No abstract

Onega Bay is the largest bay in the White Sea, characterised by shallow depth, a range of sediment types and strong tidal currents. All these factors provide conditions for high species richness and biomass. This study reviews data from three surveys of sublittoral macrobenthos undertaken by Russian institutes: the benthic survey covering the entire Onega Bay in 1952; the survey performed in the northern part of the area in 1981/90, and a study carried out in 2006 in the eastern part of the bay. In total, data from 107 stations were analysed. The data in different surveys were collected by different grab types. The datasets of both 1981/90 and 2006 overlap the 1952 survey area. The pattern of biomass distribution was consistent between the years of survey and was characterised by the low biomass at the northern periphery of the bay and the highest biomass observed in the coastal waters of the Solovetsky Islands. Bivalves and cirripeds (mostly Modiolus modiolus, Arctica islandica, Balanus balanus and Verucca stroemia) dominated in biomass. Neither the biomass share of dominant species nor the frequency of occurrence of several common species in these groups changed markedly between 1952 and 1981/90. Although the results of the 2006 survey appear somewhat different from the patterns of previous years, this does not indicate major changes in the benthic communities, because the survey in 2006 was designed in a different way and its overlap with the 1952 survey was minimal. However, the dominant species (by biomass) –A. islandica, M. modiolus and V. stroemia– held their leading positions. Results of the multidimensional scaling analysis based on the biomass data for all taxa encountered in the 1952 survey indicate considerable mixing of the samples from all surveys. This may be interpreted as the absence of major shifts in the sublittoral communities of the macrobenthos of Onega Bay at decadal scale. This kind of stability may be explained by an oceanographical regime resilient to climate variation and a relatively low anthropogenic environmental impact when compared to other shallow European seas.

This study presents an inventory of the sublittoral macrobenthic fauna of the Gorlo Strait, based on historical surveys (1922, 1980s) and an investigation carried out in 2004. A comparison of the species lists was carried out, giving particular attention to current nomenclature, synonymies and biogeographical affinity. Differences in species lists can be explained by differences in sampling gear and design, but generally species lists are complementary. The total number of species in all surveys amounts to 322, with an additional 39 taxa unidentified to species level. All the species identified represent 254 genera and 166 families. The macrobenthic fauna of the Gorlo is thus generally rich but mostly consists of rarely occurring species. This is discussed in the light of specific environmental conditions of the Gorlo, in particular low primary productivity in the water column, strong tidal currents and the unstable lithodynamics. The combined species list was characterised by high taxonomic distinctness index (96) sensu Clarke and Warwick (1998); the indices calculated for particular surveys showed only slight and mostly statistically nonsignificant differences from this value. The biogeographic structure of species composition of Gorlo does not differ between years, with the Arctic-boreal species constituting the majority (about 60%) and the Boreal and Arctic species having nearly equal shares (about 15%). Although our study revealed few North Atlantic species not hitherto recorded in the White Sea, stable shares of species with particular biogeographical affinity at the decadal scale, stability of the taxonomic distinctness indices and small differences in the composition of the core of most commonly occurring species indicate the absence of major shifts in the faunal composition: current climatic changes most probably have not yet significantly affected specific oceanographical conditions and benthic habitats of the Gorlo which shape the local macrobenthic fauna.