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Asia Monitor
UNU e-Newsletter Issue 20. March 2007 Harmful Algal Bloom Monitoring Via Satellite in Northern Borneo
Dr. Chun Knee Tan, Global Environmental Information Center, Coordinator
Borneo Island, located in the Southeast Asia, is the third largest island in the world. Administratively, Borneo is divided by Malaysia, Brunei and Indonesia. Borneo Island is strongly influence by the Asia monsoon, namely northeast monsoon (November – February) and southwest monsoon (May – August).
Harmful algal bloom (HAB), or “red tide”, has occurred intermittedly around northern Borneo since 1976. The HAB event is caused by Phyrodinium bahamense var. compressum, which can, in turn, cause Paralytic Shellfish Poisonings (PSP). The most serious PSP outbreak occurred in 1976 and resulted in 202 PSP cases and 7 deaths. In early 2005, one PSP fatality case was reported in Sabah, Malaysia. Researchers found that the bi-annual Phyrodinium bloom coincided with the onset of monsoon wind, and it could also have been influenced by the El-Nino.
During late 2003, Cochlodinium polykrikoides, a species of algae that caused severe fisherie damage in East Asia, was found starting to bloom in northern Borneo. Studies in Japan and Korea found optimum conditions for Cochlodinium bloom to be 1) salinity 32-34 psu; 2) temperature 25-28oC and; 3) good sunlight—all similar, to the oceanographic conditions in Borneo. The Cochlodinium bloom was suspected to have originated from water ballasting activities. However, recent DNA analysis showed the species bloom in northern Borneo to be independent from the species in Korean or Japanese waters where it is not from the East Asia origin.
Using MODIS Aqua satellite, scientists have been monitoring HAB in northern Borneo since early 2004. The objectives of this activity are to provide HAB monitoring information and to investigate the cause(s) of HAB occurrence in northern Borneo. Daily MODIS Aqua images are processed and distributed to local authorities in Sabah, Sarawak and Brunei, and uploaded to the website (http://sg.geocities.com/myredtide/Index.htm). The reports from this monitoring effort have been used as additional information for the ground HAB monitoring program in Brunei and Sabah.
Analysis of satellite images revealed that the Cochlodinium bloom had very high chlorophyll a levels, signalling strong optical absorption characteristics. Results showed that the Baram River plume and upwelling in Northern Borneo provided the source of nutrients for the Cochlodinium bloom in the offshore region. The occurrence of an upwelling event was noticed off the northern tip of Borneo Island and could be related to the northeast monsoon wind. In 2004, the bloom from Northern Borneo had crossed the Balabac Straits, reaching Palawan Island in Philippine. In 2005, Cochlodinium bloom from Sabah, Malaysia reached Palawan Island and caused serious aquaculture damages in Philippine. In early 2007, the bloom of Cochlodinium has already caused damage to aquaculture at Sabah, Malaysia.
Recent chlorophyll a images from the MODIS Aqua Satellite show the oceanographic conditions at northern Borneo during March 2007. Chlorophyll a is used as a measure of phytoplankton biomass in the water. As the phytoplankton increase, the chlorophyll a detected using satellite will also increase. The figure on the left was taken on 1 March 2007, while the figure on the right taken on 8 March 2007. The black color in the image indicates cloud or no data, while the land area is outlined in white. During normal conditions, the offshore region of northern Borneo is very low in chlorophyll a (blue color). When there is a very large phytoplankton bloom, the chlorophyll a will increase (red color).
On 1 March 2007, very high chlorophyll a was observed extending about 300 km from the northern tip of Borneo Island in a southwest direction. One week later, they found the chlorophyll a levels to have spread into a few large patches. Some of the high chlorophyll a patches appeared to be approaching the coastal area. This information is very useful for the early detection and preparation for HAB mitigation in the region. The combination of satellite monitoring and ground survey will help to establish an effective HAB management system.
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