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The keystone role of Antarctic krill, Euphausia superba Dana, in Southern Ocean ecosystems, means it is essential to understand the factors controlling their abundance and secondary production. One such factor that remains poorly known is the role of parasites. A recent study of krill diet using DNA analysis of gut contents provided a snapshot of the parasites present within 170 E. superba guts in a small area along the West Antarctic Peninsula. These parasites included Metschnikowia spp. fungi, Haptoglossa sp. peronosporomycetes, Lankesteria and Paralecudina spp. apicomplexa, Stegophorus sp. nematodes, and Pseudocollinia spp. ciliates. Of these parasites, Metschnikowia spp. fungi and Pseudocollinia spp. ciliates had previously been observed in E. superba , as had other genera of apicomplexans, though not Lankesteria and Paralecudina. In contrast, nematodes had previously only been observed in eggs of E. superba , and there are no literature reports of peronosporomycetes in euphausiids. Pseudocollinia spp., parasitoids which obligately kill their host, were the most frequently observed infection, with a prevalence of 12%. The wide range of observed parasites and the relatively high frequency of infections suggest parasites may play a more important role than previously acknowledged in E. superba ecology and population dynamics. [ABSTRACT FROM AUTHOR]

The copepod species Calanus glacialis is an important component of arctic marine food webs, where it is the numerically dominant zooplankton grazer and serves as a major prey item for fish, seabirds, and other predators. These copepods are typically considered to be phytoplanktivorous, although they are also known to feed on microzooplankton, and little is known about their diet in fall and winter. To investigate their feeding, C. glacialis gut contents were analyzed over an annual cycle in a seasonally ice covered arctic fjord using next generation sequencing of 18S rDNA. During the spring bloom, diatoms, particularly Thalassiosira spp., were important contributors to the dietary sequence reads. In addition to diatoms, Chytridiomycetes, fungal parasites of diatoms, also made up a large proportion of dietary sequence reads during this productive season. This provides one of the first indications of the potential importance of the mycoloop in marine environments. Just prior to the spring bloom, chaetognath sequences dominated the prey sequence reads from C. glacialis, suggesting potential predation on eggs or other early life stages of chaetognaths by C. glacialis. Other indications of omnivorous feeding outside of the spring bloom period included sequence reads from polychaetes in summer, at the time of peak polychaete larval abundance, and from Metridia spp. (Copepoda) in winter in prey sequences from C. glacialis. Incorporating such predation into our knowledge of Calanus spp. behaviour may help refine our understanding of Calanus spp. ecology, and potential responses of C. glacialis to ongoing climate change. [ABSTRACT FROM AUTHOR]

Pseudocalanus copepods are small, abundant zooplankton in the Bering Sea ecosystem that play an important role in transferring primary production to fish and other higher trophic-level predators. Four morphologically cryptic species, the primarily arctic Pseudocalanus minutus and Pseudocalanus acuspes , and the more temperate Pseudocalanus newmani and Pseudocalanus mimus , are found within the Bering Sea. Pseudocalanus are generally considered phytoplanktivores. However, their feeding is poorly known, despite their importance to the ecosystem. In situ feeding by the three most abundant Pseudocalanus congeners, P. minutus , P. newmani , and P. acuspes , was investigated by sequencing partial 18S rDNA (ribosomal Deoxyribonucleic Acid) of gut contents from 225 individuals sampled from 8 stations across the Bering Sea in May and June of 2010. The 28,456 prey 18S rDNA sequences obtained clustered into 138 distinct prey items with a 97% similarity cut-off, and included diatoms, dinoflagellates, microzooplankton, mesozooplankton, and vascular plants. Pseudocalanus diets reflected variations in the environment, with phytoplankton sequences relatively more abundant in copepods from stations with higher water-column chlorophyll a concentrations. Feeding differences were observed between species. P. acuspes diet contained relatively more heterotrophic dinoflagellate sequences, and was significantly different from that of P. minutus and P. newmani, both of which contained relatively more diatom sequences, and between which no significant difference was observed. Feeding differences between the two primarily arctic species may be a mechanism of niche partitioning between these spatially co-located congeners and may have implications for the effects of climate change on the success of these abundant zooplankters and their many predators in this ecosystem. [ABSTRACT FROM AUTHOR]

Parasites are not typically considered to be important components of polar marine ecosystems. It was therefore surprising when 18S rDNA surveys of protists in the West Antarctic Peninsula in winter revealed high abundances of parasite sequences. Parasite sequences made up, on average, over half (52%) of sequence reads in samples from deep water in winter. Winter surface water and sediment samples contained relatively fewer, but still strikingly high, parasite sequence reads (13 and 9%, respectively), while surface water samples in summer contained fewer parasite sequences (1.8%). A total of 1028 distinct parasite Operational Taxonomic Units were observed in winter, with the largest abundances and diversities within Syndiniales groups I and II, including Amoebophrya. Less abundant parasite sequence groups included Apicomplexa, Blastodinium, Chytriodinium, Cryptocaryon, Paradinium, Perkinsidae, Pirsonia and Ichthyophonae. Parasite sequence distributions suggested interactions with known hosts, such as diatom parasites which were mainly in the sediments, where resting spores of Chaetoceros spp. diatoms were abundant. Syndiniales sequences were correlated with radiolarian sequences, suggesting parasite-host interactions. The abundant proportions of parasite sequences indicate a potentially important role for parasites in the Antarctic marine ecosystem, with implications for plankton population dynamics, the role of the microbial loop, carbon flows and ecosystem responses to ongoing anthropogenic climate change. [ABSTRACT FROM AUTHOR]