Consultancy Report Client: Natural England
Total Page：16
File Type：pdf, Size：1020Kb
ARTOO Marine Biology Consultants Consultancy Report Client: Natural England CONDITION MONITORING OF THE LYMINGTON TO KEYHAVEN COASTAL SALINE LAGOONS, 2010 Contract Reference No. FST20/63/062-22479 by R N Bamber & R S Robbins For the attention of: Rachel Williams November 2010 Report No. R2/10/319.4 ARTOO Marine Biology Consultants LLP Ocean Quay Marina, Belvidere Road, Southampton SO14 5QY, United Kingdom Tel: +44 (0) 2380 829763 SUMMARY The Keyhaven to Lymington lagoons system is a sequence of ten coastal saline lagoons from Keyhaven Lagoon to Normandy Farm, running along the northern shore-line of the western Solent, Hampshire; almost all of these lagoons are within the Solent and Isle of Wight Lagoons SAC. They have the most intensive and comprehensive history of ecological surveying of any coastal saline lagoons in the UK. The ten lagoons of the Keyhaven to Lymington system are (from west to east): 1. Keyhaven Lagoon 2. Fish Tail Lagoon 3. The Butts Lagoon 4. Pennington Lagoon 5. Oxey Lagoon South 6. Oxey Lagoon East 7. Oxey Lagoon North 8. Salterns Lagoon 9. Eight Acre Pond 10. Normandy Farm Lagoon To the east, across the mouth of the Lymington River, Lisle Court Lagoon is a linear, low- salinity system, previously surveyed in 1997. All of these lagoons were surveyed in October 2010. Results were compared with those from previous surveys over the last 13 years, including annual quantitative surveys of some of these lagoons over the last decade. The data were also compared with quantitative data from a range of saline lagoons and paralagoonal sites in order to classify them in terms of lagoon “quality” and conservation merit. The ten lagoons of the Keyhaven-Lymington sequence fall in two sections, with the low- salinity systems to the west of the Pennington Sewer of less conservation value. Keyhaven Lagoon was found to have recovered from its previous hypohaline state as a result of redirecting the freshwater flows across the marsh to landward. It is now of undoubted conservation merit, with two scheduled species present, and adds to the diversity of this lagoonal system. Fishtail Lagoon is best regarded simply as an overflow basin for Pennington Stream. It functions as a roosting site for waterfowl. It is not anticipated to show any ecological improvement in the foreseeable future. Butts Lagoon, the one lagoon without a sea-wall overflow sluice, remains a problem, as its basin has no facility sufficient to allow the outflow of excessive freshwater after periods of high rainfall. As a result, it has remained a hypohaline system with a poor and impoverished fauna, of no conservation merit. No improvement in this condition is anticipated without site engineering. This lagoon is part of the SAC. The Lagoons to the east of the Pennington Sewer are high salinity systems, with dense and diverse communities including lagoonal-specialist and scheduled species, and all are of high conservation merit and justify their representation within the SAC. Pennington Lagoon suffers to an extent at its eastern end from intrusion of lower-salinity water from the adjacent Butts Lagoon, which needs addressing. The loss of the Ruppia bed in Eight Acre Pond is of some concern, although no reason for its disappearance is known. It is likely that this loss of the ENLag.Veg biotope is responsible for the collapse of the Gammarus insensibilis population in this lagoon. The use of this site as a sailing club should not be affecting the plants adversely. Lisle Court Lagoon is essentially a hypohaline brackish pond rather than a saline lagoon, and is of little conservation merit other than in offering some diversity to the habitats of this shoreline and hinterland. Even then, none of the species present is unique to this habitat, as, other than Ruppia, they occur (or would be expected to occur) in the adjacent salt-marsh or nearby freshwater habitats. Most of the Keyhaven to Lymington lagoons studied herein (including Lisle Court) have been relatively stable in the long term. They are all relatively isolated from anthropogenic pressures other than the sailing club at Eight Acre Pond. The present results appear to confirm the consistency of their communities and habitat regime found in the previous surveys over the last two decades. Usefully, the intensive surveys of the SAC lagoons over the last decade has enable detailed interpretation of those habitats, and have identified the issues of degradation at Butts and Pennington lagoons (Keyhaven Lagoon having been “rescued”) and the recent deterioration in the ENLag.Veg biotope at Eight Acre Pond. Overall, other than Lisle Court, lagoons to the east of Pennington Sewer all fell into the “Good High Salinity” lagoons category, and their high conservation status and long-term stability were confirmed. ARTOO Marine Biology Consultants 4 INTRODUCTION Coastal saline lagoons are a Priority Habitat under the EU Council Directive 92/43/EEC on the Conservation of natural habitats and of wild fauna and flora, 1992 (the “Habitats & Species Directive”). As such, they are commonly features of site conservation designations (such as SSSIs) as well as being appropriate as Special Areas of Conservation (SACs) in their own right. Along the northern shore-line of the western Solent, Hampshire, there is a sequence of ten coastal saline lagoons from Keyhaven to Normandy Farm, known as the Keyhaven to Lymington lagoons system (Fig. 1), almost all of which is within the Solent and Isle of Wight Lagoons SAC. These lagoons are formed behind the sea-wall which was reconstructed in 1992 (Sheader & Rowe, 1993), although the lagoons which existed on these sites prior to the new wall construction were deemed to be “worthy of conservation” (Sheader & Sheader, 1989). The easternmost lagoon, Normandy Farm Lagoon was constructed in 1990 as a wetland reserve habitat to replace a system of ditches and pools, and to supply gravel for the new sea-wall construction. The earliest documented studies of these lagoons relate to the Nature Conservancy Council‟s collation of the Great Britain lagoonal resource in the early 1980s. Undergraduate studies were undertaken in 1983-1984 on the lagoons either side of the Pennington Sewer (Reffel, 1984; Richmond, 1984), together with a review of the entire system by Sheader and Sheader (1985) and a more intensive study of Eight Acre Pond by Shabbeer (1985). In 1996, eight of these lagoons (not including Keyhaven and Fishtail Lagoons) were proposed as part of the SAC owing to their having had, inter alia, good populations of lagoonal specialist species, including four species protected under schedules 5 and 8 of the Wildlife and Countryside Act (1981), viz. the starlet sea-anemone Nematostella vectensis and the “lagoon sand shrimp” Gammarus insensibilis, as well as the foxtail stonewort Lamprothamnium papulosum and, historically, the “lagoon sand worm” Armandia cirrhosa. After a number of less intensive studies, and irregular unreported surveys and data collection, the system was reassessed in the light of its SAC candidature in 1996 (Bamber, 1997a), and revisited as part of a comprehensive study of the saline lagoons of the Solent region in 1997 (Bamber et al., 1998). The historic data for the Keyhaven-Lymington lagoons system, notably including detailed and site-specific data which had only appeared in summarized form in the published or grey literature, was collated by Bamber (2000). During 2000, as part of an EU-funded LIFE project, detailed surveys were undertaken in Spring and Autumn to determine the current status of the habitat as reflected in the communities, and of the specialist and scheduled species. The entire system was mapped in detail using GPS, resulting in MapInfo files for the SAC and associated lagoons (Bamber & Evans, 2001). Engineering of the groundwater system around Keyhaven and Fishtail lagoons and Pennington Stream was undertaken under the LIFE project in 2002-2003. Between 2000 and 2009 inclusive, the lagoons were surveyed annually, initially under the auspices of the LIFE project and the Environment Agency, and then of Hampshire County Council, although detailed community analyses were restricted to the western lagoons for the years 2003 to 2008 inclusive (Bamber et al., 2001; 2002; Bamber & Evans, 2003; Bamber et al., 2003; 2004; Bamber & Evans, 2004; Bamber, 2005; Bamber & Salvador, 2006; 2008; 2009; Bamber & Robbins, 2010). ARTOO Marine Biology Consultants 5 Subsequent to the reconstruction of the sea-wall along this coastline in the 1990s, changes in the distribution of these species have occurred. Thus, Armandia cirrhosa appears to have been absent from Eight-Acre Pond during this century. The number of species in Normandy Farm lagoon has increased, including the first record of foxtail stonewort there in 1999. The specialist community in The Salterns lagoon has extended along the lagoon and become more diverse. The specialist community in the lagoons from Oxey Marsh to Keyhaven Lagoon declined in the early years of this decade, more so to the west, where, in particular, the lagoon sand shrimp and the starlet sea anemone were not recorded from the Lagoons west of the Pennington Sewer between 2000 and 2005. The community of Oxey North lagoon collapsed in 2003, but has since shown recovery. During the Solent lagoons review of 1997 (Bamber et al., 1998), the linear pool inside the shingle-bank sea-wall at Lisle Court, Hampshire (Lisle Court Lagoon) was surveyed as a potential saline lagoon. A 250 mm diameter pipe extends from the lagoon through the shingle-bank onto the adjacent Solent shore amongst saltmarsh, which allows drainage of surface-water from the lagoon, but sea-water ingress only occurs on the highest tides (or by overtopping). No scheduled or lagoonal-specialist species were discovered, and this site was deemed to be a low-salinity habitat of little conservation merit.