ONCE AGAIN ON THE RELATIONSHIP BETWEEN SPECIES DIVERSITY AND BEDROCK COMPOSITION: A CASE STUDY OF THE UNIQUE MRAMORNY ISLAND, VON’GA BAY, WHITE SEA

Abstract

Сarbonate rocks of unique Mramorny (Marble) Island (65.420921 N, 34.631167 E) constitute a ca. 5-40 m thick lens-shaped body thrown into isoclinal folds. They are associated, interbedded and deformed jointly with amphibolites and are cut by granite-aplites. Their major minerals are dolomite (ca. 70-90%), calcite, biotite and hornblende. Isotopic data show that Mramorny Island carbonate rocks are endogenously igneous carbonatites. Geochronology data date the magmatic stage of carbonatite formation to 2420±20 Ma and metamorphic alterations of this rock to 1845±15 Ma. During the survey in 2018, 82 species of vascular plants, 25 mosses and 44 lichens were recorded from the island. The vascular plant flora was not very specific, but richer in species compared to other White Sea islands of similar size. High frequencies and abundances were noted also for such calciphilous species as Botrychium lunaria, Draba incana and Saxifraga cespitosa. The moss flora was not rich, but the proportion of calciphilous species was quite high – there occurred Brachythecium glareosum, Brachythecium turgidum, Distichium inclinatum and Ditrichum flexicaule. For Brachythecium glareosum Mramorny Island is the only location among White Sea islands where the species has been found. The calciphilous lichens encountered were Bilimbia sabuletorum, Caloplaca stillicidiorum, Candelariella aurella, Cladonia pocillum, Fuscopannaria praetermissa, and Xanthoria elegans. Five species (Rhodiola rosea, Brachythecium glareosum, Brachythecium turgidum, Distichium inclinatum and Ramalina subfarinacea) are listed in the regional Red Data Book. The unique geological structure of the island has had the most pronounced effect on the bryoflora, less so on the lichen flora, and the weakest effect on the flora of vascular plants. The latter can be attributed to the small size of the island and the peculiarities of its relief, which leads to an almost unhindered transport of carbonatite weathering products into the sea by rainfall and seawater.

Keywords

• carbonate rocks, insular biogeography, vascular plants, mosses, lichens, republic of karelia