Explore the Deep Sea
Tools & Techniques
Nets to catch plankton, plus instruments to collect information about the water.
What is it?
A computer-controlled system of nets and other equipment which is towed behind the ship. There are 9 nets all together, mounted on a rectangular aluminum frame.
How does it work?
- On top is a flow meter and instruments that measure the water's conductivity (a measure of salinity), temperature and depth.
- There is also a transmissometer to measure turbidity (that is, how cloudy the water is due to suspended particles).
- All this information about the seawater is transmitted in real time up a cable to a computer on the ship. It helps the scientists on deck know when to instruct the MOCNESS to open and close its various nets.
- After it returns to the surface, the biologists rinse the nets into buckets and examine the contents.
Why is it used?
The MOCNESS can be towed through the "plume" of water that rises from a hydrothermal vent, to collect living organisms such as plankton. Biologists are especially interested in how larval stages of hot vent life might spread from vent to vent. So they are using the MOCNESS to discover where larvae are found. Since one of the nets is open on the way down to the vent field, and another on the way back up, the MOCNESS can also catch some curious creatures in transit, such as this fish (left).