Water quality — Guidance standard on monitoring freshwater pearl mussel Margaritifera margaritifera populations and theirenvironment BSI Standards Publication... Introduction This Europe
Requirements for a sustainable Margaritifera population
General
Monitoring Margaritifera populations involves three key methods: a) direct assessment of the pearl mussel population; b) direct evaluation of the pearl mussel habitat; and c) tracking environmental indicators affecting the pearl mussel, utilizing databases or new surveys, as detailed in Clause 5.
Monitoring Margaritifera populations is essential for various reasons, including understanding environmental factors affecting their survival Key types of investigations include detailed baseline monitoring, routine surveillance, assessing causes of decline, conducting ecological impact assessments, and evaluating the effectiveness of management measures.
Viable populations of Margaritifera are primarily located in undisturbed streams, leading to a scarcity of collected water quality data Often, significant issues have already developed before data collection begins Consequently, initial studies in rivers with Margaritifera do not serve as baseline reference conditions; instead, they act as preliminary surveys to track progress toward rehabilitation or ongoing decline in future assessments.
Targets for assessing whether Margaritifera populations are in sustainable condition are given in informative Annex B.
Monitoring
To successfully restore declining pearl mussel populations to a favorable condition, it is crucial to gather sufficient information on Margaritifera populations in high-quality habitats that support the successful recruitment of young mussels.
Monitoring should begin with a comprehensive set of samples and surveys as outlined in Table 1 to establish a baseline Following this, the monitoring frequency should be determined by the assessed risk to the population, with certain aspects requiring more frequent checks In cases where negative pressures are observed, investigative monitoring may be necessary to identify their causes Key attributes of pearl mussel populations that need to be monitored are detailed in Table 1.
Mussel surveys should be conducted through wading with a bathyscope or by snorkelling/SCUBA diving in the river Counting mussels can be done in specific river stretches or estimated using transects, which helps in assessing their distribution and density It is essential to utilize standard methods established for the respective country during the survey Additionally, fixed and repeatable monitoring transects should be set up to track changes in mussel distribution, density, substrate composition, and the presence of filamentous algae, macrophytes, and fine sediment.
Population structure should be assessed by measuring the lengths of mussels including those mussels buried within the substrate
NOTE 1 In some countries, standard methods do not include investigations of buried mussels
To assess recent reproductive success in a mussel population, it is crucial to conduct demographic counts in stable habitats, ensuring rapid measurements and careful replacement of mussels and substrate To minimize population damage, the number of quadrats examined should be limited, well-spaced, and surveyed by trained workers during low-flow and low-turbidity conditions Measurements must be taken randomly within suitable mussel habitats, resulting in distinct size profiles that represent the river's population For monitoring, returning to the same general areas for repeat surveys is recommended, with at least 250 mussels measured per profile In smaller populations, combining measurements from different river sections may be necessary, and quadrats should ideally be positioned near, but not directly on, permanent transects.
NOTE 2 This standard is principally concerned with surveying mussels in relatively shallow water However, surveys of mussels in deep water can also be undertaken using an underwater camera or by diving
Table 1 — Checklist of monitoring recommended on mussel attributes in rivers with
Aspect Method Output (units) Notes
/SCUBA survey counts Map Once thoroughly to create a baseline with checks during 6 year survey
Population density Wading or snorkelling/
SCUBA survey counts (including transects)
Every 6 years, more frequently if needed for investigative monitoring (normally through repeating transect counts)
Individual mussel size Quadrat analysis Mussel measurement
(mm) 5 mm class size grouping is recommended Demography should be assessed every 6 years or more frequently for investigative monitoring
Analyzing the population age structure and growth rates of mussels is crucial, particularly in establishing age-size relationships for juveniles and young mussels It is important to focus on size ranges for mussels under 5 years and under 20 years, given their potential lifespan of around 100 years These age-size relationships will differ for mussels with shorter or longer lifespans However, caution must be exercised, as frequently removing mussels to determine age structure can be detrimental to their populations.
Brooding levels Visual, sub-sample of mussel adults checked using otoscope by trained expert
Age (%) of surveyed mussels with evidence of brooding, based on a sample of
To be undertaken where no other evidence of recruitment has been found.
Training and quality assurance for pearl mussel survey and assessment
Pearl mussel survey
Surveyor training is crucial for maintaining consistency, accuracy, and precision in the field It is important for surveyors to have a solid understanding of the biology of pearl mussels to comprehend the rationale behind the methods employed and to recognize the importance of careful application to prevent harm to these species.
Training for Margaritifera surveys must be structured to match the required survey level, ranging from non-invasive adult counts to specialized demographic quadrat analysis It is essential for surveyors to have qualifications in snorkelling or SCUBA diving before undertaking Margaritifera survey training While counting adult mussels can be taught to a broad audience, handling both adults and juveniles should be reserved for experts Generally, more experienced surveyors are more likely to conduct accurate surveys, and if survey experience is infrequent, regular refresher courses are advisable.
Training for mussel surveys should encompass essential topics such as health and safety education, techniques for monitoring mussels without causing harm, and the planning of surveys that address access and permission issues Participants must learn to conduct comprehensive mussel counts and population estimates, utilizing methods like wading with a bathyscope and snorkel or SCUBA surveys Additionally, training should cover the establishment of permanent monitoring transects, including surveying and relocating them with photographic documentation Accurate completion of recording forms, conducting juvenile searches, and developing demographic profiles require expert training Finally, trainees should be equipped to report survey results, compile license returns, map mussel habitats, and gather data on river corridors and land use.
Training should ideally include a certification system and offer regular refresher courses It must encompass a variety of river types relevant to the certification area and involve practical experience in rivers requiring wading with a bathyscope, as well as those necessitating snorkel or SCUBA surveys Additionally, comprehensive manuals of techniques should fully support the training process.
Before certification, course participants must conduct a trial survey to ensure accuracy It is essential to implement procedures that evaluate the results from various surveyors on identical river stretches If a surveyor's results consistently differ from those of experts, additional training should be provided Certification should only be granted when the survey results are confirmed to be accurate.
Training manuals
Training manuals must align with established standards and national requirements, providing essential background information and clear instructions for conducting surveys They should offer precise descriptions of the features to be recorded and guidelines for data maintenance and presentation Additionally, the text should be complemented by illustrative materials such as photographs, videos, and CDs to enhance the understanding of survey details.
Data entry and validation
Ensuring error-free data transfer from field sheets to databases and Geographical Information Systems (GIS) is crucial Implementing quality assurance methods, such as double data entry by two operators and subsequent verification of identical results, is essential Data corruption may arise during system updates or information transfers, necessitating a checking procedure post-changes Additionally, sensitive data regarding Margaritifera populations must be disclosed in accordance with national protocols for endangered species.
Licences
Margaritifera surveys must be conducted under a license, adhering to all imposed conditions Accurate data on the distribution and status of Margaritifera is crucial Typically, a survey license is granted with the expectation that the collected data will be submitted to the relevant authority.
5 Monitoring the environmental conditions needed to support Margaritifera margaritifera populations
General
Water quality assessment, along with the evaluation of hydromorphology, fish, and macroinvertebrate characteristics in pearl mussel rivers, must be conducted by qualified personnel It is essential to adhere to national protocols, and surveyors must secure the necessary licenses prior to commencing their work.
Maintaining high water quality is crucial for the sustainability of Margaritifera populations, as declines in water quality, along with flow changes and sedimentation, can lead to reduced recruitment and potential extinction This article outlines the ecological requirements of Margaritifera in three key areas: fish hosts, water quality, and hydromorphology, which encompasses flow and habitat structure It is important to recognize that these factors are interconnected, and their combined effects must be considered when assessing the needs of specific pearl mussel populations.
In addition, it is important to assess the requirements of Margaritifera populations in a way that takes account of the differences between rivers
The necessity of monitoring specific aspects in investigations depends on the purpose of the monitoring, as not all parameters need to be assessed for every study Automated continuous samplers are particularly beneficial for measuring in situ parameters in rivers with poor juvenile recruitment In cases where water quality remains consistently high, standard monitoring under the EC Water Framework Directive (WFD) may suffice, but it is recommended that these rivers be incorporated into the WFD sampling program.
Table 2, Table 3, and Table 5 provide an inventory of methods that are useful for monitoring a range of standard Informative Annex C describes the conditions under which sustainable populations of
Margaritifera have been found to occur
National standards bodies, along with CEN and ISO, have developed numerous water quality standard methods pertinent to pearl mussel research These standards facilitate chemical, ecological, and hydrological analyses, allowing for national and international comparisons of pearl mussel rivers Such comparisons enhance the understanding of the requirements for maintaining or restoring pearl mussel populations However, since the critical parameters may differ among populations, it is essential to consult relevant experts knowledgeable in water quality standards before planning environmental surveys in pearl mussel rivers Typically, these experts are affiliated with statutory environmental regulators or nature conservation bodies responsible for the implementation of the Water Framework Directive (WFD) and the Habitats Directive.
Fish hosts
Fish host species
Determining the species and density of host fish for mussel populations is essential, along with assessing whether encystment is occurring In the absence of sufficient data, electrofishing should be conducted twice, following standard methods (EN 14011:2003) The first survey should take place in early autumn to identify suitable fish hosts downstream of mussel beds, while the second survey in late spring should focus on the presence of yearling fish near permanent mussel habitats During the second survey, fish should be examined for visible encystment of glochidia on their gills More comprehensive studies on fish numbers and glochidial encystment can be performed, but the outlined procedures represent the minimum requirements.
To assess fish species composition and densities, electrofishing should be conducted in areas likely to support glochidial attachment, particularly downstream of pearl mussel sites Investigations should focus on stream sections of at least 50 meters, considering river size, current velocity, and technical feasibility In cases where net blocking and multiple electrofishing runs are impractical, minimum density values must be reported Additionally, if a valid correction factor for catch efficiency is available, it should also be included in the findings.
Gathering data on pearl mussel host species is essential, but understanding other fish species and their habitat preferences can also aid in identifying and addressing issues when fish hosts are lacking.
Table 2 — Checklist of monitoring recommended on fish hosts in rivers with Margaritifera
Aspect Method Output (units) Notes
Numbers of 0+ fish in autumn Electrofishing Numbers per 100 m 2 Baseline in all rivers, with fish density surveyed every
3 to 6 years Electrofished site should be downstream of large beds of mussels
Numbers of yearling fish in spring Electrofishing Numbers per 100 m 2
Numbers of encysted fish in spring
Electrofishing and visual check of gills Percentage of host fish caught that are encysted
Estimated density of glochidia per fish (and by fish species)
Inspection should be done at a time when the cysts are visible to the naked eye, so that fish do not need to be harmed.
Barriers to fish migration
Conducting a survey and evaluation of fish barriers in the catchment is essential for a comprehensive risk assessment and fluvial audit, particularly in areas where 0+ host fish are rare or missing These barriers can be effectively identified through morphological assessments or water quality surveys.
Host suitability
If resident fish are found to be unsuitable hosts for the mussel population, an investigation is necessary It is essential to test both the resident fish and other potential fish hosts for compatibility with the mussels.
Water quality
General
A summary of water quality monitoring recommendations is given in Table 3.
Phosphorus
Phosphorus (P) monitoring in rivers is typically part of broader water quality assessments, with samples collected monthly or at longer intervals Annual mean or median values are often used for inter- or intra-catchment comparisons, helping to establish background levels However, this approach has limitations for Margaritifera monitoring, as a single spike in phosphorus can lead to increased algal productivity, reduced oxygen levels in riverbed gravels, and significant losses in recruitment efforts over several years.
Effective phosphorus monitoring must be tailored to the specific requirements of each catchment area In cases where the risk of elevated phosphorus levels is minimal, routine sampling may be adequate However, if there are indications of occasional or frequent departures from oligotrophic conditions, more comprehensive investigative monitoring will be necessary.
For effective interpretation of results, phosphorus should be measured as both total phosphorus (total P) and dissolved phosphorus (molybdate-reactive phosphorus, MRP), reported in mg/l P Total P serves as an indicator of eutrophication, while MRP indicates phosphorus available for uptake It is important to use filtered and unfiltered total P samples appropriately, as they provide different information relevant to each investigation.
Phosphorus monitoring should be conducted alongside regular assessments of filamentous algae and macrophytes, as excessive growth of these organisms necessitates further investigation To identify nutrient sources, a series of water samples must be collected For point sources like septic tanks and urban wastewater plants, sampling during low flow conditions is advisable, as nutrient concentrations peak at these times Conversely, for diffuse sources such as agricultural runoff, sampling during rising flood conditions is more effective, allowing for the detection of phosphorus before it is fully absorbed by algae and plants Given that natural levels of MRP in oligotrophic systems can be extremely low (