Deep Breathing: In Situ Respiration Rates of Bathypelagic Animals

A critical factor required to quantify the carbon flux through meso- and bathypelagic ecosystems is the accurate measurement of oxygen consumption rates for the animals within these communities. While an abundance of metabolic rate data for many meso- and bathypelagic species is available in the literature, these determinations were made primarily by taking animals that were captured by net, extracted from the depth and pressures that they normally experience, and then incubated at atmospheric pressure in the lab. More recent, submersibles have allowed more gentle collection techniques, thus reducing the trauma of collection, but the incubations were still primarily made after forced decompression, under laboratory conditions quite different from the animals’ natural environment. In the case of deeper living bathypelagic organisms, many do not survive capture and transport to the surface and researchers have had to rely upon metabolic enzyme activity measurements to estimate respiration rates.

In an effort to determine if removing deep-sea animals from their natural environment affects their respiration rates, and to directly measure the respiration rates of those animals that don’t survive at atmospheric pressure, MBARI developed an ROV-deployed, eight chamber, in situ Midwater Respirometry System (MRS). Stable electronics, optical oxygen sensors, quartz-walled chambers, and pumps for circulating, flushing and injections have been incorporated into the MRS. The result is a very stable system that allows us to manipulate conditions within the chambers, as needed, for specific experiments. The MRS enables us to collect animals at depth with an ROV, and then deploy the MRS module onto a mooring in the midwater for 24 to 48 hours at the approximate depth of collection while experimental manipulations are made, and continuous oxygen and temperature measurements are recorded.

The focus of this presentation will be on the results of over 10 years of MRS–derived respiration rates for a variety of bathypelagic fishes, jellies, crustaceans and worms collected between 1800 to 3000 m in depth. Our in situ rates will then be compared to laboratory measured and/or enzyme-derived rates available in the literature, as well as, our own shipboard measurements for the few species that survive at atmospheric pressure.