Glacial meltwater and seasonality influence community composition of diazotrophs in Arctic coastal and open waters.

The Arctic Ocean is particularly affected by climate change with unknown consequences for primary productivity. Diazotrophs-prokaryotes capable of converting atmospheric nitrogen to ammonia-have been detected in the often nitrogen-limited Arctic Ocean but distribution and community composition dynamics are largely unknown. We performed amplicon sequencing of the diazotroph marker gene nifH from glacial rivers, coastal, and open ocean regions and identified regionally distinct Arctic communities. Proteobacterial diazotrophs dominated all seasons, epi- to mesopelagic depths and rivers to open waters and, surprisingly, Cyanobacteria were only sporadically identified in coastal and freshwaters. The upstream environment of glacial rivers influenced diazotroph diversity, and in marine samples putative anaerobic sulphate-reducers showed seasonal succession with highest prevalence in summer to polar night. Betaproteobacteria (Burkholderiales, Nitrosomonadales, and Rhodocyclales) were typically found in rivers and freshwater-influenced waters, and Delta- (Desulfuromonadales, Desulfobacterales, and Desulfovibrionales) and Gammaproteobacteria in marine waters. The identified community composition dynamics, likely driven by runoff, inorganic nutrients, particulate organic carbon, and seasonality, imply diazotrophy a phenotype of ecological relevance with expected responsiveness to ongoing climate change. Our study largely expands baseline knowledge of Arctic diazotrophs-a prerequisite to understand underpinning of nitrogen fixation-and supports nitrogen fixation as a contributor of new nitrogen in the rapidly changing Arctic Ocean.

Personality-dependent inter- and intraspecific foraging competition in the invasive round goby, Neogobius melanostomus.

This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as "bold," fish that took more time to resume movement were categorized as "shy" and those that fell in between these two categories were determined to have "intermediate" boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Therefore, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus; nonetheless, results also show that competition is also governed by other mechanisms that require further study.

Summer sea ice melt and wastewater are important local sources of microlitter to Svalbard waters.

Human activities leave traces of marine litter around the globe. The Arctic is, despite its remoteness, emerging as an area of no exception to this environmental issue. Arctic sea ice has previously been found to constitute a temporal sink of microplastics, but the potential release and subsequent fate of microplastics in the marine environment are yet unknown. Furthermore, the relative importance of local sources of microplastics in the Arctic marine environment is under discussion. In this study, the concentration and distribution of anthropogenic microparticles (AMPs, <5 mm, including microplastics) have been investigated in marine waters and sea ice of Svalbard. Seawater samples throughout the water column and floating sea ice samples were collected along a transect originating in Rijpfjorden, reaching northwards to the sea ice-edge. Seawater samples were also collected along a transect extending westwards from head to mouth of Kongsfjorden. Samples were collected throughout the water column with stations positioned to enable detection of potential AMP emissions from the wastewater outlet in Ny-Ålesund. Along both transects, environmental parameters were measured to explore potential correlations with AMP distribution. High concentrations of AMPs were detected in sea ice (158 ±â€¯155 AMPs L-1). Based on both AMP concentrations and characteristics, AMPs identified in seawater of the marginal ice zone are to a large extent likely released during the melting of sea ice. The release of AMPs during summer melting of sea ice was concomitantly taking place with the ice-edge bloom, suggesting increased bioavailability to Arctic marine biota. Concentrations of AMPs were up to an order of magnitude higher in Kongsfjorden (up to 48.0 AMPs L-1) than in Rijpfjorden (up to 7.4 AMPs L-1). The distribution and composition of AMPs in Kongsfjorden suggest the wastewater outlet in Ny-Ålesund to be a likely source. Our results emphasize the importance of local point- and diffuse sources of AMPs in the Arctic and stress the urgency of considering their associated environmental impact. Implementation of regulatory policy is of importance, particularly since human activities and environmental pressures are increasing in the Arctic.

Nitrogen Fixation in a Changing Arctic Ocean: An Overlooked Source of Nitrogen?

The Arctic Ocean is the smallest ocean on Earth, yet estimated to play a substantial role as a global carbon sink. As climate change is rapidly changing fundamental components of the Arctic, it is of local and global importance to understand and predict consequences for its carbon dynamics. Primary production in the Arctic Ocean is often nitrogen-limited, and this is predicted to increase in some regions. It is therefore of critical interest that biological nitrogen fixation, a process where some bacteria and archaea termed diazotrophs convert nitrogen gas to bioavailable ammonia, has now been detected in the Arctic Ocean. Several studies report diverse and active diazotrophs on various temporal and spatial scales across the Arctic Ocean. Their ecology and biogeochemical impact remain poorly known, and nitrogen fixation is so far absent from models of primary production in the Arctic Ocean. The composition of the diazotroph community appears distinct from other oceans - challenging paradigms of function and regulation of nitrogen fixation. There is evidence of both symbiotic cyanobacterial nitrogen fixation and heterotrophic diazotrophy, but large regions are not yet sampled, and the sparse quantitative data hamper conclusive insights. Hence, it remains to be determined to what extent nitrogen fixation represents a hitherto overlooked source of new nitrogen to consider when predicting future productivity of the Arctic Ocean. Here, we discuss current knowledge on diazotroph distribution, composition, and activity in pelagic and sea ice-associated environments of the Arctic Ocean. Based on this, we identify gaps and outline pertinent research questions in the context of a climate change-influenced Arctic Ocean - with the aim of guiding and encouraging future research on nitrogen fixation in this region.

Personality- and size-related metabolic performance in invasive round goby (Neogobius melanostomus).

Differences between individuals in behavioral type (i.e. animal personality) are ecologically and evolutionarily important because they can have significant effects on fitness components such as growth and predation risk. In the present study we are used the invasive round goby (Neogobius melanostomus) from an established population in controlled experiments to examine the relationships among personality, metabolic performance, and growth rate (inferred as size-at-age). Boldness was measured as the time to return to normal behavior after a simulated predator attack, where fish with shorter freezing times were categorized as "bold" and fish with longer times were categorized as "shy." We show that bold fish have significantly higher standard metabolic rate (SMR) than their shy conspecifics, whereas there was no difference between personality types in their maximum metabolic rate (MMR) or aerobic scope (AS). Bold fish furthermore had a smaller size-at-age as compared to shy fish. Together this provides evidence of a metabolic underpinning of personality where the high-SMR bold fish require more resources to sustain basic life functions than their low-SMR shy conspecifics, indicating that bold round goby from established populations with high densities (and high competition for food) pay a price of reduced growth rate.

An efficient and gentle enzymatic digestion protocol for the extraction of microplastics from bivalve tissue.

Standardized methods for the digestion of biota for microplastic analysis are currently lacking. Chemical methods can be effective, but can also cause damage to some polymers. Enzymatic methods are known to be gentler, but often laborious, expensive and time consuming. A novel tissue digestion method with pancreatic enzymes and a pH buffer (Tris) is here presented in a comparison to a commonly applied digestion protocol with potassium hydroxide. The novel protocol demonstrates a highly efficient removal of bivalve tissue (97.7 ±â€¯0.2% dry weight loss) already over-night. Furthermore, it induces no impairment in terms of ability to correctly identify four pre-weathered plastic polymers and six textile fiber polymers by Fourier transform infrared spectroscopy after exposure. The high-throughput protocol requires minimal handling, is of low cost and does not pose risk to the performer or the environment. It is therefore suggested as a candidate for a standardized digestion protocol, enabling successful analysis of microplastics ingested by bivalves.