The phase shift phenomenon, which is the change of coral reef communities to algal communities, seems to occur in some areas of the country.
The zooxanthellate corals are not able to carry on their photosynthetic function because they do not have access to sunlight due to the thick algal growths that can reach half a meter to one meter in height for certain species of brown algae. So coral colonies ultimately die, and the reef becomes dominated by algae over time. Zooxanthellate coral recruits are not able to take a foothold in such reefs. Many reef-associated species gradually disappear and reduction of species richness results.
The ecological mechanisms causing phase shift are not yet fully understood. However, it is believed that herbivorous fishes (such as parrotfishes) play an important role in that they graze on algae thus controlling their growth and preventing them from shading the corals. This phenomenon deserves to be studied in order to mitigate its effects.
We have just surveyed two shoal reefs in Milagros, Masbate in the Asid Gulf. Both clearly exhibited clear evidence of phase shift, with the dominant brown algae Sargassum (two species) clearly showing dominance during the southwest monsoon months.
These algae cover 30-80 percent (average of 50 percent) of the bottom area. They grow on dead coral substrate. Hard corals have remained healthy only on reef slopes; the reef flats are practically unproductive of fish, being covered with the algae. Corals shaded by the algae are mostly dead.
From our interviews, we learned that a year ago, these algae were not dominant on these two reefs, which have been declared marine protected areas. From our observations, it will take a long protection time for these two reefs to yield fishery products.
The fishes found on these reefs were few. Practically no parrot fishes and surgeon fishes were seen. Few schooling fish species (e.g., caesionids) were observed. Only one or two snappers and groupers were seen. Labrids (small species) were found to be of moderate numbers. Fish biomass was very low (ca 5-10 kilograms per 1,000 square meters of bottom area).
The two reefs, despite a two-year protection by the local municipal environment, certainly do not generate individuals to add to the fishable stock outside the no-take reserve.
The factors that probably brought about the present condition of the reefs could be excess nutrients from fertilizers found in runoff water coming from rice fields. These nutrients especially nitrates from fertilizers could probably explain the eutrophication of coastal waters, which were silty during our visit in June when the southwest monsoon winds were blowing. Silt was also found deposited on both reefs.
From our interviews, we learned that these reefs have been subjected to a number of human-induced stresses, namely, destructive fishing methods, for decades prior to protection and continuing until now. Such stresses have probably weakened the resilience of these reefs to many forms of disturbance.
Throughout the Asid Gulf, reports on widespread violation of fishery laws have been communicated to us. These reports deal with intentional destruction of habitats of fishes by dynamite blasting and violation of the 10-15 kilometer ban on commercial fishing.
Many commercial fishers coming from outside of Asid Gulf ignore this law. And what is more disturbing is that while some of the mayors of towns around the gulf are serious in implementing this ban, the prosecutors and judges appear to be uncooperative.
One mayor complained of pressures from other government officials to return confiscated boats and fishing gears to the owners who allegedly committed violations.
Overall, destruction of our marine resources is continuing, despite efforts of some of our concerned citizens to protect and manage them (examples, two functional no-take marine reserves in the Masbate Pass established and maintained by Mayor Socrates Tuason of Masbate City).
At the same time, the population of the country is increasing, adding to the human pressure on coastal resources. It is obvious that there is a problem that cannot be ignored.