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Detection of endangered species is invaluable for conservation efforts, yet many traditional sampling techniques are ineffective at low population abundances or during certain periods of the year. Here, we compared results from a newly developed eDNA approach and the traditional observational method for the endangered pool frog (Pelophylax lessonae). Analysis using an occupancy-modeling framework indicated that the probability of pools being occupied using eDNA (0.93) was higher than for the traditional method of counting calling males and silent observed individuals (0.72). Detailed analysis revealed complementarity among the methods. That is, the traditional method gave a high rate of observation in June, whereas eDNA gave at least as many or more observations during other parts of the year. Discrepancies among the methods depended on the dominant lifecycle stage, and eDNA concentrations were higher when juveniles were present than at times when spawning occurred. eDNA concentrations were also positively related to P. lessonae observations. Our study demonstrates that an eDNA protocol for monitoring of endangered amphibian species can be particularly valuable during periods when individuals are hard to detect by observational methods, and provides guidance to sampling efforts for research and monitoring programs in other regions and systems.

Assessing the relative importance of environmental conditions and community interactions is necessary for evaluating the sensitivity of biological communities to anthropogenic change. Phytoplankton communities have a central role in aquatic food webs and biogeochemical cycles, therefore, consequences of differing community sensitivities may have broad ecosystem effects. Using two long‐term time series (28 and 20 years) from the Baltic Sea, we evaluated coastal and offshore major phytoplankton taxonomic group biovolume patterns over annual and monthly time‐scales and assessed their response to environmental drivers and biotic interactions. Overall, coastal phytoplankton responded more strongly to environmental anomalies than offshore phytoplankton, although the specific environmental driver changed with time scale. A trend indicating a state shift in annual biovolume anomalies occurred at both sites and the shift's timing at the coastal site closely tracked other long‐term Baltic Sea ecosystem shifts. Cyanobacteria and the autotrophic ciliate Mesodinium rubrum were more strongly related than other groups to this trend with opposing relationships that were consistent across sites. On a monthly scale, biotic interactions within communities were rare and did not overlap between the coastal and offshore sites. Annual scales may be better able to assess general patterns across habitat types in the Baltic Sea, but monthly community dynamics may differ at relatively small spatial scales and consequently respond differently to future change.

Scale is a key to determining which processes drive community structure. We analyse size distributions of phytoplankton to determine time scales at which we can observe either fixed environmental characteristics underlying communities structure or competition-driven size distributions. Using multiple statistical tests, we characterise size distributions of phytoplankton from 20-year time series in two sites of the Baltic Sea. At large temporal scales (5-20 years), size distributions are unimodal, indicating that fundamental barriers to existence are here subtler than in other systems. Frequency distributions of the average size of the species weighted by biovolume are multimodal over large time scales, although this is the product of often unimodal short-term (

Knowledge of diet compositions is important in ecological research. There are many methods available and nu- merous aspects of diet composition. Here we used modelling to evaluate how well different diet analysis methods describe the "true" diet of fish, expressed in mass percentages. The methods studied were both basic methods (frequency of occur- rence, dominance, numeric, mass, points) and composite indices (Index of Relative Importance, Comparative Feeding In- dex). Analyses were based on both averaged stomach content of individual fish and on pooled content from several fish. Prey preference, prey size, and evacuation rate influenced the performance of the diet analysis methods. The basic methods performed better than composite indices. Mass and points methods produced diet compositions most similar to the true diet and were also most robust, indicating that these methods should be used to describe energetic-nutritional sources of fish. Resume : Il importe de connaitre la composition du regime alimentaire en recherche en ecologie. De nombreuses methodes sont disponibles pour determiner la composition du regime alimentaire, qui comporte de nombreux aspects. Nous avons uti- lise la modelisation pour evaluer comment differentes methodes d'analyse du regime alimentaire decrivent l'alimentation « reelle » des poissons, exprimee en terme de pourcentages de la masse. Les methodes etudiees reposent tant sur des para- metres de base (frequence de l'occurrence, dominance, numerique, masse, points) que des indices composites (indice d'im- portance relative, indice comparatif d'alimentation). Les analyses sont basees sur le contenant stomacal moyen d'individus et sur le contenu stomacal combine de plusieurs poissons. La performance des methodes d'analyse de l'alimentation est in- fluencee par les preferences des proies, la taille des proies et le taux d'elimination. La performance des methodes reposant sur des parametres de base s'avere superieure a celle de methodes faisant appel a des indices composites. Les methodes re- posant sur la masse et les points produisent les compositions du regime alimentaire qui s'approchent le plus du regime reel et sont egalement les plus robustes. Ces resultats indiquent que ces deux methodes devraient etre utilisees pour decrire les sources d'energie-d'alimentation des poissons. (Traduit par la Redaction)

The Baltic Proper is a semi-enclosed, highly productive basin of the Baltic Sea with a low biodiversity, where only a few key species drive the system's dynamics. Recently, an ecosystem regime shif ...

Lundström, K., Hjerne, O., Lunneryd, S-G., and Karlsson, O. 2010. Understanding the diet composition of marine mammals: grey seals (Halichoerus grypus) in the Baltic Sea. – ICES Journal of Marine Science, 67: 1230–1239. Dietary studies are important in understanding the ecological role of marine mammals and in formulating appropriate management plans in terms of their interactions with fisheries. The validity of such studies has, however, often been compromised by unrepresentative sampling procedures, resulting in false weight being given to external factors seeming to influence diet composition. The bias caused by non-random sampling was examined, using canonical correspondence analysis to assess how the prey species composition in digestive tract samples of Baltic grey seals (Halichoerus grypus) was related to spatial, temporal, and demographic factors and to whether the samples were collected in association with fishing gear or not (“sampling condition”). Geographic region explained the largest fraction of the observed variation, followed by sampling condition, age group, and year. Season and gender were not statistically significant. Segregation of the two age categories “pups” and “juveniles–adults”, and the two geographic categories “Baltic proper” and “Gulf of Bothnia” are proposed to estimate the diet and fish consumption of the Baltic grey seal population as a whole. Atlantic herring was the most commonly recovered prey item in all areas and age groups, followed by European sprat in the south, and common whitefish in the north. Pups had eaten relatively more small non-commercial species than older seals.

The ecosystems of coastal and enclosed seas are under increasing anthropogenic pressure worldwide, with Chesapeake Bay, the Gulf of Mexico and the Black and Baltic Seas as well known examples. We use an ecosystem model (Ecopath with Ecosim, EwE) to show that reduced top-down control (seal predation) and increased bottom-up forcing (eutrophication) can largely explain the historical dynamics of the main fish stocks (cod, herring and sprat) in the Baltic Sea between 1900 and 1980. Based on these results and the historical fish stock development we identify two major ecological transitions. A shift from seal to cod domination was caused by a virtual elimination of marine mammals followed by a shift from an oligotrophic to a eutrophic state. A third shift from cod to clupeid domination in the late 1980s has previously been explained by overfishing of cod and climatic changes. We propose that the shift from an oligotrophic to a eutrophic state represents a true regime shift with a stabilizing mechanism for a hysteresis phenomenon. There are also mechanisms that could stabilize the shift from a cod to clupeid dominated ecosystem, but there are no indications that the ecosystem has been pushed that far yet. We argue that the shifts in the Baltic Sea are a consequence of human impacts, although variations in climate may have influenced their timing, magnitude and persistence.

Based on an earlier published ecosystem model, we have explored possible effects of different management scenarios for the Baltic Sea. The scenarios include an oligotrophication of the system, a drastic increase in the number of seals, and changes in the fishery management. From these simulations we conclude that fisheries, seals, and eutrophication all have strong and interacting impacts on the ecosystem. These interactions call for integrated management. The modeling highlights the potential for conflicts among management mandates such as flourishing fisheries, rebuilt seal populations, and substantially reduced eutrophication. The results also suggest that fisheries management reference points have to be adjusted in response to changes in the presence of natural predators or ecosystem productivity.

Many studies show that fish and fisheries management can be important to freshwater nutrient dynamics, but similar reports from marine environments are scarce. In the Baltic Sea, we estimate the removal of nutrients by the fishery to be 1.4% and 7% of the total nitrogen and phosphorus load to the Baltic Sea. Moreover, compared with the anthropogenic load of nutrients that reaches the open sea, the fishery removes 2.4% and 18% of the nitrogen and phosphorus. In addition, we show that the summer increase of fish biomass can explain up to one third of the summer decrease in ‘‘total phosphorus’’ in the upper 40 m of the water column. This suggests that fish may compete with primary producers (particularly cyanobacteria) for phosphorus. The fish and the fishery can thus influence nutrient dynamics in marine systems substantially, and this should be considered in ecosystem oriented fisheries management.

The reproductive success and thus abundance and distribution of dab, plaice, and flounder in the Baltic Sea, a large brackish water area, is restricted by salinity. By measuring spermatozoa mobility and fertilisation rates at different salinities and determining the salinity at which eggs are neutrally buoyant, the salinity requirements for successful egg development were assessed. The results were used for the evaluation of potential spawning areas and for stock discrimination by analyses of differences in the salinity requirements of fish from different areas (ICES Subdivisions (SD) 23-28). The results suggest that there are two stocks of dab and successful reproduction may occur in the Sound (SD 23) and, occasionally, in the Arkona and Bornholm basins (SD 24 and SD 25). Opportunities for successful reproduction of plaice exist regularly in the Arkona and Bornholm basins and occasionally in the Gdansk and Gotland basins (SD 26 and SD 28). No differences in salinity requirements for fish from SD 24-28 suggest one stock of plaice in the Baltic proper. There are two different types of flounder, one with demersal eggs and the other with pelagic eggs. The former, constituting one distinct stock, may reproduce successfully as far north as the Bothnian Sea and the Gulf of Finland (SD 30 and SD 32), up to the 6 psu isohaline. For flounder with pelagic eggs, opportunities for the eggs to obtain neutral buoyancy suggest that successful reproduction may occur regularly in the Sound, the Arkona, and Bornholm basins as well as in the Gdansk and Gotland basins, and that there are three stocks of flounder with pelagic eggs.

Overfishing is a major problem in the world fisheries. Constant harvest rate strategies, with catches proportional to the abundance of the target species, stimulates investments when stock sizes are large, often resulting in an overcapacity when the stocks decrease. These investment incentives are weaker under a constant catch strategy, since there are less reasons to have a catching and fish processing capacity that is larger than the allowed constant catch. We have explored the potential of a management strategy based on constant catches, by modelling the fishery on the eastern Baltic Sea cod (Gadus morhua L.). To avoid the low long-term yield (LTY) often resulting from a strict constant catch approach, we developed a quasi-constant catch (QCC) strategy based on alternative constant catch levels and two overfishing criteria. Normal catches are allowed when the spawning stock biomass is above a certain level. When the spawning stock biomass falls below this level, catches are reduced to a given extent. If the spawning stock biomass falls below a second and lower threshold, the fishery is closed. The QCC strategy was tested with a model based on the same basic premises as the multi-species virtual population analyses (MSVPA) for Baltic Sea cod, developed within ICES. In addition, recruitment processes were included and probability analyses were done to estimate different risks of overfishing. According to the model, the LTY with the QCC strategy was 10% lower than with the constant harvest rate strategy. However, the QCC approach had the advantage of smaller variation in catches, potentially resulting in a better utilisation of the fishery capacity. The capacity utilisation was better with the QCC strategy relative to the constant harvest rate strategy, especially in fisheries where catch quotas are based on assessments with substantial errors. Furthermore, QCC gave a better capacity utilisation in fisheries where the size of the fleet and processing capacity is non-flexible and when effective fish finding techniques are used. A more effective capacity utilisation could counterbalance the disadvantage of the lower LTY compared to the constant harvest rate strategy. The QCC approach is hence an interesting and competitive management strategy, that is likely to be more effective in avoiding the emergence overcapitalisation and overfishing of long-lived species like the Baltic cod. QCC may also allow catch quotas to be set for more than 1 year, provided that the stock size of the target species is relatively large.

Changes in climate, in combination with intensive exploitation of marine resources, have caused large-scale reorganizations in many of the world's marine ecosystems during the past decades. The Baltic Sea in Northern Europe is one of the systems most affected. In addition to being exposed to persistent eutrophication, intensive fishing, and one of the world's fastest rates of warming in the last two decades of the 20th century, accelerated climate change including atmospheric warming and changes in precipitation is projected for this region during the 21st century. Here, we used a new multimodel approach to project how the interaction of climate, nutrient loads, and cod fishing may affect the future of the open Central Baltic Sea food web. Regionally downscaled global climate scenarios were, in combination with three nutrient load scenarios, used to drive an ensemble of three regional biogeochemical models (BGMs). An Ecopath with Ecosim food web model was then forced with the BGM results from different nutrient-climate scenarios in combination with two different cod fishing scenarios. The results showed that regional management is likely to play a major role in determining the future of the Baltic Sea ecosystem. By the end of the 21st century, for example, the combination of intensive cod fishing and high nutrient loads projected a strongly eutrophicated and sprat-dominated ecosystem, whereas low cod fishing in combination with low nutrient loads resulted in a cod-dominated ecosystem with eutrophication levels close to present. Also, nonlinearities were observed in the sensitivity of different trophic groups to nutrient loads or fishing depending on the combination of the two. Finally, many climate variables and species biomasses were projected to levels unseen in the past. Hence, the risk for ecological surprises needs to be addressed, particularly when the results are discussed in the ecosystem-based management context.

Models that can project ecosystem dynamics under changing environmental conditions are in high demand. The application of such models, however, requires model validation together with analyses of model uncertainties, which are both often overlooked. We carried out a simplified model uncertainty and sensitivity analysis on an Ecopath with Ecosim food-web model of the Baltic Proper (BaltProWeb) and found the model sensitive to both variations in the input data of pre-identified key groups and environmental forcing. Model uncertainties grew particularly high in future climate change scenarios. For example, cod fishery recommendations that resulted in viable stocks in the original model failed after data uncertainties were introduced. In addition, addressing the trophic control dynamics produced by the food-web model proved as a useful tool for both model validation, and for studying the food-web function. These results indicate that presenting model uncertainties is necessary to alleviate ecological surprises in marine ecosystem management.