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Plankton in the Ross Sea
Plankton, which means floating, are microscopic organisms that drift in either saltwater or freshwater. These organisms can be animals, plants or bacteria. Despite their minute size they play an important role in the lives of a wide variety of other life forms.
Plant plankton - phytoplankton - is the ‘grass’ of the sea. Like their cousins on land, in order to be able to grow they need light (to provide the energy for growth), water, carbon dioxide and nutrients. Phytoplankton range in size from extremely small - less than 0.001 of a millimeter (mm), to substantially bigger - on a phytoplankton scale - of about half a millimeter in length. Phytoplankton are at the bottom of the food chain in the sea providing the food for animal plankton. As such they can be regarded as one of the producers of the ocean.
Animal plankton or zooplankton are typically classified based on their size into:
- microzooplankton (less than 0.2 mm)
- mesozooplankton (0.2 to 20 mm in length)
- ‘larger’ macrozooplankton (longer than 20 mm)
The size of the zooplankton influences what they eat.
- Microzooplankton tend to eat the very small phytoplankton and the bacterioplankton.
- Mesozooplankton eat the larger phytoplankton, microzooplankton and each other.
- Macrozooplankton eat mesozooplankton and also other macrozooplankton smaller than themselves.
One of the best known zooplankton in the Southern Ocean is krill. These are macrozooplankton and are the food for a wide range of organisms including whales.
Bacterioplankton are free-living bacteria in the water. These bacteria are very important in the food web as they break down organic material and make nutrients available for the phytoplankton.
IPY Blogs week 5
The Continuous Plankton Recorder
Since the start of the voyage we have used a Continuous Plankton Recorder (CPR) to collect plankton samples from a wide range of environments between Wellington and the Ross Sea. The CPR technology has been used world wide since the 1950s whereby a roll of filtering silk in a special container is wound very slowly forward as the CPR continuously moves through the water trapping plankton. During this voyage we have seen distinct areas with high concentrations of zooplankton in the water, typically coinciding with high concentrations of phytoplankton. Our work forms part of a much larger international programme that is collecting samples from the oceans all around Antarctica.
Written by Julie Hall
Catching krill – where bigger is better
Krill or euphausiids are an important food source for seals, whales, penguins, fish and even people. Although they are classed as zooplankton, krill can swim and swim fast! This makes them very hard to catch. When we use the regular fine-mesh plankton nets like the MOCNESS – krill are able to get out of the way. Therefore we fit the MOCNESS with bright strobe lights, which temporarily blinds them (like a possum in the headlights of a car) and allows us to scoop them up. On this survey we also use a midwater fish trawl to catch the krill, these work so well that not even the speedy krill can get away!
Written by Richard O’Driscoll
Marine bacteria
With 10 to 20 thousand bacterial species in 1 litre of seawater, microbes in the ocean represent the greatest biomass on the planet. Bacterial numbers can be even as high as a billion per litre (that’s one with nine zeros). Marine bacteria come in all different colours, shapes and sizes. During this voyage we get a chance to determine what bacteria are in the Ross Sea, possibly discovering new species along the way. We are sampling both the water and sediments for bacteria. Onboard we plate them on agar and filter water so that we can extract DNA. The DNA collected will be analysed in the laboratory and the species determined through cloning and sequencing of the DNA.
Written by Els Maas
See videos Sampling bacteria and Sampling zooplankton
Zooplankton
The MOCNESS (Multiple Opening and Closing Net and Environmental Sampling) also referred to as the ‘octopus’, has nine trigger nets that open and close at set depths to collect zooplankton from different depths. Some animals we catch look like aliens, most being big enough to be visible to the naked eye up to 10 centimetres long, including jellyfish, predatory swimming worms, salps and more. Interestingly salps and their cousins - sea squirts are more closely related to humans than any other invertebrate! At shallow depths we collect lots of phytoplankton which looks like a green soup. This is an important food source for zooplankton species, which are in turn are food for larger animals further up the food chain.
Written by Lisa Bryant
Water sampling
Water sampling is being carried out using a CTD (Conductivity Temperature Depth) rosette. The CTD has twenty-four 10 litre sampling bottles. The top and bottom of each bottle, connected by bungee cord, are stretched open and latched prior to the CTD being lowered into the ocean. Sensors in the frame record salinity, conductivity, temperature and the amount of phytoplankton in the water. These data help researchers decide what depths they need water samples collected from. During this voyage extracting the water from the CTD bottles has not always been easy. On several occasions the -12ºC air temperature on deck has meant the taps on the bottles and sometimes the water samples have frozen up as soon as the CTD came out of the water.
Written by Stu Pickmere
See video Collecting samples with the CTD
