My research interests encompass the physiology and ecology of symbiotic autotrophic marine microbes and their invertebrate hosts. These types of symbiotic associations are extremely important in the world's oceans, where symbiont dependent species are often the primary ecosystem-structuring organisms in both shallow tropical environments, such as coral reefs, and in the deep sea where biomass may be limiting. The importance of the symbioses between algae and tropical invertebrates (such as corals, clams, and anemones) has long been recognized, and has been studied by biologists for over 100 years. However, it wasn't until after the discovery of the deep-sea hydrothermal vents in 1977 that associations between chemoautotrophic bacteria and marine invertebrates were known (or for the most part even imagined). In these symbiotic associations, the bacterial symbionts oxidize reduced sulfur compounds as an energy source, fix carbon dioxide into organic carbon compounds (like green plants), and supply the bulk nutritional needs of their hosts. Often the hosts do not even have a mouth, gut, or anus.

Although chemoautotrophic symbiosis were first discovered in the animals found around the rather exotic environments of deep-sea hydrothermal vents, we now realize that this type of association is wide-spread in the marine environment. In the last ten years chemoautotrophic symbionts have been found in hundreds of different animals inhabiting such diverse environments as mudflats, mangrove swamps, and sewage outflows, as well as in a variety of deep-sea cold-seep and hydrothermal vent sites.

Because many of the associations I study are found in the deep-sea, much of my research begins with oceanographic expeditions conducted in conjunction with research submarines such as the deep submergence vehicles Alvin and Johnson Sea Link. My laboratory is currently involved in research projects at hydrothermal vents sites on the East Pacific Rise and hydrocarbon-seep sites in the Gulf of Mexico. Ecological studies designed to elucidate the relations between the animals, distribution and venting hydrothermal fluid, or reduced chemicals in interstitial waters, are conducted using submersibles. Physiological investigations (such as determination of condition, growth rate, or symbiont complement) of the animals and their symbionts are conducted in conjunction with the ecological studies in order to provide further insight into the physiological ecology of these symbiotic associations.

Another major thrust of my research has been to investigate interactions between the symbiont and host, the role of the host in providing the needs of their symbionts, and the input of the symbionts into the host's nutrition. These studies are both mechanistic and quantitative in nature, and use approaches ranging from molecular to organismal. Many chemoautotrophic symbionts require hydrogen sulfide as an energy source. Hydrogen sulfide is an extremely toxic substance at concentrations as low as a few micromolar, and the animals that harbor these symbionts often live in environments where sulfide levels reach several hundred micromolar. Obviously, they must be specially adapted to the chemoautotrophic lifestyle. Not only must they tolerate this toxic chemical, but they must also transport it to their symbionts, which are housed inside cells within the host's tissues. The specific adaptations differ in different animal groups (as do the specific requirements of the symbionts of different animal groups), and my research has been directed at understanding a variety of the "strategies" employed in chemoautotrophic symbioses.

In addition to studies that can be conducted only while at sea, my laboratory works extensively with a few model species that are collected from relatively shallow environments (from 1 to 1000 meters) and can be maintained alive in the laboratory without the use of specialized pressure gear. These species (one of which contains methanotrophic symbionts) are used in detailed investigations of interactions between the hosts and symbionts.

The discovery and subsequent study of chemoautotrophic symbioses and communities has caught the interest of both the general public and the scientific community, and new associations, and communities are constantly being discovered and reported. The unique mode of life represented by these animals has provided new insights into a variety of basic biological, geochemical, and oceanographic phenomena. The recent realization of the pandemic distribution of these symbioses means that we can no longer view them as biological oddities found only in isolated, remote sites, but must realize their central role to many communities in all of the world's oceans.