Geology topics

Eirik H. Henriksen

Publications and source records attributed to Eirik H. Henriksen.

3 recordsLinked to original sources

USGS2020

High parasite diversity in the amphipod Gammarus lacustris in a subarctic lake

Amphipods are often key species in aquatic food webs due to their functional roles in the ecosystem and as intermediate hosts for trophically transmitted parasites. Amphipods can also host many parasite species, yet few studies address the entire parasite community of a gammarid population, precluding a more dynamic understanding of the food web. We set out to identify and quantify the parasite community of Gammarus lacustris to understand the contributions of the amphipod and its parasites to the Takvatn food web. We identified seven parasite taxa: a direct life cycle gregarine, Rotundula sp., and larval stages of two digenean trematode genera, two cestodes, one nematode, and one acanthocephalan. The larval parasites use either birds or fishes as final hosts. Bird parasites predominated, with trematode Plagiorchis sp. having the highest prevalence (69%) and mean abundance (2.7). Fish parasites were also common, including trematodes Crepidostomum spp., nematode Cystidicola farionis , and cestode Cyathocephalus truncatus (prevalences 13, 6, and 3%, respectively). Five parasites depend entirely on G. lacustris to complete their life cycle. At least 11.4% of the overall parasite diversity in the lake was dependent on G. lacustris , and 16% of the helminth diversity required or used the amphipod in their life cycles. These dependencies reveal that in addition to being a key prey item in subarctic lakes, G. lacustris is also an important host for maintaining parasite diversity in such ecosystems.

Takvatn↗

USGS2019

Fish culling reduces tapeworm burden in Arctic charr by increasing parasite mortality rather than by reducing density‐dependent transmission

Two common Dibothriocephalus (formerly Diphyllobothrium ) tapeworm species were significantly reduced by experimental culling of their fish host Arctic charr ( Salvelinus alpinus ) in a subarctic lake. Between 1984 and 1991, funnel traps were used to cull ~35 metric tons of Arctic charr, reducing charr density by ~80%. As charr densities decreased, tapeworm prevalence and then intensity also declined over the following three decades, with D. dendriticus (formerly dendriticum ) responding faster than D. ditremus (formerly ditremum ). The two main hypotheses for how culling a host can decrease parasitism are reductions in parasite transmission due to reduced host density and reductions in parasite survival through increases in host mortality rates. We found little evidence that charr density was the main driver for reduced parasite transmission. Instead, decreased survivorship in charr, initially, through fishing‐induced changes in charr age structure, and later through increased predation rates by brown trout, led to increased parasite mortality. Although brown trout, which increased significantly after fish culling, are also hosts, they are often too big for the final host birds to eat, thus becoming parasite sinks. Synthesis and applications . Fish populations with heavy parasite burdens constitute a management problem. Our results show how fish culling can indirectly reduce transmitted parasites through increased parasite mortality. Managing overcrowded fish populations by culling can produce two desirable outcomes: an increase in fish growth rates and reduced parasite burdens.

Journal of Applied Ecology↗

USGS2017

Molecular analyses reveal high species diversity of trematodes in a sub-Arctic lake

To identify trematode diversity and life-cycles in the sub-Arctic Lake Takvatn, Norway, we characterised 120 trematode isolates from mollusc first intermediate hosts, metacercariae from second intermediate host fishes and invertebrates, and adults from fish and invertebrate definitive hosts, using molecular techniques. Phylogenies based on nuclear and/or mtDNA revealed high species richness (24 species or species-level genetic lineages), and uncovered trematode diversity (16 putative new species) from five families typical in lake ecosystems (Allocreadiidae, Diplostomidae, Plagiorchiidae, Schistosomatidae and Strigeidae). Sampling potential invertebrate hosts allowed matching of sequence data for different stages, thus achieving molecular elucidation of trematode life-cycles and exploration of host-parasite interactions. Phylogenetic analyses also helped identify three major mollusc intermediate hosts (Radix balthica, Pisidium casertanum and Sphaerium sp.) in the lake. Our findings increase the known trematode diversity at the sub-Arctic Lake Takvatn, showing that digenean diversity is high in this otherwise depauperate sub-Arctic freshwater ecosystem, and indicating that sub-Arctic and Arctic ecosystems may be characterised by unique trematode assemblages.

Lake Takvatn↗