Seasonal abundance and activity of sympagic meiofauna in Van Mijenfjorden, Svalbard

The importance of landfast ice as a nursery and breeding ground for Arctic marine invertebrates was studied in Van Mijenfjorden (77°N, 15/16°W), southwestern Svalbard from March to May 2017. The collection of first-year ice cores with stations along a depth gradient allowed the investigation of both temporal and spatial differences in sympagic meiofauna community composition and abundance. Furthermore, water column samples were retrieved to examine the strength of sympagic-pelagic coupling. Overall, 13 taxa were identified from the ice and 15 taxa from the water column with low abundances of dominant ice fauna in the water samples. Total sympagic metazoan abundance peaked in late April with over 25,000 ind m-2, due to the reproduction of ice-associated nematodes. Throughout spring the presence of sexually mature nematodes and eggs supported the notion that sea ice in Van Mijenfjorden, especially at the main station (vMF/Mn – 50 m water depth), served as a breeding and reproductive ground to ice nematodes.Comparatively, through tight sympagic-benthic coupling, in late April, higher abundances of juvenile polychaetes (7,661 to 8,900 ind m-2), in the lowermost 10 cm of the ice, were recorded at the innermost stations (2 - 14 m water depth), compared to deeper stations (> 50 m water depth) (0 to 865 ind m-2). They were utilizing the sea ice as a nursery ground and refuge from predators. Higher growth rates and faster development of polychaete juvenile morphological features indicative of maturation were observed in situ, as well as in a growth experiment that mimicked natural ice algae concentrations. Conclusively, ice nematodes and juvenile polychaetes inhabited the sea ice in Van Mijenfjorden to exploit the highly concentrated ice algae located in the lowermost three centimeters of the ice for reproduction and growth. Molecular tools revealed that all sympagic nematodes, apart from one individual from Wahlenbergfjorden (Nordauslandet, Svalbard), belong to the genus Halomonhystera and the family Monhysteridae, which are known from sea ice habitats. Juvenile polychaetes belonged to the family Spionidae, which is known to reside in sea ice in other parts of the Arctic

The occurrence of Nematoda in coastal sea ice on Svalbard (European Arctic) determined with the 18S small subunit rRNA gene

Understanding the diversity and functioning of Arctic sea ice ecosystems is vital to evaluate and predict the impact of current and future climate change. In the microscopic communities inhabiting the brine channels inside sea ice, nematodes often dominate numerically and act as bacterivores and herbivores. Despite nematodes great abundances and known ecological roles, molecular tools have not been applied to investigate their species diversity in sea ice. In an attempt to begin establishing a molecular baseline for species diversity of sea ice nematodes, we Sanger sequenced 74 specimens from four locations around Svalbard (European Arctic), using the 18S rRNA barcode. Currently available nucleotide reference databases are both underpopulated with representative marine nematode taxa and contain a substantial number of misidentified organisms. Together, these limitations inhibited the ability to identify marine specimens collected in this study with certainty. Nevertheless, our molecular data indicate the presence of two genera in sea ice on Svalbard—Theristus and Halomonhystera. While it is possible that the latter represents a novel ice nematode species, future studies, including morphometric analysis, are needed to verify our molecular findings. We leverage the assignment of molecular information to robustly identify nematodes and provide the first insight into the diversity of sea ice nematodes in the European Arctic. We advocate for an intensified cooperation between molecular and morphological taxonomists to expedite the establishment of baseline surveys that are required to predict biological consequences of the diminishing sea ice habitat in the future

Seasonal abundance and activity of sympagic meiofauna in Van Mijenfjorden, Svalbard

The importance of landfast ice as a nursery and breeding ground for Arctic marine invertebrates was studied in Van Mijenfjorden (77°N, 15/16°W), southwestern Svalbard from March to May 2017. The collection of first-year ice cores with stations along a depth gradient allowed the investigation of both temporal and spatial differences in sympagic meiofauna community composition and abundance. Furthermore, water column samples were retrieved to examine the strength of sympagic-pelagic coupling. Overall, 13 taxa were identified from the ice and 15 taxa from the water column with low abundances of dominant ice fauna in the water samples. Total sympagic metazoan abundance peaked in late April with over 25,000 ind m-2, due to the reproduction of ice-associated nematodes. Throughout spring the presence of sexually mature nematodes and eggs supported the notion that sea ice in Van Mijenfjorden, especially at the main station (vMF/Mn – 50 m water depth), served as a breeding and reproductive ground to ice nematodes

Temporal and spatial variability of sympagic metazoans in a high-Arctic fjord, Svalbard

Svalbard is one of the fastest warming regions in the Arctic including massive loss in fjord sea ice both in terms of area coverage, ice thickness and duration. Sea ice is a habitat for a wide variety of microscopic flora and fauna, and we know little about the impact of accelerated loss of sea ice on this unique sea ice community. Here, we present the first study on the seasonal progression and spatial distribution of the sympagic meiofauna community, in a Svalbard fjord. Further, the meiofauna community in sea ice versus the water column below were compared to investigate the link between the two habitats. In total, we found 12 taxa associated with the sea ice and 15 taxa in the water column below with 11 taxa occurring in both habitats. However, a Canonical-analysis (CA) showed that despite similarities in taxa the two mediums were distinctly different (potentially) due to the low abundance of ice nematodes and polychaete juveniles, in pelagic samples. Temporally, ice meiofauna abundances ranged from 9.7 to 25.3 x 103 ind m-2 from beginning of March to end of April, following the seasonal build-up of ice algal biomass from 0.02 to 15.99 mg Chl a m-2 during the same time span. For the transect stations, the lowest ice meiofauna abundance was recorded at the outermost station (VMF2) with 1.6 x 103 ind m-2 and the highest abundance at the mid-station MS with 25.3 x 103 ind m-2. Our results indicate that fjord ice harbors most ice algae and sympagic meiofauna in its lower 10-cm with highest values in the lowermost 2-cm, at the sea ice water interface. Sympagic meiofauna communities were mostly dominated by nematodes or polychaete juveniles. We observed the phenology of ice nematodes through the maturation of females and hatching of juveniles from eggs. Polychaete larvae developed (quickly) into juveniles and grew morphological features indicative of readiness for settlement. Thus, we propose, that as with other parts of the Arctic, sea ice in Svalbard fjords plays an important role in the life cycle of ice nematodes and for accelerating the growth of polychaete larvae. Loss of coastal sea ice may therefore negatively impact coastal biodiversity and affect recruitment for some benthic infauna in Svalbard

Interactive effects of ocean acidification and temperature on oxygen uptake rates in Calanus hyperboreus nauplii

The Arctic region is undergoing rapid and significant changes, characterized by high rates of acidification and warming. These transformations prompt critical questions about the resilience of marine communities in the face of environmental change. In the Arctic, marine zooplankton and in particular calanoid copepods play a vital role in the food web. Changes in environmental conditions could disrupt zooplankton communities, posing detrimental consequences for the entire ecosystem. Copepod early-life stages have been shown to be particularly sensitive to environmental stressors since they represent a bottleneck in the life cycle. Here, we investigated the responses of 4-day old Calanus hyperboreus nauplii when exposed to acidification (pH 7.5 and 8.1) and warming (0 and 3°C), both independently and in combination. Naupliar respiration rates increased when exposed to a combination of acidification and warming, but not when exposed to the stressors individually. Moreover, we found no discernible differences in lipid content and fatty acid (FA) composition of the nauplii across the different experimental treatments. Wax esters accounted for approximately 75% of the lipid reserves, and high amounts of long chain fatty acids 20:1 and 22:1, crucial for the reproduction cycle in copepods, were also detected. Our results indicate a sensitivity of these nauplii to a combination of acidification and warming, but not to the individual stressors, aligning with a growing body of evidence from related studies. This study sheds light on the potential implications of global change for Arctic copepod populations by elucidating the responses of early-life stages to these environmental stressors