Blog 6 – The Monster Net

Today we deployed the MOCNESS (Multiple Opening and Closing Nets and Environmental Sampling System). I love the name of this net as well as its beautiful engineering design. This magnificent instrument is composed of 10 black nets on its metal frame programmed to open and close at different depths to collect samples of zooplankton, krill, copepods, jellyfish, and many other organisms.


Preparing for MOCNESS deployment requires a deck check of its components and mechanisms to ensure that each of the nets will trip or open at the specified time. Each of the nets is electronically and mechanically connected through electrical wire. A stepping motor rotates in three steps to release the net. At that moment, a lever releases the cable and one net opens, closing the previous net. This process is repeated until all nets have been open and shut at the desired depths.



Dave Jensen, scientist, doing the deck check before deployment of the MOCNESS.

The system also includes a CTD probe used to measure the levels of salinity, temperature, and depth of the ocean. Plus a fluorometer is attached to measure amounts of chlorophyll in the water. In addition, the transmissometer is a type of sensor that allows us to measure the transparency of the water. It detects the amount of light that passes through a cylinder of ocean water.



Keith Shadle, oceanographic technician, directing the deployment of the MOCNESS for everyone’s safety.

Once the deck check is done, the MOCNESS team carefully lowers the net into the ocean. Four people hold lines of wire or rope to prevent the 800 pound net from swinging side to side while the winch lifts the MOCNESS and then lowers it to depths that can reach up to 800 meters (2,624 feet) or more.



Dr. Mark Ohman, chief principal investigator, Irina Köster, visiting graduate student, and Keith Shadle monitoring data and controlling accurate net tripping.

Scientists utilize data and samples from the MOCNESS net tows to better understand the vertical distribution of living organisms in the ocean. They are also interested in the limiting factors such as light conditions. For example, more or less light reaching certain depths of the ocean can affect the depths where the zooplankton (animal plankton) live. Net tows are done at different times of the day, usually one at noon and one at night. Night tows can give scientists a better idea of migratory zooplankton that move closer to the surface to feed.


It is impressive to watch the MOCNESS enter the ocean as its nets fill with air and take the shape of giant tentacles. Its retrieval from the ocean can be as impressive when its frame is covered in types of gelatinous plankton called salps or pyrosomes, as if returning from underwater MOCNESS battle.


MOCNESS returns from deep ocean waters covered in pyrosomes.