Factors Influencing the Abundance and Coverage of Ramalina sp. Lichens on Selected Three Mangrove Species

Abstract

Mangrove ecosystems are vital and highly threatened coastal habitats, and lichens of the genus Ramalina serve as important bioindicators. However, their distribution in Sri Lankan mangroves remains critically understudied. This study investigated the abundance and coverage of Ramalina lichens on three key mangrove species: Excoecaria agallocha, Rhizophora mucronata, and Lumnitzera racemosa in Rekawa Lagoon to determine the influence of host tree characteristics and microenvironmental conditions. Data were systematically collected over one month (3^rd of November to 3^rd of December 2024) from a total of 90 randomly selected trees (30 per species), recording lichen abundance, coverage, tree height. Regression analysis revealed that canopy cover was the dominant factor, showing a strong positive correlation (p<0.0001) with lichen abundance across all three species. The regression equations between lichen abundance and canopy cover were: E. agallocha-Number of lichens=6.442+34.15 canopy cover (R² = 64.0%, p=0.000); R. mucronata-Number of lichens =-2.689+44.98 canopy cover (R²=74.7%, p=0.000); and L. racemosa-Number of Lichens=-23.98+65.12 canopy cover (R²=94.8%, p=0.000). These results suggest that a dense canopy is crucial for creating a stable microclimate, particularly consistent moisture, necessary for the fruticose Ramalina growth form. Tree height, however, exhibited species-specific influences, with the following regression equations: E. agallocha - Number of lichens = 11.65+0.0726 Tree height (R²=63.7%, p=0.000); R. mucronata-Number of lichens=78.87-0.1017 Tree height (R²=66.4%, p=0.000); and L. racemosa-Number of lichens=91.42-0.2129 Tree height (R²=62.6%, p=0.000). Multiple regression analysis further confirmed that canopy cover had a consistent positive effect, while tree height varied by species: E. agallocha-Number of lichens=5.94+0.0425 Tree height +20.32 canopy cover; R. mucronata - Number of lichens=41.9-0.0567 Tree height+24.17 canopy cover; and L. racemosa-Number of lichens=-6.85-0.0368 Tree height +57.99 canopy cover. A one-way ANOVA indicated no statistically significant difference in overall lichen coverage among the three-mangrove species (p=0.270). These findings highlight that the distribution of Ramalina sp. lichens is driven by a combination of overarching environmental factors (canopy cover) and host-species-specific traits (tree height), offering valuable insight for ecological monitoring and conservation of mangrove canopy integrity.

Keywords: Ramalina sp., Lichens, Mangrove species, Abundance and coverage, Bioindicators