Let’s descend fast to the bottom – wait, no STOP!

March 26, 2013

Today, our dive site was the deep Midwater Respirometry System (MRS) site again. Each morning we start our dives at 6:30 a.m., which means the ROV pilots are prepping for the dive before 6:00 a.m. This morning, we started descending quickly to a depth of 2,700 meters (8,800 feet). This poses a conundrum for us because we want to get to depth quickly, but we also want to see all of the cool things along the way. It is a delicate balance between going too fast to see anything of interest and going just fast enough that when we see something interesting, the pilots can stop the ROV before the animal is long gone.

Today, we must have hit the sweet spot in our descent speed because at 1,700 meters (5,500 feet), Bruce Robison (at the science camera) spotted a large squid, Gonatus sp. brooding an egg sack. The pilots were able to stop the descending vehicle in time to watch this amazing find. This reproductive strategy was first described in 2005 by MBARI midwater scientists. It was the first squid described to brood eggs.

Shallow-water squids lay their eggs on the seafloor, but since mesopelagic squids spend their entire life in the water column and there is no substrate where they could lay eggs, some species, like Gonatus onyx, encase their eggs in a gelatinous material that allows them to carry thousands of eggs in their arms. Since that research was published, we have seen a few more brooding Gonatus sp., and another species, Bathyteuthis berryi brooding eggs. It is possible that many other mesopelagic squids brood their eggs, but these are the only two genera that we’ve observed brooding eggs in MBARI’s 25 years of ROV exploration.

This brooding Gonatus sp. is holding thousands of eggs in an eggcase in her arms.

This brooding Gonatus sp. is holding thousands of eggs in an eggcase in her arms.

After observing the brooding Gonatus sp. for quite a few minutes and getting some great video, we continued descending at our fast pace. Within minutes, we yelled “STOP” again and the pilots were able to stop in time for us to observe another rare animal in the midwater. We call it the “Mystery Mollusc” because when the midwater lab first observed it years ago, they didn’t even know what group it belonged to. Bruce Robison has since been working on describing it and has discovered that it is a mollusc, closely related to snails! We watched this animal and collected it so that Bruce can use this specimen to answer a few more outstanding questions before he publishes the description and gives our mystery a name!

I’d like to personally thank our ROV pilots Knute Brekke, Mark Talkovic, Randy Prickett, Bryan Schaefer, and Ben Erwin, who put up with our constantly changing wishes in the control room (let’s go fast down to 2,700 meters, no, STOP, no never mind, it wasn’t interesting, no STOP!, etc.) We have high expectations of them because they always deliver!

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This “Mystery Mollusc” is related to snails, even though it has no shell. The pink part in the middle of its body is digestive gland and stomach. The oral hood on the left surrounds the mouth and the “tentacles” to the right undulate when it swims.

—Susan von Thun