Download 122 ON THE OCCURRENCE OF ZOSTERA NOLTII HORNEMANN

Analele ştiinţifice ale Universităţii “Al. I. Cuza” Iaşi
Tomul LIV, fasc. 2, s.II a. Biologie vegetală, 2008
ON THE OCCURRENCE OF ZOSTERA NOLTII HORNEMANN AT THE
ROMANIAN COAST OF THE BLACK SEA
V. SURUGIU*
Abstract. The finding of a small Zostera noltii patch (~20 m2) at the Romanian Black Sea coast is
reported. The systematics as well as the geographical distribution of this species is briefly reviewed. Some
ecological characteristics of this species are also provided. The causes of the declining of Zostera noltii
beds at the Romanian coast of the Black Sea are discussed.
Key words: seagrass beds, Zostera noltii, distribution, Romanian coast, Black Sea
Introduction
The dwarf eelgrass Zostera noltii (Hornem.) Toml. & Posl. belongs to the family
Zosteraceae Dumortier, 1829. This family together with the families Cymodoceae,
Posidoniaceae, and Hydrocharitaceae forms an ecological group of aquatic angiosperms
adapted to live in the marine environment [5]. Representatives of these families are
collectively called seagrasses due to their grass-like appearance.
At the Romanian coast, there is also present another species of the genus Zostera, the
common eelgrass Z. marina L. [6, 12]. In the past both these eelgrass species covered with
a lush growth the bottom of marine lagoons Sinoie, Zmeica and Goloviţa [14]. Isolated
patches were reported also at Cape Midia [2] and Agigea [3]. At that time one even spoke
about the exploitation of eelgrasses and their use as surrogate for artificial wool, as stuffing
material for pillows and mattresses and for packing up eggs, pieces of furniture and other
fragile objects [1, 11].
In the last 40 years, due to pollution and eutrophication, seagrasses have declined
drastically in abundance, not only at the Romanian coast, but also in the entire Black Sea.
The aim of this paper is to reveal the actual status of Zostera noltii beds at the Romanian
coast of the Black Sea. Although Zostera noltii is distinguishable from Z. marina, in many
cases the authors have cited these plants simply as “Zostera”, irrespective of whether they
refer to one or another species. In order to prevent the confusion between these two species
of eelgrass an identification key is provided.
Material and methods
The dwarf eelgrass patch was identified at Mangalia (43°48'18.0"N;
028°35'31.9"E), between 1.3-1.9 m deep, on sandy substrate, in a small embayment formed
by a dyke (Fig. 1). The patch is approximately 7 m long and 5 m wide. Samples of Zostera
*
“Al. I. Cuza” University of Iaşi, Faculty of Biology, Bd. Carol I, no. 20A, 700506, Iaşi, Romania
e-mail: [email protected]
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noltii were taken by snorkelling on 26th May 2005, 30th June 2005, 4th August 2006, and 8th
August 2006. Voucher specimens were herborised and deposited in the Herbarium
collection of the Faculty of Biology, “Alexandru Ioan Cuza” University of Iasi. The in situ
photographs were taken with a digital ReefMaster DC 310 underwater camera. All the
specimens collected were checked against the species description from the speciality
literature [6, 9].
Fig. 1 – Location of the Zostera noltii meadow at Mangalia (43°48'18.0"N; 028°35'31.9"E).
Results and discussions
Systematics
Zostera (Zosterella) noltii Hornemann, Fl. Dan. 12(35): 3, tab. 2041 (1832)
(Dwarf eelgrass)
Fig. 2, 3
Zostera marina auct. non L.–Phucagrostis minor Cavol., Phucagr. Anth. XIV, Pl.
2 (1792) nom. invalid.–Zostera trinervis Stokes, in Bot. Mat. Med. 4: 319 (1812)
nom. illeg.–Zostera nana Mertens ex Roth, Enum. Pl. Phan. Germ. 1: 8 (1827)
nom. invalid.–Zostera minor (Cavol.) Nolte ex Reichenb., Icon. Fl. Germ. 7: 2
(1845).–Zostera pumila Le Gall in Congr. Sc. France 16: 96, 144 (1850).
Description.–Colour is grass-green. Rhizomes 0.5-2 mm in diameter, with 1-4 roots at each
node. Internodes 4-35 mm long. In cross-section the strengthening fibre bundles occur in
the innermost layer of the outer cortex of the rhizome. Sterile shoots (leaves) alternately
arranged and flattened. The leaf sheath at the base clasps the stem but is not fused into a
tube, 4-5 cm long. Leaf blades 6-22 cm long and 0.5-1.5 mm wide, with approximately (1)3
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irregularly spaced veins. The tips of leaves initially rounded, but, as the plant matures, they
become notched (emarginate), often asymmetric. Generative shoots lateral, unbranched or
with a few branches near the base, shorter and narrower than the sterile shoots; with 1-6
spathes. Spathal sheath 12-20 mm long and 1.3-2 mm wide. Spadix lanceolate with 4-5
staminate flowers and 4-5 pistillate flowers. Fruit ellipsoid, 1.5-2 mm long; pericarp dark
brown. Seeds smooth, white in colour, 1.5-2.0 mm long, excluding the style. 2n = 12.
Biology.–Hermaphrodite, perennial herb. Flowering period extends from June to August
[6]. In the British Isles the plant retains its leaves throughout the winter. Main method of
reproduction is by vegetative growth. However, seedling germination appears to be also
important. In the Black Sea peaks of asexual reproduction occur in spring and autumn,
when regrowth of the rhizome system is the most intense [7].
Habitat.–Intertidal, between mean high water neap and mean low water neap. In waters
with reduced salinity Zostera notii grows deeper and may become permanently submerged.
Thus, in the Black Sea the species occurs from 0.6 m down to 8-10 m deep. In
Mediterranean the dwarf eelgrass may grow down to 20 m deep. Inhabit sandy or muddy
sand substate. Euryhaline species, very tolerant to desiccation. The lower salinity limit is
about 15 g l−1. The plant is restricted to sheltered sites such as estuaries, salt marshes, bays
and lagoons. At Mangalia it was found in association with Cladophora sericea (Fig. 2).
Geographical distribution.–The species is distributed along the Atlantic coasts of Europe
and northern Africa, extending from southern Scandinavia (Norway) to the tropic of Cancer
(Mauritania and Senegal). It also occurs around the British Isles, in the Baltic Sea,
Mediterranean Sea, Adriatic Sea, Black Sea, Sea of Azov, Caspian Sea and Aral Sea [4].
It the Black Sea dwarf eelgrass was recorded in the Sevastopol Bay, along the Caucasian
coast (gulf of Anapa, gulf of Novorosiisk, gulf of Gelendjik), gulf of Karkinit, Tendrovsky,
and Burgas Bay [8].
At the Romanian coast the presence of Zostera noltii meadows was previously reported at
Mamaia, Agigea, Cape Midia, Mangalia, lake Razim, lake Goloviţa and Sinoie lagoon [2,
3, 7, 14].
Key to the Zostera species from the Black Sea
1. Rhizome thin, with 1-4 roots at each node. Leaves 6-22 cm long and 0.5-1.5 mm wide,
with one principal vein; leaf-sheaths open with open margins overlapping; leaf tip
emarginate. Generative shoot lateral. Retinacula present. Seeds smooth .........................
................................................................................................. Zostera (Zosterella) noltii
- Rhizome thick, with numerous roots at each node. Leaves 50-150 cm long and 3.07.0(9.0) mm wide, with 3 to 5(9) principal veins; leaf-sheaths closed, tubular, rupturing
with age; leaf tip obtuse to slightly mucronate. Generative shoot terminal. Retinacula
absent. Seeds with 16-25 longitudinal ridges ........................... Zostera (Zostera) marina
In the Black Sea marine phanerogames are represented by 6 species: Zostera
marina, Z. noltii, Potamogeton pectinatus, Ruppia maritima, R. spiralis, and Zannichellia
major [8]. However, only the two species belonging to the genus Zostera, commonly
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known as “eelgrasses”, are considered to be fully confined to the marine environment. The
remaining species forms the so-called “eurysaline” group, an ecological group of flowering
aquatic plants tolerant of considerable changes in salinity from full-strength seawater to
freshwater [5].
The eelgrass biocoenosis is an important element of shallow-water coastal benthic
environments [9]. Seagrass beds are among the most productive marine communities. The
standing biomass of dwarf eelgrass in the Black Sea ranges from 126 g m−2 (Gulf of
Karkinit) to 380 g m−2 (Gulf of Anapa) [12]. The production of Zostera noltii is estimated
to 15 g fresh weight/kg/day.
As key primary producers, the eelgrasses represent an important source of food for many
organisms, especially in the form of detritus. Although, Zostera noltii is grazed directly by
waterfowl and by some fish species [6]. The dense, matted root system of eelgrasses
stabilise the soft sediments, and thus reduce coastal erosion. Also, seagrass beds increase
habitat diversity, providing shelter for a wide variety of marine organisms [2, 9].
Zostera noltii occurs on sedimentary substrata, in areas sheltered from water
motion (currents and waves). Because Romanian coast is exposed to north-south
alongshore current and to strong winter storms, it offers very few suitable conditions for
eelgrass grow. Extensive carpets of eelgrasses were present only in the quiet brackish water
lagoons. However, sparse Zostera shrubs were reported in front of Agigea at 0.8-1 m depth
[3, 7]. Denser mats were found at Cape Midia [7]. Recently Teacă et al. [13] indicated on
the presence of small areas (approx. 30×30 cm) populated by small eelgrass Zostera sp.
(most probably Z. noltii) at Mamaia Casino and Mangalia, on a sandy-silty texture
substrate, in the proximity of the protective wave-breaking dam.
The decline of seagrasses in relatively open areas of the Romanian coast, as well as in the
entire Black Sea, is due principally to the eutrophication. The nutrient enrichment of water
increased the phytoplankton density, thus decreasing the transparency and diminishing the
amount of light that can reach the bottom. The light penetration is also reduced by the
siltation of near-shore sediments due to littoral works and to the construction of protective
dams. Another cause for the decline of eelgrasses is the collapse of fishing in the Black Sea
which reduced grazing on the epiphytes that live on the grass blades. The overgrowth of
epiphytes thus prevents or reduces light intensity at the surface of the grass blade. Thus, the
blades of the dwarf eelgrass observed at Mangalia were densely covered by various
microscopic algae.
The freezing of the sea may also have dramatic deleterious effects due to the ice scour [9].
However, the severe frost of the sea occurred during the 2005-2006 winter had no
detectable impact upon the size and density of the meadow from Mangalia.
As a result of a gradual reduction of salinity in all Romanian littoral lakes from
polyhaline to ahaline over the last 40 years, vast fields of eelgrasses have disappeared
completely.
Because at the Romanian littoral Zostera noltii occurs very sparsely and is
threatened to extinction it must be put under protection.
.
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Fig. 2 – Zostera noltii meadow at Mangalia.
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Acknowledgements
I am much indebted to my colleague Dr. C. Mânzu for checking the identification of the species and for
helpful advice
Fig. 3 – The habit of Zostera noltii (Hornem.) Toml. & Posl.
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