Zostera Biotope Monitoring in the UK: Some Examples
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
Morecambe Bay cSAC - a UK Marine SACs Project
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.
Changes in the Zostera bed at Leigh, Outer Thames:
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
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 Clouds 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
(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). OBrien (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
Loughs 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.