GLOBAL WARMING AND FISHERIES
Richard S. Appeldoorn, PhD.
Professor
Department of Marine Sciences
University of Puerto Rico, Mayagüez
Fishing is one of the oldest economic activities in Puerto Rico and has deep roots in the strong
socio-cultural framework of the island. The commercial fishery lands 4 million pounds of fish
and shellfish, with a dockside value of $10 million. As an extractive process, or “new wealth”
the value to the economy increases 7 fold, and this is renewable. The recreational fishery rivals
the commercial sector in catch and is equally important in supporting the tourist economy.
Fisheries production is dependent upon a series of complex interactions between a species and its
biotic and abiotic environment. Species have physiological limits relative to high and low
temperatures, dispersal and genetic exchange depend on current patterns set up by winds and
temperatures, key habitats such as mangroves and seagrass feed and shelter juveniles, while
healthy coral reefs are home to our most important commercial species such as snappers,
groupers and spiny lobster. Significant changes within these components threaten the health of
the overall system in ways that are non-linear and complex. Present models of climate change
predict the following: sea temperatures will increase, sea level will rise, hurricanes will be
become more severe with respect to winds and rainfall, and the oceans will become more acidic.
Each of these could severely impact species and the ecosystems that support their production.
Many tropical organisms live near their upper thermal limit; any increase could result in mass
mortalities. Already we have seen the devastating impact of coral bleaching. Studies now show
that both the spatial extent of bleaching and the local intensity increase exponentially with even
the modest temperature increases seen to date. On the other hand some species appear to depend
on periods of low temperature; this is the case of red hind, one of our most important commercial
groupers. Studies indicate that low temperatures may be important to trigger the onset of
reproduction, and ominously, over the past four decades annual minimum temperatures have
risen at a rate faster than that of maximum temperatures.
A modest increase in sea level of 12 inches is expected this century, enough to cause our coast
lines to recede by up to 100 feet. However, this assumes the ice sheets of Greenland and
Antarctica remain intact. The major threat of sea level rise to fisheries will be the loss of coastal
protection if the growth of coral reefs cannot keep pace. Given the current status of reefs and the
added threats climate change brings, there is significant doubt as to whether this can happen.
Without coastal protection, the key habitats of mangroves and seagrass beds will be lost, and
coastal turbidity will increase.
More intense hurricanes will have two impacts: direct habitat destruction from waves and
increased runoff from greater rainfall, with concomitant increases in turbidity, eutrophication and
sedimentation. Again, critical coastal habitats, particularly seagrass beds and coral reefs will be
threatened. Empirical studies in Puerto Rico have clearly shown a direct and negative impact of
turbidity on coral and reef fish communities. Already our reefs are suffering from substantial
seasonal or sustained increases in the overgrowth of corals by algae and cyanobacteria.
Perhaps the biggest unknown is the impact of “acidification” of the oceans. The primary sink for
carbon dioxide released into the atmosphere is the ocean. A direct chemical reaction of water
and carbon dioxide leads to the production of carbonic acid. More carbon dioxide – more acid.
Why is this important? Coral, mollusks, many planktonic organisms make their skeletons from
calcium carbonate. The more acidic the water, the more difficult and energy demanding it will
be for these organisms to grow. Eventually the point can be reached, estimated as mid century if
carbon dioxide levels are not reduced, where calcium carbonate exposed to water will dissolve.
The overall impact of these threats is difficult to quantify. Hurricanes can cause severe damage,
but their impacts are often limited in space and time. The more insidious impacts will probably
be in the form of sustained habitat deterioration, loss of productive capacity and changes in
community composition.
What can be done to avoid or reduce these impacts? While Puerto Rico must do its part in
reducing the emission of greenhouse gases, it will be the success or failure of the global
community as a whole the will determine final outcomes. What Puerto Rico can and must do,
and as soon as possible, is greatly reduce the land-based sources of stress (sedimentation,
eutrophication, contamination), for it is only in a healthy environment that corals and other
organisms can achieve the growth and productivity rates needed to forestall the effects of rising
temperature, rising sea level, and rising acidity. This is a daunting task and one that falls beyond
the sole responsibility of the Department of Natural and Environmental Resources, to all local
and federal agencies, particularly the Planning Board, the judiciary, private industry, agriculture
and the public at large.