The coastal waters of Bolinao, Pangasinan, Philippines experienced environmental changes
over a 10-year period (1995-2005), the most significant effect of which was the major
fish kill event in 2002 that coincided with the first reported Philippine bloom of
a dinoflagellate Prorocentrum minimum. Days before the bloom, dissolved oxygen was
< 2.0 mg/l in the waters that were stratified. These conditions may be linked to the
uncontrolled proliferation of fish pens and cages to more than double the allowable
limit of 544 units for Bolinao waters. Mariculture activities release organic matter
from unconsumed feed and fecal material that accumulate in the water and sediments.
In over 10 years, water quality conditions have become eutrophic with ammonia increasing
by 56%, nitrite by 35%, nitrate by 90%, and phosphate by 67%. The addition of more
fish pens and cages placed additional stress to this poorly flushed, shallow area
that affected water quality due to changes in the water residence time.