Daria Blinova, Igor Manushin
Knipovich Polar Research Institute of Marine Fisheries and Oceanography, Murmansk, Russia Abstract
This research presents data on the distribution of key species of bivalves in the cold and warm periods in the Barents Sea. The analysis of the available data on water temperature, depth and biomass of mollusks was conducted to reveal the relationships between the distribution and the environment parameters. The estimation of varieties of species reactions under climate changes for key species of bivalve mollusks is given.
Keywords: Barents Sea, bivalves, environment, climate changes Introduction
In the modern period of climatic changes, especially well visible in the Arctic, attempts are being made to predict the distribution of species under different scenarios of temperature fluctuations. As a source for modeling probable species distribution, it is necessary to have a sufficient amount of data based on a long-term observation series. PINRO hydrobiological studies, started as early as the 20s of the 20th century, can provide a large amount of data of the distribution of specific species for various environmental factors. Previous studies have shown that total biomass of benthos has lower values during cold periods and higher values during warm periods (Manushin et al., 2013).
However, changes in the biomass of individual taxa may differ from this pattern.
Material and methods
The biomass data of bivalve mollusks from bottom grab samples from 1924 to 2017 were used. For this period, four climatic periods were noted in the Barents Sea (Boytsov, 2012; Trofimov, Karsakov, Ivshin, 2018): cold (I) started before 1900 and ended in 1929 (benthic samples were taken of 1924-1929) warm (II) - 1930-1961 (samples of 1930-1935, 1937, 1939, 1945, 1947-1950 and 1955-1956), cold (III) - 1962-1987 (samples of 1968-1972, 1975, 1976, 1978) and continuing warm (IV) - from 1988 (samples of 2003-2017) (Table 1). Ecological characteristics at any periods were considered for 15 species of bivalve mollusks: Astarte elliptica, Bathyarca glacialis, Bathyarca pectunculoides, Chlamys islandica, Ciliatocardium ciliatum, Crenella decussate, Macoma calcarea, Mya truncata, Nuculana pernula, Serripes groenlandicus, Similipecten greenlandicus, Yoldia hyperborea, Yoldiella intermedia, Yoldiella lenticula, Yoldiella lucida. These species could be reliably determined and frequently occurred in the Barents Sea.
The “Statistica 10” software package was used to visualize the ranges of the ecological characteristics of bivalves, where:
And also to calculate the average values:
Table 1. Number of measurements of the near bottom temperature (T), habitat depth (D) and biomass (B) of mollusks
At different periods, the station positions differed significantly, therefore, for comparison, the average values of macrozoobenthos biomass in the water area under consideration were calculated in two ways:
1 – The average biomass was calculated from actual station data (341 stations for the period 1924-1929, 771 stations for 1930-1950, 369 stations for 1968-1970, and 591 stations for 2003-2017;
stations were taken into account located only on the studied area with accounting).
2 – The average biomass was calculated using an interpolation method: the station data was converted into the metadata of the regular grid nodes (100x100) using the “Inverse Distance to Power” method (98 stations over the period 1924-1929, 234 stations over 1930-1950, 141 stations per 1968-1970 and 218 stations from 2003-2017; in this case, for greater accuracy, the influence of stations located not only on the studied water area, but also near its borders was taken into account using the Surfer Version 11.1.719 program. Nodes not related to the area under consideration were not counted. The average biomass in the studied area was calculated as the average biomass in the remaining nodes of the interpolation lattice; in total, extrapolated data of 7049, 6780, 7125 and 7174 nodes were used in the calculations, respectively.
In this paper, the weight of the mollusks is given for alcoholized specimens without conversion to live (wet) weight.
Results and discussion
For the period 1924-2017 the distribution of the total biomass of bivalve mollusks in the Barents Sea was changed only slightly: large biomass was recorded along the coast of the Novaya Zemlya archipelago and southeast of the Spitsbergen archipelago (Figure 1). From one climatic period to another, only the values of biomass changed. In the first period, the largest biomass were noted in the southeast of the sea, where they reached 618.3 g/m2 in the Pechora Sea. The second period was warmer and the mollusk biomass values were higher. This is indicated by the maximum values, which reached 1200 g/m2 in the area of Cape Kanin Nos, 900 g/m2 in the Rybach'ya Bank, 600 g/m2 in the area of the Sukhoy Nos and the Melkovod'ye Gusinoy Zemli. It is assumed that the true values of the biomass of mollusks were higher, because bottom grading works in the southeast of the Barents Sea, where traditionally high values of the biomass of mollusks are noted, were
practically not carried out. This was followed by a cold period in which there was a significant decrease in biomass. As before, the highest values were observed in the southeast of the sea, where they reached 510 g/m2. In the last, the warmest period, the Spitsbergen bank and the Pechora Sea have become areas with maximum biomass, with maximum values of 1200 and 1100 g/m2, respectively. The data obtained for the last two periods can be considered the most accurate, since the grid of stations covers almost the entire sea.
Figure 1. Bivalve mollusks biomass distribution in the Barents Sea in different climatic periods.
The maximum average biomass of bivalve mollusks, according to both actual and model data, was recorded in the Barents Sea in I and IV climatic periods (Figure 2). Thus, the Bivalvia communities show high biomass in both cold and warm periods. This means that parameters such as temperature and sea ice extent themselves do not play a significant role for biomass values, and other, possibly internal, factors play a decisive role. Therefore, changes in the biomass of individual species were considered.
Figure 2. Average biomass values (g / m2) of bivalve mollusks according to actual (left) and model data (right) with the standard error in the studied area.
The ecology and biomass dynamics of 15 species, which are well identified even at an early age and constitute a significant part of the total biomass of bivalve mollusks, were considered. Of the selected species, 9 were identified, whose trends in biomass changes were the same as the changes characteristic of the whole group of bivalve mollusks. These are Ciliatocardium ciliatum, Serripes groenlandicus, Crenella decussata, Macoma calcarea, Nuculana pernula, Similipecten greenlandicus, Yoldia hyperborea, Yoldiella intermedia, Yoldiella lenticula.
The other 5 species (Chlamys islandica, Bathyarca glacialis, Mya truncata, Astarte elliptica, Yoldiella lucida) react to changes in the environment in the same way as most benthic organisms:
biomass increases in warm periods and decreases in cold ones. The exception is Bathyarca pectunculoides, which biomass changes does not allow to attribute it to any of the groups.
For each species, graphs of changes in the depths and temperatures of the occurrence of mollusks in each of the periods were compiled. As a result of the analysis, individual characteristics of the reaction to climate change in each species were noted. We consider a few examples (Ciliatocardium ciliatum from the first group, Chlamys islandica from the second and Bathyarca pectunculoides).
In the second half of the 20s, the species Ciliatocardium ciliatum was distributed mainly in the southeastern and central parts of the Barents Sea (Figure 3). With climate changes, the distribution of this species did not change significantly, only the frequency of occurrence of mollusks in the central part of the sea from the Spitsbergen archipelago to Novaya Zemlya increased. Throughout the entire period of studies of this species, a slight increase in its median values of temperature was noted; the depth of the mollusks increased only in the second period (Figure 4).
Figure 3. Biomass distribution of Ciliatocardium ciliatum in the Barents Sea.
A typical representative of the second group is the Icelandic scallop Chlamys islandica. In warm periods, the species occupies a larger water area than in cold ones, both in traditional habitats and in new ones (shallow waters along the Novaya Zemlya archipelago) (Figure 5). The average biomass at the stations is also greater in warm years than in cold ones (Figure 6). The median depth of habitat gradually decreases over the entire observation period, while the temperature of the presence
of representatives of the species in the first three periods remains unchanged, and only in the last period increases.
Figure 4. From left to right: Median depth (m) and temperature (°С) of Ciliatocardium ciliatum occurence, as well as their average biomass values (g/m2).
Figure 5. Biomass distribution of Chlamys islandica in the Barents Sea.
Figure 6. From left to right: median depth (m) and temperature (°С) of Chlamys islandica occurence, as well as their average biomass values (g/m2) in the studied area.
Individuals of the warm-water Bathyarca pectunculoides react to climate change quite differently.
This species was found mainly in the southwestern part of the sea, where the bottom temperature has positive values and was single encountered north of 76º (Figure 7). Its biomass is higher, although not significantly, in cold periods than in warm periods (Figure 8). In cold periods, this species is found in deeper parts of the sea than in warm. The habitat temperature of the species in the Barents Sea is about the same for the first three climatic periods and significantly higher in present.
Figure 7. Biomass distribution of Bathyarca pectunculoides in the Barents Sea.
Figure 8. From left to right: median depth (m) and temperature (°С) of Bathyarca pectunculoides, as well as their average biomass values (g/m2) in the studied area.
Changes in biomass and habitat conditions of certain species of bivalve mollusks in different climatic periods in large areas show that the characteristics of their distribution and the dynamics of biomass depend both on a complex set of factors (temperature, depth, ice cover, soil, amount of food, etc.) and on ecological plasticity of the species. For example, a species under the influence of changes in temperature can either disappear in a given area, or change its depth. Moreover, this reaction will depend not only on the ecological plasticity of the species, but also on the duration and impact force - large individuals of bivalve mollusks living for 10–20 years and making the main contribution to biomass can safely survive several years of adverse conditions. Thus, in order to predict the reaction of a species to climate change, it is necessary to know its “history” of habitat in
Conclusions
Long-term forecasting of the distribution and biomass of certain species of bivalve mollusks is impossible without long-term (of several generations) and detailed studies of their reactions to the external environment.
References
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Manushin, I.E., Anisimova, N.A., Lyubin, P.A., Vyaznikova, V.A., Zakharov, D.V. 2013. Changes in biomass of macrozoobenthos in the eastern part of the Barents Sea during last century // ICES CM 2013/B:16. 2 pp.
Trofimov, A., Karsakov A., Ivshin V. 2018. Climate changes in the Barents Sea over the last half century (in this book).