January 29, 2003

MOCNESS – Multiple Opening and Closing Net and Environmental Sensing System
By Rachel McEvers, Project Oceanica

The MOCNESS will be one of the main pieces of equipment used on this cruise. The MOCNESS samples plankton, which are small organisms that are at the mercy of ocean currents. During this cruise, the scientists are targeting ichthyoplankton (fish larvae) and zooplankton (small animals such as crab larvae and copepods). Phytoplankton (small single cell plants) will be sampled using a different piece of equipment.

The MOCNESS has a series of (below: MOCNESS net mesh .5mm) plankton nets, in this case nine, that are towed at different depths. The mesh on the nets is half a millimeter (or 505 microns). This size mesh is good for collecting ichthyoplankton. The scientists have also added three zooplankton nets within three of the existing ichthyoplankton nets. The mesh on the zooplankton nets is about 60/1000 of a millimeter (or 64 microns). If you’d like to have a MOCNESS of your own, it costs about $50,000, nets included, so start saving now!

Here’s how the MOCNESS works. The nets are gathered together and attached to a frame. They each have a gate at their mouth, which allows the net to open and close when appropriate. On the MOCNESS frame is a computer, a battery, a motor and various other instruments that help the scientists gather data and control the nets. The MOCNESS is connected to a computer on the ship through a cable that also allows the ship to pull the MOCNESS. The cable can withstand ~6000 pounds of pull, while still allowing the MOCNESS and computer on the ship to talk to one another. A crane will lift the MOCNESS with nets still gathered together and lower it into the water.

( at left: the MOCNESS frame) A winch will then let out the cable and the MOCNESS will sink to a certain depth. The scientists will close the first net and open the second net by sending a message from the computer on the ship, through the cable, to the MOCNESS computer. The MOCNESS will also send information through the cable to shipboard computer allowing the scientists to “see” the angle of the net, the volume of water flow filtered by the net, the water temperature, the water salinity and many other variables. This information is sent every 2 seconds from the MOCNESS to the shipboard computer. When that net has been towed for 5 minutes, the scientists will send another message to the MOCNESS to close the second net and open the third net. Each successive net is a little less deep than those before it, so that the scientists will get samples from different depths in the water column. On this cruise, samples will be taken at nine specific depths from 200 meters deep to the surface.

The messy part comes when the nets are brought to the surface. Normally there is a plastic “cup” or “codend” at the bottom of the plankton net, but if the temperature is too low, these plastic cups can get brittle and break. Therefore, the scientists during this cruise will just tie the ends of the nets tightly and wash the samples from the net with a hose. The samples will be preserved and taken back to (at left: the MOCNESS at the surface) the lab at the end of the cruise for sorting and identification. It takes scientists several hours to sort and identify the plankton in one sample. 48 samples will be collected per day for the next 2 weeks!!

Career of the day

Rachel McEvers, Program Manager for Project Oceanica

Rachel’s organization, Project Oceanica is located on the campus of the College of Charleston in Charleston, SC. Oceanica is funded by NOAA’s National Ocean Service. She has a Bachelor’s degree in both Public Relations and Marine Biology. Rachel decided she wanted to be a marine scientist when she was very young. She was always fascinated by TV shows and books that anything to do with ocean creatures.

Rachel participates on research cruises throughout the southeast and helps create educational and outreach products from the science operations conducted on the cruises. She also helps instruct high school students on one-day research cruises and helps run the administrative aspect of Project Oceanica.

The thing she likes best about her job is being outdoors and near the ocean. The thing she likes least is being cooped up in her office when she’s not outside! If she could be any sea creature she would be a gulper eel. Why? Because “they’re so strange looking and live in such an alien environment. They’re just bizarre.”