Krill vs. the R/V Thompson

Let me tell you a story about an inch long critter that crippled the ship last night.

 

Two of the euphausids, or krill, that shut down the ship

Meet the Euphausid. It is a relative of shrimp and is better known by its common name: krill. It is an important link in the food web. It eats phytoplankton and is eaten by many other larger animals, including fish and baleen whales. Since they are eaten by so many other animals, they have developed several behaviors to help decrease the chance of becoming dinner. One is that they form large swarms – safety in numbers! Another is that because several of their predators rely on sight to find prey, the krill travel down into deeper waters where it is dark to hide during the day, and then at night travel up to the surface where the phytoplankton are to eat in the cloak of darkness. Both of these behaviors are critical to our story.

Last night after dinner, the ship engines unexpectedly shut down and the ship lost all power. Not good. Luckily there are generators on board to power lights, but unknown engine failure equals lots of stress. The crew was stressed because they had to quickly find and fix whatever issue caused the ship to die. Scientist John Mickett and his Wave Chaser team was stressed because their instrument that the ship was towing was only 30 meters off the bottom of the ocean, and they were worried about damaging the instrument if we drifted to an area that was shallower than where we lost power. Having no power meant that they were unable to pull the instrument back up to the ship.

What the crew eventually found was that a large swarm of krill had been pulled into the ship’s seawater intake hose and had completely clogged the filter, not allowing any water into the system. Seawater is constantly pulled into the engine to cool it, like a radiator in a car, so the clog and lack of new seawater triggered the ship to shut down. Once the crew cleared out the krill, the ship was back in business.

In chatting with John Mickett earlier today, he mentioned that he was surprised that the swarm of krill did not show up on their data. Part of the equipment that the Wave Chasers are using is a sonar instrument called BioSonics that can detect fish schools and zooplankton layers. 

The BioSonics instrument is the vertical metal pole attached to the side of the ship. The BioSonics sensors are about 3 meters (9 feet) below the surface of the water.

The Wave Chasers can see internal waves with this device as it goes past a zooplankton layer, making it move up and down  just like how waves look at the surface of the ocean.

The data from BioSonics is displayed in real-time so that scientists can see if they have found an internal wave. This plot shows a cross-section of the ocean, with the surface of the ocean along the top. Some small internal waves are seen where the light blue and dark blue meet on this plot. In the lower dark blue layer, the vertically grouped dots and lines are most likely fish.

Due to the krill’s predator avoidance behaviors I mentioned earlier - forming large swarms and coming to the surface at night – they were right in line with the seawater intake valve at the bottom of the ship’s hull. Since the BioSonics instrument is deployed about 3 meters (9 feet) below the surface of the water, it is conceivable that the swarm was not detected by the sonar because they were camped out within a couple feet from the surface of the water.  

Tom, a science teacher from Bainbridge Island, checking out the krill.

Luckily everything worked out in the end. The ship was back in business quickly and there were no lasting impacts on equipment. Moral of the story – Large swarms of krill: great for fish and whales, not great for ship intake valves.