Coral Reefs - More Danger Than Originally Thought?

A review of: Mao-Jones, J., Ritchie, K.B., Jones, L.E., Ellner, S.P., (2010), How microbial community composition regulates coral disease development, PLoS Biology, March 2010 Issue, 44-51

Coral reefs are one of the most delicate and fragile ecosystems on the planet, they are also the habitats that hold over a quarter of all marine species. These two facts result in them being of huge importance to the marine system as a whole, with one small problem facing the symbiotic dinoflagellate zooxanthellae leading to catastrophic effects to the entire ecosystem, it is for this reason that corals are constantly monitored for chemical, physical and microbial change.

Microbes pose a huge threat to corals, with infectious diseases being a leading cause for the increased worldwide coral reef decline. The effects of these diseases are worsened when coupled with the dangers of coral bleaching, caused by an increase in ocean temperatures, which can actually make corals more susceptible to microbial disease. The wide use of the Vibro spp. in tests has been extremely beneficial to understanding the risks posed by disease and possible ways to reduce this risk.

This study looks into using a model to test how the Vibro spp. in corals has an effect on spatial gradients, production of a mucus layer and the abundances of other microbial life. The model used consists of two main rules, that microbial populations are measured in units of growth limiting substrate, and that there is no external inoculation. Once these have been made, the model uses the abundance of pathogenic microbes and the abundance of antibiotic producing beneficial microbes plus antibiotics and substrate.

Results show that models can show insights into the problems that corals face, a rising temperature of oceans, causing an increased susceptibility to pathogens. There can be two states that corals face microbial, and these are the domination of pathogens, and the domination of beneficial microbes, the model can help predict changes that can occur in the balance between these two states due to a number of factors, such as an increase in temperature. However, findings of the model indicate that even if the stress of heat is removed, the corals susceptibility to pathogens can remain and this shift in balance is enough to rid the coral of the beneficial microbial community. This model is highly dependent on the assumptions of the beneficial microbes antibiotic abilities, which can cause unexpected shifts in the outcomes of the models. This is mostly due to the model being carried out int he SMC which can host much more microbial life than the natural ocean. Results show that a shift between the two states is much more favorable to go towards the direction of the pathogen as opposed to the beneficial microbes.

As this model allows for numerous factors to be tested, including factors that directly affect coral susceptibility such as poor water quality, an increase in temperature and poor quality of habitat, it is a very good model for investigating the effects of pathogens on the beneficial microbes that allow the corals to survive.