Global warming to reduce fish catch

Posted: 18 November 2010

Author: Henrylito D Tacio

Rising sea level is seen by many scientists as the most serious likely consequence of global warming.

“A continuing rise in average global sea level would inundate parts of many heavily populated river deltas and the cities on them, making them uninhabitable, and would destroy many beaches around the world,” said the Intergovernmental Panel on Climate Change, a group of 2,000 scientists which advises the United Nations.

Coral polyps
Coral polyps. Photo credit: Seaweb

“Sea level has been rising 0.2 centimetre per year,” disclosed Dr. Laura David, an oceanographer from the University of the Philippines’ Marine Science Institute who was invited by a media workshop convened by the Philippine Network of Environmental Journalists.

Dr. David explained on the impacts and challenges of climate change among coastal communities. Climate change, she lamented, is usually associated with land because it is where the people live. As such, coastal areas are hardly taken into account so that even the Philippine agenda on climate change adaptation has only one line on marine resources.

“We usually associate climate change with typhoons and destroyed houses rather than what is happening in the sea. But climate change is actually beyond destruction and structures. It also pertains to food security contributed by coastal areas,” she said.

According to the National Framework Strategy on Climate Change 2010-2022, fisheries account for about four percent of the country’s gross domestic product. The fisheries sector employs an estimated million people – 26 per cent in aquaculture operations, 6 per cent in commercial fishing and 68 percent in marine and freshwater municipal fishing.

Fish caught off the Philippines
The Filipinos are a fish-eating people. Photo credit: Henrylito Tacio

Basically, Filipinos are fish-eating people and they largely depend on seafood for their viands. According to a study, a Filipino eats an average of 28.3 kilogrammes of fish annually.

“We still have enough fish now but with global warming we may have problems in the next five to ten years unless we do something about it,” warns Dr. Rafael D. Guerrero III, former executive director of the Laguna-based Philippine Council for Aquatic and Marine Research and Development (PCAMRD).

Most of the fishes harvested in the Philippines rely much on three coastal environments: coral reefs, seagrasses, and mangroves. All three are likely to suffer from the impacts caused by sea level rise and changes in ocean temperature.

The Philippine coral reefs, the second largest in Southeast Asia, are estimated to cover an area of 26,000 square kilometres and hold 2,177 species of fish. Much of these are critical to survival of coastal communities.

Coral reefs are sensitive to global warming because the organisms living within them would leave once the temperature within their environment increases. Without these organisms, Dr. David pointed out, the corals will die.

In fact, increased temperature is one stressor that can cause coral reefs to bleach, which in turn diminish their growth and threaten critical habitat for fish and other marine resources.

“An increase of one to two degrees Centigrade can cause corals to bleach, as they expel the algae that provide them with food and lend them their vibrant colors,” explained Molly O'Meara, a staff researcher at the Washington-based Worldwatch Institute. “Sustained increase of 3-4 degrees Centigrade can cause significant coral death.”

On their growing stage, fish rely so much on seagrasses as sources of food. The Philippines has 18 species along its coasts, making the country with the second highest (after Western Australia's more than 30 species) in terms of the number of seagrasses in the world.

Unfortunately, seagrasses are fast disappearing from Philippine waters. “My present estimate of seagrass areas in the country is roughly 978 square kilometers; but this is only from 48 sites nationwide comprising only about 13% of the entire length of its coastline,” says Dr. Miguel Fortes, the country’s foremost expert on seagrasses. “So you can imagine its huge extent if the entire coastline of the country surveyed?”

Strong typhoons, as a result of climate change, will suffocate seagrasses by silts washed away from the mountains. According to Dr. David, murky waters are also bad to sea grasses because they prevent the sunlight from reaching the seagrasses. Although when the water gets clearer, the grasses may recover but some of them may die also.

Sea grasses
Sea grasses. Photo credit: Dr Miguel Fortes

“In corals and seagrasses, sea level rise will affect amount and wavelength of light that can penetrate the water and consequently affect primary productivity,” Dr. David pointed out.

Dr. Fortes said coral reefs with their associated seagrasses could potentially supply more than 20 percent of the fish catch in the Philippines. “A total of 1,384 individuals and 55 species from 25 fish families were identified from five seagrass sites in the country,” he reports. “Five times as many fish live over seagrass beds than over sea floors made up of mud, shells, and sand.”

In short, where there’s seagrass, there’s fish, and for the average Filipino, where there’s fish, there is food and livelihood.

The resilient mangroves are not spared from the consequences of climate change. Quoting data from the United Nations, Dr. David said that 13 per cent of the world’s mangroves “will be drowned by 2100.”

“There are 25 to 30 species of true mangrove trees and an equal number of associated species,” says Dr. Fortes. All of them are very important to marine life. They serve as sanctuaries and feeding grounds for fish that nibble on detritus (fallen and decaying leaves) trapped in the vegetation, and on the bark and leaves of living trees.

“(Mangroves) are important feeding sites for many commercially important fish species (mullet, tilapia, eel, and especially milkfish), shrimps, prawns, mollusks, crabs, and sea cucumbers,” a World Bank report notes. “Fry that gather in mangrove areas are very important for aquaculture.”

The three coastal ecosystems are very important to various fish species. There are those that will be greatly affected if one habitat is destroyed. Most likely to suffer from the perils of climate change is lapu-lapu (grouper) as it grows in different stages in the three ecosystems.

Dr Laura David, oceanographer
Dr Laura David, Filipino oceanographer. Photo credit: Henrylito Tacio

When young, the grouper lives in mangroves and goes to sea grass areas when it’s bigger. It lives in coral bed upon maturity. “So when one of these systems is destroyed, it is the first one to vanish,” Dr. David said.

She urged Filipinos to protect these ecologically-fragile ecosystems, which she considers as allies. They are not only sources of food, but they also help in protecting people living near the seashore.

“Coral reefs, seagrasses and mangrove provide protection to coastal communities as they naturally buffer against high-energy waves, even under the scenario of sea level rise,” Dr. David declared.

Global warming refers to an increase in average global temperatures, which in turn cause climate change. “To completely understand why global warming happens, it is important to know that our atmosphere, which is made up of gases such as nitrogen, oxygen, and carbon dioxide as well as water vapor, has a profound influence on Earth's surface temperature,” explains the Washington-based Worldwatch Institute.

Gases such as carbon dioxide and methane absorb heat, thus reducing the amount that escapes back to space. “As the atmosphere absorbs heat energy,” Worldwatch notes, “it warms the oceans and the surface of the Earth. This process is called the greenhouse effect. Without this effect, the Earth’s atmosphere would average about 50 degrees Fahrenheit colder, making it impossible to sustain life on Earth. Rising levels of heat absorbing greenhouse gases such as carbon dioxide in the atmosphere will increase global temperatures (called global warming).” 

Henrylito Tacio is a Contributing Editor of this website, covering South East Asia.