During this cruise we study the first trophic levels. Particularly we study the zooplankton, those small organisms that feed on the phytoplankton, the primary producers (the equivalent of the vegetal in the terrestrial ecosystems). They are often smaller than 1 mm and they drift with the current. However they can swim and migrate vertically toward the surface or deep waters.
The zooplankton is in turn consumed by small predators such as fish larvae and if it does not have a direct interest for fisheries in our region, it is very important for the whole food web.
We study the zooplankton using a sampling gear with 5 nets that we can open and close at the desired depth. We sample the depth layers of 600-400m, 400-300, 300-200, and 100m to the surface. In general the layer between the surface and 100m depth is the richest.
We collect small quantities of zooplankton that has a pinkish colour and is mainly constituted of crutaceans that we cannot really observe without a microscope. Samples are stored in formalin and they will be analysed later to identify the species present using a microscope, to count them and to determine their weight.
Preparing the zooplankton multinet
Transferring the zooplankton from the collector to vials for preservation
A zooplankton sample
A closer look to the zooplankton sample
One of the objectives of the PUFFALIS cruise is the inventory of the micronecton species in the Coral Sea. Some of the individual fishes sampled in the micronecton net are juveniles or larvae. It is often very difficult to identify the latter to species because they do not yet have the morphological characteristics or the colour patterns which make it possible to differentiate them as adults from closely related species.
A useful approach to the determination of an individual to species is DNA barcoding. The species is characterized by a characteristic DNA sequence. This sequence remains the same whatever the stage of development of the individual, from embryo to adult. The DNA sequence of the larva or juvenile thus allows its identification to species by simply searching the same sequence in a reference database established on a collection of adult fish.
Each fish caught in the micronecton net is thus photographed and a sub-sample of tissue (e.g., a fin clip) is kept dry on a sheet of paper. This sub-sample is the source of the DNA which is then sequenced in a laboratory equipped for molecular biology. DNA sequences will be compared to existing databases, which they will contribute to enrich.
Extravagant: some of the representatives of the Coral Sea micronekton
The tray with the collected fishes sorted by species (left) and paper sheet with the corresponding dry-tissue subsamples (right)
We did our first night sampling station last night. It is not easy to work in such rough sea conditions. It could even be dangerous, especially when manipulating heavy equipment. We decided not to sample the zooplankton as there is a risk of damaging the equipment and injuring those who handle it.
Contrary to what happens during the day, the acoustic signal at night showed us an accumulation of organisms in the so-called epipelagic layer about 45 m under the surface. The small fish, squid and crustaceans that constitute the micronecton migrate towards shallower water at night to feed. During the day, they occur deeper, supposedly to avoid predators that use daylight to spot their prey. We trawled at 45 m depth and were able to sample many ostracods, which are small crustaceans with a spherical shell, Myctophidae or lanternfish which migrated from deeper layers, a number of squids, and leptocephala which are the larvae of eel-like fishes including eels, congers and moray eels.
After a short night we resumed the operations this morning, with the usual series of measurements. The working conditions remained difficult because of the rough sea. We have installed the waterproof casing of a small underwater camera on the net (thanks to our friends from Soproner). Our aim is to obtain images of the animals at the very moment they are caught by the net. We proceed step by step: after having tested the holding device, we now want to test whether the casing resists to the pressure at 200 m depth. When retrieving the casing, we observed droplets of water inside the casing, which lets us question the water-tightness of the o-ring. We are going to ty again.
The catch of the night; the small dots are ostracods, small round crustaceans
A Myctophidae or lanternfish
Setting up the underwater house of the camera on the trawl to test if it is waterproof
A wedge-tailed shearwater passes close to the RV Alis, on sampling station no. 5 this morning
Yesterday night we were unable to reach the night station as initially planned. A water pipe on board was leaking and we had to seek protection in the lagoon to quietly repair it.
This morning we went out to the sea again, to reach sampling station no. 3. The manoeuvers are clearly faster than yesterday: everybody has found their marks now. The ship rolls with the swell, which does not help working on board. Tonight, the wind speed is about 30 knots.
The bad weather affects the quality of the data acquired on a continuous mode, like the echosounder data. The ship sends an acoustic ping to the bottom of the ocean. The acoustic signal is sent back to the ship when it meets fish or other animals. The return signal thus informs us on the quantity of organisms present, and at which depth these organisms occur. This tool is a precious one, for it enables the detection of fish schools. Here, we use acoustics to estimate the depth at which we will tow the trawl, so as to correctly sample the micronecton.
Inside the scientific room, in front of the echosouder screens
The acoustic signal at four different frequencies. The white vertical bars result from a lack of signal at reception, because of the bad sea
Some of the juvenile fishes collected today with the micronecton net
We arrived at the first sampling station early this morning. The land was still visible. The echosounder indicated a depth lower than 1000 m. As some of the instruments are immersed down to 600 m, we have to ensure that sufficient depth remains under them to avoid hitting some possible underwater features. We had to move offshore until we reached grounds with 1000 m depth.
The operations started soon after 07:00 this morning. Two rosettes with sampling bottles and CTD, the instrument that yields information on temperature and salinity according to depth, were cast. A fluorescence sensor also enables us to locate the deep chlorophyll maximum. This morning, this peak was remarkably shallow, at 68 m, when usually it occurs at around 100 m depth.
As usual at the beginning of this kind of expedition, adjustments are necessary. The TAPS acoustic profiler, which gives acoustic data on the zooplankton did not run at first cast, but no problem occurred at the second cast. Fine-tuning was also compulsory with the zooplankton net. The yield of the first trait of micronecton net was relatively poor: a few gelatinous organisms, a few stomatopoda larvae, and, luckily, a beautiful lobster larva. The second micronecton net enabled us to harvest a number of small fishes including a cornetfish, a frogfish, a juvenile yellow trevally, a couple of small flatfishes, and a superb surgeonfish juvenile.
At the surface of the sea, the ballet of shearwaters and petrels indicates the proximity of the Pindaï breeding colony. Tomorrow morning, we will start working at the second day-time sampling station, much further offshore.
On the deck we can see the zooplankton net, the rosette to collect water on the right and above the blue micronekton net
A stomatopoda captured in the micronecton net: transparent, but wearing an armor ornamented with sharp spines
A small flatfish, barely 3 cm long, captured in the open ocean
The wedge-tailed shearwater, master of the wind, master of the ocean
We left Noumea harbour this morning at 10am under a clear sky. We are steaming towards the north to reach Pindaï area in the northern Province to start sampling the following morning. We made the most of the calm sea while we were in the lagoon protected by the reef and we conducted a safety exercise. Seven short and one long siren-call mean we have to abandon ship. Everybody has to grab their own life jacket and wear it and also grab their own survival suit. We check that all the crew is present and we receive some safety information from the officers. It is now time to try and wear the survival suit, a dry suit that allows surviving longer is the water in case of sinking.
After the exercise we continue to organise all the equipment and we start preparing the vials for the first sampling station the following morning. We also prepare the zooplankton net which has 5 nets fixed to a frame with a mechanism that allow to successively open and close each net to samples different layers of the water column.
It is now 6pm, birds are observed all around the vessel. From the porthole we can see about 30 birds that are flying towards the land.
RV Alis leaves Noumea harbour
Assembling the zooplankton net
Hundreds of shearwaters were seen this afternoon off the reef, flying over the ocean looking for prey
Last day to prepare everything before departing. We spent the day getting all the equipment onboard. There is a lot of equipment to try and fit in a small lab and we need to make sure everything is easily reached but at the same time we need to make sure it will not move in case of bad weather. It is a little bit like a Tetris game.
The crew is also very busy to prepare the vessel and particularly because we are using new equipment compared to previous cruises. We have a smaller trawl but a bigger CTD with 12 bottles instead of 8. We need to use the large winch and the crew has to build a protection box around it to avoid the trawl to get tangled in it.
We are 18 people onboard leaving for 2 weeks so it requires a lot of preparation in the kitchen. This is the last day to get all the food needed and particularly fresh fruits and vegetables. But Jacques and Gaby, the kitchen crew, are used to it and we know we will be well feed and will have enough to eat.
Tetris game in the lab
Protecting the main winch to avoid that the micronecton trawl, in blue above, gets tangled in the winch
Fresh fruits and vegetables for 2 weeks
Ready for a new cruise for the Biopelagos project (BEST 2.0 programme of the European Union)
R/V Alis in Noumea Harbour
Still in the framework of the BIOPELAGOS project, we are getting ready to go back at sea for yet another cruise in New Caledonia waters, a few months after the NECTALIS 5 cruise. This cruise is somewhat different from the Nectalis series and it has been named PUFFALIS in reference to “puffin fouquet”, the French name of the wedge-tailed shearwater (Ardenna pacifica), a well-known seabird in New Caledonia. It has a dark plumage and we particularly notice it from January to April when it reproduces. It digs burrows in the sand and bird couples gather into colonies located by the seaside. At night their characteristic calls sound like baby cry and keep the campers awake.
The goal of the Puffalis cruise is to characterise the feeding grounds of the shearwater at sea. Are there any specific current conditions? Is there a lot of zooplankton there? What are the fish that can be preyed upon by the birds? Is there a need to protect those feeding grounds? Do the tuna come and feed at the same place? These are questions we will try to start answering but we are expecting more questions to be raised.
For this cruise we have the support of a scientific team on land that started working early March. They are ornithologists who are working on the shearwater colony located in Pindaï in the northern province of New Caledonia. They glue small GPS on the back of the seabirds, let them go several at sea where they feed and recover the equipment when the birds come back to their burrow to feed their chicks.
The information collected is crucial as it indicates where the birds are feeding at sea. With those data we have been able to establish a sampling plan to go and collect data at sea. As for the Nectalis cruises we collect data on the physical and chemical characteristics of the ocean (currents, temperature, salinity, nitrate, silicate, phosphate…), and on the biology (phytoplankton, zooplankton and micronekton, the small fish, squids and crustaceans eaten by the seabirds and the tuna)
The Puffalis cruise is starting on the 18th of March and a team of 6 scientists from IRD and SPC will get onboard for 2 weeks, coming back on the 2nd of April. We planned to stop in the Northern Province to meet students to explain them our work and exchanges ideas.
A wedge-tailed shearwater (Ardenna pacifica) in front of its nest
The thin lines are seabird tracks at sea and the thick dark line with white diamonds shows the provisional cruise plan of the Puffalis cruise