The answer to this question, according to scientists who have studied coral reefs in the Great Barrier Reef and the Caribbean, is the notion that overfishing by man has reduced the abundance of parrotfishes and surgeonfishes, both of which supposedly control the benthos.
Coral reefs that are lacking in abundance of these fishes develop into algal communities — a phenomenon called phase shift.
This top to bottom paradigm abounds in scientific literature today, and is widely-accepted by marine biologists.
In southern Philippines, many coral reefs are heavily fished, and have shifted to fleshy algal communities, which provide observable evidence of the top to bottom theory. So it appears easy to accept the theory.
In other areas, however, we noted that some reefs (e.g. those in Masbate) are near sources of pollution from land, which could also drive the shift to algal communities.
How much of the phase shift examples are due in part to pollution should be investigated. In general, it seems that phase shifts may be due to several factors acting together.
Scientists at the SU Angelo King Center for Research & Environmental Management led by Dr. Rene Abesamis are studying the ecology of parrotfishes, and their possible potential role in causing phase shifts.
Thus far, parrotfishes have increased in abundance after two typhoons reduced portions of some reefs to coral rubble.
In science, theories are acceptable only as long as there is no evidence to the contrary.
In fact, there is evidence for the contrary view, the bottom-up notion, based on our research in the four no-take marine reserves in the Bohol Sea, which have been studied and monitored for more than four decades.
This view and other findings on fisheries that have been published are results of our long term studies on marine protected areas.
The contrary paradigm states that the parrotfishes are controlled by the benthos.
A paper first-authored by our colleague Prof. G.R. Russ, who is one of the top world marine biologists at James Cook University in Australia, has been completed for publication.
One of the conclusions is the current notion that “the control of the benthos by parrotfishes no doubt occurs, but we should not be too quick to apply the paradigm to all coral reefs at all times.”
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