Leg 2: Midwater Biology
The focus of the midwater biology team's research will be the Gulf of California's oxygen minimum zone (OMZ) and its influence on the physiology, diversity, and ecology of midwater animals. The primary areas of focus will be the gulf's central and southern basins. The research conducted will be based on dives performed by the ROV Doc Ricketts and supplemented by blue-water scuba diving and midwater trawling.
The OMZ is a dominant feature of the gulf's water column—it is five times larger and much closer to the surface than the OMZ in the Monterey Bay. This permanent physical feature causes many animals in the Gulf of California to be forced upward toward the surface, making the near-surface layers more crowded than in other parts of the ocean, particularly during the day. Some species shift their vertical distributions below the OMZ, which moves them further from the food-rich surface layers. Still other species have apparently found physiological or behavioral adaptations that allow them to regularly enter the layer.
MBARI scientists hypothesize that the unusual vertical distribution and migration patterns displayed by the gulf's midwater fauna are driven chiefly by the characteristics of the OMZ. Also, the degree to which these patterns occur is directly related to the strength and breadth of the OMZ, which vary from basin to basin. In order to investigate these issues, scientists will measure the physiological and behavioral capabilities of various midwater species to deal with low levels of oxygen.
This work will be conducted by using ROV-based surveys to determine the precise vertical distribution and abundance patterns of the principal species. Most of the researchers on this cruise specialize in "gelatinous zooplankton"—jellyfish-like siphonophores and ctenophores which can dominate midwater ecosystems. These are usually overlooked on expeditions which either focus on benthic habitats, or which do not have ROVs like Doc Ricketts, which is capable of collecting minuscule, transparent animals.
We will also be deploying some special blue LED lights on the ROV, to image the fluorescence of gulf inhabitants. Fish, in particular, have impressive fluorescent properties. Additionally, blue-water scuba and midwater trawling will provide access to shallower and smaller organisms that the Doc Ricketts cannot observe.
The gulf's unique environment has favored the development of communities dominated by very few taxa. Unlike the relatively even distribution of species that we find off California, samples in these semi-enclosed basins are frequently dominated by particular species. This distinctive community structure may reflect the future state of the ocean in other regions. Measuring the relative abundance and distribution of gulf species, and observing their adaptations to their extreme environment will provide important data which can be used to anticipate how other seas will be affected by similar oceanographic changes (warming, eutrophication, fishing pressure).
We are also interested in looking at the biodiversity of this region as compared with our own using molecular techniques and morphological studies. The geographic barriers for species are not always well defined in the ocean, and genetic techniques can help us determine where these boundaries occur.
The significance of this research is much broader than the Eastern Tropical Pacific and its OMZ. Increased carbon dioxide input has been predicted to expand oxygen minimum layers in many other parts of the ocean. We need to reach a better understanding of this phenomenon in order to gain a predictive capability with regard to this prospect.