The role of water mass advection in staging of the Southern Ocean Salpa thompsoni populations.

Salpa thompsoni is an important grazer in the Southern Ocean. Their abundance in the western Antarctic Peninsula is highly variable, varying by up to 5000-fold inter-annually. Here, we use a particle-tracking model to simulate the potential dispersal of salp populations from a source location in the Antarctic Circumpolar Current (ACC) to the Palmer Long Term Ecological Research (PAL LTER) study area. Tracking simulations are run from 1998 to 2015, and compared against both a stationary salp population model simulated at the PAL LTER study area and observations from the PAL LTER program. The tracking simulation was able to recreate closely the long-term trend and the higher abundances at the slope stations. The higher abundances observed at slope stations are likely due to the advection of salp populations from a source location in the ACC, highlighting the significant role of water mass circulation in the distribution and abundance of Southern Ocean salp populations.

Contamination of planktonic food webs in the Mediterranean Sea: Setting the frame for the MERITE-HIPPOCAMPE oceanographic cruise (spring 2019).

This paper looks at experiential feedback and the technical and scientific challenges tied to the MERITE-HIPPOCAMPE cruise that took place in the Mediterranean Sea in spring 2019. This cruise proposes an innovative approach to investigate the accumulation and transfer of inorganic and organic contaminants within the planktonic food webs. We present detailed information on how the cruise worked, including 1) the cruise track and sampling stations, 2) the overall strategy, based mainly on the collection of plankton, suspended particles and water at the deep chlorophyll maximum, and the separation of these particles and planktonic organisms into various size fractions, as well as the collection of atmospheric deposition, 3) the operations performed and material used at each station, and 4) the sequence of operations and main parameters analysed. The paper also provides the main environmental conditions that were prevailing during the campaign. Lastly, we present the types of articles produced based on work completed by the cruise that are part of this special issue.

The complete mitochondrial genome of the southern calanoid copepod Calanus simillimus Giesbrecht, 1902.

The complete mitochondrial genome of Calanus simillimus is 27,876 bp in length (GenBank accession OK500294) and containing 13 protein-coding genes (PCGs), 2 rRNA genes, 22 transfer RNA genes. The gene order is novel compared to other Calanus species and copepods with sequenced mitogenomes. Phylogenetic analysis suggests that C. simillimus represent a fourth group within Calanus genus in addition to C. hyperboreus, C. finmarchicus and C. helgolandicus groups. The complete mitochondrial genome of C. simillimus will be useful for species identification, population genetics, phylogenetic and evolutionary studies among copepods.

Using stable isotopes to infer stock-specific high-seas distribution of maturing sockeye salmon in the North Pacific.

The stock-specific distribution of maturing salmon in the North Pacific has been a persistent information gap that has prevented us from determining the ocean conditions experienced by individual stocks. This continues to impede understanding of the role of ocean conditions in stock-specific population dynamics. We assessed scale archives for 17 sockeye salmon (Oncorhynchus nerka) stocks covering the entire North Pacific, from the Columbia River (Washington State and British Columbia) to Kamchatka Peninsula (Russia), to infer salmon locations during their last growing season before returning to their spawning grounds. The approach used, first pioneered in salmon stocks in the Atlantic, relies on the relationship between temporal changes in δ13C in salmon scales and sea surface temperature to estimate salmon distribution based on correlation strength. An advantage of this approach is that it does not require fish sampling at sea, but relies on existing fishery agency collections of salmon scales. Significant correlations were found for 7 of the stocks allowing us to propose plausible feeding grounds. Complementary information from δ15N, historical tagging studies, and connectivity analysis were used to further refine distribution estimates. This study is a first step toward estimating stock-specific distributions of salmon in the North Pacific and provides a basis for the application of the approach to other salmon scale archives. This information has the potential to improve our ability to relate stock dynamics to ocean conditions, ultimately enabling improved stock management. For example, our estimated distributions of Bristol Bay and NE Pacific stocks demonstrated that they occupy different areas with a number of the former being distributed in the high productivity shelf waters of the Aleutian Islands and Bering Sea. This may explain why these stocks seem to have responded differently to changes in ocean conditions, and the long-term trend of increased productivity of Bristol Bay sockeye.

A major Calanus finmarchicus overwintering population inside a deep fjord in northern Norway: implications for cod larvae recruitment success.

High Calanus finmarchicus abundances were recorded in wintertime in Vestfjorden, close to the main cod breeding grounds off Lofoten and Vesterålen, northern Norway. The mean abundance for locations with water depth >500 m was ∼37000 ind. m-2 (range: 26700-49000 ind. m-2). To our knowledge, this is the first report of massive overwintering of C. finmarchicus on the Norwegian shelf. Because of the observed size and location of this population, we argue that local overwintering on the northern Norwegian shelf can contribute significantly to sustain a C. finmarchicus population on the shelf during the period of first feeding for cod larvae. This is supported by a particle tracking model.

Super-aggregations of krill and humpback whales in Wilhelmina Bay, Antarctic Peninsula.

Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP), and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km(2)) of humpback whales (Megaptera novaeangliae) feeding on a super-aggregation of Antarctic krill (Euphausia superba) in Wilhelmina Bay. The krill biomass was approximately 2 million tons, distributed over an area of 100 km(2) at densities of up to 2000 individuals m(-3); reports of such 'super-aggregations' of krill have been absent in the scientific literature for >20 years. Retentive circulation patterns in the Bay entrained phytoplankton and meso-zooplankton that were grazed by the krill. Tagged whales rested during daylight hours and fed intensively throughout the night as krill migrated toward the surface. We infer that the previously unstudied WAP embayments are important foraging areas for whales during autumn and, furthermore, that meso-scale variation in the distribution of whales and their prey are important features of this system. Recent decreases in the abundance of Antarctic krill around the WAP have been linked to reductions in sea ice, mediated by rapid climate change in this area. At the same time, baleen whale populations in the Southern Ocean, which feed primarily on krill, are recovering from past exploitation. Consideration of these features and the effects of climate change on krill dynamics are critical to managing both krill harvests and the recovery of baleen whales in the Southern Ocean.