Zostera Biotope Monitoring in the UK: Some Examples

Morecambe Bay cSAC

Changes in the Zostera bed at Leigh, Outer Thames: 1946 –1974

Chesil and the Fleet cSAC

Plymouth Sound and Estuaries cSAC

The Fal and Helford cSAC

The Isles of Scilly complex cSAC


Strangford Lough MNR and cSAC

The purpose of this section is to provide a very brief overview of the kinds of research, survey and monitoring that have been undertaken in some of the marine SACs with respect to Zostera biotopes. Much of the data gathered by this work is incorporated in the previous chapters of this report.

Davison (1997a) provides detailed information describing the occurrence of Zostera biotopes in sixteen marine sites around the UK, fifteen of which are cSACs.

Morecambe Bay cSAC - a UK Marine SACs Project demonstration site

Between 1992 and 1997, work has been undertaken on the intertidal Zostera beds in the Barrow and Walney Island areas of Morecambe Bay, relating to the construction and laying of two gas pipelines. During this work, areas of Z. angustifolia and Z. noltii were destroyed by the clearance of a 150 m wide swathe and the excavation of a trench. To assist recovery, the surface sediments of the Zostera bed were removed, stored and consequently replaced. The recovery has been monitored. Populations to the north of the pipelines have been recovering, albeit slowly and patchily. However, populations to the south of the pipeline have decreased or disappeared (I. Tittley, pers. comm.).

Changes in the Zostera bed at Leigh, Outer Thames: 1946 -1974

Aerial photographs of the Zostera bed at Leigh were available for a number of years, and allowed Wyer et al. (1977) to map the changes in distribution. At this site, Z. noltii and Z. angustifolia grew together, with Z. noltii predominant on free-draining hummocks and Z. angustifolia predominant in the wetter depressions between the hummocks. Flood damage in 1953 severely affected the bed, which had previously been decimated by the wasting disease between 1930-1935, but Wyer et al., (1977) reported that the bed appeared to have successfully recovered and expanded. However, no further information on this site has been published since 1977.

Chesil and the Fleet cSAC - a UK Marine SACs Project demonstration site

Whittaker (1989, 1981) assessed the seasonal distribution of seagrass meadows within the Fleet, and Holmes (1983, 1985, 1993) undertook detailed monitoring work. Within the seagrass meadows two eelgrasses, Z. angustifolia and Z. noltii, occur together with two tassel weeds, Ruppia cirrhosa and R. maritima. Holmes’ (1983) baseline assessment found Z. angustifolia to be the most abundant seagrass species, although monospecific stands Zostera were uncommon. In some areas, all four species occurred together forming mixed stands. West of Rodden Point R. cirrhosa was dominant. From this point east, the dominance changed gradually with the Zostera species becoming dominant within the main body of the lagoon, from Herbury Point to Lynch Cove. In addition to this west-east transition, there was a north- south transition, with Z. angustifolia dominant along the southern shore and in the main body of the Fleet, while Z. noltii was dominant or co-dominant in the coves of the northern shore.

Dyrynda and Cleator (1995) completed a series of cross-lagoonal transects, mapping benthic communities and providing information on variations in vegetation cover, sediment composition and invertebrate population structure. The distributions of the seagrass meadows across the lagoon were found to be generally consistent with the Holmes surveys, with Z. angustifolia predominant within the Littlesea and Moonfleet sites and more mixed seagrass populations at the Langton Herring and Cloud’s Hill sites. High levels of competition were observed between the seagrasses and green algal mats.

In the spring of 1995, a one year, integrated seasonal monitoring study, funded by WWF-UK, was undertaken at a cross-channel transect, situated at Langton Hive Point (Dyrynda, in prep.). Monitoring involved 1-2 monthly observations of percentage vegetation cover, recording the presence of conspicuous invertebrates and fish and the quantitative sampling of invertebrates. Trial monitoring work included the use of video transects to assess vegetation cover and a specific fish survey.

Plymouth Sound and Estuaries cSAC - a UK Marine SACs Project demonstration site

The Department of Biological Sciences, University of Plymouth is currently instigating a varied programme of research, in the form of honours research projects and field courses, in the Yealm Estuary (part of the SAC), and Salcombe-Kingsbridge Estuary

(not within the SAC) (A. Rowden, pers. comm.).

As a result of the English Nature Zostera mapping workshop (November 1996), University of Plymouth students that had carried out Zostera research were to be employed by the District Council to map the extent and relative density of these beds in the early summer of 1997. A research project has also been advertised within the English Nature College - English Nature Links Scheme titled ‘Comparative biodiversity study of two eelgrass beds of the Salcombe - Kingsbridge Estuary’. It is likely that Plymouth University will undertake this research and instigate other projects in the future.

The Fal and Helford cSAC

A number of surveys have been undertaken in the Helford (Gardener, 1934; Bishop, 1983; Turk, 1986; Rostron, 1987). As a result of concerns being expressed that the diversity and abundance of species in the Helford had declined, a Steering Group was formed in 1985, to undertake a twelve month survey of the area. The baseline Helford River Survey report was produced by Covey & Hocking in 1987. Intertidal Zostera were noted to have disappeared from many areas and the faunal diversity of these sites was found to have declined. However, four new records for subtidal beds were obtained. Giesen (1988) investigated seven sites but Z. marina was not found, either subtidally or intertidally. To date, monitoring reports to the Helford VMCA have been published for the surveys undertaken in 1988, 1989, 1990 and 1993 (Hocking, 1989; Turk, 1990; Tompsett 1991; Tompsett, 1994a, b). Local divers are undertaking subtidal mapping of the extent and relative density of these beds (R. Covey, pers. comm.).

The Isles of Scilly complex cSAC

Fowler & Pilley (1992) reviewed the monitoring techniques that had been applied to subtidal Z. marina beds in the Isles of Scilly, initially undertaken by the NCC and continued by English Nature. In the baseline survey in 1984, the shoots emerging from the substratum within a quadrat were counted and then destructively sampled to allow the number of leaves, leaf length, the number of flowering shoots and number of flower heads per shoot to be counted. Conspicuous species present on the leaves, bases of the shoots and on and within the surrounding sediment were also recorded. Observations on the general structure of the bed were made and photographs of the community and individual species were taken. In 1985, quadrat (0.1 m2) data was gathered at 0.5 m intervals along 10 m transect lines that radiated out, on the eight primary magnetic compass bearings, from a central marker. Between 1986 and 1988, the same methods were used but the level of data gathering varied. No annual surveys were undertaken in 1989 and 1990. In 1988 and 1991, plants were examined for symptoms of wasting disease. No symptoms were observed in 1988, but the disease was found to be present in 1991. In 1991 Sargassum muticum was recorded at all the survey sites.

During the summer of 1996, an aerial photo-mapping exercise was undertaken to map the distribution of Zostera and estimate densities of the beds. The preliminary results were ground-truthed by Coral Cay Conservation Sub Aqua Club (Irving et al., 1998).


The Zostera beds of North Haven, Skomer (part of the Pembrokeshire Islands cSAC) have been well-studied and are monitored on a regular basis as part of the Skomer Marine Nature Reserve work programme. Trigg (1998) undertook undergraduate research on temporal changes in the distribution and abundance of Z. marina in North Haven and the possible effects on the benthic community structure.

The three Zostera beds of Milford Haven (also part of the Pembrokeshire Islands cSAC) were surveyed in 1978, 1979, 1981 and 1986 (K. Hiscock, 1987). In 1994 and 1995, Pembrokeshire National Park undertook a survey of Milford Haven, to re-map the location, extent and density of Z. angustifolia as part of an ongoing programme of research and monitoring administered by the Milford Haven Waterway Environment Monitoring Steering Group. It is likely that repeat surveys will be undertaken in the future (Howe, 1994; RSPB, 1995). O’Brien (1996) investigated the effects of disturbance on Zostera populations in Milford Haven, while Hodges & Howe (1997) monitored three populations of Z. angustifolia following the Sea Empress oil spill.

The Zostera bed in the Severn Estuary pSAC is found near the turbidity maximum of the Severn, probably the most turbid estuary in the UK. This bed has been monitored in recent years in relation to the impacts of the Second Severn Crossing. Sediment accretion around the cofferdam for the Second Severn Crossing appears to have caused a decrease in the area of the Zostera bed in the Severn Estuary pSAC (M. Hill, pers. comm.).

Strangford Lough MNR and cSAC - a UK Marine SACs Project demonstration site

The Zostera beds of Strangford Lough have been mapped by Lynn (1936), Bleakley (1971) and Corbett (1980). Considerable research has been undertaken investigating wigeon and Brent geese interactions and their dependence upon the Lough’s Zostera beds. Portig (1997) surveyed the Zostera resources of the Lough for his Ph.D. research thesis on the utilisation of Zostera by wildfowl. The relevant information from this study is outlined in Chapters IV and V.

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