Genetic Scorecard Indicator - Sugar Kelp

There is no direct evidence of population decline in Scotland, though indications from northeast England might suggest that southeast Scotland may have had larger populations of Saccharina in the recent past, extending to greater depths (Forster et al., 2024). There is little risk of diversity loss in Scotland through population changes in the near future.

Population definitions:

Populations have been defined based on genetic evidence, with detection of genetic structure among sampled populations taken as evidence for separate genetic populations. In Scotland, genome-wide data from west coast populations suggests the presence of at least 3 sub-populations, centred around the Clyde, the Inner Hebrides as far as Skye, and the Outer Hebrides and north-west (Thomson, 2021). East coast populations have not been analysed in detail, but data from Jaugeon et al. 2025 show that east coast populations are more closely related to northern populations, than to Inner Hebrides and Irish populations. Orkney and Shetland remain unsampled. Based on this data, 3 populations (or 4 if separating north coast and east coast populations) can be delineated around Scotland. All populations remain in apparently healthy condition. Across the rest of the UK, the number of distinct genetic populations is hard to define, but there is evidence for three additional gene pools: Jaugeon et al. 2025 reported a distinct population from Cornwall, as well as distinct populations from nearby North Sea populations (although not from UK coastlines). Mooney et al. (2018) reported structuring of populations from the Isle of Man and the Clyde area, and differentiation between populations in Strangford Lough and the north coast of Northern Ireland. 

Ne500: The proporition of populations that have an effective population size of more than 500. 

• Proportion of populations with Ne > 500 in Scotland = unknown
• Proportion of populations with Ne > 500 in UK = unknown

The effective population size of Saccharina latissima in the UK is not meaningfully assessable, but from assumptions based around population size, reproduction and dispersal, it is likely to be unbounded, even within sub-populations. 

PM: Proportion of populations that existed in 2000 that still exist in 2025.

• Proportion of populations maintained in Scotland = 4/4
• Proportion of populations maintained in UK = 7/7

Functional variation

There is no evidence of loss of functional variation at present, and the immediate risk is small. Marine heatwaves do present a risk to functional diversity in the near future, especially for southern UK populations facing increased extreme heat events, and cold-adapted northerly populations (Straub et al., 2019; Teagle & Smale, 2018). Increased competition with Laminaria ochroleuca, a warm-water kelp expanding its northern range, may also heighten pressure on S. latissima (Smale et al., 2015). 

Divergent lineages

No evidence of isolated population loss or decline in specific populations or lineages. Southern populations, and isolated populations, such as Clyde Sea populations, may be more at risk of marine heatwave events in the future.  

Hybridisation/ Introgression

There are no known cases of natural hybridisation in Saccharina with other related species in the UK. S. angustissima is a debated species reported from the US which is likely to interbreed with S. latissima (Li et al., 2022). It has so far not been described from the UK (though similar morphotypes have been observed (Thomson, 2021). 

Introgression from seaweed farms to wild populations presents a minor risk through the introduction of maladapted genotypes and reduced diversity and Ne. Farm population genetic diversity has been observed to be much lower than wild populations (Jaugeon et al., 2025; Bråtelund et al., 2025). Current farm practices stipulate the use of local source populations for seeding reducing the risk (Goecke et al. 2020). Population genetic data from farms suggests these recommendations are being adhered to (Jaugeon et al., 2025). The scale of cultivation in the west coast of Scotland compared to the likely large Ne of S. latissima in the wild also precludes significant effects from introgression. This should be monitored in the future though as the scale of cultivation and the breeding of cultivars intensifies (Sæther et al., 2024) 

Low turnover - constraints on adaptive opportunities

Dispersal range remains uncertain but is thought to be in the range of meters to 10s of kilometres. Short generation time, high turnover in populations, and large functional diversity over local environmental gradients suggests plenty of opportunities for adaptation (Diehl et al., 2024). 

Scotland

• Risk: Negligible
• Mitigation: Some mitigation around farming, likely to be effective at present 

Great Britain/UK

• Risk: Negligible
• Mitigation: Some mitigation around farming, likely to be effective at present 

Overall Genetic Health status explanation

Widespread distribution and dispersal, large effective population size, and high abundance and turnover ensure negligible risks from cultivation or harvesting. MPA networks, restoration and recovery projects, and ex situ representation further support resilience. Greatest threats in the future are from marine heatwave events and potential ecosystem shifts (grazers), as well as longer term range shifts of invasive species and diseases, for instance Sargassum muticum.  It can be reasonably assumed that all UK populations of S. latissima persist in good health.

In situ genetic threat level

• In situ Risk for Scotland: Negligible
• In situ Risk for UK: Negligible

Large, connected populations, mid-distribution range, high potential for adaption. 

Confidence in in situ threat level

• Confidence score for Scotland: High
• Confidence score for UK: High

Assessment based on reasonable genetic data for UK and EU populations, well characterised biology, and well-defined population trends. 

Well represented. Genotype banking for S. latissima has been carried out across the UK and Europe, for research and cultivation purposes (GENIALG, 2021; SAMS, 2025).

Saccharina latissimi is a key component of the priority marine feature (PMF) ‘Kelp and seaweed communities on sublittoral sediment’. This means that National Marine Plan General Policy GEN 9b applies, ensuring that development and use of the marine environment does not have a significant effect on the national status of the habitat. 

Saccharina latissimi stands are likely to benefit from the wider effects of MPA designations. The Scottish Biodiversity Strategy to 2045, the Scottish Biodiversity Duty and UK Marine Strategy Good Environmental Status provide further drivers to ensure biological diversity is restored, and ecosystems are safeguarded. 

At least two projects in England are looking at active restoration approaches, including seeding techniques (Forster et al., 2024; Wilding et al., 2022). 

Seaweed farming guidance in the UK currently recommends the use of local genotypes and high genetic diversity broodstocks to reduce the potential for introgression of maladapted genotypes and low nursery N(e) effects. 

Population

Demographic

Genetic

A baseline of Scottish population genetics was undertaken in 2019 (Thomson, 2021). Ad-hoc sampling for population genetics has also been undertaken across the UK (Mooney et al., 2018; Jaugeon et al., 2025) 

Increasing interest for cultivation strains is likely to increase the availability of genetic data on cultivated populations.