Project: Midwater animal models: Optical measurement of metabolic transitions in pelagic biota

Description from NSF award abstract:
Despite encompassing more than 99% of the livable space on the planet, the midwater environment and its inhabitants are among the least studied on the planet, primarily due to their remoteness and the technological limitations that have precluded direct study. The use of optical techniques, including spectroscopy and video image analysis, for direct, non-invasive imaging of physiological function transforms midwater animals (zooplankton and micronekton) into ideal physiological models. In this case, transparency, a ubiquitous camouflage strategy in the pelagic environment, allows, literally speaking, insights into animal physiology (i.e. it facilitates physiological imaging). Thus, it is now possible to conduct physiological experiments on midwater animals that are of equal complexity, but greater temporal resolution, to those routinely performed on more robust fishes and mammals. The present project is a novel combination of less invasive sampling and optical physiological methods that will elucidate the metabolic strategies employed by midwater organisms for survival in the extreme hypoxia characterizing much of the midwater environment. The investigators will further use the changing CO2 concentrations through these oxygen minimum zones as a natural laboratory to test physiological responses to ocean acidification. They will quantify metabolic transitions relating to oxygen concentration for ecologically important, but understudied, midwater organisms. They will test hypotheses relating transparency (i.e. visibility by predators) and metabolic rates as an indication of the capacity for predator avoidance. Specifically, the investigators will measure blood oxygen binding, heart rate, stroke volume, ventilation rate and volume, oxidation state of the tissues (NAD+:NADH) and whole-animal oxygen consumption rates. Not all of the above parameters are relevant to all species to be studied. They will study transparent representatives from a broad spectrum of zooplankton and micronektonic groups, including fishes, larvaceans, chaetognaths, polychaetes, jellies, salps, amphipods, and gastropods but will focus on cephalopods because of 1) their closed circulatory systems and blood oxygen binding proteins allow the full development and utilization of optical physiological techniques and 2) because unique aspects of their physiology are of special interest for hypoxia tolerance and render them vulnerable to ocean acidification.

This project provides a model for an integrated approach to studying the ecological physiology of pelagic organisms. The approach has potential to reveal the tolerance of oceanic organisms to global warming and ocean acidification. Furthermore, oxygen minimum zones are expanding with potentially severe consequences for oceanic biota.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Results:
Refer to this excerpt from the second-year project report (PDF) for more information about the project's activities and findings.