Updates from researchers on the R/V Western Flyer:
Monday, December 16, 2019
Taking the pulse of the Octopus Garden:
A small section of the Octopus Garden showing aggregations of octopus (Muusoctopus robustus). Nearly all are females on their nests. A single male is wandering across the foreground.
We were excited to send the ROV down 3,300 meters (just over two miles!) to the Octopus Garden, a site discovered a couple years ago where thousands of female octopuses nest in warm hydrothermal springs. As the ROV sank through surface waters we saw many pyrosomes again, but today there were many more sea butterflies (pteropods) flapping through the water filtering food. Soon they were gone and after nearly two hours, the ROV approached the bottom.
We positioned the oxygen/temperature sensor as close as possible to the octopuses to measure the temperature and oxygen levels of exhaled waters.
We found the Octopus Garden pretty quickly using the ROV “ultrashort baseline” navigation system. There is no GPS underwater, so how do you know where the ROV is at any time? A sonic ping from the ship is sent down and once heard, the ROV pings back. Four receivers mounted on a pole dropped into the water during dives “hear” the ROV ping. The difference in the times the different receivers hear the ROV ping can be used to triangulate the position and depth of the ROV. It works great, at least under relatively calm seas.
Once we found the octopuses, we started to measure the temperature of the warm springs around the egg clusters. We wonder why they choose to nest in the springs, rather than in any rocky spot that seems suitable for laying eggs. We were also trying to measure the respiration rates of the octopuses by recording the oxygen concentration of their exhaled waters, compared to the oxygen in the water the octopus inhales. For each animal, we also measured their breathing rate—it varied from on to 11 per minute. We expect that in warmer water, the octopuses’ respiration rates and oxygen consumption will be higher. After this dive, we have quite a bit of video as well as oxygen and temperature measurements to process. Once that is complete, we may understand quite a bit more about any advantage these octopuses gain from nesting in cozy warm waters.
Measuring temperature in egg clusters.