Distribution of bivalve mollusks Macoma golikovi Scarlato and Kafanov, 1988 and Macoma calcarea (Gmelin, 1791) in the shallow-water hydrothermal ecosystem of Kraternaya Bight (Yankich Island, Kuril Islands): connection with feeding type and hydrothermal activity of Ushishir Volcano

Abstract

Kraternaya Bight (Yankich Island, the Kuril Islands) is a submerged crater of the active Ushishir Volcano characterized by terrestrial and underwater gasohydrothermal activity. The gasohydrothermal activity of the volcano produces a great influence on the physico-chemical characteristics of water column, as well as planktonic and bottom communities of marine organisms of the bight. The bivalve mollusks Macoma golikovi and Macoma calcarea are dominant macrobenthos species of Kraternaya Bight, which inhabit all the zones of underwater volcanic activity. Macoma golikovi occurs at a depth of 1–45 m. This species forms the densest aggregations (with an average biomass of 500–800 g m −2 and a population density of 500–700 ind. m −2) at a depth of 3–15 m, on steep underwater crater slopes (40–45°), on slightly silted gravel. The majority of gasohydrothermal vents are located at that depth. Macoma calcarea occurs at a depth of 5–55 m. In contrast to Macoma golikovi, this species is dominant at a depth of 25–40 m, on gentle slopes of the crater (to 20°), on silt and silty sand. That depth is less subjected to the influence of volcanic products. Its average biomass is 450–750 g m −2 with a population density of 200–450 ind. m −2 there. It is assumed that the differences in the distribution are due the fact that Macoma golikovi is mainly a suspension-feeder in Kraternaya Bight, and Macoma calcarea is a deposit-feeder. The studies conducted between 1987 and 1997 on the quantitative distribution of Macoma golikovi and Macoma calcarea in four areas of the bight, which had different intensity, temperature and chemical composition of gasohydrothermal vents and volcanic water seeping showed that both species formed settlements with lesser density in the area of the gasohydrothermal vents containing hydrogen sulfide. Beyond the area of volcanic activity, these species were most abundant. In 1993 and 1995, the mortality of the populations of the bivalve mollusks was observed in the areas of hydrogen sulfide gasohydrothermal vents and volcanic water seeping. In other areas of the bight, their abundance decreased sharply suggesting a relationship to the gasohydrothermal activity of the volcano in those years. Circumstantial evidence for this suggestion was that in 1993, the maximal concentrations of Fe, Zn, Cd, and Mn were observed in the tissues of both species. Macoma golikovi accumulated 5–10 times more Zn than Macoma calcarea. The concentration of Zn in the tissues of Macoma golikovi reached 2000 μg g −1.