Monday, 19 January 2009

Coral destruction by Aspergillus

For some years now Aspergillus has been infecting and in some cases killing the sea fans (Gorgonia ventalina) off the Caribbean coast.
The image on the left shows an infection that began at a single point of infection and which has gradually expanded outwards.
The frond is a light purple colour where it is healthy but takes on a much darker hue of purple around the infection, and this indicates where the coral is dying (see link for more details) whereas the green central area is dead coral.

This Youtube movie shows the researchers examining the damaged corals, narrating as they go. There is a second part of this movie here.

Corals are thought to be similar to ourselves in that they can resist infections as long as they are healthy, so why are these corals becoming infected?

  1. Garrison et.el. suggest that the mould is blown over from Saharan Africa, suggesting that the Carribean reefs are bening overwhelmed by the fungi carried by this dust. My feeling is that this might provide a source for the infection but there must be more to it than this - Aspergillus is found everywhere regardless of dust storms. Garrison et al. 2003. African and Asian dust: from desert soils to coral reefs. BioScience 53: 469-481.
  2. Global warming. We know the seas are getting warmer and this may well contribute to making the coral more susceptible to infection.
  3. More recent research has shown nutrient enrichment can increase coral disease. Infection by Aspergillus is noticeably patchy throughout the Carribean so it could be that nutrient rich pollutants are present in those areas. Bruno et al. 2003. Nutrient enrichment can increase the severity of coral diseases. Ecology Letters 6: 1056-1061.
We must conclude that there could be a variety of reasons for the large scale die-off of corals in the Caribbean. It is not only sea warming - otherwise why would disease be worse in some areas? Pollutants may also have a major effect.
This shows why we must always not accept the first, most obvious cause for a problem without question, there is often an underlying less obvious contributor to the situation.

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