Zostera marina Linnaeus
Includes Zostera angustifolia, a very similar entity
with narrow leaves, although some authors consider that it
should be treated as a separate species.
Common names: Eelgrass, Common Eelgrass, Wigeon
grass, Broad-leaved grass wrack, Marlee, Sedge, Slitch, Sweet
Sea-grass (Eng.). Bilearach (Irish and Scots Gaelic)
Zostère marine (Fr.). Da ye zao (Chinese).
Description: Perennial, grass-like but with
longer and broader leaves than most grasses; 20-50 cm long
(occasionally to 110 cm), 5-10 mm wide, with 5-11 veins and
rounded leaf tips, developing at intervals in groups from
rhizoids ramifying extensively in the substratum; the leaf
sheath forms a tube around stem; reproductive shoot terminal,
branched and up to 15 mm long; inflorescences consisting of
peduncles 15-100 mm, free portion 2-3 cm; spathes 10 or more,
sheath 4-8 cm; blade 5-20 cm; spadix linear; staminate and
pistillate flowers 1-20, apex acute or mucronate. Staminate
flowers: bracts absent or rarely 1 subtending most proximal
flower; pollen sacs 4-5. Pistillate flowers: ovary 2-3 mm, style
1-3 mm. Fruits ellipsoid to ovoid, 2-5 mm, often beaked, with
15-25 distinct ribs; rhizome with fibre bundles in the outermost
layer of cortex. Flowering in spring and early summer
Habitat: intertidal in pools with shelly sand
down to 10 m in sand and find gravel, often forming dense swards
in the subtidal, supporting a diverse fauna and flora and may
act as a nursery for fish and shellfish. Blades in sand tend to
be narrower than those in mud. Picture above is plants in pools
at Finavarra, Co. Clare, Ireland.
Key characteristics: One of two marine grasses
in NE Atlantic; Zostera noltei (also known as
Z. nana and as Z. noltii) occurs in estuaries high up
in the intertidal on shelly mud.
Link: Information above partly modified from
MarLin
and
Flora of North America.
Distribution: Common all around Britain and
Ireland but most abundant on W and SW coasts. Widespread in N
Hemisphere, adapted to the cold waters of the North Atlantic and
North Pacific. In Europe found from the Arctic of N Norway south
to the Spain; western and eastern basins of the Mediterranean
and in the Black Sea. In the western Atlantic from Newfoundland
south to North Carolina. In the Pacific from Alaska south to
Baja California, and from Pacific Russia, Japan, Korea south to
China, Myanmar and Thailand. It is particularly abundant in the
Baltic where it grows well at 5 ppt.
Uses: Sea-grass was used in historical times
for thatching purposes, and it was supposed to last longer than
straw. It was also used for stuffing matresses and pillows and
as an insulating material. Intertidal and shallow subtidal
swards are an important feeding resource for wildfowl in Britain
and Ireland, particularly Brent Geese and Wigeon.
Decline: The pathodgenic slime mold
Labryrinthula zosterae Porter & Muehlstein (Phylum
Labyrinthulomycota), not described until 1991, caused the
so-called "Wasting disease" of Zostera maina resulting in large-scale losses of eelgrass beds in the 1930s;
localized populations are said to be still affected by the slime
mold today.
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