of Natural Resources (funded by the
World Wildlife Fund for Nature), did a
series of studies to assess the impact of
the eruption on marine life and mangrove
communities.
The UPMSI report by Mr. Michael
Atrigenio, Dr. Porfirio Alifio of the UPMSI
and Mr. Ricardo Bifla of the National
Mapping and Resource Information
Authority (NAMRIA)1 pointed out where
reef areas in the Zambales coast are
predominantly affected. Using pre-emption
coral reef data from UPMSI and Haribon
in the area, the group compared estimates
of reef cover and of suspended sediment
concentration on reefs, and how these
affected water turbidity along the ashfall
area and in waters where volcanic ashes
and lahar flowed through the rivers.
Fig. 3. Mudflow map (shaded), Isopach line for ashfall deposit (cm) and location of
transects and life-form category totals. (Compiled from the data of M.P. Atrigenlo,
P. AUΛo and ft. Blha)
The satellite image obtained by
Atrigenio et al. (Fig. 2) of the Zambales
coast shows very turbid waters spanning
3 km from the coast and relatively turbid
waters extending up to 10 km. The image
shows a northward water current due to
the southwesterly monsoonal winds which
blow from May to November. This means
that the volcanic materials during this
period tend to flow north rather than
toward the southern part of Zambales.
Dead coral cover is high where water
has become turbid, and where volcanic
sediments have concentrated (Fig. 3).
There is also a high percentage of dead
corals in areas far from Pinatubo, related
to other causes such as the usual Siltation
from nearby rivers.
It can be deduced from Fig. 3 that
most of the suspended sediment comes
from the MaIoma and Sto. Tomas rivers
and was spreading northward to settle
on this area’s reefs. However, when the
monsoonal winds change direction, it is
likely that nearby reefs in the southern
area will also be affected. The group
expressed the need for a long-term
monitoring strategy to be able to respond
effectively to the changing scenarios in
these coastal areas.
Effects on
Coral Reef Fishes
With degraded coral reefs, what is
left for fish communities dependent on
them? This is answered in a study done
by Messrs. DomingoOchavillo andHomer
Hernandez and Dr. Aliflo. Their report3
is on fish and coral censuses of five sites
along the coast of Zambales.
Their results show that there is a
decline of fish biomass (Fig. 4) in coastal
areas which received ashfall, with the
decline becoming greater as ash deposits
increase. Coral cover and fish biomass
increased with decreasing ash deposits.
Fish biomass decline may have been
due to mortality from ashfall deposit,
starvation due to loss of food caused by
thedeeɪineof prey abundance (alsocovered
by ash), and emigration due to habitat
loss. Decline of fish abundance could
also be a result of loss of habitat and
disorientation, making the fish more
vulnerable to predators and fishing
pressure. This vulnerability to fishing
pressure was anecdotally suggested by
fishers’ reports of big catches immediately
after the eruption, which later abruptly
declined.
The authors concluded that fish
abundance will take a long time to recover
due to the heavy mortality of corals and
the intermittent lahar flows reaching
coastal areas through the rivers. High
sedimentation on reefs will also change
the community structure of the coral
reef fishes, as these are dependent on
the corals and their associated organisms.
Growth rates, susceptibility to predation
and even recruitment Ofjuveniles might
also be affected. The overall consequence
of this is direct economic losses to the
communities dependent on fishing.
JANUARY 1992