Modiolus modiolus Communities of Onega Bay, White Sea: How Stable Are They over Time and Space?

Abstract

Macrozoobenthic communities of Onega Bay of the White Sea were studied in 2010 at ten stations, which repeated the survey sites performed in the 1950s and 1980s by the staff of the White Sea Biological Station, USSR Academy of Sciences. Benthic communities where bivalve mollusks dominated by biomass were observed at all sites investigated in 2010. The stations were divided into two main groups; Modiolus modiolus was the dominant species in the first one, Clinocardium ciliatum in combination with various bivalve species as subdominants dominated in the second. There were also communities in which Hiatella arctica and Macoma calcarea dominated; each community was recorded at only one station. Due to the inability to follow accurately the sampling methods and the peculiarities of primary processing used in the historical surveys, the comparison of the data was carried out using only bivalves, because this was the most reliably defined group that unquestionably dominated in all communities. No significant changes were found in bivalve dominance. The replacement of the blue mussel settlement with a Hiatella arctica community was observed at a shallow depth (13 m). Deeper than 40 m, the dominants changed: Clinocardium ciliatum by Mya truncata (1952), Elliptica elliptica by Macoma calcarea (1981), and Clinocardium ciliatum by Macoma calcarea (2010); these changes were most likely associated with the patchy distribution of these key forms. Modiolus modiolus communities, observed in Onega Bay in 1952 and 1981 at depths of less than 40 m, were found in the same places in 2010. The stability of macrobenthic communities, where large, long-lived bivalves dominated (in particular, Modiolus), was most likely due to the absence of significant changes in the environmental conditions and of an anthropogenic load in Onega Bay during at least the second half of the XX century and the early XXI century.