Investigating the prey spectrum of two co-occurring Themisto amphipods in the Fram Strait (Atlantic-Arctic gateway) using DNA metabarcoding

charlotte.havermans [ at ]


Pelagic amphipods are a key zooplankton group in polar regions. In the Arctic Ocean, the two hyperiid amphipod species Themisto libellula and Themisto abyssorum are dominating the pelagic community. They are not only an important food source for higher trophic levels, but also important predators able to control the zooplankton standing stock in some Arctic regions. In recent years, several studies using stereomicroscopy and biomarkers were conducted to study the diet of T. libellula and T. abyssorum. These studies suggested a diet mainly consisting of the most abundant zooplankton species including copepods, euphausiids and chaetognaths. It was also found that the two amphipods are covering different niches in the Arctic ecosystem, with T. libellula being more dependent on the ice-algal pathway. This leads to the assumption that the two amphipods are differently impacted by the ongoing Atlantification and sea ice retreat. In this study, DNA metabarcoding was used to assess the prey spectrum at high taxonomic resolution and potentially detect so far overlooked gelatinous zooplankton in the diet of these predators. The results indicate that the two predators are feeding on different zooplankton and ichthyoplankton species and hence, do not compete for food. Additionally, calanoid copepods do not seem to be as important as assumed in the diet in the summer months. The diet within one predator species different between the different sampling localities. T.libellula’s diet consisted of ice-associated species like Calanus glacialis and Boreogadus saida in regions with cold, Arctic waters, while these prey species were not found at stations with Atlantic waters. This leads to the assumption that a sympagic fueled diet for this species is rather linked to the location than to a preferred prey type. The diet of T. abyssorum was dominated by the chaetognath Eukrohnia hamata, but high variability was observed between the stations. At locations with Atlantic influence, RRA (relative read abundances) for Calanus finmarchicus were higher than at stations with Arctic impact. In some samples of both predators, sequences belonging to several hydrozoan species, e.g., Nanomia cara and Aglantha digitale, were detected. Those findings were not linked to certain locations, but they show that the amphipods are able to feed on gelatinous zooplankton, although the do not make up a major part of their diet. The broad prey spectrum found for T. libellula shows that this flexible species may be able to adapt its diet to changes in the zooplankton community caused by climate change and sea ice retreat. To fully understand Themisto’s feeding behavior, more sampling is needed, ideally combining DNA metabarcoding and biomarkers, to assess then both short-term and long-term diet.

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Dischereit, A. (2021): Investigating the prey spectrum of two co-occurring Themisto amphipods in the Fram Strait (Atlantic-Arctic gateway) using DNA metabarcoding , Master thesis, University of Hamburg.

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