These days, satellite imageries are used to predict ocean areas with high primary productivity as indicated by the presence of substantial chlorophyll concentration in the water. This high chlorophyll content is in turn due to the availability of nutrients (nitrates and phosphates) used in photosynthesis.
In oceanic areas, the source of nutrients can only be the sea bottom. The nutrients are brought to the sea surface by upwellings, and are used by phytoplankton for photosynthesis.
A food chain develops. Phytoplankton is fed upon by zooplankton, which become the food for plankton-feeding fish. The planktivorous fish are fed upon by small, pelagic carnivorous fish, which may in turn support larger, top carnivores, such as Spanish mackerels, billfishes, marlins, and tuna. Therefore, one expectation of an upwelling area is its high primary and secondary production.
Thus, oceanic food chains and food webs begin with the production of plankton, and the critical oceanographic process that makes this happen is upwelling.
Incidentally, each time energy is transferred from one trophic level to the next higher level, much energy is lost as heat. One can understand why top carnivores are very costly to produce in terms of energy — and also in terms of money.
The satellite method, however, is costly. Marine biologists prefer to use more traditional methods. One of these methods is to infer the presence of upwellings from the natural consequences on fish. We did this in predicting some years ago the presence of upwelling in the Dapitan Strait, the part of the Bohol Sea between Dapitan City and southern Negros.
The basis was the observation of a thriving sardine canning industry, and a rich fishery of small pelagics in Dipology City.
Sardines are plankton feeders, and it is logical to expect that the high production of this fish is due to the availability of nutrients from the bottom of the Strait.
As it turned out, the satellite imagery confirmed the presence of upwelling, and a recent oceanographic study also confirmed it.
The latter also explained the mechanism of the upwelling, including the deep inflow of Sulu Sea water to Bohol Sea, and the outflow of the surface water of the Bohol Sea coming from the Pacific Ocean.
It has long been obvious to marine biologists that the high production of sardines and top predators in the Dapitan Strait was because of the permanent upwelling in this Strait. The presence of sardines in other parts of the Zamboanga Peninsula indicates that similar upwellings could be present there.
One intriguing question is: Will upwellings in Philippine seas remain despite climate change? The answer based on opinions of experts is we do not know. It is difficult to speculate, but it appears that should these upwellings disappear, the productivity of our seas may be altered and could cause social and economic difficulties for our people.