Midwater ecology
Lead Scientist: Bruce Robison
Project Manager: Kim Reisenbichler

The midwater ecology project focuses on three groups of gelatinous animals: larvaceans, siphonophores, and hydromedusae. Filter-feeding larvaceans are the principal consumers of particulate matter such as phytoplankton cells and marine snow at mesopelagic depths down to 1,000 meters. Siphonophores and medusae are dominant mesopelagic predators, feeding on a broad range of other species. Despite the importance of these animals to the ecology of midwater communities, their fragile, gelatinous structures make them nearly impossible to study by conventional methods. With the advent of ROV-based in situ research, significant progress is now being made toward assessing their ecological roles and measuring their contribution to midwater productivity.

As in 1999, we will continue to use ROV transects to make quantitative measurements of the vertical distributions, abundances, and seasonal variations of these animal groups. In situ observations will provide data on trophic (feeding) relationships and behavior patterns. The collection of live specimens will provide material for stomach content analyses and for laboratory studies on respiration and reproduction, and feeding, digestion and assimilation. Each of these parameters is important for accurately modeling energy flow through these fundamental links in the mesopelagic food web.

At depths between 650 and 850 meters, a pronounced oxygen-minimum layer constitutes the physical and chemical lower boundary of the mesopelagic community in Monterey Bay. This layer is an ecologically important transition zone between the mesopelagic and bathypelagic faunas, and contains a unique assemblage of species. We will continue to investigate this layer, working with other institute researchers to collect and identify microbes from within the region of reduced oxygen, and from the "milky layer" just below it. We believe that microorganisms are essential agents in the creation and maintenance of these layers.

Bioluminescence is a pervasive characteristic of midwater animals. Understanding its mechanisms and how it is utilized is a key to understanding mesopelagic ecology. In 1999 we broadened this avenue of our research by initiating studies on the molecular biology of luminescent and fluorescent proteins from gelatinous zooplankton. This work continues to expand our knowledge of the kinds of photoproteins found in deep-sea animals, and is contributing to progress in ecology, taxonomy, and biochemistry. This research is being conducted in conjunction with MBARI’s program in molecular biology.