Maija Balode

Variability in inorganic and organic nitrogen uptake associated with riverine nutrient input in the Gulf of Riga, Baltic Sea

Concentrations and rates of uptake of dissolved organic nitrogen (DON, free amino acids, and urea) and inorganic nitrogen (DIN, nitrate, and ammonium) were measured along two transects in the Gulf of Riga, a sub-basin of the Baltic Sea, during May and July 1996. Concentrations of total dissolved nitrogen (TDN) were 23±3 μg-at N 1−1 in the northern region (mouth) and 41±5 μg-at N 1−1 in the southern region (head) of the Gulf. Rates of nitrogen uptake, determined with15N-labeled substrates, reflected differences in TDN concentration between the regions. In May, uptake of DIN+DON measured 0.17 and 0.43 μg-at N 1−1 h−1 in the northern and southern parts of the Gulf, respectively. In July, DIN+DON uptake measured 0.38 and 0.68 μg-at N 1−1 h−1 in the north and south, respectively. Most of the variability in total nitrogen flux between the northern and southern regions was due to heterogeneity of DON utilization. Uptake of urea and dissolved free amino acid were up to 6 and 3 times greater in the south compared to the north. As evidenced by size-fractionation, plankton size structure appeared to play a role in the uptake of DON. The community in the southern part was largely composed of cells <5 μm, while up to 67% of the community in the northern part was composed of cells >5 μm. Our results indicate that DON was a major source of nitrogen to phytoplankton, particularly in the southern part of the Gulf.

Spatial distribution of phytoplankton in the Gulf of Riga during spring and summer stages

Distribution patterns of chlorophyll a, phytoplankton species and biomass were studied in the Gulf of Riga, one of the most eutrophicated areas of the Baltic Sea. Quasi-synoptic measurements were carried out during four seasonal stages (spring bloom 1995, early-summer stage 1994, cyanobacterial bloom 1994, and late summer stage 1993). For each stage, common factor analysis was used to simplify the highly correlated patterns of nutrients, salinity, temperature and the depth of mixed layer. Obtained latent variables were used to explain spatial distribution of phytoplankton. Generally, the distribution of phytoplankton variables followed closely the patterns of nutrient rich fresh water. During the spring bloom in 1995, the spatial structures of phytoplankton biomass (4–27 mg l−1) and chlorophyll a (13–50 μg l−1) were well explained (r=0.68 and 0.69, respectively, p<0.01) by common factor loaded by inorganic N, total N and P, salinity and the depth of mixed layer. The early-summer stage in 1994 was characterized by homogenous distribution of algal biomass and low concentrations of inorganic N and P. At this stage, the decreasing amount of total N and P from the southern Gulf of Riga towards the northern part of the Gulf was accompanied with the decrease of chlorophyll a concentrations and the increase of relative importance of picoplankton (algae <2 μm). Intense bloom of cyanobacteria (Aphanizomenon flos-aquae (L.) Ralfs) took place in 1994 after warming up of the surface layer. The abundance of A. flos-aquae was related to the common structure of N, P and fresh water and the bloom was most dense (up to 6.6 mg l−1) in the southern Gulf. At the same time, the contribution of picoplankton from total chlorophyll a was high (up to 60%) in the northern Gulf affected less by the nutrient load. The late summer phase in 1993 was characterized by high heterotrophic activities and the phytoplankton community was dominated by cryptomonads (on the average 50% of total biomass). At that stage the distribution of phytoplankton was obviously governed by biological interactions and the multivariate methods were not especially successful to explain the spatial distribution of the main components of phytoplankton community. Excluding the late summer phase, the statistical methods used in this study revealed well the relationships between phytoplankton variables and nutrient rich fresh water. It is evident that nutrient load from the River Daugava is a reason for higher phytoplankton biomass in the southern Gulf of Riga, especially during bloom occasions.

The role of inorganic and organic nutrients on the development of phytoplankton along a transect from the Daugava River mouth to the Open Baltic, in spring and summer 1999

The importance of dissolved silicate (DSi), dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), phosphate and dissolved organic phosphorus (DOP) on algal growth is analysed for the Gulf of Riga and the adjacent open Baltic Sea. The results of three cruises (May, June, and July, 1999) along a transect across the Gulf of Riga from the entrance to the Daugava River to the open Baltic are presented. Nutrient-limitation was identified on the basis of available nutrient concentrations and stoichiometric analysis. In spring, phosphate appeared to be the algal-growth-potential-limiting nutrient at the entrance of the Daugava River, DSi in the central Gulf, and DIN at the open Baltic station. There was no correlation between limiting nutrient and spring phytoplankton community structure. Both the DIN and phosphate pools of the upper mixed layer were exhausted by mid-May, except at the river mouth. In summer there was a good correlation between phytoplankton biomass and DOP along the transect. Contrary to the situation in the open Baltic, the lower layer DIN/phosphate ratio in the Gulf of Riga significantly exceeds the Redfield ratio, and upwelling likely does not favour nitrogen-fixing species. Therefore, the upper layer DOP pool should be regarded as potentially the main source of phosphorus for nitrogen-fixing cyanobacteria in the Gulf of Riga.

SEDIMENT QUALITY ASSESSMENT USING GMELINOIDES FASCIATUS AND MONOPOREIA AFFINIS (AMPHIPODA, GAMMARIDEA) IN THE NORTHEASTERN BALTIC SEA

Crustaceans in the order Amphipoda are sensitive organisms for the assessment of sediment quality. In this work we performed 10-day toxicity tests on muddy sediments collected from a total of 29 sites in the Gulf of Finland, the Gulf of Riga and the Gulf of Bothnia (northeastern Baltic Sea) using Baltic Sea species such as the native amphipod Monoporeia affinis (Bousfield, 1989) and the invasive amphipod Gmelinoides fasciatus (Stebbing, 1899), and also compared these results with those of bioassays carried out using the standard test species, laboratory-cultivated amphipod Hyalella azteca (Saussure, 1858). The sediment samples (three cm of the upper layer) were collected by a GEMAX Dual Corer during the R/V “Aranda” cruises in August and September of 2009 and 2010. Toxicity of sediments in bioassays with M. affinis and G. fasciatus gave varied results depending on the amphipod species used. The lowest quality of sediments determined using M. affinis was recorded at sites located in the offshore and deepwater areas (60-100 m depths) of the Gulf of Finland characterized by hypoxic/anoxic conditions. Toxicity testing applying G. fasciatus showed that sediments at >50% of the study sites in the Gulf of Finland and in the Gulf of Riga can be assessed as highly contaminated. Males of G. fasciatus were significantly more sensitive to potential contamination in sediments than females. The lower survival of males under contaminant stress may result in a skewed sex ratio in natural populations and in a decline of reproduction success. The survival rate of G. fasciatus in the toxicity tests correlated positively with the Shannon diversity index (calculated for macrozoobenthos at the study sites), weight losses on ignition (%) in sediments, and it also showed a negative relation with the bottom water oxygen content (mg/l). The results suggest that G. fasciatus is the more sensitive species of the three amphipods tested and can be used as a indicator of sediment quality in the Baltic Sea and other water bodies.

TOXICO-RESISTANCE OF BALTIC AMPHIPOD SPECIES TO HEAVY METALS

Benthic organisms are important components of aquatic ecosystems and have been widely used to assess environmental pollution. Being very sensitive to a wide range of toxicants amphipods are often used as test objects in eco-toxicological studies. The aim of this study was to compare toxico-resistance of various Baltic amphipod species to exposure of heavy metals. The acute toxicity (48-h LC50 and 96-h LC50) of cadmium (CdCl2), copper (CuSO4) and zinc (ZnSO4 ⋅ 7H2O) was detected experimentally, using juveniles and adults of brackish water amphipods, Monoporeia affinis, Bathyporeia pilosa, Gammarus tigrinus, Pontogammarus robustoides and the freshwater amphipod Gammarus pulex as test objects. Amphipods were collected in Latvian territorial waters of the Open Baltic Sea, the Gulf of Riga and in a freshwater body (Kalkugrava canal). Sensitivity of native amphipod species was compared to Hyalella azteca (a species widespread in North America; a strain obtained from the Chesapeake Culture Collection, Hayes, VA, U.S.A.). High sensitivity of all tested amphipod species, except M. affinis, to heavy metals was observed. A two-way ANOVA analysis showed significant differences in toxico-resistance of selected test objects ( p < 0 . 05 ). The highest toxico-resistance was shown by the brackish water amphipod M. affinis (96-h LC50: Cd 5.16 mg/l; Cu 5.68 mg/l; Zn 11.31 mg/l), but the lowest by the freshwater species G. pulex and H. azteca (96-h LC50 for Cd 0.005 and 0.007 mg/l, accordingly). Cadmium was the most toxic from the tested heavy metals, followed by copper and zinc.

An integrated assessment of pollution and biological effects in flounder, mussels and sediment in the southern Baltic Sea coastal area

Organic and metal contaminants and biological effects were investigated in flounder, mussels, and sediments in the southern Baltic Sea coastal area in order to assess environmental quality status in that area. Four sites were selected, including two within the Gulf of Gdańsk (GoG). In biota and sediment at each site, DDTs dominated over PCBs and PBDEs were the least abundant among organic contaminants. Their concentrations decreased progressively outward from GoG. Among metal contaminants, the levels of Hg, Pb, and Cd were elevated in GoG. Biomarkers in flounder, EROD activity and DNA SB, showed moderate positive correlations with organic and metal contaminants. In flounder, the integrated biomarker index (IBR/n) presented a spatial trend coherent with chemical pollution index (CPI), but there was no clear spatial correspondence between IBR/n and CPI in mussels nor between sediment toxicity index (STI) and sediment CPI. The integrated assessment of contaminant and biological effect data against available assessment criteria indicated that in biota, the contaminant assessment thresholds were most often exceeded by CB-118, heptachlor, PBDE, and Hg (in the GoG sediments by p,p′-DDT, Hg and Cd), while of the biological determinants, the threshold was breeched by AChE activity in mussels in GoG. Applying the ICES/OSPAR traffic-light approach showed that of the 50 parameters assessed at each site, there were 18% of determinants in the red color category in the two GoG sites and 8% of determinants in the two sites outside GoG, which indicated that none of the four investigated sites attained good environmental status (GES).

Comparison of effects on crustaceans: carbon nanoparticles and molybdenum compounds nanowires

Carbon nanomaterials (CNM) and molybdenum compound nanostructures are materials with various applications yet little is known regarding the toxicity of these nanoparticles in pristine form in aquatic environment. Daphnia magna standard acute toxicity test (EN ISO 6341:1996; freshwater) and Artemia salina standard acute toxicity test (ArtoxKit standard method; 15 ppt saltwater) were applied to assess the toxicity of non-modified CNM and molybdenum compound nanowires in water. It has been observed that CNM are more toxic in freshwater suspensions and somewhat more toxic than the tested molybdenum compound nanowires.

Challenges and opportunities of local fisheries management: pikeperch, Sander lucioperca (Actinopterygii: Perciformes: Percidae), in Pärnu Bay, northern Gulf of Riga, Baltic Sea

A local stock of pikeperch, Sander lucioperca (Linnaeus, 1758), adapted to brackish water conditions, is a valuable fishery resource in Parnu Bay (Vetemaa et al. 2000, 2006), a shallow bay in the Estonian exclusive economic zone in the Northern Gulf of Riga (Fig. 1). Despite fishing regulations, which were established in Estonia as early as in the 1920s, this stock has been heavily exploited since the early 1930s, when large-scale export of this fish from Estonia started. After low catches in the 1960s new, biologically justified measures to protect pikeperch were implemented, such as protected areas and the use of artificial spawning substrates to increase recruitment. Catches then improved and reached 300 t in the early 1990s (Erm et al. 2003). After Estonia regained independence in 1991, new export markets for pikeperch opened and privatization of state farms offered local fishermen cheap access to fishing gear. With Estonia’s low average wages in the early 1990s and high first-buyer prices for pikeperch, the average catch of pikeperch needed to provide the equivalent of an average monthly gross wage ranged from 43 kg in 1993 to 240 kg in 1999 (Vetemaa et al. 2000, 2006). Consequently, pikeperch catches increased drastically and its fishing mortality rose to the highest level ever recorded. Young age groups, including immature fish, became an important part of the catches. This was caused by Estonia’s weak legal instruments for regulating fisheries in the 1990s (Vetemaa et al. 2002) and by insufficient funding for enforcing the legal minimum size of ACTA ICHTHYOLOGICA ET PISCATORIA (2013) 43 (2): 151–161 DOI: 10.3750/AIP2013.43.2.08

Insight into the studies of the practical use of microalgae in the former Soviet Union

Microalgae have been intensively cultivated and used in the national economy of the Soviet Union in Russia (Moscow, Leningrad, Pushcino, Krasnoyarsk, Irkutsk), the Ukraine, Byelorussia (Minsk), Azerbaijan (Baku), Uzbekistan (Tashkent), Latvia (Riga) and other former Soviet republics. The first studies on the practical use of microalgae started already at the beginning of last century and were connected with treatment of waste water in biological ponds. Ecophysiological studies of marine plankton algae in mono- and mixed cultures as well as in experimental systems with zooplankton organisms started at the end of the 1950s. In the 1960s, started to apply different equipments for cultivation of microalgae in open water basins and closed ecological systems. Research innovations were introduced in agriculture. The productivity of aquatic ecosystems and the distribution of energy within food chains were studied. Intensive research on microalgae continued, paying attention to the chemical composition, physiological and biochemical features. Nutrient supply appeared as one of the main problem for productivity of algal cultures, along with the procession, biochemistry of nutrients and nutrition value of organic matter produced by algae. The most attention was paid to the Chroococcales proteins and possibilities for their use in man-made closed ecological systems. The potential use of microalgae for regeneration of the atmosphere and purification of water in spacecrafts was studied. During the 1970s attention was paid to the role of algae in self-purification processes and biodegradation of surface-active substances in water bodies. Research in microalgae as bioindicators for the assessment of environment quality of aquatic ecosystems and as test objects for biotesting of natural and waste waters was conducted from the 1970s to 1980s.