Are juveniles as tolerant to salinity stress as adults? A case study of Northern European, Ponto‐Caspian and North American species

Aim: Global biodiversity and ecosystems are highly impacted by anthropogenic activities, such as climate change and introduction of non-indigenous species. As numerous species from the Ponto-Caspian region have established in the North and Baltic Seas, as well as in the Laurentian Great Lakes, there have been large number of studies examining environmental tolerance of these species to determine their future potential to spread. However, many of those studies were conducted only on adult stages, while neglecting the possibility that early life history stages might not be equally resilient. Location: Northern European, Ponto-Caspian and North American regions. Methods: To determine whether juveniles would demonstrate the same environmental tolerance as their parents, we examined the salinity tolerance of adults and juveniles of one Northern European (Gammarus salinus), one Ponto-Caspian (Pontogammarus maeoticus) and one North American species (Gammarus tigrinus). Additionally, we compared our study to that of Paiva et al. (Global Change Biology, 24, 2018, 2708), who tested the salinity tolerance of the same species using only adults. Results: Our study determined that both adults and juveniles of all three species tolerated wide ranges of salinity, with juveniles of G. salinus tolerating only slightly narrower salinity range than their parents, while those of P. maeoticus and G. tigrinus much narrower range. Additionally, we determined better survival and higher growth rates of juveniles of G. salinus in higher salinities and better survival of P. maeoticus in lower salinities. Main conclusions: Based on juvenile salinity tolerance, our study further supported findings of Paiva et al. (2018), where Northern European species may be adapted to marine, while Ponto-Caspian to lower saline and freshwater environments. The North American species is probably adapted to intermediate salinities. As juveniles do not tolerate the same salinity stress as adults, we emphasize the importance of testing all life history stages when predicting species resilience to environmental stressors

Euryhalinity of Ponto-Caspian invaders in their native and introduced regions

In the past several decades, Ponto-Caspian species have established in freshwater and brackish habitats of the North and Baltic Sea and Great Lakes-St. Lawrence River region in much higher numbers than expected based on introduction effort (i.e. shipping frequency) and environmental conditions between these regions. Several studies have suggested that Ponto-Caspian taxa are euryhaline and might be able to adapt rapidly to changing salinity conditions, and therefore may be more successful colonizers than species from other regions. To determine the realized niche in the native and introduced habitats of Ponto-Caspian invaders and to assess whether they have expanded their salinity tolerance during the invasion process, we conducted a literature search to assess the salinity ranges of 55 Ponto-Caspian species in their native and introduced ranges. Our results confirmed that the majority of those species occupied a wide range of salinity in their native and introduced habitats. Approximately 50% of species were reported from both freshwater and brackish habitats (0–18 PSU) in their native region, occupying a salinity range of at least 10 PSU difference. In general, the number of species tended to decline as salinity increased in both native and introduced habitats. More than 90% of Ponto-Caspian invaders occupied freshwater (< 0–0.5 PSU) habitats, while 18% did not occur above 18 PSU. Overall, 46% of species were reported from a narrower salinity range in their introduced compared to their native region. Consequently, our study revealed significantly broader salinity ranges in native compared to introduced habitats. As our results suggest that the majority of Ponto-Caspian invaders occupy freshwater and brackish habitats in their native region, the recent numerous invasions of freshwater and brackish areas by these species should not be a surprise. Therefore, managers and policy makers should take into account that the majority of Ponto-Caspian invaders originate from fresh water or low salinities and develop new regulations to prevent future invasions from the Ponto-Caspian region, as well as from areas highly invaded by Ponto-Caspian taxa such as Northern Europe

in situ experiment

The increasing amount of plastic littered into the sea may provide a new substratum for benthic organisms. These marine fouling communities on plastic have not received much scientific attention. We present, to our knowledge, the first comprehensive analysis of their macroscopic community composition, their primary production and the polymer degradation comparing conventional polyethylene (PE) and a biodegradable starch-based plastic blend in coastal benthic and pelagic habitats in the Mediterranean Sea. The biomass of the fouling layer increased significantly over time and all samples became heavy enough to sink to the seafloor. The fouling communities, consisting of 21 families, were distinct between habitats, but not between polymer types. Positive primary production was measured in the pelagic, but not in the benthic habitat, suggesting that large accumulations of floating plastic could pose a source of oxygen for local ecosystems, as well as a carbon sink. Contrary to PE, the biodegradable plastic showed a significant loss of tensile strength and disintegrated over time in both habitats. These results indicate that in the marine environment, biodegradable polymers may disintegrate at higher rates than conventional polymers. This should be considered for the development of new materials, environmental risk assessment and waste management strategies

Hospitalized patients dying with SARS-CoV-2 infection—an analysis of patient characteristics and management in ICU and general ward of the LEOSS registry

BACKGROUND: COVID-19 is a severe disease with a high need for intensive care treatment and a high mortality rate in hospitalized patients. The objective of this study was to describe and compare the clinical characteristics and the management of patients dying with SARS-CoV-2 infection in the acute medical and intensive care setting. METHODS: Descriptive analysis of dying patients enrolled in the Lean European Open Survey on SARS-CoV-2 Infected Patients (LEOSS), a non-interventional cohort study, between March 18 and November 18, 2020. Symptoms, comorbidities and management of patients, including palliative care involvement, were compared between general ward and intensive care unit (ICU) by univariate analysis. RESULTS: 580/4310 (13%) SARS-CoV-2 infected patients died. Among 580 patients 67% were treated on ICU and 33% on a general ward. The spectrum of comorbidities and symptoms was broad with more comorbidities (≥ four comorbidities: 52% versus 25%) and a higher age distribution (>65 years: 98% versus 70%) in patients on the general ward. 69% of patients were in an at least complicated phase at diagnosis of the SARS-CoV-2 infection with a higher proportion of patients in a critical phase or dying the day of diagnosis treated on ICU (36% versus 11%). While most patients admitted to ICU came from home (71%), patients treated on the general ward came likewise from home and nursing home (44% respectively) and were more frequently on palliative care before admission (29% versus 7%). A palliative care team was involved in dying patients in 15%. Personal contacts were limited but more often documented in patients treated on ICU (68% versus 47%). CONCLUSION: Patients dying with SARS-CoV-2 infection suffer from high symptom burden and often deteriorate early with a demand for ICU treatment. Therefor a demand for palliative care expertise with early involvement seems to exist

The role of Antarctic krill and salps in the carbon cycle at the Antarctic Peninsula

Antarctic krill, Euphausia superba, and the salp Salpa thompsoni are the most abundant macrozooplankton in the Southern Ocean and thus among the most important grazers of phytoplankton. Both species play an important role in biogeochemical cycles by the production of large, carbon-rich and fast sinking faecal pellets, but the extent and magnitude of their contribution to the flux of particulate organic carbon (POC) remain uncertain. Krill and salps occupy very different ecological niches and differ markedly in the way they fuel the lower and higher food webs. Krill is a key species in the Southern Ocean ecosystem connecting phytoplankton and apex predators, including whales, seals, and sea birds. Salps are a less important food source for apex predators, but can feed on a wider food size-range than krill and control phytoplankton blooms. Over the past decades, krill and salps have shown dramatic changes in their distribution and abundance in the Southern Ocean. In response to warming temperatures and declining sea ice, salps have moved southward and expanded into previously krill dominated areas. In some regions along the Western Antarctic Peninsula (WAP), salps have replaced krill as the dominant grazer species. A long-term shift in the dominance from krill to salps is expected to have cascading effects on the food web with unknown consequences for biogeochemical cycles. However, studies directly comparing the role of krill and salps were so far lacking. This dissertation provides a first-time direct comparison of the role of krill and salps in the carbon cycle at the Antarctic Peninsula by comparing the diet and faecal pellet composition of krill and salps, as well as the contribution of their faecal pellets to the total flux of POC. To shed light on the diet and faecal pellets composition of krill and salps, their stomach contents were compared to the ambient plankton community and to the composition of the faecal pellets produced by either species using 18S metabarcoding. Krill are suggested to be selective filter feeders, while salps have been previously assumed to feed indiscriminately on a wide size range of particles. The direct comparison of the stomach content to the in situ plankton community showed that neither species’ diet reflected the composition of the plankton community, suggesting that in contrast to the accepted paradigm not only krill, but also salps are selective feeders. In addition, the comparison of the stomach contents showed that krill and salps had similar diets, which could enhance the competition between both species. This competition could be augmented by salps’ ability to rapidly reproduce in favourable conditions, posing further pressure on krill populations, which are targeted by commercial fishery and are already affected by climatic changes and are more susceptible to warming temperatures than salps. In contrast to the stomach contents, the composition of the faecal pellets produced by krill and salps showed significant differences. Krill pellets consisted for the most part of flagellate remains, while salp pellets were composed to equal shares of diatom and flagellate remains, implying that salp faecal pellets sink at higher velocities than krill pellets due to the ballasting effect of the diatom derived opal. In addition, the higher proportion of diatoms in the faecal pellets of salps compared to their stomach content suggests a low assimilation efficiency of diatoms. In addition, in this thesis several methodological aspects of diet composition studies were assessed. Molecular analyses such as 18S metabarcoding require a rapid inactivation of digestive enzymes and DNA nucleases and therefore depend on suitable sample processing and preservation methods. To investigate this, the effect of different processing procedures on the prey community of the stomachs of krill and salps was compared, showing that in species with highly active and efficient digestive enzymes, like krill, the detection of rapidly digested prey organisms, e.g. gelatinous plankton, is negatively affected by a prolonged sample processing time. In addition, different variable regions of the 18S rRNA gene were compared to assess differences between the two marker regions. This comparison of the 18S regions V4 and V7 showed that the composition of prey communities retrieved from either marker region differ significantly, suggesting that different regions of the 18S rRNA gene might not be suitable for a direct comparison within or between studies. Finally, the signals of dietary fatty acid markers from stomach and tissue samples of krill and salps were compared. Fatty acid markers differed significantly between stomach and tissue samples, indicating that for the differentiation of short- and long-term signals and to detect differences in the assimilation efficiency, it is critical to separate digestive tract and tissue for the analysis of fatty acids. To further investigate the role of krill and salps in the biological carbon pump at the Antarctic Peninsula, a direct comparison of the contribution of krill and salp faecal pellets to the total flux of carbon was conducted. Consecutively deployed sediment traps were combined with vertical profiles of an in situ particle camera system at a high temporal resolution. These in situ measurements were referenced with on-board experiments of the production, carbon content, and microbial degradation of krill and salp faecal pellets, and estimates of the in situ biomass of krill and salps. On average, the potential faecal pellet production of krill was lower than that of salps, while both species contributed equally to the carbon flux at 200 and 300 m. Thus, krill pellets were exported at higher efficiencies, while the majority of salp faecal pellets were retained in the upper 200 m of the water column. However, the presence of large, dense krill swarms, which were observed near some of the deployed sediment traps, increased the flux of krill faecal pellets by almost two orders of magnitude. These results support the notion that krill swarms can produce ‘rains’ of faecal pellets that exceed the capacities of detritus feeders and therefore lead to disproportionately high fluxes of krill faecal pellets and low attenuation rates. Microbial degradation rates of salp pellets accounted for only about one percent per day and could not explain the high turnover rate of salp pellets. Thus, fragmentation by zooplankton seems to be a key process controlling the flux of salp pellets. Due to the fragile structure of salp faecal pellets, the organic matter therein might be more easily accessible for scavengers and suspension feeders compared to krill pellets. Increased recycling of salp pellets might therefore lead to an additional release of nutrients in the surface ocean, benefiting zooplankton and microorganisms. This dissertation provides new insights into the role of krill and salps in the carbon cycle at the Antarctic Peninsula and expands the knowledge on the potential consequences of a long-term shift from krill to salps in the Southern Ocean. Opposite to the thus far accepted paradigm, salp faecal pellets seem to be less efficient in exporting carbon out of the euphotic zone to the deep ocean, but are mostly retained in the surface layer. This could lead to a less efficient biological carbon pump, but fuel the food web in the mixed layer, including microorganisms and zooplankton. Thus, on the long-term less carbon could be exported and sequestered in the Southern Ocean, which would be augmented by the increasing salp abundances and the poleward shift of krill. In addition, similar diets of krill and salps could lead to competitive removal of prey, which might be a critical factor driving krill and salps apart on spatial and temporal scales

Data for Euryhalinity of Ponto-Caspian invaders in their native and introduced regions

In the past decades, Ponto-Caspian species established in freshwater and brackish habitats of the North and Baltic Sea and Great Lakes-St. Lawrence River region in much higher numbers than expected based on introduction effort (i.e. shipping frequency) and environmental conditions between these regions. Several studies suggested that Ponto-Caspian taxa are euryhaline and might be able to adapt rapidly to changing salinity conditions, and therefore might be more successful colonizers than species from other regions. To determine the realized niche in the native and introduced habitats of Ponto-Caspian invaders and to assess whether they expanded their salinity tolerance during the invasion process, we conducted a literature search to assess the salinity ranges of 55 Ponto-Caspian species in their native and introduced region. Our results confirmed that the majority of those species occupied a wide range of salinity in their native and introduced habitats. Approximately 50 % of the species were reported from both freshwater and brackish habitats (0-18 PSU) in their native region, occupying a salinity range of at least 10 PSU difference. In general, the number of species tended to decline as salinity increased in both native and introduced habitats. More than 90 % of the Ponto-Caspian invaders occupied freshwater (0-0.5 PSU) habitats, while 18 % did not occur above 18 PSU. Due to the limitation of our dataset, we were not able to confirm shifts in salinity tolerance during the invasion process. However, as our results suggest that the majority of the Ponto-Caspian invaders occupy freshwater and brackish habitats in their native region, the recent numerous invasions of freshwater and brackish areas by those species should not be a surprise. Therefore, managers and policy makers should take into account that the majority of Ponto-Caspian invaders originate from fresh water or low salinities and develop new regulations to prevent future invasions from the Ponto-Caspian region, as well as from areas highly invaded by Ponto-Caspian taxa such as Northern Europe

Artificial selection experiments with the Ponto-Caspian amphipod Pontogammarus maeoticus

Recently, Ponto-Caspian species (i.e. area of Azov, Black and Caspian Seas) have invaded brackish and freshwater habitats of the North and Baltic Seas and the Laurentian Great Lakes in much higher numbers than expected based on shipping frequency and environmental conditions among these regions. Therefore, it has been hypothesized that Ponto-Caspian species may have inherent advantages over other species in colonizing new habitats, or that they are of freshwater origin. To test these hypotheses, we conducted artificial selection experiment on Ponto-Caspian amphipod Pontogammarus maeoticus collected from 10 PSU to evaluate adaptation capacity of this species to different salinities. Our results indicated that selection to lower salinity than that of population's ambient salinity is possible. Though, generation time in lower salinity conditions took slightly longer. On the contrary, selection to higher salinity was unsuccessful. Taking into account the results from this and previous studies and the geological history of the Ponto-Caspian region, we suggest that majority of the Ponto-Caspian relict fauna might be of freshwater origin and lack necessary genetic background for adaptation to fully marine conditions. Further selection studies using more species and populations, as well as molecular techniques, should be conducted to confirm this hypothesis on a broader scale. Consequently, if Ponto-Caspian relict species are of freshwater origin, the perception that they are better colonizers than species from other regions might be inclined by the fact that areas with biggest introduction frequency of nonindigenous species (i.e., shipping ports) are environmentally variable habitats which often include freshwater conditions