Zoogeographical groups of fish species are associated with specific water masses. Rel-ative distribution and abundance of fish species belonging to different zoogeographic groups are of interest because these fish will respond differently to climate variability and change. Since they are not commercial species, fishing does not directly contribute to changes in abundance and distribution of these species. Different zoogeographic groups also tend to differ in their trophic ecology: many of the Arctic species are small, resident, and feed mainly on invertebrates; whereas, most boreal and mainly boreal species are migratory and piscivorous.
Therefore, the relative abundance of these spe-cies should influence foodweb structure and dynamics. Comparing changes in relative abundance and distribution of species classified into zoogeographical groups based on established criteria from the literature, is relatively simple and does not rely on sophis-ticated statistical methods — like those used to study changes in the Barents Sea fish community, e.g. Fossheim et al., 2015 and Frainer et al., 2017.
Andriashev and Chernova (1995) classified Barents Sea fish species into seven zoogeo-graphical groups: widely distributed, south boreal, mainly boreal, Arctic-boreal, mainly Arctic, and Arctic. In the recent publication, “Marine Fishes of the Arctic Re-gion” (Mecklenburg et al., 2018), some fish species were reclassified into six zoogeo-graphical groups: widely distributed, boreal, boreal, mainly boreal, Arctic-boreal, mainly Arctic and Arctic. We use the Andrashev and Chernova classification scheme here, since it is more comprehensive and includes a larger number of species occurring in the Barents Sea. We give the change in distribution of different zoogeographic group species from the BESS survey 2004–2017 (Figure 3.7.1).
It was found that each year south boreal and boreal species occurred in southern and southwestern areas of the Barents Sea, while Arctic and mainly Arctic species occur in northern and northeastern areas. Arctic-boreal species were observed in central, north-ern, and northeastern areas. Mainly boreal species were observed throughout survey areas during 2004–2017 (Figure 3.7.1).
Generally, since the onset of the ecosystem survey in 2004, a decrease of the area of species from Arctic, mainly Arctic, and Arctic-boreal group has been observed (Figure 3.7.1). This may be due to change in the direction of survey from south to north in 2017;whereas, the direction was from north to south in 2016. Northern areas were sampled during September in 2017; whereas they were sampled during August (one month ear-lier) in 2016. Southern areas were sampled during August in 2017; whereas they were sampled during September in 2016. Water mass temperature differs between August and September, and species distribution may shift with changing water mass temper-ature; this might explain the differences observed between 2016 and 2017.
Figure 3.7.1. Distribution of non-commercial fish species from different zoogeographic groups dur-ing the ecosystem survey 2004–2009. Size of circle corresponds to abundance (individuals per nau-tical mile, only bottom-trawl stations were used, both pelagic and demersal species are included).
Figure 3.7.1 (continued). Distribution of non-commercial fish species from different zoogeographic groups during the ecosystem survey 2010–2017. Size of circle corresponds to abundance (individu-als per nautical mile, only bottom-trawl stations were used, both pelagic and demersal species are included).
Since the onset of BESS in 2004, a decrease in the distribution area of species from Arc-tic, mainly Arctic, and Arctic-boreal zoogeographic groups have been observed.
In 2017, both distribution area and abundance of species, categorized as Arctic and mainly Arctic zoogeographic groups, increased relative to 2016. The ecosystem survey covered the northern area during September in 2017, but during August in 2016. Con-versely, the survey covered the southern area during August in 2017 and during Sep-tember in 2016. Water mass temperature differs between August and September, and since species distribution may shift with water mass distribution, this might explain the difference between 2016 and 2017.
Due to different survey area coverage from year-to-year, it is difficult to analyse inter-annual variability. It is therefore necessary to choose areas that have been sampled consistently each year, and use these data to evaluate trends and determine how well the new zoogeographic classification system (Mecklenburg et al., 2018) applies to spe-cies in the Barents Sea ecosystem.
Benthos: Interannual fluctuation of the fauna biogeographical structure.
To visualize the border areas between prevailing Boreal and Arctic fauna, the biogeo-graphical index (BGI) was developed (Manuchin et al., 2012); boreal-arctic fauna are not included. The index can be calculated with different parameters (biomass, abun-dance, number of the species etc.) using the following equation:
where: Pa – quantitative parameter of arctic species; Pb – quantitative parameter of boreal species.
BGI ranges from 1 (only boreal species are present at the trawl station) to -1 (only arctic species are present); 0 value indicates an equal ratio between boreal and arctic species. Situations where neither boreal nor arctic species are present will result a “0” BGI value (equal ratio between boreal and arctic species).
The BGI distribution in in 2017 indicates that the southern Barents Sea- southern part of Svalbard, Svalbard Bank, and the Pechora Sea in the East- is dominated by boreal fauna (Figure 3.7.2).
Figure 3.7.2. The distribution of the biogeographical Index (BGI) of the megabenthos in the Barents Sea according to ecosystem data from 2017. Ba – biomass of arctic species; Bb – biomass of boreal species; black line is the border of the equal ratio of the boreal and arctic species in the terms of biomass.
Interannual fluctuation in the BGI, calculated using total biomass, show the same dy-namic as biomass anomalies (Figure 3.7.3). The lowest BGI value (2009) corresponds to the coldest year (2003) with a 6-year time delay.
Figure 3.7.3. Dynamics of the Biogeographical index (BGI) during 2006–2017 (black line) and indi-cators of the oceanographic condition of the Barents Sea: % area of the Barents Sea bottom covered by arctic water (blue bars) (WGIBAR report 2017, Figure 3.1.17), and the temperature anomalies in the Kola sections (red line) (http://www.pinro.ru).
In summary, the short timeline of benthic monitoring, combined with technical issues and data gaps/poor coverage, make it difficult to determine long time-trends. But, in-terannual fluctuations in the hydrological and biological parameters suggest that a de-crease in benthic biomass may be recorded 6-7 years after a cold period.