Organic Pollution and Its Impact on the Microbiology of Coastal Marine Environments: A Philippine Perspective

Abstract

Organic pollution has changed marine coastal environments in both metropolitan and rural regions of the Philippines. This is documented for metropolitan Manila Bay and rural Lingayen Gulf with mariculture zones in Bolinao Bay. After less than a decade of intensive milk fish farming, organic feed and waste inputs apparently triggered negative feed back responses. These culminated in a devastating mass kill of cultivated as well as wild fish stocks in February 2002. This event appeared to be the combined result of oxygen depletion and a red tide harmful algae bloom. Subsequent minor fish kills affected a limited number of net cages mainly in stratified waters at drastically reduced salinities (down to 5) during the SW monsoonal rainy season.

Mesophilic vibrios from the fish farming area showed higher resistance to antibiotics than off-shore isolates and comprised several species of opportunistic pathogens, including Vibrio cholerae during the outbreak of a cholera epidemic in the coastal region.

Sediment traps revealed that 1 kg of (net) dry weight m $^{-2}$ d $^{-1}$ (or 50% of the average daily feed input to a fish cage) contributed to the sinking flux of particulate organic matter. Sediment cores mirror enormous near-source increases of organic matter input and deposition during the last decade. As a result of roughly eight years of intensive fish farming the sea floor of Bolinao Bay is covered with a 15–30 cm thick layer of watery sulfidic sediment (Eh=−250 to −150 mV). Due to the continued production of organic matter mineralization via microbe-mediated sulfaterespiration pathways, neritic sediments of the fish farming area are void of burrowing macrofauna. Comparisons with intertidal sediments of similar texture and redox potential reveal two orders of magnitude higher activities of key enzymes involved in organic matter recycling such as scleroproteases. This is at least partially attributable to abundant macrofaunal bioturbation in sulfidic intertidal sediments of the Bay. The extraordinary recycling potential of bioturbated and vegetated intertidal sediments remains a challenge to biogeochemical management options to circumvent the predominance of H $_2$ S-producing sulfate-respiration in organic matter remineralization.