Analysis of fish parasitofauna in Vistula Lagoon (the Baltic Sea)

The characteristics of parasitofauna (81 species) of 15 fish species from Vistula Lagoon (the Baltic Sea) are given. Parasites with a direct developmental cycle dominate. Parasites with a complicated developmental cycle are represented mainly by species developed through zoobenthos. Some of the parasites testify to the deterioration of the ecological state of the lagoon. A zoogeographic analysis of fish parasitofauna has shown the presence of five faunistic complexes. In Vistula Lagoon freshwater species dominate, but marine species are also recorded. Species that appeared in the lagoon as a result of human commercial activity are also registered.     

Phenology of cryptomonads and the CRY1 lineage in a coastal brackish lagoon (Vistula Lagoon,Baltic Sea)

Cryptomonadales have acquired their plastids by secondary endosymbiosis. A novel clade—CRY1—has been discovered at the base of the Cryptomonadales tree, but it remains unknown whether it contains plastids. Cryptomonadales are also an important component of phytoplankton assemblages. However, they cannot be readily identified in fixed samples, and knowledge on dynamics and distribution of specific taxa is scarce. We investigated the phenology of the CRY1 lineage, three cryptomonadales clades and a species Proteomonas sulcata in a brackish lagoon of the Baltic Sea (salinity 0.3–3.9) using fluorescence in situ hybridization. A newly design probe revealed that specimens of the CRY1 lineage were aplastidic. This adds evidence against the chromalveolate hypothesis, and suggests that the evolution of cryptomonadales’ plastids might have been shorter than is currently assumed. The CRY1 lineage was the most abundant cryptomonad clade in the lagoon. All of the studied cryptomonads peaked in spring at the most freshwater station, except for P. sulcata that peaked in summer and autumn. Salinity and concentration of dissolved inorganic nitrogen most significantly affected their distribution and dynamics. Our findings contribute to the ecology and evolution of cryptomonads, and may advance understanding of evolutionary relationships within the eukaryotic tree of life.     

Invasions of alien gammarid species and retreat of natives in the Vistula Lagoon (Baltic Sea, Poland)

During the last decades of the twentieth century, the alien gammarid species Gammarus tigrinus, Dikerogammarus haemobaphes, Pontogammarus robustoides and Obesogammarus crassus invaded the lower Vistula River and its deltaic, partly brackish regions. In brackish waters of the Vistula Lagoon the native Atlantic-boreal species Gammarus zaddachi and Gammarus duebeni have been replaced or at least outnumbered by the aliens. As compared to our earlier studies, through the years 1998–2004 we could observe nearly total decline of the native gammarid populations along the coasts of the Lagoon, and overdomination of the North-American G. tigrinus in most places. Possible reasons for the observed phenomena are e.g. increasing pollution and eutrophication of the Lagoon accompanied by competition between the native and the alien species.     

Differences in temperature conditions and somatic growth rate of larval and early juvenile spring-spawned herring from the Vistula Lagoon, Baltic Sea manifested in the otolith to fish size relationship

Larval and juvenile herring Clupea harengus collected in the Polish part of the Vistula Lagoon in May-July 1997 had hatched between 17 April and 9 June and originated from three cohorts. The spawning season began on 1 March at 3·8° C and was completed on 3 June at 12·7° C. Mortality among larvae was high in the first 2 weeks of April, probably associated with significant temperature decrease at the beginning of the spawning season. The growth of 10–48 mm L _S herring was linear, highest for larvae and juveniles from the first cohort (0·58 mm mm^-1 day^-1), slower for the second cohort (0·55 mm mm^-1 day^-1) and the slowest for the third cohort (0·45 mm mm day^-1). Temperature effects on the growth were inconclusive and potentially unfavourable feeding conditions in June might have been responsible for the relatively slow growth of third cohort larvae and juveniles.
Relationships between otolith size (perimeter, length, width, area, and weight) and fish size ( L _S) differed among the three cohorts, related mostly to the positive temperature effect on otolith growth, individuals growing in warmer water had larger otoliths. Although a negative growth rate effect was observed as well, it was less significant.     

Deep‐water fish assemblages in the central‐western Mediterranean (south Sardinian deep‐waters)

This paper explores structure and spatial distribution of fish assemblages in an area of the central‐western Mediterranean Sea (south Sardinian deep‐waters) at depths between 546 and 1598 m. A total of 67 species (12 chondrichthyes and 55 teleosteans) were sampled. Multivariate analysis showed a clear pattern of zonation. Three main assemblages were identified within the vertical range investigated: the first situated in the shallower area between 546 and 699 m, the second group between 720 and 1099 m, and the third between 1145 and 1598 m. Abundance values declined with increasing depth. Highest biomass values were found at depths of 720–1099 m with the presence of larger species such as Galeus melastomus, Mora moro, Trachyrhynchus scabrus and Alepocephalus rostratus. Species richness decreased with depth. The deepest bottoms of the central‐western Mediterranean Sea shelter an ichthyofauna dominated by small to medium‐sized species living in a food‐scarce environment in which some large mobile fishes are widespread.     

Influence of water temperature and net tending frequency on the condition of fish bycatch in a small-scale inland commercial fyke net fishery

To date, most studies of commercial fisheries bycatch have focused on mortality at time of capture as an endpoint. However, sub-lethal indicators of organismal condition have the potential to reveal mechanisms associated with mortality (both at time of capture and post-release) and opportunities for improving fish welfare. In this study, we simulated commercial fishing efforts in inland lakes with fyke nets during a typical fishing season (early April to late June) in southeastern Ontario, Canada, where bycatch of non-target fish species had previously been documented. Using non-target gamefish (i.e., largemouth bass [Micropterus salmoides, Lacépède], northern pike [Esox Lucius, L.]), as well as a target species (i.e., bluegill [Lepomis macrochirus, Rafinesque]), we examined the sub-lethal consequences of capture (e.g., blood physiology, reflex impairment, and injury) and compared the effects of being retained in the net for two different durations (i.e., two or six days) over a range of water temperatures (i.e., 3–28 °C). Sub-lethal physiological disturbances (i.e., blood glucose and lactate) in largemouth bass and bluegill tended to be greater at higher water temperatures. However, fish retained for six days generally did not exhibit greater stress than those retained for two days, with the exception of plasma glucose in largemouth bass. Reflex impairment was similar among temperature and retention periods. Fish retained in nets experienced a range of injuries (including fin frays, scale loss, and mouth damage) that had the potential to facilitate the development of opportunistic pathogenic infections. Greater incidences of injury on fish bycatch tended to be associated with higher temperatures and longer retention. To reduce physiological disturbances and injury that could lead to delayed mortality, we suggest that regulations for inland commercial fishers require them to check their nets more frequently as water temperatures increase. We suggest that future studies of bycatch incorporate sub-lethal endpoints given that they serve as an objective measure of fish welfare and can provide quantitative mechanistic information to support management actions.     

Assessing nature and dynamics of POM in transitional environment (the Curonian Lagoon,SE Baltic Sea) using a stable isotope approach

The nature of the particulate organic matter (POM) as well as its temporal and spatial distribution and dynamics in the Curonian Lagoon (south-eastern part of the Baltic Sea) were investigated. The organic matter was characterized by the organic carbon and nitrogen content, δ¹³C and δ¹⁵N signatures as well as POC/Chl-a and C/N ratios. Additionally, data on hydrological, chemical and biological parameters were used for better understanding the POM distribution and dynamics. The sampling was performed at 13 stations in the Curonian Lagoon and its outflow in the Baltic Sea during the 2012–2013 period. Samples were also collected at the Nemunas River mouth in order to test the riverine impact. Obtained results showed that isotopic values of carbon and nitrogen ranged from −36.1‰ to −25.2‰ and from −0.9‰ to 15.5‰, respectively. The isotopic composition, together with the low C/N molar (∼7) and POC/Chl-a ratios (<100) of the POM, suggested the dominance of living phytoplankton in POM throughout the year with the higher input of detrital material (C/N >10, POC/Chl-a ratios >100) in late autumn − winter.The results of multivariate analysis evidenced a spatial distinction of POM distribution in the northern-transitional and central confined areas and allowed us to distinguish the main driving factors. The seasonal variation of the δ¹³C and δ¹⁵N values in POM (towards higher δ¹³C and lower δ¹⁵N values in the summer − early autumn period and lower δ¹³C and higher δ¹⁵N values in the late autumn − spring period) was determined by combination of factors such as availability of inorganic carbon and nitrogen, the riverine discharge, seasonal phytoplankton succession and by the short-term saline water intrusion to the northern-transitional part of the lagoon.     

Reproductive strategy of the alien Ponto-Caspian cladocerans Cercopagis pengoi (Ostroumov, 1891) in the Baltic Sea (by example of the Vistula Lagoon)

Early and prolonged sexual reproduction has been registered in the population of Cercopagis pengoi within the Vistula Lagoon relative to its original habitat. Decrease in the role of parthenogenesis and increase in the frequency of gamogenesis have been registered in the population under study. It has been accompanied by reduction in the average number of parthenogenetic eggs per female and increase in the production of gamogenetic eggs relative to the Caspian Sea.     

Uranium and thorium in muscle tissue of fish taken from the southern Baltic

The determination of U and Th was carried out on pooled samples of muscle tissue of cod (Gadus morhua), herring (Clupea harengus), sprat (Sprattus sprattus) and some other species of fish caught in 1981 in the southern Baltic. The levels of U obtained in the present study are generally within the ranges presented by other authors for fish from different aquatic regions of the world. The concentrations of U are similar to those found for Th in Baltic fish analysed. The concentration factors CF_U(Th), discrimination factors DF_U/Th and Th/U ratios (by weight) were calculated and discussed. These coefficients were also compared with values determined in other Baltic organisms. Transfer of U and Th along a food chain from potential prey (diet) to fish as predator (consumer) was quantified with a transfer factor.     

Organochlorine,Organophosphoric and Organotin Contaminants,Aromatic and Aliphatic Hydrocarbons and Heavy Metals in Sediments of the Ports from the Polish Part of the Vistula Lagoon (Baltic Sea)

The concentrations of polycyclic aromatic and petroleum hydrocarbons, polychlorinated biphenyls, dioxins, organochlorine and organophosphoric pesticides, tributyltin and metals were determined in sediments of the approach fairways to the main ports in the Polish part of the Vistula Lagoon and of the Elbl?g River. Analyzed sediments contained low concentrations of all contaminants, except petroleum hydrocarbons. The average petroleum hydrocarbons’ (PHCs) concentration was 630 mg kg^?1, indicating significant pollution with petroleum hydrocarbons. The highest concentrations of analyzed contaminants were identified in the vicinity of Elbl?g, part of the Vistula Lagoon under the most anthropogenic pressure.     

Distribution of Streblospio benedicti (Webster, 1879) and Manayunkia aestuarina (Bourne, 1883) (Annelida: Polychaeta) in the Vistula Lagoon of the Baltic Sea

The polychaetes Streblospio benedicti (Webster, 1879) and Manayunkia aestuarina (Bourne, 1883) have been recorded in the Vistula Lagoon of the Baltic Sea since the mid 1990s. The impact that salinity and the necrozooplankton (dead plankton) concentration in the near-bottom layer have on their distributional patterns was studied. The spatial distribution of these polychaetes depends on the water salinity; however, no correlation was found between their abundance and the necrozooplankton concentration. An area of high necrozooplankton concentration was defined for the near-bottom water layer in the central part of the lagoon; its position is mostly determined by the currents. We assume that the sustainable presence of S. benedicti and M. aestuarina is supported by their opportunistic species biology patterns and the lagoon hydrology, even in the last decade of unfavorable water mineralization conditions.     

Ecological classification of macroalgae and angiosperm communities of inner coastal waters in the southern Baltic Sea

A classification system of macroalgae and angiosperms for the inner coastal waters of the Baltic coast of Mecklenburg-Vorpommern (Germany) was developed according to the guidelines of the European Water Framework Directive. These guidelines ask for a five-step classification scheme (high, good, moderate, poor, bad) of the ecological state based on submerged macrophytes.The approach is based on the comparison of the occurrence and distribution of plant communities in 1999–2003 with historical data of submerged macrophytes and their community structure. Due to the lack of appropriate data, historical depth distribution limits of plant communities were calculated based on modelled historical underwater light climate.Despite the fact of very heterogeneous salinities (0.5–20.0 practical salinity units, psu) and substrate types (silty–sandy) in the study area, two general main criteria were identified as appropriate indicators of eutrophic degradation of the inner coastal waters: (1) the lower distribution depth of plant communities and (2) the loss of charophyte-dominated plant communities. Based on these two criteria, a five-step classification scheme is proposed for the characterisation of the ecological state. The depth limit boundaries between the ecological classes were calculated by 5, 25, 50 and 75% reduction of the water transparency. Based on this calculation, the ecological status is described by the gradual upward shift of the vegetation depth limit. Complementary to the decrease of depth limits the loss of charophyte-dominated plant communities characterises the border between moderate and poor ecological conditions.     

Within‐lake distribution patterns of fish assemblages: the relative roles of spatial,temporal and random environmental factors in assessing fish assemblages using gillnets in a large and shallow temperate lake

In this study, the relative role of spatio‐temporal factors and associated environmental variables (water transparency and temperature) were quantified in relation to gillnet samples of fishes in a large and shallow lake (Lake Balaton, Hungary). Most of the variance (56·1%) in the relative abundance data (%) was related to the vertical segregation of fishes. This gradient substantially affected the catch per unit effort (CPUE) by number of the dominant species, the surface‐oriented bleak Alburnus alburnus and the benthic common bream Abramis brama. It also influenced total CPUE, mean fish mass and species richness and diversity. At the lake level, horizontal habitat heterogeneity (i.e. littoral v. offshore) accounted for only 8·3% of the total variance in relative abundance data, but was important in structuring the CPUE of the ruffe Gymnocephalus cernua and the pikeperch Sander lucioperca. The longitudinal environmental gradient (i.e. lake basin), year and season of sampling, water transparency and temperature had significant effects on relative abundance only at the habitat level, but were also important components of variability of CPUE in some species at the lake level. As sampling schemes need to consider the main gradients in fish assemblage distributions, the use of surface and pelagic gillnets should be more intensively incorporated in the study and monitoring of fish assemblages in shallow lakes and lake habitats.     

Species assemblages of pelagic fish embryos in the southern North Sea between 1984 and 2000

The occurrence and abundance of the pelagic eggs of southern North Sea spring-spawning fish were analysed between 1984 and 2000. Species number varied between six (1986) and 14 (1999) and was positively correlated with sea surface temperature. With one exception, dab eggs were always the most abundant and usually highly dominant. Ranking of species depended on temperature, but no significant differences in ranking between years was discernible. Although with the increase in temperature in the 1990s a change in species assemblage was evident [species belonging to the boreal-Mediterranean (Lusitanian) group became more apparent in the species assemblage] this did not lead to an increased species diversity (Shannon Index) or a change in other community parameters. It appears that the recent developments regarding spawning stock biomass of commercial North Sea fish is reflected in the declining egg abundance of the respective commercial and larger species (i.e. cod, flounder, plaice) and an increase in abundance of the eggs of small species (i.e. long rough dab, rockling) over the years. Received in revised form: 5 November 2001 Electronic Publication     

Comparing the fish assemblages and food‐web structures of large floodplain rivers

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Ontogenetic and spatial variation in size‐selective mortality of a marine fish

Although body size can affect individual fitness, ontogenetic and spatial variation in the ecology of an organism may determine the relative advantages of size and growth. During an 8‐year field study in the Bahamas, we examined selective mortality on size and growth throughout the entire reef‐associated life phase of a common coral‐reef fish, Stegastes partitus (the bicolour damselfish). On average, faster‐growing juveniles experienced greater mortality, though as adults, larger individuals had higher survival. Comparing patterns of selection observed at four separate populations revealed that greater population density was associated with stronger selection for larger adult size. Large adults may be favoured because they are superior competitors and less susceptible to gape‐limited predators. Laboratory experiments suggested that selective mortality of fast‐growing juveniles was likely because of risk‐prone foraging behaviour. These patterns suggest that variation in ecological interactions may lead to complex patterns of lifetime selection on body size.     

Sulfate reduction, methanogenesis, and methane oxidation in the upper sediments of the Vistula and Curonian Lagoons, Baltic Sea

Microbiological, biogeochemical, and isotope geochemical investigations of the upper sediments of the Vistula and Curonian lagoons, Baltic Sea, were carried out. High content of organic matter in the sediments was responsible for the high numbers (over 10¹⁰ cells cm^?3) and activity of heterotrophic microorganisms. The calculated integral rates of dark CO₂ assimilation for the upper 30 cm of the sediments varied 12.5 to 38.8 mmol m^?2 day^?1 and were somewhat higher in the Curonian Lagoon than in the Vistula Lagoon. Integral rates of sulfate reduction were higher in the more saline Vistula Lagoon. Rapid consumption of sulfates of the pore water resulted in intensified methanogenesis, with significantly higher rates detected in the silts of the Curonian Lagoon. High rates of methanogenesis in the Curonian Lagoon correlated with higher methane levels in its upper sediments and near-bottom water. The highest rates of methane oxidation were detected in the uppermost sediment horizons (oxidized or slightly reduced), which was an indication of the barrier role of aerobic methanotrophic bacteria. The calculated methane flows from the sediments into the water column were 0.45 and 0.007 mmol m^?2 day^?1 for the Vistula and Curonian Lagoons, respectively. Low methane flow from the sediments of the Curonian Lagoon resulted probably from the specific weather (wind) conditions during sampling. The near-stormy conditions in the Curonian Lagoon caused sediment detachment, resulting in methane release into the water column.     

Invariant scaling relationship between functional dissimilarity and co‐occurrence in fish assemblages of the Patos Lagoon estuary (Brazil): environmental filtering consistently overshadows competitive exclusion

Determining how assembly rules (e.g. limiting similarity, environmental filtering and neutrality) shape community structure along environmental gradients and across spatial scales is still controversial. The study of functional relationships between coexisting species may help to disentangle among these assembly rules. Here, we compared pairwise functional dissimilarities between fish species to their corresponding pairwise co‐occurrences. Fish assemblages (n = 835) were sampled monthly in Patos‐Mirim system (Brazil) using both bottom trawling and beach seining. Species occurrences were recorded and functional traits related to locomotion and food acquisition were measured on several individuals from each species. The region studied was divided in two areas corresponding to each side of a floodgate located in São Gonçalo Channel: a freshwater channel up the floodgate and, down the floodgate, the Patos Lagoon estuary. The relationship between functional dissimilarity and co‐occurrence between species pairs was assessed using quantile regressions for each month and at different spatial scales. Overall, quantile regression coefficients between functional dissimilarities (either based on locomotion types or feeding habits) and co‐occurrence values were negative, suggesting that co‐occurrence increases with functional redundancy regardless of spatial scale. Our results support the assumption that environmental filters have more influence than biotic interactions on the structure of fish assemblages even locally.