Project Title: Microbial Ecology of Deep-Sea Corals

Principal Investigators: F. Rohwer and O. Pantos, San Diego State University

It is widely recognized that prokaryotes, both Bacteria and Archaea, are vital components of all marine ecosystems. These microbes regulate the transfer of energy and nutrients to higher trophic levels and influence global carbon and nutrient cycles. For example, ~80% of the primary production in the equatorial and subtropical North Pacific Ocean is carried out by autotrophic bacteria, and secondary production by marine heterotrophic prokaryotes accounts for ~50% of the carbon fixed by photosynthesis in the world's ocean. On average there are a million prokaryotes per ml of seawater.

Corals and other sessile organisms live within and depend on this soup of marine microbes. By associating with specific prokaryotes, a coral colony may gain important metabolic functions such as chemoautotrophy or nitrogen fixation. Tropical, reef-building corals encourage the growth of specific microbes by the secretion of specialized mucus. In turn, the microbes form colonies on the mucus surface and create "inhibition zones" by physical occupation of space, sequestration of nutrients, and production of antibiotics. These inhibition zones prevent colonization by outside microbes, which include opportunistic pathogens.

Several studies have applied modem microbial ecology methods to investigate the microbes living with tropical, reef-building corals. These new avenues of research are showing that when viewing a coral reef, it is necessary to imagine the surfaces, crevices, and animals as landscapes of highly diverse, ecologically structured microbial communities. The associations of the coral animal, prokaryotes, zooxanthellae, fungi, and other undefined components help define the niche that a coral colony occupies. Disrupting the relationships between microbes and corals has the potential to collapse the whole community.

In the proposed research, these studies of microbe-coral interactions will be extended to deep sea corals to:

1. Determine how many microbes live on deep sea corals - Microscopy will be used to count Bacteria, Archaea, phage, and protists living on deep sea corals.

2. Determine how fast microbes are growing on the corals - In tropical reef corals, the growth rates of coral-associated microbes are tightly regulated. These growth rates of coral-associated microbes can be changed by some anthropogenic stressors, which can lead to disease and coral death. The growth rates of deep sea coral-associated microbes will be determined using tracer and microscopy techniques.

3. Determine the types of microbes that live on deep sea corals - Every tropical coral species studied so far appears to have a specific microbiota (i.e., associations between one coral species and a specific species or group of bacteria). We will determine if deep sea corals also have specific microbial associations.