-89143-21-3 . download at [1] .
  3. ↑ a b c John Kuo, C. den Hartog: Seagrass taxonomy and identification key. Chapter 2 In: FT Short & RG Coles (editors): Global Seagrass Research Methods. Elsevier, 2001. ISBN 978-0-08-052561-7 . (= Developments in Aquaculture and Fisheries Science 33)
  4. ↑ Matthias Bergbauer, Bernd Humberg: What lives in the Mediterranean. Kosmos Verlag, ISBN 978-3-440-15233-1 , p. 48.
  5. ↑ C. den Hartog, J. Hennen, Th. MPA Noten, RJ van Wijk: Chromosome numbers of the European seagrasses. In: Plant Systematics and Evolution , Volume 156 (1/2), 1987, pp. 55-59. doi: 10.1007 / BF00937201 JSTOR 23673788
  6. ↑ Sign on the bay, with reference to: “Maritime Habitat Data of the Maltese Islands, MEPA , 2003; Data collected by Joseph A. Borg & Patrick J. Schembri, 2002 ".
  7. ^ OSPAR Commission (lead author Beatriz Ayala): Background Document for Cymodocea meadows. Biodiversity Series, Publication Number: 487/2010. ISBN 978-1-907390-28-9 .
  8. ↑ Cymodocea nodosa In: MD Guiry in MD Guiry, GM Guiry, 2017: AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. , accessed on May 11, 2017.
  9. ^ Gitte Petersen, Ole Seberg, Frederick T. Short, Miguel D. Fortes: Complete genomic congruence but non-monophyly of Cymodocea (Cymodoceaceae), a small group of seagrasses. In: Taxon , Volume 63 (1), 2014, pp. 3–8. doi: 10.12705 / 631.2
  10. ↑ Cornelis den Hartog: The sea-grasses of the world. North Holland Pub. Co., Amsterdam 1970. (= negotiating of the Koninklijke Nederlandsche Akademie van Wetenschappen, Afdeeling Natuurkunde. Tweede sectie; d. 59, no. 1), on page 15.

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