Rapid spatial genetic differentiation in an invasive species, the round goby Neogobius melanostomus in the Baltic Sea

We analysed the pattern of genetic differentiation among six newly established (around 10 generations) sites of the round goby (Neogobius melanostomus) in the southern Baltic Sea by means of nine microsatellite loci and in total 183 individuals. All but one site were within 30 km from each other. We found statistically significant genetic differentiation in ten out of 15 comparisons after Bonferroni correction, and since the species is newly introduced this has happened in less than ten generations. The largest genetic differentiation was found between the two most divergent habitats, while sites with a similar habitat were not significantly differentiated. Estimates of gene flow (Nm) were low and ranged from 1.5 to 5.5. A large proportion of individuals were assigned to one site (Puck), suggesting that this site has acted as a source to the other sites.     

Seasonal depth distribution and thermal experience of the non-indigenous round goby Neogobius melanostomus in the Baltic Sea: implications to key trophic relations

Biological Invasions - Native to the Ponto-Caspian region, the benthic round goby (Neogobius melanostomus) has invaded several European inland waterbodies as well as the North American Great Lakes...     

The food web positioning and trophic niche of the non-indigenous round goby: a comparison between two Baltic Sea populations

Native species may show invasiveness toward a recipient ecosystem through increases in abundance as a result of artificial stocking events. Salmonid species are typical examples of native invaders whose abundance is increased after stocking with hatchery fish. This study evaluated the effects of hatchery chum salmon fry on sympatric wild masu salmon fry, benthic invertebrate prey, and algae, after a single stocking event in Mamachi stream, Hokkaido, northern Japan. The results suggested that the stocked hatchery chum salmon fry decreased the foraging efficiency and growth of the wild masu salmon fry through interspecific competition, and depressed the abundance of Ephemerellidae and total grazer invertebrates (Glossosomatidae, Heptageniidae, and Baetidae) through predation. Also, the hatchery chum salmon fry may increase algal biomass through depression of grazer abundance by predation (top-down effect). These results suggested that a single release of hatchery chum salmon fry into a stream may influence the recipient stream ecosystem.     

Predator and prey: the role of the round goby Neogobius melanostomus in the western Baltic

Different studies on the position of the non-indigenous species Neogobius melanostomus within the coastal food web of the Pomeranian Bay (western Baltic) were performed, resulting in a quantitative and qualitative species list of prey organisms found in the stomachs of the invader and an estimation concerning the importance of round goby as prey for different resident predators. It seems that the colonization process is not fully completed yet, but the results reveal that the species is already established in the food web 16 years after the first observation within the study area. The results show that N. melanostomus feed upon a wide range of different resident organisms. While a direct predation effect on native fish species appears rather unlikely, indirect effects such as competition cannot yet be excluded. In addition, our results reveal an ontogenetic diet shift and that the round goby itself already serves as an important prey for piscivorous fish and seabirds. Finally, we formulate different hypotheses based on our results which will require further research.     

Invasion genetics of the Eurasian round goby in North America: tracing sources and spread patterns

The Eurasian round goby Neogobius melanostomus ( Apollonia melanostoma ) invaded the North American Great Lakes in 1990 through ballast water, spread rapidly, and now is widely distributed and moving through adjacent tributaries. We analyse its genetic diversity and divergence patterns among 25 North American ( N  = 744) and 22 Eurasian ( N  = 414) locations using mitochondrial DNA cytochrome b gene sequences and seven nuclear microsatellite loci in order to: (i) identify the invasion's founding source(s), (ii) test for founder effects, (iii) evaluate whether the invasive range is genetically heterogeneous, and (iv) determine whether fringe and central areas differ in genetic diversity. Tests include F _ST analogues, neighbour-joining trees, haplotype networks, Bayesian assignment, Monmonier barrier analysis, and three-dimensional factorial correspondence analysis. We recovered 13 cytochrome b haplotypes and 232 microsatellite alleles in North America and compared these to variation we previously described across Eurasia. Results show: (i) the southern Dnieper River population was the primary Eurasian donor source for the round goby's invasion of North America, likely supplemented by some alleles from the Dniester and Southern Bug rivers, (ii) the overall invasion has high genetic diversity and experienced no founder effect, (iii) there is significant genetic structuring across North America, and (iv) some expansion areas show reduced numbers of alleles, whereas others appear to reflect secondary colonization. Sampling sites in Lake Huron's Saginaw Bay and Lake Ontario significantly differ from all others, having unique alleles that apparently originated from separate introductions. Substantial genetic variation, multiple founding sources, large number of propagules, and population structure thus likely aided the goby's ecological success.     

Invasion patterns in riparian habitats: The role of anthropogenic pressure in temperate streams

The riparian flora and the level of invasion in the rivers of the Cantabric watershed in Spain were studied in relation to the ecological status and the anthropogenic pressure. The level of invasion was also analyzed in different riparian habitats: forests, river bars and man-made slopes. For this purpose, 18 sites were sampled and a list of native and alien plant species was made along a 100-m strip at each site. The habitat/s where alien species were found and their abundance per habitat and in the total area were also indicated. Out of 112 alien taxa found, 51 were classified as invasive. Exotic plants native to America were the most common (35%). The level of invasion was significantly higher in the sampling sites subject to high levels of hydrological and morphological disturbances, proxies of the anthropogenic pressure. River bars and man-made slopes supported similar number of alien plant species, higher than forests. We suggest that disturbance in river banks should be minimized as much as possible in order to diminish the risk of invasion.     

Swimming performance and invasion potential of the round goby

European round gobies (Neogobius melanostomus) are displacing several important native North American fish species. Controlling their invasion is contingent on understanding their swimming inclination and potential. We assessed goby swimming inclination by recording activity in a 2 m flume over a ~24 h period, and swimming potential using a critical swimming (U _crit) test, as well as burst tests in still and flowing water. When given the choice to move, gobies covered as much as 14 m/h, with a slight bias towards nocturnal activity and an overall upstream preference. When confined and coerced to perform a U _crit test, they burst-and-held to achieve 35.5 ± 1.1 cm/s. Thirty minutes following U _crit, they were able to burst-and-coast in a sprint test to almost twice this speed. In still water, they exhibited startle bursts of up to 163 cm/s. We provide a swimming endurance model that indicates flow rates would need to be >125 cm/s to prevent upstream movement, and free of refuge areas in which to recover. The current study shows that the round goby is a surprisingly powerful swimmer with the capacity to continue its invasion should hydrologic control be absent.     

Evidence for predatory control of the invasive round goby

We coupled bioenergetics modeling with bottom trawl survey results to evaluate the capacity of piscivorous fish in eastern Lake Erie to exert predatory control of the invading population of round goby Neogobius melanostomus. In the offshore (>20 m deep) waters of eastern Lake Erie, burbot Lota lota is a native top predator, feeding on a suite of prey fishes. The round goby invaded eastern Lake Erie during the late 1990s, and round goby population size increased dramatically during 1999–2004. According to annual bottom trawl survey results, round goby abundance in offshore waters peaked in 2004, but then declined during 2004–2008. Coincidentally, round goby became an important component of burbot diet beginning in 2003. Using bottom trawling and gill netting, we estimated adult burbot abundance and age structure in eastern Lake Erie during 2007. Diet composition and energy density of eastern Lake Erie burbot were also determined during 2007. This information, along with estimates of burbot growth, burbot mortality, burbot water temperature regime, and energy densities of prey fish from the literature, were incorporated into a bioenergetics model application to estimate annual consumption of round goby by the adult burbot population. Results indicated that the adult burbot population in eastern Lake Erie annually consumed 1,361 metric tons of round goby. Based on the results of bottom trawling, we estimated the biomass of yearling and older round goby in offshore waters eastern Lake Erie during 2007–2008 to be 2,232 metric tons. Thus, the adult burbot population was feeding on round goby at an annual rate equal to 61% of the estimated round goby standing stock. We concluded that the burbot population had high potential to exert predatory control on round goby in offshore waters of eastern Lake Erie.     

Eutrophication in the Baltic Sea

Fish consumption is increasing globally. Overfishing puts pressure on fisheries, but aquaculture provides an alternative to satisfy the growing need for seafood. However, nutrient emissions from aquaculture contribute to eutrophication, and raising fish from the top of the food chain is inefficient. Here we use the approach of industrial ecology and report ImPACT decomposition analysis of the drivers of nutrient emissions to the Baltic Sea from rainbow trout aquaculture in Finland during 1980?2007. During this period, the nitrogen load studied increased markedly and was 522 tonnes in 2007. The phosphorus load quadrupled and then returned to its original level of about 65 tonnes. The Finnish population increased slightly, while the average affluence level increased significantly. Total salmonid consumption increased substantially during the period. The increasing percentage of imported salmonids and improvements in domestic aquaculture technology ended the period of strong growth of emissions in the 1980s. Decreasing the nutrient load through reductions in salmonid consumption in the future is unlikely, due to health benefits and consumer preferences. Replacing domestic production with import of salmonids raises questions regarding outsourcing of the environmental impact, and regarding rural development in Finland. Major improvements in production technology are not in sight. New perspectives on rainbow trout aquaculture may be needed, including using feed from the Baltic Sea, thus closing the nutrient cycle or changing consumption and production to herbivorous fish species.     

Measurements of salmonid population performance in relation to habitat in eastern Newfoundland streams

The density, biomass and estimated production of brook trout Salvelinus fontinalis and Atlantic salmon Salmo salar were related to habitat factors in streams of Terra Nova National Park, Newfoundland, Canada. Fish communities at 29 sites (18 brooks; 15 watersheds) were sampled in the summer of 2002, 2003 and 2005. Salmonid density, biomass per unit area and production (derived from biomass and fish size using allometric P:B relationships) were compared with site habitat characteristics (wetted width, lactustrine habitat, per cent riffle habitat, canopy coverage and stream gradient), using an interactive stepwise multiple linear regression. Salmonid biomass (mean: 2·87 g m^?2; range: 0·33–10·88 g m^?2) and estimated production (mean: 3·05 g m^?2 year^?1; range: 0·32–10·98 g m^?2 year^?1) within the study area varied by an order of magnitude, however, habitat variables accounted for much of this variation. Specifically, wetted width and lacustrine area of the tributary played important roles in explaining density, biomass and production. Wetted width was important for all measurements of brook trout and total salmonids while lacustrine area was important for all measurements of Atlantic salmon and played a lesser role in total salmonid biomass. Other factors such as the percentage of riffle habitat, site gradient and canopy coverage provided modest improvements to the fit of some relationships. When models using the same environmental factors were compared, those using production estimates derived from allometric P:B equations in the literature provided improved predictive capability than did those from direct density and biomass estimates. It is proposed that allometric P:B relationships have utility in improving comparisons of stream fish communities, particularly in studies with insufficient resources to measure production directly.     

Effectiveness of nutrient enhancement as a remediation or compensation strategy of salmonid fisheries in culturally oligotrophic lakes and streams in temperate climates

Productivity of temperate streams and lakes is often limited by availability of key nutrients, and nutrient‐poor habitats are termed oligotrophic. Oligotrophic streams and lakes occur naturally, but often are a product of human activities (cultural oligotrophication), such as the creation of dams. Cultural oligotrophication has resulted in declining productivity in streams and lakes, a condition that can manifest itself in collapsing salmonid fish stocks. To counteract lost productivity as part of restoration or compensation measures, managers often add nutrient via fertilizers to enhance fisheries production. However, these programs are not always successful, and this article reviews available literature to identify patterns that may influence success of nutrient enhancement programs. Overall fertilization of lakes and streams will almost certainly increase primary producer and invertebrate populations. While it is likely that fertilization will also increase fishery production, it is far from certain. The magnitude of this change is unpredictable, and the success of a fertilization program will vary greatly between years, habitat, and microhabitats. Regardless, if fertilization is coupled with holistic monitoring of the food web and ecosystem, then it is likely to be an effective technique to enhance fishery productivity in active restoration of compensation programs. However, the benefits of fertilization will not outlast the fertilization project, and care must be exercised when ceasing active fertilization. When compared to other restoration/compensation strategies such as fish ladders or trap and transport, fertilization may be a cost‐effective method to enhance fishery production. Finally, recommendations are discussed to increase the probability of fertilization success.     

The seminal vesicle synthesizes steroids in the round goby Neogobius melanostomus

In this study, we examine the possible contribution of the seminal vesicles of the male round goby to the production of putative steroidal pheromones. A previous study showed that the testes of the round goby are rich in steroid-producing Leydig-like cells; and when incubated in vitro, convert tritiated androstenedione to at least six other steroids, including one not previously identified in fish--namely 3alpha-hydroxy-5beta-androstane-11,17-dione (11-oxo-etiocholanolone, 11-oxo-ETIO). The seminal vesicles of reproductively mature males were examined by conventional histology, transmission electron microscopy and immunocytochemistry (utilizing an antibody against 3beta-hydroxysteroid dehydrogenase--a key enzyme in vertebrate steroid synthesis). All three procedures identified Leydig cells in the proximal and medial regions of the seminal vesicles. In vitro incubation of seminal vesicles with tritiated androstenedione demonstrated biosynthesis of 11-oxo-androstenedione, 11-oxo-testosterone (more commonly known as 11-ketotestosterone) and 11 oxo-ETIO. These data indicate that the seminal vesicles, as well as the testes are involved in the synthesis of steroidal compounds that may function as pheromones.     

Differential modes of selection on the rhodopsin gene in coastal Baltic and North Sea populations of the sand goby,Pomatoschistus minutus

An excellent model to elucidate the mechanisms and importance of evolution in the marine environment is the spectral tuning mechanism of the visual pigment in vertebrates. In the sand goby Pomatoschistus minutus (Teleostei; Gobiidae), a distribution‐wide study showed that spatial variation at the rhodopsin gene (RH1) matches the characteristics of specific light environments. This match suggests that populations are locally adapted to selective light regimes targeting the RH1 gene. If so, then the direction of selection should depend on the regional spatial and temporal stability of the light conditions. We tested this prediction by comparing goby populations from two regions: the Baltic Sea, characterized by divergent, but temporally stable light conditions, and the North Sea, characterized by locally heterogeneous and temporally variable light conditions. RH1 sequences of 491 Pomatoschistus minutus individuals from 15 locations were analysed. We found that variation at the RH1 gene in the Baltic populations showed signatures of diversifying selection, whereas the RH1 gene in the North Sea showed signatures of stabilizing selection. These different modes of selection are consistent with the regional light conditions and hence support our predictions, but may also be influenced by migration between the open sea and more turbid estuarine environments. An interesting observation is that within one gene, synonymous and non‐synonymous SNPs show a totally different pattern between populations. Population differentiation based on non‐synonymous SNPs of the RH1 gene correlated with spectral variation of the local environment of the sand goby populations. In contrast, the differentiation based on synonymous SNPs of RH1 reflects more the neutral historical pattern of the species.     

The presence of Couch's goby in the Mediterranean Sea

Known distribution of Couch's goby, Gobius couchi Miller & El-Tawil, 1974 formerly limited to the British Isles, appears now to be extended to the Mediterranean. A new specimen collected at the island of Ischia, near Naples, Italy, is described.     

Temporal patterns in growth and survival of the round goby Neogobius melanostomus

Monthly, overwinter and annual instantaneous growth rates for round goby Neogobius melanostomus were calculated with maximal growth occurring in July and August and almost no growth observed between ice appearance (October) and melt (March). Annual absolute growth rates averaged 27·3 ± 1·9 mm for males and 19·8 ± 2·4 mm for females. The most parsimonious Cormack–Jolly–Seber model indicated that both the survival and recapture probabilities were dependent on sampling date, but not sex. Survival estimates remained high throughout the 13 month study with a median weekly survival probability of 0·920 (25 and 75% quartiles: 0·767 and 0·991), an overwinter survival probability of 99% and an annual survival rate of 67%. Survival probabilities were lowest for both sexes near the completion of the N. melanostomus reproductive season in July and August which supports existing evidence of higher mortality after reproduction, while challenging the paradigm that male N. melanostomus suffer comparatively higher mortality as a result of reproduction than females. Evidence indicating that growth and mortality rates are highest at the end of the reproductive season not only highlights seasonal variability in N. melanostomus natural history, but may also guide the control of this invasive species to periods when they are most vulnerable.     

First record of the Norway goby in the Adriatic Sea

One male and four female Norway gobies Pomatoschistus norvegicus are reported from the Adriatic Sea.     

Sensitivity of salmonid freshwater life history in western US streams to future climate conditions

We projected effects of mid‐21st century climate on the early life growth of Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) in western United States streams. Air temperature and snowpack trends projected from observed 20th century trends were used to predict future seasonal stream temperatures. Fish growth from winter to summer was projected with temperature‐dependent models of egg development and juvenile growth. Based on temperature data from 115 sites, by mid‐21st century, the effects of climate change are projected to be mixed. Fish in warm‐region streams that are currently cooled by snow melt will grow less, and fish in suboptimally cool streams will grow more. Relative to 20th century conditions, by mid‐21st century juvenile salmonids' weights are expected to be lower in the Columbia Basin and California Central Valley, but unchanged or greater in coastal and mountain streams. Because fish weight affects fish survival, the predicted changes in weight could impact population fitness depending on other factors such as density effects, food quality and quantity changes, habitat alterations, etc. The level of year‐to‐year variability in stream temperatures is high and our analysis suggests that identifying effects of climate change over the natural variability will be difficult except in a few streams.     

Status of Biodiversity in the Baltic Sea

The brackish Baltic Sea hosts species of various origins and environmental tolerances. These immigrated to the sea 10,000 to 15,000 years ago or have been introduced to the area over the relatively recent history of the system. The Baltic Sea has only one known endemic species. While information on some abiotic parameters extends back as long as five centuries and first quantitative snapshot data on biota (on exploited fish populations) originate generally from the same time, international coordination of research began in the early twentieth century. Continuous, annual Baltic Sea-wide long-term datasets on several organism groups (plankton, benthos, fish) are generally available since the mid-1950s. Based on a variety of available data sources (published papers, reports, grey literature, unpublished data), the Baltic Sea, incl. Kattegat, hosts altogether at least 6,065 species, including at least 1,700 phytoplankton, 442 phytobenthos, at least 1,199 zooplankton, at least 569 meiozoobenthos, 1,476 macrozoobenthos, at least 380 vertebrate parasites, about 200 fish, 3 seal, and 83 bird species. In general, but not in all organism groups, high sub-regional total species richness is associated with elevated salinity. Although in comparison with fully marine areas the Baltic Sea supports fewer species, several facets of the system''s diversity remain underexplored to this day, such as micro-organisms, foraminiferans, meiobenthos and parasites. In the future, climate change and its interactions with multiple anthropogenic forcings are likely to have major impacts on the Baltic biodiversity.