A DNA-based investigation of endolithic community succession on shells of the limpet Patella depressa Pennant 1777

Biotic and abiotic calcium carbonate structures are used as a substrate by bioeroding organisms, or euendoliths, worldwide. Euendoliths can have serious ecological effects on living hosts, and with global increases in ocean acidification and warming, the efficiency of erosion by marine euendoliths is likely to increase. Here, we used growth curve data for the limpet Patella depressa and 16S rRNA sequencing to explore succession in the endolithic community on the shells of P. depressa throughout its range across Great Britain. Limpet age correlated well with the extent of erosion within sites, but differed among sites, with those at the centre of the host range showing greater erosion when corrected for age. Alpha-diversity and richness of cyanobacteria decreased with the extent of erosion, particularly during the earlier stages of erosion. A decrease in the accumulation rate of Amplicon Sequence Variants (ASVs) occurred at around 80 % of cumulative ASVs, at a shell age of between 1.4 and 2.7 years. Cyanobacterial community composition differed among the shells from the different sites, but despite these differences, there were no discernable patterns in the abundance of specific taxa that were associated with limpet age or the extent of erosion. The results revealed that, when examined at a high taxonomic resolution, cyanobacterial community succession is more complex than previously thought, and may be site-specific. However, the trends observed indicate that cyanobacterial community succession occurs on calcifying organisms in vivo, with a shift towards a climax community after 1.4–2.7 years for P. depressa.