Microbial partnerships

Many marine organisms depend on microbes to survive and, as a result, critical partnerships are formed.

For example, the mutually beneficial symbiosis that corals have with single-celled algae known as zooxanthella is fundamental to the existence of coral reefs.

Zooxanthellae (like plants) use photosynthesis to make their food, and this provides the coral with nutrition. In exchange, the coral provides the microbes with a safe home and some essential nutrients. This completely dependent partnership is called a “symbiotic relationship”

Several studies have shown that the particular type of zooxanthellae that forms the symbiotic relationship with the coral may determine the coral’s physiological characteristics. For example, corals hosting one type of zooxanthella might grow fast while corals with another type may have higher tolerance of extreme temperatures.

The coral-algal symbiosis is a delicate partnership, and can be disrupted by the combination of high temperature and strong light. These are the classic summer conditions leading to coral bleaching, especially when temperatures are elevated for sustained periods.

Until recently, coral bleaching looked like a simple mismatch between the needs of the two partners but the whole interconnected coral colony (often referred to as the coral ‘holobiont’) is now known to include the coral, multiple genetic types of zooxanthellae, fungi, algae that grows on hard surfaces (“endolithic” algae) and various bacterial species.

The interactions within this holobiont will form the basis of future AIMS research to understand the biochemical and molecular mechanisms behind coral bleaching. Our aim is to improve our fundamental understanding of the coral-algal symbiosis and to help predict its stability and adaptability in the face of changing external conditions.

Marine microbes are also involved in a variety of important symbiotic relationships with other marine invertebrates including sponges, sea anemones, jellyfish, molluscs, echinoderms and nematodes.

Potential synergies in these relationships include enhancement of nutrition (as with corals), enhancement of thermal tolerance, assistance with reproduction, contribution to structural rigidity, waste reduction and the production of secondary metabolites used in defence, immune competence and other functions that promote the survival of multicellular organisms in complex, hostile and changing environments.

AIMS is studying micro-organisms known to occur in sponges and testing these relationships by experiments mimicking expected climate change.

Coral bleaching tolerance and adaptation

November 7, 2007