Gulf of California 2015, Leg 2 – Midwater Ecology

February 22-March 3, 2015

The second leg of this expedition will be concentrated in the Gulf of California’s central and southern basins to better understand the oxygen minimum zone in this area and its influence on the ecology and physiology of midwater animals.

Researchers on this leg hypothesize that the unusual composition, vertical distribution, and migration patterns of the Gulf of California’s midwater fauna are driven chiefly by the characteristics of the oxygen minimum zone (OMZ), which vary from basin to basin within the Gulf. The effects of hypoxic (low oxygen) water include physiological and behavioral adaptations that allow some species to inhabit the OMZ during daylight hours, vertical distribution patters for some species that are compressed above the OMZ, and unusual diel vertical migration cycles.

To investigate these issues researchers will determine the vertical distribution, migration and abundance patterns of the principal midwater species, measure their oxygen consumption rates, observe their behavior and activity levels in situ, and study their trophic linkages.

Quantifying the relative abundance and distribution of species in the Gulf and their adapations to their extreme environment will provide important data which can be used to anticipate how other seas will be affected by ongoing changes that lead to similar conditions such as warming and acidification.

Logbook

Today, these jellies, Chiarella centripetalis,were abundant between 200 and 300 meters deep.

Wrapping up a productive cruise

Today we completed our leg of the Gulf of California expedition with a half-day ROV dive close to the port where the Western Flyer docks near La Paz. It was an incredibly productive cruise with ROV Doc Ricketts dives every day, MiniROV dives most days, midwater trawls most nights, and even a few nights of jigging for squid!
Close-up of the head and chin lure of Stomias atriventer. Photo by Karen Osborn.

Food web ecology

As we near the end of the midwater ecology leg, scientists onboard are beginning to piece together a unique collection of observations and data gathered from ROV dives and midwater trawls.
The rare deep-sea squid Ancistrocheirus was hiding in an ink cloud when we approached it.

Unique organisms in the deep sea

In addition to documenting the ecological zonation of the water column in the Gulf of California, we are venturing into parts of the ocean that have likely not been explored by humans before, in particular, not with the deep-sea observational tools we are using during this cruise.
Karen Osborn retrieves the suction bucket from the mini ROV after it is secured on deck. The vehicle’s suction sampler has eight buckets for collecting samples.

MiniROV and ROV Doc Ricketts

Today was another very successful day aboard the Western Flyer, with nearly six-hour dives with both the MiniROV and ROV Doc Ricketts.
The midwater octopus Japetella diaphana is relatively common in the Gulf at depths around 800 meters.

Oxygen minimum zones

Henk-Jan Hoving's collaborative work with Bruce Robison and the Midwater Ecology Group will eventually allow a comparison of the distribution of pelagic animals between areas with oxygen minimum zones of different intensity in different ocean basins.
Kim works with the Midwater Respirometry System in the wet lab. He will keep individual animals in the system for up to 24 hours, measuring the change in oxygen concentration per volume of water.

Coping with low oxygen levels

Today we observed quite a few deep-sea fish that seem to be coping with the low oxygen level of the deep midwaters here in the Gulf.
Around sunrise, the pilots and crew deployed the mini ROV from the fantail of the Western Flyer. On the left, you can see the tether spool attached to the deck.

MiniROV deployment

We began the day bright and early, ready to deploy the MiniROV. This small ROV was designed as a fly-away system that could be shipped anywhere in the world and used on any ship. It has been used to explore Arctic seafloors multiple times. Now it’s getting the chance to explore the warm midwater here in the Gulf of California.
Clockwise from upper left: Carinaria japonica, a heteropod that is abundant in these tropical waters, but rare in Monterey Bay; Serrivomer, a type of deep-sea eel found here and at home; Grimalditeuthis bonplandi, a deep-sea squid that we are seeing for only the second time in MBARI’s 27 years of deep-sea exploration; Japetella diaphana, a species of midwater octopus that is relatively abundant in the Gulf compared to Monterey Bay. A few of the scientists onboard this cruise published research on Grimalditeuthis bonplandi in 2013, speculating that they may use their tentacles to lure prey.

ROV Doc Ricketts to the rescue

Upon arrival in La Paz, the midwater scientists were asked to mobilize a day early so the ROV Doc Ricketts could be used to help rescue MBARI's autonomous underwater vehicle which was operating nearby, off the R/V Rachel Carson.