SEAFDEC is developing an early warning system for pollution in mariculture parks

From good to bad to worse, left to right. After a very detailed sediment color chart  is developed, fish farmers may be able to visually assess their cages’ impact and  take action to head off fish killsTIGBAUAN, ILOILO – The Aquaculture Department (AQD) of the Southeast Asian Fisheries Development Center (SEAFDEC) is developing an early warning system to guard against the negative impacts of fish cages in mariculture parks.

This is certainly good news to fish cage operators who stand to lose their investment should fish kills occur and to Mother Nature itself. According to the Department of Agriculture – Bureau of Fisheries and Aquatic Resources, the government has so far put up 34 mariculture parks around the country. A sea cage measuring 10 x 10 x 6 meters in the park may produce as much fish as 10 hectares of fishpond in a cropping cycle of five months. Hence DA-BFAR's emphasis on mariculture parks to boost fish production as noted in President Arroyo's recent state-of-the-nation address.

"The early warning system is a rather simple technique," explains Dr. Joebert Toledo, Chief of SEAFDEC/AQD. "What the managers of the mariculture parks (for example, DA-BFAR) need to do is periodically collect samples of sediments, or the soil under the sea cages." Then they compare the color of their sample to a reference color chart which will let them know how far off or how near they are from ideal conditions. A very detailed sediment color chart is being developed by SEAFDEC.

The color comparison method is basically the same technique used by rice farmers to see if their rice needs additional foliar (leaf) fertilizer.

How the technique was developed

To develop the system, SEAFDEC first monitored two sites (fish cage site and non-fish cage site) at its Igang Marine Station in Nueva Valencia, Guimaras where a mariculture park is located. SEAFDEC researcher Ms. Sheila Mae S. Santander who made the study said that she compared the nutrients, presence or absence of infauna, and sulfides in the sediments collected using a core sampler. She found out that the sediment color mirrors the degree of sediment deterioration. This finding becomes the basis of the very detailed color chart being developed by SEAFDEC.

It must be noted that the Marine Science Institute of the University of the Philippines Diliman earlier conducted studies on sediment quality and also trained farmers on simple environment monitoring.

Where's all that bad stuff coming from?

Pollution in sea cages comes from the feeds given to the fish to sustain the large stocking densities. Feeds that are not eaten or digested properly, plus other waste products go into the water and some will eventually settle onto the sediment bottom. Ms. Santander said that this leads to higher sedimentation rates in the area.

"Bacteria in sediments would not be able to cope and break down all the wastes. Some of these wastes – organic matter – could be resuspended into the water column. This in turn could lead to eutrophication or over-enrichment. When this happens, microscopic plants – algae – would bloom, but when they die off, dissolved oxygen in the water could be depleted. Without oxygen, fish, like humans, would start dying."

And it is not just the fish in the cages. The toxic conditions could impact the infauna, or animals living within the sediments. One such infauna is polychaetes. Polychaetes are segmented marine worms which burrow in the sediment bottom. They play an important role in the marine environment through their burrows which serve as habitat of microorganisms. These microorganisms produce enzymes which recycle organic matter. This is very similar to the role that earthworms play in agricultural farmland. Polychaetes allow stable organic matter degradation through their burrowing. Without the burrows, the enzymes are easily washed out.

Ms. Santander also explained that sedimentation rates, ammonia and phosphate concentrations were higher in cage sites compared to non-cage sites. Dissolved oxygen was also found to be lower in the cage sites. Consequently, no polychaetes were found in these areas.

What's a park locator to do?

Should park operators or BFAR find out that the mariculture park's sediment is getting bad, SEAFDEC suggests that a "fallow period" be implemented. The fish cages may be moved into another area of the mariculture park. This allows the sediments and infauna of the threatened area to recover. Park locators should heed the advice of BFAR and SEAFDEC once the early pollution alert is issued.

Park locators should also check their feeding regimes (they may have been overfeeding). They must strictly adhere to the recommended or proper feeding management to help reduce wastes. The lesser the amount of wasted feeds, the lesser the quantity that reaches the sediment bottom, and the greater the number of polychaetes present. Park locators and managers may likewise step up their water monitoring parameters.

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