Taxonomic composition and recording of priority habitat maerl using citizen science data.

Published online
12 Apr 2024
Published by
Natural England
Content type

Jackson, A. C.

Publication language
UK & England & Irish Republic


This is a report to Natural England (NE) about the biological records for maerl held in the Seasearch database. The overarching intention is to explore distributions and spatial variability in composition of maerl biotopes. Specific objectives included comparison of diversities and compositions of assemblages of benthic taxa in (1) named maerl biotopes at Levels 4 and 5 in the JNCC marine habitat classification from different areas of Britain and Ireland and (2) named maerl biotopes against other biotopes that contain maerl (Level 4 only) from England. A new system for categorising maerl habitat was applied to all existing English records of maerl in the Seasearch database. Maps were then created showing distributions of these categories of habitat in relation to known distribution of maerl biotopes from the MHC. There were no differences in diversity among samples of Level 4 maerl biotope (SS.SMp.Mrl) from different areas of Britain and Ireland, but multivariate analyses of taxonomic composition showed differences between southern and northern areas. Similarly, there were no differences in diversity between different Level 5 maerl biotopes from different areas, but taxonomic composition of Level 5 biotopes in Scotland differed from those further South. Different Level 5 maerl biotopes from England did not differ in composition. Level 4 maerl biotope from England had similar taxonomic composition to samples of infralittoral mixed sediment (SS.SMx.IMx) that contained maerl, but differed significantly from all other Level 4 biotopes with maerl. Patterns observed are likely caused by a combination of actual patterns plus the confounding effects of small sample-sizes and inaccurate determinations of maerl biotopes. The latter is a consequence of the inability of the MHC to capture the diversity of maerl habitats and a lack of clear guidance about how to record maerl habitat. Distributions of different maerl habitats clearly occur more broadly than the known distributions of MHC maerl biotopes. Maps of a broader range of maerl habitats (including for example, dead maerl, veneers and small patches) will permit assessment of where and whether ecologically-valuable maerl habitat merits protection over and above existing conservation designations. Where statutory nature conservation bodies are legally obliged to monitor and conserve priority features of conservation interest, but where data are challenging to collect, records collected by trained volunteers and curated by Seasearch can make valuable contributions to our understanding and responsibilities. Consistency and quality of such records will be much improved if approved national guidance is made available.

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