Is the hyperiid amphipod Themisto gaudichaudii poised to displace krill in the warming region of the Southern Ocean?

• Applicant: Professor Dr. Wilhelm G. Hagen, since 4/2019
• Subject Area: Oceanography
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 274981270

In the warming Atlantic sector of the Southern Ocean, density changes of key zooplankton species have been noted over the last decades. A decline of Antarctic krill Euphausia superba is hypothesized and attributed to bottom-up processes such as alterations in phytoplankton blooms and sea-ice extent, whilst salps are on the increase further south, thriving in lower-productivity and warmer-water regions. A third key pelagic player, the hyperiid amphipod Themisto gaudichaudii, may also expand its distribution poleward. Unlike krill that is more closely associated with colder waters, Themisto’s distribution ranges from the sub-tropical coastal upwelling systems to the high Antarctic. An increasing overlap of the distributions of these three species will have significant implications for the structure of the Antarctic food webs and biogeochemical cycling. However, little is known about the likelihood and consequences of Themisto’s hypothesized range expansion and therefore, the aims of the ongoing project were to investigate its genetic and trophic connectivity. Molecular results have shown that T. gaudichaudii consists of three genetic lineages with overlapping distributions. All three lineages are characterized by a genetic homogeneity across a wide latitudinal and environmental gradient, indicating a likelihood of range expansion. Feeding experiments revealed that both krill and salps are preyed upon by Themisto. Prey preferences and potential regional variations are currently being quantified with state-of-the-art molecular methods. Based on this achieved work, demonstrating Themisto’s genetic homogeneity across the Southwest Atlantic sector, a follow-up study is proposed to elucidate, whether phenotypic plasticity of individuals from different populations differs regarding temperature tolerance. Using whole transcriptome profiling based on high-throughput RNA sequencing, changes in adaptive strategies at the population level will be investigated. Differential gene expression patterns of individuals exposed to thermal stress will be compared between two different populations of Themisto: a core population in the Antarctic Polar Front, and a population at the front line of its expansion, the Antarctic Peninsula region. This will reveal how tightly the populations are linked to different water masses, pointing towards an acclimation potential and adaptive capacity to local conditions. Transcriptome analyses will elucidate, to which biological pathways the down- or upregulated genes can be linked. These results will provide crucial insights into the range expansion dynamics of this likely climate-change winner in the Southern Ocean.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1158: Infrastructure area - Antarctic Research with Comparative Investigations in Arctic Sea Ice Areas
• Cooperation Partner: Holger Auel, Ph.D.
• Ehemalige Antragstellerin: Professorin Dr. Charlotte Havermans, Ph.D., until 4/2019