Beschreibung: Hyperiidean amphipods are a major prey for fish and seabirds. In the Southern Ocean, they are particularly abundant, with distributions ranging from the Polar Frontal Zone to Antarctic shelf waters. The species Hyperiella dilatata has previously been reported to show a peculiar anti-predatory behaviour: It captures chemically protected, gymnosome pteropods in the water column and carries them on its dorsum, like a backpack. We report this association at four oceanic sampling sites between latitudes 45° and 71° S. Molecular barcodes of both hosts and pteropods are provided and compared with those of other hyperiidean and pteropod specimens. Morphological identifications as well as molecular analyses show a so far undocumented association of Hyperiella antarctica with the pteropod Spongiobranchaea australis in the Polar Frontal Zone (Lazarev Sea). H. dilatata carried Clione limacina antarctica specimens in the Weddell Sea, as recorded previously for the Ross Sea. Lengths of the abducted pteropods varied between 1 and 5 mm, with the biggest pteropod measuring more than half the host’s size. One of the abducting amphipods was a female carrying eggs. The formation of such tandem is known to be very efficient as protection from visually hunting icefish in the crystal-clear coastal waters around the Antarctic continent; however, in the open ocean, this behaviour was so far undocumented. Here, we develop hypotheses on its origin and function.

Beschreibung: Climate change proceeding at unprecedented pace is currently redistributing life on Earth. Warming of the upper ocean and the atmosphere have altered sea ice extent and seasonal dynamics in the Arctic, and similar changes are observed in the Atlantic sector of the Southern Ocean and West Antarctic. This affects stocks of major pelagic species such as krill. A so far neglected key player, the predatory amphipod genus Themisto, covers a distribution from temperate to polar regions where it regionally represents the dominant food source for higher trophic levels. Poleward range expansions of several Themisto species have been already been documented or predicted as warming continues. In the Atlantic sector of the Southern Ocean, changes in seasonal sea ice extension are causing strong annual variations of krill stocks, whilst salps are on the rise and shifting their distribution poleward. A third key player, Themisto gaudichaudii, is now also anticipated to extend its range southward. In the Arctic, the ice-dependent Arctic T. libellula and the sub-Arctic boreal T. abyssorum co-exist. Considering the ongoing Atlantification of the Arctic, a range expansion of T. abyssorum concomitant with a retraction of T. libellula’s range are very likely to occur. Due to major knowledge gaps in the ecology, biology and genetic connectivity of Themisto species, the likelihood of range shifts and their consequences for food web structures and biogeochemical cycles remain largely unexplored. We conducted a comparative study of Themisto populations to investigate their distribution, connectivity and trophic ecology. Using population genetic methods, the species status and phylogeography of T. gaudichaudii, were characterized. A genetic homogeneity and high degree of phenotypic plasticity related to feeding morphology were revealed, indicating the potential of T. gaudichaudii lineages to thrive in regions further south. In order to predict the consequences of an increased predation pressure of T. gaudichaudii which may influence the standing stock of Antarctic krill and salps, feeding experiments and molecular diet analyses were carried out. Similar analyses were applied on Themisto species from the northern hemisphere, in order to characterize their genetic connectivity within and across different water masses (Atlantic vs. polar) in Fram Strait and East Greenland and compare with the Antarctic populations.

Beschreibung: A species history is characterized by fluctuations of its geographic limits, however, climate change is currently redistributing life on Earth. Particularly in the Arctic, waters are warming at faster rates and sea ice is thinning and contracting. Amphipod crustaceans of the genus Themisto are highly abundant in Arctic waters where they play a major role as food for higher trophic levels such as seabirds, fish and seals. Throughout the Arctic region, two congeneric species co-exist: T. libellula, a genuine Arctic species and T. abyssorum, considered sub-Arctic boreal. Despite their overlapping distributions, the two species seem to occupy distinct ecological niches and are preyed upon by different predators. T. libellula is bigger in size and feeds on copepods with a high lipid content. It is the main prey of some specialist feeders such as little auks that only feed on the largest size class, in which case T. abyssorum would not be a proper substitute as it is much smaller. Range expansion of T. abyssorum and retraction of T. libellula’s range is very likely to occur considering the ongoing Atlantification of the Arctic. However, many aspects of the biology, ecology and genetic connectivity of Arctic Themisto populations are still unstudied, despite their importance for a better understanding of the consequences of their potential distributional changes on the food web and biogeochemical cycles. In this context, we investigated the abundance, geographic and bathymetric distribution as well as the genetic connectivity of the two species T. abyssorum and T. libellula during two cruises with R/V Polarstern to Fram Strait and East Greenland.

Beschreibung: The brown shrimp Crangon crangon shows high reproduction rates, feeds opportunistically on endo- and epibenthic organisms and is apparently well adapted to variable environmental conditions. Previous electrophoretic studies revealed a high level of polymorphism and no consistent phenotype of digestive enzymes between individuals. In order to understand the biological reason of digestive enzymes polymorphism and underlying biochemical processes, we performed a transcriptome-based study of digestive enzymes of C. crangon. Detailed sequence analyses of triacylglycerol lipase, phospholipase A2, alpha-amylase, chitinase, trypsin and cathepsin L were performed to identify putative isoforms. The number of isoforms varied among enzymes: for lipases, phospholipase A2 showed a higher number of isoforms than triacylglycerol lipase, while carbohydrase chitinase showed a higher number of isoforms in comparison with alpha amylase. Furthermore, cysteine proteinases showed a lower polymorphism than serine proteinases. We propose that the expression of polymorphic digestive enzymes indicates high plasticity in food utilization by the brown shrimp. Alternative splicing may be the driving force of the heterogeneous patterns of digestive enzymes in C. crangon.

Beschreibung: Knowledge of zooplankton community structure is essential to understand ecosystem functioning. Therefore, accurate species identification is a crucial step in plankton studies. Yet, with the current array of methodologies, species richness is still largely underestimated and high-resolution distribution patterns remain unknown. A novel, cost-effective and rapid alternative to morphological or genetic approaches is the identification of species by proteomic fingerprinting based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The present study aims to demonstrate the applicability of proteomic fingerprinting for large-scale identification and quantification of the pelagic copepod family Spinocalanidae. Therefore, MALDI-TOF MS was applied to discriminate, identify and quantify adult and juvenile planktonic copepods of the ecologically important deep-sea copepod family Spinocalanidae from stratified depth samples (0–1000 m) at two stations in the eastern tropical Atlantic. Spectral peak data from 1178 spinocalanid specimens of all developmental stages were compared with a reference library of previous proteomic fingerprints of genetically and morphologically identified spinocalanid species. A comparison with the library yielded 25 valid species clusters, which were used to create fine-scale vertical distribution profiles with a high species and stage resolution. Further, we were able to show vertical habitat partitioning among cryptic species and developmental stages, which has major consequences for our understanding of niche partitioning of the mesopelagic realm. Thus, proteomic fingerprinting holds great potential in accelerating and improving community analysis, providing a powerful tool to obtain new insights into biodiversity processes, phylogeographic patterns and mechanisms of vertical distribution.

Beschreibung: Tolerance of organisms towards heterogeneous and variable environments is highly related to physiological flexibility. An effective strategy to enhance physiological flexibility is the expression of polymorphic enzymes. This seems to be the case in the brown shrimp Crangon crangon. It shows high reproduction rates, feeds opportunistically on endo- and epibenthic organisms, and is apparently well adapted to variable environmental conditions. Previous electrophoretic studies revealed a high level of polymorphism and no consistent phenotype of digestive enzymes between individuals. In order to understand the underlying biochemical processes, we carried out a transcriptome-based study of digestive enzymes of C. crangon. Detailed sequence analyses of triacylglycerol lipase, phospholipase A2, alpha amylase, chitinase, trypsin and cathepsin L were performed to identify putative isoforms. The number of isoforms, and thus the degree of polymorphism varied among enzymes: lipases and carbohydrases showed higher numbers of isoforms in enzymes that besides their extracellular function also have diverse intracellular functions. Furthermore, cysteine proteinases showed a lower polymorphism than serine proteinases. We suggest that the expression of enzyme isoforms improves the efficiency of C. crangon in gaining energy from different food sources.