Baltic Stonewort Chara baltica
Bearded Stonewort Chara canescens
Convergent Stonewort Chara connivens
Intermediate Stonewort Chara intermedia
Starry Stonewort Nitellopsis obtusa
- Species Action Plan

Ref 2/S5 Species Action Plan 5
Plan Author: Broads Authority
Plan Co-ordinator: Waterbodies Topic Group
Plan Leader: Broads Authority
Date: 4 January 2008
Stage: Final

Action Plan Summary

Current Status

National Status

  • Starry Stonewort (Nitellopsis obtusa) occurs in the Broads and a recent record from a gravel pit in Gloucestershire.
  • Convergent Stonewort (Chara connivens) has been recorded at two sites in Devon and the Broads and at two sites in East Sussex.
  • Bearded Stonewort (Chara canescens) is restricted to three sites near Peterborough, Cambridgeshire and the Outer Hebrides. It was previously recorded in 11 sites, including Norfolk.
  • Baltic Stonewort (Chara baltica) is currently known from five sites coastal sites, which are the Broads, three in the Western Isles and one site in Anglesey.
  • Intermediate Stonewort (Chara intermedia) is currently known from six sites in the Broads only; its presence is subject to extreme fluctuations.

Norfolk Status

  • Starry, Intermediate, Convergent and Baltic Stoneworts are all found within the Upper Thurne Broads in the Northern Broads. During the late nineties, there has been a gradual increase in stoneworts. However, since 2000, a sharp decline in Hickling has resulted in complete loss in this broad in 2007. Martham and Blackfleet Broads remain the sole stronghold for these four stonewort species. There are old records for Bearded Stonewort from Hickling Broad; however, it has not been found since 1965 and before then in 1954. It is now thought to be extinct in Norfolk.
  • Norfolk is the stronghold for four of these stonewort species (Starry, Intermediate, Convergent and Baltic), in the UK and Europe. Survey data from 2007 showed that the Martham Broads had the best populations; however, these populations are vulnerable, as they were the only sites where these stoneworts were recorded in the Broads. Growth of these four stonewort species was healthy and vigorous within the clear water of Martham Broads but was declining with increasing areas of bare sediment due to complete die-off (from 2006-2007). In 2007, there were no stoneworts in Hickling Broad. Horsey Mere and Heigham Sound also had almost total absence in 2007.
  • Growth depends on many complex factors and population stability may be related to salinity. Intermediate, Baltic and Starry Stonewort are larger plants and therefore have the highest biomass, whereas Convergent Stonewort is smaller and tends to be out-competed by the larger species. No new records for the Bearded Stonewort exist despite extensive surveys been carried out by the Broads Authority in recent years.

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Current factors in Norfolk causing loss or decline

The threats to the species are not fully known but are likely to include:

  • Nutrient enrichment from diffuse and point source pollution.
  • Water pollution from toxic substances such as copper and biocides in antifouling paints.
  • High salinity and ochre concentration as a result of deep drainage in the catchment and saline incursion as a result of drainage, sea level rise and climate change. Although stoneworts are tolerant of brackish conditions, performance has been shown to decline if salinity levels increase.

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Current Action in Norfolk

  • In 2003/04, an extensive research programme began in the Upper Thurne area, comprising of five PhDs, one MSc and a NERC-funded research project. The results will inform the catchment and lake management required for the Upper Thurne for improved water quality and quantity. Cranfield is focusing on the surface and groundwater hydrology, hydrodynamics of the catchment and pollutants entering the system; Stirling is carrying out remote sensing to trace pollutants; UEA is focusing on nitrogen dynamics in the surrounding wetland; and NERC research is examining the role of salinity in the stability of aquatic plants in shallow lakes and the impact of nitrogen on aquatic plant species diversity.
  • Scenarios to reduce the input of pollutants from the drained catchment plan are to be scoped by the Water Management Alliance (formerly KLCIDB), BA and NE. A feasibility study is planned to look at the achievability and practicality of these scenarios.
  • Regular monitoring and occasional searches for stonewort species take place in all of the Broads in the Upper Thurne, which is currently the key area for stoneworts in the Broads. Regular monitoring and occasional searches also occur in around 25-35 of the 63 broads on an annual basis.
  • Results from a further PhD, based at UEA and funded by Plantlife, EA and BA, on the autecology of stoneworts are being incorporated into management actions.
  • A management plan for the Upper Thurne Broads has been written by the Upper Thurne Working Group, which has representatives from all key stakeholders.
  • Several AMP schemes aim to reduce nutrient inputs from sewage treatment works at Whitlingham and Walcott and to minimise the impact of storm overflow discharge at Sutton Staithe.
  • The School of Biological Sciences at the University of East Anglia currently possesses nursery populations of Chara canescens, Chara connivens, Chara intermedia and Nitellopsis obtusa. The populations are cultured in aquaria and used for generating cuttings for laboratory experiments and re-establishment trials.

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Action Plan Objectives and Targets


Nitellopsis obtusa

  • Maintain populations of this species in ten extant sites.
  • Establish viable populations at five extant sites by 2010.
  • Establish and maintain one new metapopulation (outside the Norfolk Broads) by 2010.
  • Re-establish populations at one historic site through habitat restoration by 2010.

Chara connivens

  • Maintain populations of this species at eight extant sites.
  • Establish viable populations at four extant sites by 2010.

Chara canescens

  • Maintain, and where appropriate enhance, existing populations and, where appropriate, restore populations at former sites.
  • Maintain the range and number of sites including, where appropriate, through introduction to adjacent localities where existing localities become unsuitable.

Chara baltica

  • Maintain, and where appropriate enhance, existing populations and, where appropriate, restore populations at former sites.
  • Maintain the range and number of sites including, where appropriate, through introduction to adjacent localities where existing localities become unsuitable.

Chara intermedia

  • On new national BAP species list; targets and actions to be confirmed.


The Norfolk Stonewort Acton Plan brings together actions for five separate stonewort species. It should be noted that despite the Bearded Stonewort being considered extinct in Norfolk, it remains within the Norfolk BAP because of the capacity of stonewort populations to regenerate from oospores stored in the sediment under the right habitat conditions.

  • Maintain and enhance the population of Starry Stonewort, Convergent Stonewort, Baltic Stonewort and Intermediate Stonewort in three Upper Thurne Broads (Martham North and South and Blackfleet Broads), with no loss of species. By 2012, all waterbodies should contain self sustaining, extensive populations of these BAP stoneworts. Seven out of ten sample points should include these stoneworts. Stonewort beds should cover a minimum of 50 percent of the euphotic zone, with beds being confluent.
  • Promote expansion of one or more of the following stoneworts: Starry, Convergent, Baltic and Intermediate, to thirteen broads by 2012 (Heigham Sound, Horsey Mere, Hickling, Mautby Decoy, Upton, Strumpshaw, Cockshoot, Ormesby, Barton, Alderfen, Cromes, Buckenham and Hassingham Broads). A further six broads should be home to populations of these stoneworts by 2015 (Barnby, Little, Ormesby Little, Rollesby Belaugh and Bridge Broads). In addition, the range should be expanded to two newly created waterbodies (Whitlingham and Thorpe Marshes Broads) by 2012. Most of these waterbodies listed have more common non-BAP stoneworts present; the aim is to encourage annual occurrence of the rarer BAP stoneworts. Expansion will be mainly facilitated through habitat improvements, such as nutrient removal and biomanipulation, although reintroduction into suitable broads should be considered where appropriate.
  • By 2012, establish one experimental population of one or more of the following stoneworts: Starry, Convergent, Baltic and Intermediate, in a waterbody outside Broadland, which is less likely to be affected by sea level rise and coastal breach.
  • Re-establish a population of Bearded Stonewort at one, suitable historic site in Norfolk through habitat restoration or re-introduction by 2012.

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