Oil troubles waters

OUR PLANET 9.5 - Oceans

Oil troubles waters


describes the effects of the oil industry
on vital tropical ecosystems

pumpjackThe sea provides a vast array of natural resources for thousands of local communities in the tropics. But the presence of the oil industry has significant social and environmental impacts, both from accidents and from routine activities like seismic exploration, drilling and the generation of polluting wastes.

When accidents occur, sessile life (species attached to surfaces such as rocks or the seabed) is the first to be affected: its mortality increases as oil accumulates, although certain organisms, like gastropods, tolerate it better. Some species regenerate in a year, while others - sea urchins for example - can take more than four years to recover completely.

Long-term damage

Coral reefs are also severely affected. Rich in biodiversity and vital for sustaining local fisheries, they resist erosion and storms and stabilize coasts, especially in low-lying tropical areas. But they take decades to recover from an oil spill. The rate of photosynthesis in plant life is reduced, becoming a chronic problem in reefs exposed to a high level of pollution. Reproductive cells atrophy and reproductive tissues fail to develop properly - effects that can last for several years after contact with crude oil - reducing reproductive rates and thus population density. Oil also alters the composition of species in the reef habitat. For example, the greater body area of branching corals leads to a greater absorption of oil, and thus a relatively higher mortality rate than among other species.

Mangroves are also very important to society, the economy and ecology as habitats for many fish and molluscs and a source of raw materials for communities in the surrounding area. And they, too, are affected by the oil industry. Its activities interrupt the flow of both freshwater and seawater into mangroves and within them, affecting drainage patterns, plant life and the soil, and causing a general lack of stability. Dredging - to make channels or deepen and widen existing ones - can completely destroy the affected area: the wider and deeper the channel, the more the damage. Results include large-scale erosion, death of plant life, stunting of seedlings, suffocation and poisoning of anchoring roots, and a reduction in absorptive ones. The top canopy of the mature trees that do survive deteriorates, producing fewer leaves and buds. Mangroves can take several decades to regenerate. Moreover, no way is known of cleaning polluted sediment from the forest floor without destroying the forest itself.

Seagrass beds found in shallow water, especially along tropical coastlines, can also suffer, with widespread impacts on both the immediate and surrounding environments. They stabilize the seabed, trap sediments, improve water quality, and directly nourish more than 340 species of marine fauna, which suffer when the food chain is disrupted. Some seagrass species are extremely fragile, dying on contact with crude oil and finding it very difficult to regenerate. Those with limited means of dispersal and low reproductive rates are particularly hard-hit in the long term, whereas species with higher reproductive rates recover more quickly.

Threat to nesting areas

Finally, the presence of oil in tropical coastal ecosystems can have serious consequences for species which nest in sand. Eggs absorb moisture from the surrounding environment, and with it any hydrocarbons present. Oil pollution in nesting areas can thus have catastrophic repercussions on reproduction. It delays the hatching of turtle eggs and causes abnormalities in the turtle shell, especially when the eggs are exposed to pollution during the early stages of development, though in the later stages, too, turtle embryos are very sensitive to the toxic effects of oil. Wild duck eggs are also susceptible to pollution. Embryos need to increase their oxygen intake as they develop, but oil can hinder their growth by blocking the egg pores, often resulting in death.

Thus, the oil industry threatens many of the most important marine ecosystems in the tropics

Elizabeth Bravo is Research Coordinator at the Oilwatch Secretariat, Quito, Ecuador.

Complementary articles in other issues:
Mark Moody-Stuart: Picking up the gauntlet (Climate & Action) 1998
John Browne: A new partnership to make a difference (Climate Change) 1997
Ruben Mnatsakanian: A poisoned legacy (Chemicals) 1997
Alemayehu Wodageneh: Trouble in store (Chemicals) 1997
Barbara Dinham: Getting off the pesticide treadmill (Food) 1996

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