Zostera marina

Tracheophyta MagnoliopsidaZosteraceaeZosteraZostera marina

Ecology

Z. marina is a perennial which grows in the subtidal zone, on substrates of gravel, sand or sandy mud in areas which are protected from full exposure. It descends to depths of about 4 metres. Lowland.

Status

Native

World Distribution

Circumpolar Wide-temperate element.

Broad Habitats

Light (Ellenberg): 6

Moisture (Ellenberg): 12

Reaction (Ellenberg): 8

Nitrogen (Ellenberg): 6

8

Salt Tolerance (Ellenberg): 8

January Mean Temperature (Celsius): 4.5

July Mean Temperature (Celsius): 14.6

Annual Precipitation (mm): 1156

Length: 50

Perennation - primary

Perennial

Life Form - primary

Perennial hydrophyte (perennial water plant)

Woodiness

Herbaceous

Clonality - primary

Rhizome far-creeping

Count of 10km squares in Great Britain: 296

Count of 10km squares in Ireland: 68

Count of 10km squares in the Channel Isles: 13

Atlas Change Index: -0.86

Distribution information

JNCC Designations

NBNSYS0000002123

Scarce Atlas Account

Scarce Atlas Account: 

Zostera marina L.

Eelgrass

Status: scarce

 

The most truly marine of the Zostera species, this is essentially a sub-tidal plant, extending from slightly above low water of spring tides to a depth of about 4 metres on British coasts but 10 metres in the Mediterranean, depending on the clarity of the water (Tutin 1942). It is generally found on coarser substrates than Z. angustifolia, such as sand and sandy mud (Gubbay 1988) or fine gravel (Clapham, Tutin & Moore 1987), but avoiding brackish water or very exposed coasts. In places it forms dense sub-tidal meadows. It can support significant communities of marine organisms and is an important food for some wildfowl. 

The reproduction of this perennial species is similar to that of the closely related Z. angustifolia.

This species showed a marked decline throughout its range from 1931 to 1934, after a major outbreak of a wasting disease. This is generally attributed to the micro-organism Labyrinthula macrocystis, but other environmental factors may have put populations under stress, allowing the parasite to flourish. Populations made some recovery after the 1930s outbreak, but rarely to their former abundance and Labyrinthula may have remained endemic. Tutin (1942) suggests that the plant might still be found in small quantities at most of its old localities, but it may be overlooked at some of these sites due to lower densities.

Trawling, cockle-fishing, bait-digging and other human activities can have localised effects, leading to erosion and eventual displacement of Zostera. Short, Ibelings & Hartog (1988) and Turk (1989) recorded a re-appearance of the wasting disease in the late 1980s, which, together with the long-term consequences of increased human pressure on coastal sites, could lead to further declines in future.

Z. marina is recorded from the Mediterranean to the coasts of Norwegian Lapland, and on the Atlantic and Pacific coasts of North America.

While a considerable part of the decline apparent on the map can be attributed to disease and environmental factors, some reflects stricter recording standards. Many early records undoubtedly refer to leaves or uprooted plants on the strandline (Turk 1986). On the other hand, many established colonies are inaccessible even at spring tides, and may be overlooked by land-locked botanists.

 

M. & S. Scott

PLANTATT - Attributes of British and Irish plants. (.zip 1455KB) This dataset was compiled and published in 2004, and last updated in November 2008. Download includes an Excel spreadsheet of the attributes, and a PDF explaining the background and nomenclature. Note that the PDF version is the booklet as published, whereas the Excel spreadsheet incorporates subsequent corrections. A hardcopy can be purchased from the Centre for Ecology and Hydrology.

Atlas text references