Euendolithic shell-boring cyanobacteria and chlorophytes from the saline lagoon Ahivadolimni on Milos Island, Greece

Samples of typical estuarine mollusc shells (Cerastoderma glauca, Abra ovata and Hydrobia acuta), differing in appearance, size and age, were collected from littoral habitats of a saline water lagoon (Ahivadolimni on Milos Island, Greece). Each shell sample was examined for the distribution, frequency and taxonomy of its shell-boring cyanobacteria and chlorophytes, and the associated attached (epizoic) diatoms. The euendolithic microflora was extracted using Pereny's solution and observed by light microscopy (LM). The results of microbial penetration (traces of euendoliths) were examined by scanning electron microscopy (SEM) after a hypochlorite treatment. The three-dimensional patterns of microbial penetration (boring patterns) were investigated under SEM by applying the resin-casting technique for modern euendoliths. Of the five euendolithic cyanobacteria found, one (Cyanosaccus atticus) was established from Greek marine biotopes, three (Hyella caespitosa var. arbuscula, H. inconstans and H. reptans) are second records and new for Europe, whereas one cyanobacterium (Leptolyngbya terebrans = Plectonema terebrans) and the three euendolithic chlorophytes found (Phaeophila dendroides, Ostreobium quekettii and Gomontia polyriza) show a cosmopolitan distribution. A survey of the diatoms found as epizoic on the mollusc shells (30 taxa) shows that most of them are typical representatives of marine to brackish water of coasts and estuarine areas. A systematic account of all euendoliths found in the mollusc shells is given. The morphological variability of the cyanobacterium Hyella inconstans, and of the chlorophytes Ostreobium quekettii and Gomontia polyriza is presented, with extended taxonomic comments for the latter species. The susceptibility of molluscs to infestation, as well as the morphological variability, world distribution and penetration patterns of the euendoliths within the host mollusc shells are also discussed.