Phytoplankton production in the coastal water is to a large degree influenced by local hydrologic and meteorological factors, including fresh water runoff, wind mixing, tidal regime, as well as ice melting in the coastal areas. As for the open ocean the annual phytoplankton cycle could be divided into phases (winter, spring, summer, and autumn) as for the open areas. Along the Barents Sea coastal line there is large variation in the onset of the different phases along the Russian and Norwegian coast.
During the winter phase (November – mid March) the biomass and diversity of the phytoplankton is low and highly mosaic spatial distribution in abundance and biomass of microalgae (Druzhkov et al., 1997). The dominating group of the phytoplankton is diatoms, often a mix of pennales and centric forms in some areas, whereas dinoflagellates are more common in other. It is likely that also pico- and nanoflagellates are present in this period.
During the spring phase (mid March to early June) there is an increase in the phytoplankton biomass. The spring bloom will start as soon as the water column shows some degree of stratification. The start point of the spring bloom varies from year to year. It may start early, peaking at the end of March, or later peaking in May or even as late as early June. However, in generally the spring bloom maximum occur during April and early May. During the spring bloom the dominating phytoplankton group is diatoms. The bloom could be dominated by several species and different species could be dominating in different areas. There could also be differences between years in dominating species.
In some areas, there is a clear development in the diatom community with some species following others. Species that is dominating during this spring period will be Chaetoceros curvisetus, C. furcellarus, C. diadema, C. holsaticus, C. socialis, Chaetoceros contortus, C. debilis, C. decipiens, C. Diadema, Navicula vanhoeffenii, N. pelagica, Nitzschia grunowii, Thalassiosita gravida, T. hyalina, T. nordenskioeldii, Thalassionema nitzschioides, Fragilariopsis oceanica and Skeletonema. In addition to diatoms, the haptophyte Phaeocystis pouchetii could contribute significant to the total spring bloom biomasses in some areas. However, in most cases Phaeocystis forms blooms a short period after the main top of the spring bloom. In some areas there is a marked second spring bloom in June, often connected to fresh water runoff from land. This bloom varies every year in timing, in quantitative characteristics and in qualitative composition. In the end of the spring period, as the diatom biomass decrease, flagellates are dominating and Pyramimonas and cryptomonads (e.g. Plagioselmis spp. and Teleaulax acuta ) have their yearly maximum in June together with other naked flagellates. The dinoflagellate Heterocapsa rotundata, Protoperidinium depressum and small naked dinoflagellates are also common in this post blooming period.
As the phytoplankton community enters the summer phase (June to the end of August) the abundance is reduced and new species are coming in. In this period there are large differences between sampling areas, with a high degree of mosaic in the phytoplankton horizontal distribution. In some sections diatoms (Pseudo-nitzschia “delicatissima type”, Skeletonema, Chaetoceros contortus, C. laciniosus, C. diadema, Chaetoceros wighamii, Dactyliosolen fragilissimus, Leptocylindrus minimus, Leptocylindrus danicus,Thalassionema nitzschioides) are dominating and forming smaller blooms. In other areas dinoflagellates, such as small athecate dinoflagellates (<20 µm), several species of the genus Protoperidinium, Scrippsiella trochoidea, Heterocapsa triquetra, Prorocentrum minimum, are more prominent. Smaller flagellates will also be an important part of the phytoplankton community. Later in this period (July-August) dinoflagellates become more common along the coast, especially species in the genus Ceratium and Dinophysis. In the later years large blooms of Emiliania huxleyi has been observed in July-August, covering large areas along the Norwegian Barents Sea coast.
During the autumn phase the biomass and diversity decrease until it reach winter situation during November. The phytoplankton community is dominated by dinoflagellates (Ceratium sp, Dinophysis spp, Scrippsiella sp and Protoperidinium spp). Even though the phytoplankton biomass is decreasing during this phase, some species of Ceratium might form high biomass blooms during August in some coastal areas. Generally diatoms are few in autumn, but in early autumn Chetoceros affinis and Proboscia alata may be of some importance.
Vertical distribution of phytoplankton during the whole year depends on the density of water mass: in the autumn-winter period, when seasonal pycnocline is absent, pelagic micro algae are evenly distributed along the entire water column; during the spring bloom, the center of the community is localized on the surface horizon; once the summer stratification is established, maximal abundance of phytoplankton occurs at the depth of 15-20 m, placed right above the pycnocline (Druzhkov et al., 1997; Larionov, 1997). In autumn-winter during period of absence of seasonal pycnocline, the phytoplankton is distributed evenly in the water column from the surface to the depth of main pycnocline bedding.
As mentioned above, this succession cycle is characterized by high stability despite annual climatic variability (warming, cooling, etc). Even more so – those deviations in cycle that are observed in different geographical regions of the sea don’t affect its main structure, and differences are only due to the terms of the start and length of the hydrological seasons. However, this conclusion is fully valid only for the open part of the Barents Sea. Data, presented above, shows that phytoplankton in the coastal areas shows significant variations.
Even more variations in the seasonal succession are found in estuarine areas (Kola gulf, Pechora bay, etc). Apparently, microalgal communities of the open waters have a strong developmental dependency on changes in the “global” climatic and oceanological factors (level of insolation, sea ice dynamics, and water mass distribution). While in estuaries, the main role belongs to the local processes – tidal and wind activity, fresh water input and mesoscale level hydrophysical structure of the water mass. For the coastal ecosystems, there is an intermediate situation, when during the different stages of development of phytoplanktonic communities main role belongs either to the first or a second group of factors (Larionov, 2002). This theoretical conclusion is very important in practical sense – for the complex research projects of the Arctic marine ecosystems with the purpose of forecasting possible negative consequences as a result of their exploitation. In essence, these differences define the reaction to the anthropogenic impact that causes change in the environmental parameters. Estuaries and, to a lesser degree, coastal ecosystems, experiencing a large number of ongoing local processes and well-adapted to such conditions after a long evolutionary period, accept disturbances in biotope just like an appearance of a new additional factor. They react quickly to the environmental change and the effect is basically imperceptible for the structure as a whole or is very limited in time and space.
