Year: 2020, Number: 4, Pages: 3-24
This paper is dedicated to the 35th anniversary of the beginning of the biological studies in Kraternaya Bight of Yankich Island in the submarine Ushishir volcano crater (the central Kuril Islands). Here, in different areas of the shallow-water volcanism, microphytobenthos diatoms were studied for the first time. The study is focused on the diatom composition and abundance in the algobacterial mats in August – September 1985 and 1986. Samples from different beds (sand, pebbles, boulders, stones) at depths ranging from 3 to 15 m and at water temperatures 6–25 °C were taken by Dr. V. G. Tarasov using scuba diving equipment. The study of diatoms in the algobacterial mats on different substrates and at different temperatures of the gas-thermal waters is important due to the fact that Kraternaya Bight in the Russian waters of the Kuril Islands has unique conditions for the development of high abundance and biodiversity of the volcanic underwater inhabitants. Therefore the aim of this work is to study the composition of benthic diatoms in algobacterial mats in different areas of the cold shallow-water gas-hydrothermal vents of Kraternaya Bight. A list of 100 taxa of the phylum Bacillariophyta (23 orders, 33 families and 45 genera) is given. There are three classes of Coscinodiscophyceae (18 taxa), Fragilariophyceae (17) and Bacillariophyceae (65). 14 taxa were common at all stations, and 72% are marine species, 31% –cosmopolites and 17% – β– mesosaprobionts. Depending on the color of the biolayer covering the bottom of the sea, three varieties of the algobacterial mats were distinguished. At Station 1, in the area of the western cold hydrothermal vent with red-brown and brown mats on sands (3–15 m depth, 3–8 °C), 69 taxa were found with a total diatom community abundance 311•106 cells•L-1 with the dominant pennate benthic species Pleurosigma elongatum (104•106 cells•L-1) and Cocconeis costata (37.8•106 cells•L-1). At Station 2, in the area of the eastern hot hydrothermal vent with white mats (3–5 m depth, 20–25 °C) on pebbles and stones, 74 taxa were found with a total diatom community abundance 798.9•106 cells•L-1. Among them, Melosira moniliformis (155.6•106 cells•L-1) and small cells of pennate species Achnanthes sp. (100•106 cells•L-1) and pelagic Thalassiosira anguste-lineata (66.7•106 cells•L-1) were dominant. At Station 3, the area of the northern cold gas hydrotherms (6–8 m depth, 6–8 °C) on boulders, 21 taxa was found with the predominance of benthopelagic colonial of the centric diatom Paralia sulcata and pennate colonial of Fragillaria striatula. The biological diversity and ecological flexibility allow benthic diatoms to adapt to extreme environmental conditions, including those in Kraternaya Bight.