#02 - All you ever wanted to know about the MSA

This second issue of The Nature Intelligence Newsletter will tell you all you need to know about the Mean Species Abundance (MSA) metric, one of the leading metric to assess the positive and negative impacts of economic activities on one aspect of biodiversity, ecosystems. We will cover:

1. Where does the MSA fit within all the elements of biodiversity which need to be measured?
2. What is the definition of MSA?
3. How can it be measured with field data from ecological surveys?
4. Is it the right horse? Is it going to be the ecosystem condition metric everybody agrees on?

Where does the MSA stands with regards to other aspects of biodiversity?

UN Biodiversity (the Convention on Biological Diversity or CBD) distinguishes three aspects of biodiversity:

1. Ecosystems
2. Species
3. Genes

The #MeanSpeciesAbundance measures one aspect: ecosystems.

It is a realm (or ecosystem-agnostic) metric which can be used both for direct measurement of ecosystem condition (though it is very difficult and costly, see below) and inferred based on pressures.

How is the MSA defined?

The definition

Other similar metrics

Its main competitors are other ecosystem condition realm metrics:

- Potentially Disappeared Fraction (PDF)

- Ecosystem Integrity Index (EII)

- Biodiversity Intactness Index (BII)

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The Ecosystem Integrity Index is also a realm metric and inferred through pressure-impact relationships. By contrast, forest canopy density is an example of an ecosystem-specific metric: it specifically covers forests.

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Conversely, the STAR metric is complementary to the MSA, as it measures species risk of extinction and not ecosystem condition.

How to use direct measurement of biodiversity state to assess the MSA of a site?

What is the “market share” of the MSA metric?

The MSA is leading the pack in terms of ecosystem condition assessments for corporates and financial institutions

The MSA was the leading metric (almost the only aggregated metric) used by French financial institutions in their 2022 mandatory reporting.

It is used by a dozen tools, covering most business applications and focus areas, from sites/projects to financial assets, as shown in the excellent mapping below (I'll make a more detailed post about this mapping in the near future): all the tools in dark green use MSA as their (or one of their) main metric.

What are the strengths of the MSA?

In Appendix 4 of a position paper drafted by several veteran biodiversity data providers (see PDF in the post below), an excellent and rare comparison table with other metrics highlights the strength of the MSA:

1. Scalable thanks to pressure-impact relationships
2. Linked to the Global Biodiversity Framework: MSA is a complementary indicator of the GBF and linkable to trajectories aligned with its Goal A
3. Proven and tested through use by businesses for 4 years
4. Can be aggregated at corporate, national or global levels and disaggregated at the site level
5. Meets the criteria for a good disclosure metric set out by the TNFD: comparable, science-based yet pragmatic, allows to reflect value-chain impacts, reflects both positive and negative impacts, aligned with global goals while flexible

The MSA is explicitely referenced in the recently published GRI101 biodiversity standard and is cited in leading frameworks such as the #TNFD or #SBTN.

And what about its weaknesses?

The MSA is of course not perfect. Its limits include:

• Lack of a clear definition of the undisturbed state to facilitate direct measurement of MSA through ecological surveys
• Lack of a standardised protocol to directly measure it through field measurement (though work is ongoing to improve this), and lack of databases of undisturbed densities for most species

The limitations of GLOBIO, the model which provides pressure-impact relationships to calculate MSA.km2 remaining biodiversity or impacts, also apply to measurement of biodiversity state based on pressures:

• Absence of pressure-impact relationships for certain biodiversity loss drivers (invasive alien species in particular)
• Total absence of cause-effect relationships regarding marine biodiversity

By contrast, the limitations of the GLOBIO-IMAGE global layer of MSA values around the world do not affect the MSA itself since this layer is not necessary to evaluate corporate impacts

On top of these limitations, it should be reminded that by design, the MSA only covers one aspect of biodiversity, ecosystem condition (and for expert readers, it covers the composition element of ecosystem condition, not the function or structure elements).

Optimising economic activites to minimise negative impacts expressed in MSA would thus lead to protecting and restoring healthy ecosystems but it may lead to choices detrimental to some endangered species for example. This is not a limitation of the metric but rather a feature.

That is why it is necessary to use the MSA together with at least one separate metric, focused on the risk of extinction of species, such as STAR.

Happy to get your thoughts in comments! Please let me know if there is a topic you'd like me to cover in the future!

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Credits: the cover of this issue was made using Bing Image Creator, it is a first go at representing MSA metaphorically as akin to a "green liquid of life", with an healthy ecosystem similar to a glass almost full of this liquid, and a disturbed ecosystem similar to a glass with less liquid. Stay tuned in the coming months as we improve this picture and make it available for everyone to explain MSA simply!