The Video Plankton Recorder (VPR) is one of the pieces of scientific equipment we put into the water. It was invented by Cabell Davis at Woods Hole Oceanographic Institution (WHOI). Josh Eaton and Robb Hagg run the VPR on this cruise, and our Chief Scientist, Dennis McGillicuddy, works with the scientific data it collects along with his graduate student, Elise Olson.
As I’ve mentioned before, the VPR is like an underwater airplane. It works a lot like an airplane, complete with wings, and active control surfaces such as a rudder, elevator, and aileron (the yellow pieces in the drawing below). The active surfaces control the pitch and the roll of the VPR to create a stable platform for the delicate instruments that it carries. As it flies through the water, a strobe in the right (starboard) wing and a digital camera in the nose cone photograph a cubic centimeter of water located half way in between (labeled Imaged Volume in the drawing below). The VPR is essentially a towed microscope allowing us to peer into the small world of plankton (Image credit: Andrew Girard).

Deploying the VPR
Deploying the VPR is always fun to watch. It’s a large piece of equipment, and the ship has to be moving at 6 knots for the deployment, which makes for a bit of a show. It takes 6 people to deploy the VPR, and everyone has to work together to get it in safely. The positions required for deployment are the following:
· Deck Boss – coordinates the actions of everyone for safe deployments and recoveries
· Winch Operator – follows the direction of the deck boss to launch and recover the instrument
· Wire Fair Leader -guides the tow cable onto the winch
· Flight Controller – sends flight commands to the instrument
· Tagline Handlers (2)- help control the instrument as it transitions from the deck to the air to the water
Here’s a video of a VPR deployment. Josh (the Deck Boss) was wearing the camera on his hard hat, so you’re getting a first person viewing of the deployment. When he turns backward, he’s communicating with Robb, who is the Winch Operator.
Seeing What the VPR Sees
The VPR can stay in the water for weeks at a time. On this trip, each tow has averaged 18 hours. During that time, the ship has to travel between 8 and 10 knots, which means that we can’t stop for CTD casts. It’s a running joke on the ship that when the VPR is in the water, everyone gets caught up on lab tests and sleep – except for the VPR group. They are constantly monitoring the VPR to ensure that it stays upright and that all of its components are working correctly.
As the VPR travels through the water, it takes 30 photographs per second. A computer then looks at each picture and determines if there is anything in focus in the frame. If there is, that object is saved as a Region Of Interest (ROI), along with the exact time and position it was observed. The ROIs, or pictures of plankton, can then be either sorted by hand or by a computer program that scientists can “train” to identify different kinds of plankton. In some of our recent tows, the VPR has been collecting upward to 50,000 images per hour, so the computer-based sorting is definitely preferred!
The VPR also has a host of oceanographic sensors on board. The two primary instruments are a small CTD and a fluorometer. This information is collected and plotted in real time. With this real time information scientists are able to make detailed survey maps of both the physical properties of the water and the plankton, which then in turn allow them to sample the ocean adaptively, focusing their observations on “where the action is”.
All of this information is used to map out the distribution of phytoplankton relative to the physical properties of the water (temperature, salinity, and density). For example, here are some images of Phaeocystis colonies taken from a recent VPR survey an eddy, which is a swirling weather system in the ocean. You saw some microscope photographs of a Phaeocystis colony in the 1/19 post. Here’s what they look like when photographed by the VPR. The first picture is of a grouping of colonies located near the surface of the water.

This one is of an individual colony located further down the water column.

These are the types of plots that are produced from the data.

The plot above is a cross-section of density from a survey that started inside an eddy and finished just outside the eddy. The up-and-down “tow-yos” (towed yo-yos) of the VPR are visible in the data, and the density is shaded in color, ranging from blue (low density) to red (high density). These data show that the density is higher inside the eddy than outside it.
Now here’s the fun part: the plankton can be mapped in exactly the same way. This plot shows that the individual Phaeocystis colonies are most abundant at about 50m depth, although they tend to reside a little deeper in the center of the eddy than they do outside of it. Also, there is a patch of high abundance located at the edge of the eddy, as indicated by the red/yellow dots near the center of the plot.

These data give us important clues as to how Phaeocystis thrives in this environment. Moreover, having this information at our fingertips allows us to sample these plankton patches with other instruments such as the CTD and Bongo nets. The VPR is yet another example of the exciting things that result when the fields of science, technology, engineering, and mathematics (STEM) work together!