August 18, 2006
There were two main sampling surveys being conducted on this ecosystem monitoring cruise. The main one was a zooplankton survey which has been going on for over thirty years. Both Jon Hare and Jerry Prezioso were involved with this. In fact, Jerry goes out to sea four times each year (November, January, May and August) to gather data for this particular survey that includes about 135 sampling sites. Prior to the start of the cruise Jerry and the ship's captain determine the optimal route for the ship taking into account the weather predications and aiming to minimize journey time and fuel consumption.
When the ship approached a sampling site, the navigations officer reduced the speed and made the following announcement: "Ten minutes to station" or "Ten minutes to bongo". This was the cue for the scientists and crew on duty to get ready and head towards the rear deck where the plankton nets were kept. The nets looked like a pair of bongo drums - hence they were usually referred to as bongos. During a sampling tow the bongos were lowered by cable to five meters above the ocean floor and then slowly brought back towards the surface. As soon as they were on deck a flow meter reading was taken from each of the nets. A flow meter is a small device strung across the opening of the nets. It produces a reading that is later used to calculate the amount of water that passed through each net, and hence the volume of water from which the plankton sample was obtained.
The next part was fun for anyone who liked using hoses. Powerful seawater hoses were used to wash down the nets. This flushed the plankton contents down to the cod end, the opening at the bottom of the net. Once at the bottom of the net the sample was emptied and collected on a sieve. Sometimes the string fastening the cod end was not well knotted and it came loose, resulting in the net coming back empty. On one occasion we encountered the opposite problem - the nets came up bulging with jellyfish, as the trawl had passed through a dense swarm of them. Each trawl produced two samples of zooplankton which were then placed in glass jars and preserved with formalin.
One jar would be used to identify the ichthyoplankton. These are the egg, larval and juvenile stages of fish. The other jar was for zooplankton identification purposes. Zooplankton consists of all other types of drifting marine animals. The identification stage of work was not done on the ship or even back at the NOAA lab, but in a lab in Poland using a sub-sample containing about 500 organisms. Each one of these 500 animals would be carefully examined and identified, if possible down to the species level. It could take up to a year for this identification stage to be completed.
Some of the bongo net samples contained dozens of reddish brown jellyfish, others were almost exclusively made up of a brown gunk consisting of copepods (tiny crustaceans, smaller than a grain of rice) and others contained quantities of slimy greenish-brown filaments (a type of colonial algae) mixed in with the zooplankton. At one New Jersey site the bongos came up loaded with transparent, extremely fragile jellyfish that had already started to disintegrate into a massive gelatinous blob that was very difficult to deal with. Jon gallantly took on this task and spent almost two hours sieving and bottling these jellyfish-laden samples.