Monterey Bay Aquarium Research Institute
2013 midwater ecology cruise

Day 2 – Expansion of the oxygen minimum zone
November 8, 2013

In yesterday's blog, I talked about the importance of studying midwater communities and the oxygen minimum zone (OMZ). I also mentioned that as the ocean warms due to climate change, OMZs are expanding. Why is that, you might ask? There are a few key factors in this expansion:

1. Warmer water holds less dissolved oxygen than colder water. While the warming of the ocean begins at the sea surface, the warming does penetrate deeper in the water column as well. This means that waters that may not have been considered by scientists as “within the OMZ” a few years ago, now are, because the increasingly warmer temperatures lead to less oxygen available for animals to respire.

2. Although the warming penetrates down past the surface waters, it is decidedly more severe near the surface. This causes stratification of the water column, where warmer water above does not mix well with cooler water below because of differences in density. Stratification restricts the mixing of this oxygen-rich surface layer with the waters below, leading to further depletion of the oxygen levels in the deep midwater.

3. Increased carbon dioxide in the atmosphere mixes with surface water and increases the amount of carbon dioxide available to phytoplankton. This increases production by phytoplankton which means that more dead and dying material will sink to deeper waters where bacteria will break it down, using up oxygen.

All of these factors lead to an OMZ that can cover a wider depth range or even cover a larger geographical area. So, how will this expansion of the OMZ affect animals in the midwater?

The midwater lab has been studying the respiration of common midwater animals for over a decade. Deep-sea animals in the lab surely behave, feed, and respire differently than they do in their natural habitat. The midwater lab developed the Midwater Respirometry System (MRS) to measure respiration of deep-sea animals in their habitat. The MRS is made up of modified detritus samplers (see photo below) that measure the oxygen levels and temperature in the sampler.

ROV pilot Randy Prickett looks on as the ROV Doc Ricketts is pulled up through the Western Flyer’s moonpool. You can see the MRS at the bottom of the vehicle.

Researchers collect animals in these chambers and hang the entire system on a mooring, leaving it there for one, two, or even more days. These data provide a more reliable measurement of respiration of the sampled animals than could be obtained in the lab. Using the MRS, researchers don’t have to account for physiological changes that might occur as the animal is brought to the surface, where all of the environmental conditions are drastically different from their deep-sea home.

Knowing how animals respire in the midwater under “normal” conditions will lead to insights about how they might be able to adapt (or be stressed) by changes in the OMZ.

Yesterday, we deployed the MRS after collecting a common member of the midwater community. This siphonophore, Nanomia bijuga, mainly eats krill and is very abundant at depths between 300 and 500 meters. Today, after the MRS hung on the mooring for 24 hours at around 300 meters, we recovered it and Kim Reisenbichler will analyze the data to see if the experiment was a success.

The primary animal that was collected and respired by the MRS was a very abundant siphonophore, Nanomia bijuga.
When the ROV is secured on board, the MRS drawer is deployed so the science team can access the samples. Bruce Robison, Rob Sherlock, and Kim recover the Nanomia bijuga from the MRS specimens for further analysis in the lab.
Today, we observed this very rare jelly, Stellamedusa ventana. It was discovered by the midwater lab in the 1990s and was named after MBARI’s ROV Ventana.

— Susan von Thun

Previous log Next log


Day 7 Day 7
November 13, 2013
Last day

Day 6 Day 6
November 12, 2013
Stayin' alive!

Day 5 Day 5
November 11, 2013
What's for dinner?

Day 4 Day 4
November 10, 2013
On the hunt for deep-living animals

Day 3 Day 3
November 9, 2013
Deep midwater respirometry system (MRS) deployment

Day 2 Day 2
November 8, 2013
Expansion of the oxygen minimum zone

whale's fluke Day 1
November 7, 2013
Why study the midwater and what the heck is OMZ?


R/V Western Flyer

The R/V Western Flyer is a small water-plane area twin hull (SWATH) oceanographic research vessel measuring 35.6 meters long and 16.2 meters wide. It was designed and constructed for MBARI to serve as the support vessel for ROV operations. Her missions include the Monterey Bay as well as extended cruises to Hawaii, Gulf of California, and the Pacific Northwest.

ROV Doc Ricketts

ROV Doc Ricketts is MBARI's next generation ROV. The system breaks new ground in providing an integrated unmanned submersible research platform, with many powerful features providing efficient, reliable and precise sampling and data collection in a wide range of missions.

Midwater respirometry system (MRS)

The MRS conducts oxygen consumption rate measurements in situ gauging the metabolism of animals without subjecting them to the stresses of transport to the surface. MRS has been modified to operate in deeper water with an expanded capacity, enabling respiration studies on animals that live deeper than 1,250 meters.

Detritus sampler

Detritus samplers are large plexiglass containers with lids that can be controlled by the pilot of the ROV and gently closed once an organism is trapped inside.


The CTDO is mounted on the ROV and takes in situ measurements of environmental parameters such as conductivity, temperature, depth, and oxygen concentration.

High frequency suction sampler

This sampler acts like a vacuum cleaner sucking up samples and depositing them into one of the 12 buckets.

 Research Team

bruce robison Bruce Robison
Senior Scientist, MBARI

Bruce Robison's research is focused on the biology and ecology of deep-sea animals, particularly those that inhabit the oceanic water column. He pioneered the use of undersea vehicles for these studies and he led the first team of scientists trained as research submersible pilots. At MBARI, his research group has focused on the development of remotely operated vehicles as platforms for deep-sea science.

kim reisenbichler Kim Reisenbichler
Research Specialist, MBARI

Kim's general area of interest is the study of midwater and deep sea animals. He has developed many tools and techniques to observe, manipulate, and collect these organisms, and to maintain the animals in the lab.

rob sherlock Rob Sherlock
Senior Research Technician, MBARI

Rob is interested in the ecology of midwater invertebrates. He has worked in the Robison lab and been involved with the Midwater Time Series since he came to MBARI in 1996, identifying and quantifying mesopelagic animals and the changes in that community over time and depth and relative to other physical factors.

kris walz Kris Walz
Research Assistant, MBARI

Kris works with the midwater ecology group, analyzing ROV video transects between 50 and 1,000 meters in depth to identify biological organisms from all taxonomic levels. Kris started working at MBARI in 1996 after finishing her master's degree at University of California, Santa Cruz. She's looking forward to going to sea this month to collect video transects and to search for deep-sea lobster larvae from the family Polychelidae.

susan von thun Susan von Thun
Senior Research Technician, MBARI

Susan works in the MBARI video lab, where her primary responsibility is to watch video taken with MBARI's remotely operated vehicles (ROVs) and make observations about the organisms, behaviors, equipment, and geological features that she sees. While annotating video, she's become adept at identifying numerous deep-sea organisms, specializing in midwater organisms. She works closely with the midwater ecology group and the bioluminescence lab to expand her knowledge of the fish, jellies, cephalopods, and other groups in the midwater.

Stephanie Bush
Postdoctoral Fellow, MBARI

Stephanie will be collecting squids and octopuses for the Monterey Bay Aquarium's upcoming cephalopod exhibit "Tentacles". She will also continue her research on deep-sea cephalopod behavior and population connectivity in planktonic animals.

goetz Freya Goetz
Museum Technician, Smithsonian Institution

Freya is collecting hyperiid amphipods, polychaetes and sampling of other animals for Karen Osborn at the Smithsonian Institution's National Museum of Natural History. The animals collected will be for a variety of projects including the study of amphipod eye structure, animal microbiomes and population genetics.

burford Ben Burford
Research Assistant

Ben's undergraduate degree encompassed terrestrial and aquatic zoology, ecology, and botany. He has become fascinated with and engrossed in the study of deep-sea ecology and behavior. This focus comes after recently completing an internship in the Robison Midwater Ecology Lab at MBARI where he examined the behavior of the deep-sea cephalopod, Chiroteuthis calyx.