Monterey Bay Aquarium Research Institute
2013 midwater ecology cruise

Day 1 – Why study the midwater and what the heck is OMZ?
November 7, 2013

We use this term “midwater” to describe the community of organisms that live in the pelagic zone. The pelagic zone can be described as any water that is neither close to the bottom nor near the shore. Most people know that the ocean covers about 70 percent of the earth’s surface, but when you take into account how deep the ocean is, you realize that this pelagic zone is a huge volume. As a result, the pelagic zone is the largest habitat on earth. Let me say that again—the largest habitat on earth! There is still so little we know about the organisms that live in the pelagic zone—from microscopic bacteria and phytoplankton to gigantic whales, squid, and gelatinous animals (to name just a few). MBARI’s midwater lab, led by Bruce Robison, is one of the few groups in the world that focus their research on the macrofauna (those we can see with the naked eye) that live in the midwater.

One of the group's areas of interest is a layer within the midwater called the oxygen minimum zone (OMZ). The OMZ is a layer where the oxygen levels are lower than that above or below. This layer usually exists in the eastern boundary of an ocean basin (like the west coasts of North and South America) where wind-driven motion causes upwelling. The nutrients brought to the surface by this upwelling causes phytoplankton to thrive near the sea surface. The phytoplankton add oxygen to the surface layers as does the mixing of air between the ocean and the atmosphere. This makes the surface waters relatively oxygen rich. Phytoplankton complete their life cycles, die, and sink down from the surface layers. Zooplankton and larger animals produce fecal material and die. All of this dead and dying material sinking through the water column is called marine snow (and it really looks like snow falling through the sky.). As the marine snow sinks, it is consumed by bacteria. The bacteria use oxygen to break down the marine snow, causing this deeper water to be depleted of oxygen. Deeper in the water column, much of this microbial breakdown has already happened, so the oxygen levels rise again where there is less consumption of particles and therefore, less consumption of oxygen.

The white dots in this image are marine snow sinking through the water column.

As the ocean warms, OMZs are expanding. (I’ll talk about why OMZs are expanding tomorrow.) It is important to understand how animals that live in the OMZ will be affected by the expansion. More importantly, what will be the effect on animals that would not be able to survive in an oxygen-poor environment? Will they be pushed shallower or deeper to find more oxygen-rich water? Will they leave certain areas altogether and only thrive where OMZs don’t exist? Will some animals become extinct? How will this affect fisheries and, therefore, economies built around fisheries? All of these questions will be a challenge to answer. By studying the midwater and the OMZ over the last 25 years, the midwater lab can make observations about how communities have changed in response to lower oxygen levels. Over the next week, we’ll describe how we study these questions.

Thanks for sticking it out and reading my primer on midwater ecology and the OMZ. As a reward for your persistence and thirst for knowledge, I’ll share some photos of an amazing feeding event we witnessed on the way to our first station today. Humpback whales, sea lions, and sea birds were amidst a feeding frenzy just a few miles offshore of Moss Landing. The past few months in Monterey Bay have brought the best whale watching in recent memory.

A humpback whale shows its fluke as it dives for another gulp of food. The dorsal fins of two more humpback whales can be seen to the right with the southern coast of Monterey Bay in the distance.

Watch this video of the sea lion raft and humpback whale feeding event. Be sure to watch with the sound on.

Question: Now you know why Monterey Bay is such a great place for whales, right?

Answer: Upwelling! Nutrients brought to the surface by upwelling cause phytoplankton to bloom and the success continues right on up the food web to the whales.

— Susan von Thun

A humpback whale shows its fluke as it dives. Photo: Knute Brekke
A humpback whale breaches. Photo: Knute Brekke
Sea lion raft close up. There were likely hundreds of sea lions making up this raft. Photo: Knute Brekke

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.