Cystidicola farionis as a swimbladder parasite of the whitefish in the Bothnian Bay

Material comprising 3167 specimens of the parasite Cystidicola farionis was assembled from 1741 individuals of the sea-spawning whitefish, Coregonus nasus in the shallow northeastern and deeper central areas of the Bothnian Bay. Occasional parasites were found in the immature fish (≦ 175 mm), but infection increased in the two larger classes as the fish aged, reaching 27% in the northeastern area, and as much as 67% in the southern area. This difference is explained partly by the more frequent feeding on Pontoporeia affinis , the intermediate host for the parasite, the deeper waters extending nearer the coast in the majority of the central and southern Bothnian Bay. The increased intensity of infection with age does not vary significantly between the areas studied. No clear seasonal fluctuations in the prevalence or intensity of infection could be found.     

Vulnerability and diet breadth predict larval and adult parasite diversity in fish of the Bothnian Bay

Recent studies of aquatic food webs show that parasite diversity is concentrated in nodes that likely favour transmission. Various aspects of parasite diversity have been observed to be correlated with the trophic level, size, diet breadth, and vulnerability to predation of hosts. However, no study has attempted to distinguish among all four correlates, which may have differential importance for trophically transmitted parasites occurring as larvae or adults. We searched for factors that best predict the diversity of larval and adult endoparasites in 4105 fish in 25 species studied over a three-year period in the Bothnian Bay, Finland. Local predator–prey relationships were determined from stomach contents, parasites, and published data in 8,229 fish in 31 species and in seals and piscivorous birds. Fish that consumed more species of prey had more diverse trophically transmitted adult parasites. Larval parasite diversity increased with the diversity of both prey and predators, but increases in predator diversity had a greater effect. Prey diversity was more strongly associated with the diversity of adult parasites than with that of larvae. The proportion of parasite species present as larvae in a host species was correlated with the diversity of its predators. There was a notable lack of association with the diversity of any parasite guild and fish length, trophic level, or trophic category. Thus, diversity is associated with different nodal properties in larval and adult parasites, and association strengths also differ, strongly reflecting the life cycles of parasites and the food chains they follow to complete transmission.     

Density and distribution of the ringed seal in the Bothnian Bay

A modified strip census of basking ringed seals in the Bothnian Bay was carried out during the last week of April and the first week of May 1988. Of the total ice covered area, 23174 km², 3236 km² (14%) was covered by the transects. The mean density in the area was 0.101 ringed seals km^-2, with substantial regional and local variation. Highest densities were found in the compact drift ice area. The estimated total population of ringed seals on the ice was 2093 in the Bothnian Bay proper and 248 in the North Quark. The 95% confidence limits of the estimates are ±24%.     

Vegetation development on the outer islands of the Bothnian Bay

This paper summarizes succession studies on the outer islands of the Bothnian Bay (Finland). The study area is characterized by consistent and relatively rapid uplift (vertical rise on average 75 cm per century). The spatial and temporal succession has been deduced from the sequence of the littoral and epilittoral vegetation as well as from the historical records of the island development.Four types of successional series are distinguished. The relationships between substrate type (boulder, gravel, sand and clay-silt shores) and 25 typical plant communities are outlined and treated as successional sequences.     

Spectrofluorimetric determination of biogenic amines (serotonin, dopamine) in Metechinorhynchus salmonis (Acanthocephala)

Identification of serotonin and dopamine in M. salmonis was conducted by means of some fluorometric methods. The presence of negligible amount of a serotonin-like component and substance close in its spectral characteristics to dopamine was shown.     

Vertebrate diets derived from trophically transmitted fish parasites in the Bothnian Bay

Parasites that are transmitted through predator–prey interactions may be used as indicators of trophic relationships between organisms. Yet, they are rarely used as such in the construction of topological (predator–prey) food webs. We constructed food webs of vertebrate trophic interactions using observed diet alone, trophically transmitted parasites alone, and the combination of the two based on data from 31 species of fish from the Bothnian Bay, Finland. The fish food web contained 530 links derived from observed diet, 724 links inferred from parasitism, and 1,058 links calculated from a combination of both stomach contents and parasites. This sub-web constructed from stomach contents had a mean of 17.1 links per fish species, while that using parasites had 23.4 links per fish. Combining the two diet indicators yielded 34.1 links per fish species, illustrating the complementarity of the two methods. Mean number of prey species per fish species was 12.5 using observed diet items, 15.8 using parasites, and 24.5 using both measures together. Mean number of predators per fish species was 7.4 using observed diet, 11.7 using parasites and 15.0 using both. A positive correlation was found between the mean number of parasites and the number of prey taxa in the diet among the fishes. Omnivorous fish had the highest diversity of both parasite species and prey items, while benthophagous fish had among the lowest. Mean total abundance and mean total prevalence of parasites correlated positively with fish size, with piscivores being the largest with the highest abundance and prevalence, while planktivores and benthivores had the lowest. Trophically transmitted parasites may be used to help construct vertebrate sub-webs and derive information about food web processes. Parasites alone provided equivalent if not more information than observed diet. However, resolution is improved by using parasites and observed diet together.     

Migratory behaviour of adult cisco, Coregonus albula L., in the Bothnian Bay

The population of adult cisco in the Bothnian Bay consists of a number of spawning populations. Each one of these returns to the same inshore area for spawning every autumn. In the summer these populations are mixed and occur mainly offshore. These are the main conclusions of an experiment in which cisco were marked with Carlin-type tags. The cisco were caught mainly in fyke nets both in the summer and in the autumn and released after tagging in the area where they had been caught. Fish tagged in the autumn and recaptured in the autumn one or more years later showed a strong affinity to the point of release, while fish from the same group recaptured in the summer had migrated far from the release site. The distribution of cisco that were tagged in the summer and caught in the autumn showed no correlation with the release site.     

Winter-time ecology in the Bothnian Bay, Baltic Sea: nutrients and algae in fast ice

Landfast ice algal communities were studied in the strongly riverine-influenced northernmost part of the Baltic Sea, the Bothnian Bay, during the winter-spring transition of 2004. The under-ice river plume, detected by its low salinity and elevated nutrient concentrations, was observed only at the station closest to the river mouth. The bottommost ice layer at this station was formed from the plume water (brine volume 0.71%). This was reflected by the low flagellate-dominated (93%) algal biomass in the bottom layer, which was one-fifth of the diatom-dominated (74%) surface-layer biomass of 88 μg C l⁻¹. Our results indicate that habitable space plays a controlling role for ice algae in the Bothnian Bay fast ice. Similarly to the water column in the Bothnian Bay, average dissolved inorganic N:P-ratios in the ice were high, varying between 12 and 265. The integrated chlorophyll a (0.1–2.2 mg m⁻²) and algal biomass in the ice (1–31 mg C m⁻²) correlated significantly (Spearman ρ = 0.79), with the highest values being measured close to the river mouth in March and during the melt season in April. Flagellates <20 μm generally dominated in both the ice and water columns in February–March. In April the main ice-algal biomass was composed of Melosira arctica and unidentified pennate diatoms, while in the water column Achnanthes taeniata, Scrippsiella hangoei and flagellates dominated. The photosynthetic efficiency (0.003–0.013 (μg C [μg chl a ⁻¹] h⁻¹)(μE m⁻²s⁻¹)⁻¹) and maximum capacity (0.18–1.11 μg C [μg chl a ⁻¹] h⁻¹) could not always be linked to the algal composition, but in the case of a clear diatom dominance, pennate species showed to be more dark-adapted than centric diatoms.     

Further observations on flagellates within sea ice in northern Bothnian Bay, the Baltic Sea

To improve our knowledge of flagellates inhabiting the Baltic Sea ice and water column during the winter, material was obtained from northern Bothnian Bay in March/April 1995. Light microscopical observations on live and fixed material and further transmission electron microscopy of whole mounts revealed 47 nanoflagellate taxa. In addition, detached scales of eight taxa were encountered. It is now evident that nearly all nanoflagellate classes are present within Bothnian Bay sea ice. The most common groups were cryptomonads, dinoflagellates, chrysophytes, prasinophytes, choanoflagellates and heterotrophic flagellates of unknown systematic position (Protista incertae sedis). Most flagellates in Baltic Sea ice biota apparently thrive in both the water column and the sea ice, while some, e.g. Paraphysomonas spp. (Chrysophyceae), heterotrophic euglenids, volvocalean chlorophytes, and some taxa of uncertain systematic affinity, are more frequently found within the sea ice. Received: 9 February 1997 / Accepted: 23 September 1997     

Structure,Dynamics and Production of Mesozooplankton Community in the Bothnian Bay,Related to Environmental Factors

Studies on the zooplankton community of the Bothnian Bay (BB), the northernmost basin of the Baltic Sea, were carried out in 1976–78. Only 8–14 taxa dominated in the zooplankton community. The highest abundances and biomasses occurred during the warmest period or immediately afterwards, in July–September. The production of zooplankton was estimated to be 3.1–7.8 g C · m⁻². a⁻¹ in the coastal area and 2.5–3.6 g C · m⁻² · a⁻¹ in the open sea. During the short growing season (June–September) the biomass turnover took place in about 11 days. The productivity of zooplankton is discussed in relation to available food of both autochthonous and allochthonous origin and compared with the other parts of the Baltic Sea.     

Potentially Active Iron,Sulfur, and Sulfate Reducing Bacteria in Skagerrak and Bothnian Bay Sediments

In many marine surface sediments, the reduction of manganese (Mn) and iron (Fe) oxides is obscured by sulfate reduction, which is regarded as the predominant anaerobic microbial respiration process. However, many dissimilatory sulfate and sulfur reducing microorganisms are known to utilize alternative electron acceptors such as metal oxides. In this study, we tested whether sulfate and sulfur reducing bacteria are linked to metal oxide reduction based on biogeochemical modeling of porewater concentration profiles of Mn²⁺ and Fe²⁺ in Bothnian Bay (BB) and Skagerrak (SK) sediments. Steady-state modeling of Fe²⁺ and Mn²⁺ porewater profiles revealed zones of net Fe (0–9 cm BB; ～10 and 20 cm SK) and Mn (0–5 cm BB; 2–8 cm SK) species transformations. 16S rRNA pyrosequencing analysis of the in-situ community showed that Desulfobacteraceae, Desulfuromonadaceae and Desulfobulbaceae were present in the zone of Fe-reduction of both sediments. Rhodobacteraceae were also detected at high relative abundance in both sediments. BB sediments appeared to harbor a greater diversity of potential Fe-reducers compared to SK. Additionally, when the upper 10 cm of sediment from the SK was incubated with lepidocrocite and acetate, Desulfuromonas was the dominant bacteria. Real-time quantitative polymerase chain reaction (qPCR) results showed decreasing dsrA gene copy numbers with depth coincided with decreased Fe-reduction activity. Our results support the idea that sulfur and sulfate reducing bacteria contribute to Fe-reduction in the upper centimeters of both sediments.     

Aerial census of ringed seals Pusa hispida basking on the ice of the Bothnian Bay, Baltic

The censuses are based on six surveys (1590 km total) carried out between 13 April and 17 May 1975 and two surveys (560 km) on 13 and 15 May 1978. The material consists of 716 observations in 1975 and 214 observations in 1978, involving 1960 and 572 ringed seal specimens respectively. The transect width was determined in retrospect on the basis of the sighting angle and sighting distance, the latter being estimated and corrected by a factor typical for each separate flight. The mean sighting distances varied from 720 to 1140 m with a range from 160 to 2450 m. On average over 3000 ringed seats were basking on the ice of the Bothnian Bay in 1975 and 1978, promising at least 4000 specimens living in the area in total. Sources of methodological bias, factors affecting the observability of the seals, and the estimation of the total population based on the numbers of basking seals are discussed.     

Shade-adapted Algae beneath Ice and Snow in the Northern Bothnian Sea

The winter-spring phytoplankton flora in the coastal waters of the northern Bothnian Sea consists mainly of marine cold water species even adapted to low light. These dinoflagellates and diatoms seem to be selectively promoted by the seven months of low light and water temperature. They are able to grow during this period of subsaturated light and have their abundance maxima around ice-break. Solar radiation measured under ice and snow cover was in the same order of magnitude as the compensation points of some of the species. In summer, these algae species vanish from the water, and surely survive in the form of inactive life stages.     

The impact of Piscirickettsia salmonis infection on genome-wide DNA methylation profile in Atlantic Salmon

Salmon rickettsial septicaemia (SRS), caused by the bacteria Piscirickettsia salmonis (P. salmonis), is responsible for significant mortality in farmed Atlantic salmon in Chile. Currently there are no effective treatments or preventive measures for this disease, although genetic selection or genome engineering to increase salmon resistance to SRS are promising strategies. The accuracy and efficiency of these strategies are usually influenced by the available biological background knowledge of the disease. The aim of this study was to investigate DNA methylation changes in response to P. salmonis infection in the head kidney and liver tissue of Atlantic salmon, and the interaction between gene expression and DNA methylation in the same tissues. The head kidney and liver methylomes of 66 juvenile salmon were profiled using reduced representation bisulphite sequencing (RRBS), and compared between P. salmonis infected animals (3 and 9 days post infection) and uninfected controls, and between SRS resistant and susceptible fish. Methylation was correlated with matching RNA-Seq data from the same animals, revealing that methylation in the first exon leads to an important repression of gene expression. Head kidney methylation showed a clear response to the infection, associated with immunological processes such as actin cytoskeleton regulation, phagocytosis, endocytosis and pathogen associated pattern receptor signaling. Our results contribute to the growing understanding of the role of methylation in regulation of gene expression and response to infectious diseases and could inform the incorporation of epigenetic markers into genomic selection for disease resistant and the design of diagnostic epigenetic markers to better manage fish health in salmon aquaculture.     

Seasonal changes in condition indices in adult mature and non-maturing burbot, Lota lota (L.), in the north-eastern Bothnian Bay, northern Finland

The population structure and seasonal changes in condition factors of the burbot in a shallow coastal region of the north-eastern Bothnian Bay are described. The significance of the so-called rest years is examined by comparing condition indices in immature or sterile and mature burbot. The somatic condition index ( K ₂), liver index ( K ₁), intestine index ( K ₁) and gonad index ( K_g ) are determined monthly in terms of organ weight in relation to body length. Approximately 30% of the whole catch of 1052 burbot were non-maturing but were 40 cm or more in length. K ₂, K ₁ and K ₁ were lowest in the autumn, when the first sign of gonad recrudescence was observed in mature burbot. The non-maturing burbot were never in poorer condition than mature ones. As mature and non-maturing burbot dissipated their energy stores during the warmest period of the summer, it is concluded that burbot spending a rest year do not accumulate and store energy reserves over the summer for the next year, and that such rest years, if they exist, do not occur for nutritional reasons.     

Feeding interactions and diet of carnivorous fishes in the Shelikhov Bay of the Sea of Okhotsk

The food spectra, trophic statuses, and feeding interrelations of three most abundant benthic carnivorous fish species inhabiting the Shelikhov Bay—the Pacific cod Gadus macrocephalus, the great sculpin Myoxocephalus polyacanthocephalus, and the Okhotsk sculpin M. ochotensis—are considered based on materials collected during the complex survey of the RV Professor Kaganovsky of the TINRO-Center, in September 2004. It was found that these species were facultative predators with wide food spectra. The significance of prey objects in the diet of the Okhotsk sculpin was as follows: crustaceans, fish, and mollusks. Great sculpin and Pacific cod preyed mostly on fish, then on crustaceans, and mollusks. Pacific cod ate equal proportions of fish and decapods. All the species had age-related variability of diet. The potential competition of great sculpin and Okhotsk sculpin for food was mitigated by the difference in the depths of their ranges, as well as by morphological (body size) and behavioral peculiarities in the areas where their habitats overlapped, and in microecosystems. The most probable competition was among Pacific cod 30–60 cm long and Okhotsk sculpin 20–50 cm in length, as well as among cod and great sculpins of all sizes.     

Denitrification and N2O effluxes in the Bothnian Bay (northern Baltic Sea) river sediments as affected by temperature under different oxygen concentrations

Denitrification rates and nitrous oxide (N₂O) effluxes were measured at different temperatures and for different oxygen concentrations in the sediments of a eutrophied river entering the Bothnian Bay. The experiments were made in a laboratory microcosm with intact sediment samples. ¹⁵N-labelling was used to measure denitrification rates (Dw). The rates were measured at four temperatures (5, 10, 15 and 20°C) and with three oxygen inputs (<0.2, 5, and 10 mg O₂ l⁻¹). The temperature response was highly affected by oxygen concentration. At higher O₂ concentrations (5 and 10 mg O₂ l⁻¹) a saturation over 10°C was observed, whereas the anoxic treatment (<0.2 mg O₂ l⁻¹) showed an exponential increase in the temperature interval with a Q ₁₀ value of 3.1. The result is described with a combined statistical model. In contrast with overall denitrification, the N₂O effluxes from sediments decreased with increasing temperature. The N₂O effluxes had a lower response to oxygen than denitrification rates. The N₂O/N₂ ratio was always below 0.02. Increased temperatures in the future could enhance denitrification rates in boreal river sediments but would not increase the amount of N₂O produced.