The biodiversity of epilithic microalgal communities colonising a Central Mediterranean coastline

Abstract

Microbial communities colonise the coastal ecosystem around the Maltese islands. However, such communities are understudied, both in Malta and in the central Mediterranean. This research aims to increase current knowledge about the biodiversity of phototrophic communities growing along a central Mediterranean rocky shoreline and is the first such study to be performed on microorganisms growing in epilithic biofilms and microbial mats along the coastline in the Maltese islands. Samples were obtained using techniques that were noninvasive to the underlying substratum. These were studied by direct observation using light and electron microscopy, by culturing in vitro, by molecular analysis via sequencing of the small subunit ribosomal ribonucleic acid genes and phylogenetic analyses. Microscopic analyses revealed highly diverse communities made of both photosynthetic and heterotrophic organisms. The predominant microorganisms were simple filamentous cyanobacteria including species of Leptolyngbya, Phormidesmis, Nodosilinea, Toxifilum, Phormidium, and Lyngbya, as well as heterocytous Calothrix and Nunduva spp. The coccal cyanobacteria included species of Aphanocapsa and Chroococcus, whereas coccal microalgae belonged to Chlorella, Chlamydomonas, and Coelastrella spp., accompanied by diatoms of Navicula sp. These results include first records of cyanobacterial and microalgal barcodes that were genetically sequenced from a coastline in the central Mediterranean. Germlings of the filamentous macroalga Cladophora were embedded in the rocky substrate that was preconditioned by biofilm growth and ciliated protozoans, micronematodes, and microcrustaceans interacted with the microbial communities. The isolation of new cyanobacterial and microalgal strains from these phototrophic communities highlights the importance of employing a combined multiphasic approach to supplement current knowledge about the biodiversity of microbial communities colonising rocky shores.