Above: Daggertooth with sharp teeth for effective hunting (Photo: Leif Nøttestad)
The water depth is typically between 4000 and 5000 meters in the Southern Ocean, so even with such a deep trawling exercise we are literally only scratching the surface area of this huge ocean.
The mesopelagic zone is characterized by low light levels, low temperature, high pressure and reduced food availability. Approximately 26 kilos of fish, 10 kilos of jellyfish and 2.5 kilos of squid were collected from 1200 m depth. The main families of fishes collected were Myctophidae, Bathylagidae, Melamphaidae, Macrouridae, Paralepididae and Anotopteridae.
The crew on deck bringing in the fish trawl consisting of a spider net of ropes, weights and wires (Photo: Helena Kawall).
This was an excellent opportunity for the Brazilian scientists to collect different species of fish for their work on the project “Evolution and Biodiversity in the Antarctic: a response of life to change”. We intend to study how fish is adapted in a krill centered ecosystem. One goal is to determine how fluorite, a toxic component that is highly concentrated in krill, moves up in the food chain and how fish metabolize this element. Samples were also collected for genotypic comparisons between species obtained here and in the same period, in King George Island, where the Brazilian Antarctic Station is located.
Another important issue of the project is to study the animals’ anatomy and morphology in order to understand how they are adapted to live in the mesopelagic environment. Fishes in this zone are rather diverse and have adaptations which include silvery or transparent to black and red coloration, large eyes, and bioluminescence. Myctophids, known as “Lantern fishes”, are among the most abundant group of mesopelagic fishes in the World's oceans, with an estimated global biomass of 550 - 660 million metric tons. In the Southern Ocean, they are a significant alternative food source for krill’s predators, such as squids and penguins. They aggregate in dense layers called the deep-scattering layer, and due to their gas bladders the fish can be detected by echosounders down to considerable depths. They have photophores, structures that produce light, used in camouflage “counterillumination” and in intraspecific communication.
Fresh sample from the deep trawl with myctophids, krill and jellyfish (Photo: Leif Nøttestad)
One of the species collected is Electrona antarctica , considered endemic (exclusive) to Antarctic waters. It feeds on copepods, ostracods, and euphausiids especially the Antarctic krill, Euphausia superba. Another myctophid species captured is Gymnoscopelus opisthopterus, a diel vertical migrator that lives between depths of 200 and 600 meters. It has large and specialized eyes to see in the dark. Fascinating specimens of daggertooth Anothopterus pharao were found (Figure 4), including a 77 cm long fish. They have razor sharp teeth and a slender and distensible body and stomach allowing them to eat preys half of its own length.
The common and endemic species Electrona Antarctica in the Southern Ocean (Photo: Leif Nøttestad)
The data collected by the Brazilian scientists will be incorporated in the SCARMarBIN of the Census of Antarctic Marine Life (CAML) an important reference to all Antarctic researchers. The samples obtained will be processed by professors, undergraduate and graduate students at different Universities in Brazil. The international cooperation established on this cruise, reflects the spirit of research in Antarctica, and especially in the International Polar Year.
Helena G. Kawall, Ph.D.
Professor at Uniandrade, Curitiba-Brazil. Brazils’ representative in CCAMLR Scientific Committee
Caroline V. Cooke, Master’s student, Department of Oceanography, Hydroacoustics Laboratory
FURG, Rio Grande-Brazil. Caroline is studying acoustics on fish for abundance estimation and ecology
All cruise journals
Map showing G.O. Sars' postition