Sampling of organisms by the pelagic plankton-necton team
Marine plankton is the set of pelagic organisms (in the water column) that cannot or cannot very actively move. Organisms of the water column that can swim belong to the necton. We talk about zooplankton for animal plankton and phytoplankton for plant plankton.
Gear used
The plankton team uses several types of nets to cover all layers of water and capture all sizes of organisms. The bongo net is a double net used both in horizontal at low speed (photo bongo 01, 02, 03) and vertical with the boat at the stop (photo vertical 01, 02, 03). The meshes are 63 μm, 200 μm, 300 μm and 500 μm. A micrometer or micron is one thousandth of a millimeter or 10-6 m. For the vertical net, the mesh used is 63 μm. The neuston net is a surface net (photo neuston 01, 02, 03), its mesh is 900μm (about one millimeter). Neuston groups all the organisms whose physiology requires the water-air interface. This net is dragged for 10 minutes at low speed. The mesopelagic trawl or IKMT (Isaacs-Kidd Mid Water Trawl) trawl is the largest of the gear used by the team, its mesh is 4 mm (mesopelagic photo 01, 02, 03). The depth of use will depend on the results of the acoustic sounder (detection of biomass in the water slices). For example, on 11 May, the mesopelagic trawl was dragged at -450m for 40 minutes. To immerse the nets, the team chooses a radial and realizes 3 stations. Operations take place day and night.
Sampling
Delphine THIBAULT recovers the contents of the collectors of the mesopelagic trawl , the horizontal bongo, the neuston net (mesopelagic photo 04, 05, bongo 04, 05, neuston 04) as soon as the gear is back on deck. Zo RASOLOARIJAO retrieves the contents of the collector from the vertical net (vertical 04). Each time a thorough rinsing with sea water is carried out so as not to leave the least organism in the collector. The crop is then weighed to the precision balance. We see Delphine and Bradley BLOWS pass the contents of the collector to the sieve to keep only the organisms (photo collection 01, 02, 03) and Jean François TERNON to the balance (photo collection 04). Then, Delphine, Zo, Bradley often helped by the rest of the team (photo collection 05, 06, 07, 08, 09, 11) will separate the collection in large taxonomic groups (fish, crustaceans, molluscs, etc.). ...). These terms are known to all but from a more rigorous point of view, the names to be used are Actinopterygians for fish, Malacostraces for crustaceans. Phytoplankton (plant plankton) is usually too small to be visible to the naked eye. Among the specimens of animals photographed are the hatchet fish (STERNOPTYCHIDAE family) (photo collection 18, 19), a dragon fish (STOMIIDAE family) (photo 20), lantern fish (MYCTOPHIDAE family), shrimps, larvae Crab and lobster (photos 12, 13, 15, 21). One of these larvae strongly inspired the monster of the saga "alien" in the cinema. There are also "gooey" like the salpes (branch of the Cordes) solitary or in colony. Some scientists believe that these colonies are in fact a single organism because each element has specialized and functions as a whole (digestion or reproduction, for example) (photo 10, 11, 22, 23). After sorting, the organisms are put in sachets and frozen or placed in formalin. One part will be used for taxonomy (species identification) and will be used to make a planktonic bestiary of Mount Walters. Another part will be used to calculate biovolumes and planktonic biomasses which, in conjunction with other measurements, will be used to measure productivity (primary production per volume of water) and to evaluate the functioning of the Walters oceanic ecosystem. Primary production is the production of organic matter by photosynthesis. Oceanic plankton is the basis of all food webs (food relations between organisms) in the oceans. If its productivity is low, biodiversity in the ecosystem may also be low.
