[Coral-List] Cyanobacteria Outbreak

[Luis Alberto Acosta Moreno]

Dear colleagues,

I appreciated all comments the e-listers sent me days ago about Providencia Island cyanobacteria outbreak. Every one gave me some clues to understand the phenomena. I would like to summarize the comments and give some answers to the questions raised.

1. Providencia Island is not an area of periodic upwelling.
2. This in an area with wastewater discharges.
3. During the outbreak the water was warm and particularly calm (0 movement).
4. The outbreak was observed mostly in shallow water (between 1 to 17m depth).
5. The specific location of major outbreak was 1322478 N – 8123573 W, there was also millions of Ctenophore in the column water.
6. The outbreak was observed by the first time during October 9-12th, but the cyanobacteria remains until we left the island in October 30th.
7. We were not in the island before this bloom, so we couldn´t observe anything in particular (e.g. intense rainfall, storms, a sudden increase of cyanobacteria). Nevertheless, locals told us that some weeks before the outbreak was heavily raining in the island after a long dry season. Furthermore, after the outbreak, during the “Sandy storm”, October 23-25th, we noted that the cyanobacteria remain in the area.
8. I don´t know which series of cyanobacteria are involved in the phenomenom observed. This is not my field of research. However, we already checked that in fact some material is cyanobacteria and some algae.
9. The study area is not cover by sand/sediment patches loaded with organic matter/fine neither mud; in contrast, the bottom is mostly coral sand.
10. We have not idea if the specie is Lyngbya majuscula, but reviewing some pictures I would say no, it is not the same.
11. There is sewage discharge nearby the sites with cyanobacteria. In the island there are approximately 4000 persons and they have not sewage treatment plant.
12. We did not measure nutrients or oxygen concentration on the reef.
13. We have not a recorded temperature, but it was close to 26-27oC. Air temperature fluctuated between 24 and 31ºC.
14. Fish and invertebrates surveys were conducted in September, a month ago the outbreak, by Coralina (state environmental agency). We have not access to those data.
15. I don’t know if the outbreak has finished. I left the island, but I am going to get new information about the actual state of the bloom through the dive shops.
16. Did you got an image during the bloom? Mapping? Check Landsat archive image during bloom and when no bloom? No I do not have any satellite image during the bloom (rather a GeoEye image for January 2012), but yes, we map the cyanobacteria distribution and cover around the island.

I look forward to your comments and suggestions.

King regards,
Alberto Acosta



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