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Oceanography

An almost dead sea

Pollution in the Bay of Santos leads to areas with no marine life

At some four kilometers from the beach, in the bay of Santos, in the state of São Paulo, Brazil, so much pollution accumulates at the bottom of the sea that it eliminates all animal life. This is one of the results of Ecosan, a project of the Oceanographic Institute of the University of São Paulo (USP), which brings together researchers from several areas to study the waters around the Bay of Santos. The group has monitored the sea from the town of Peruíbe to the town of São Sebastião, along some 200 km of shore, up to 200 m deep, in order to evaluate how the rubbish, sewage, and industrial waste discarded into the sea by one of the biggest industrial complexes and the country’s most active port are affecting sea life.

It is not hard to find what is to blame for the dead zone. That is where the sewage pipe built in 1979 discharges its load of domestic waste produced by the 1.2 million inhabitants of the Baixada Santista, the coastal area in and around Santos: 7 thousand liters per second are discharged into the bay. The high population density is the result of the dynamic economic activity in the region, which harbors the Cubatão industrial complex at the foot of the hills that rise 15 km inland from the coast. In the seventies, the pollution released into the atmosphere was already so major that it led to birth defects among the town’s newborns and caused that part of the Atlantic Forest (Mata Atlântica) to be nicknamed the “toothpick holder” due to the fallen trunks of dead trees. That is where the port of Santos is located, which, since it was first officially inaugurated at the end of the nineteenth century, has given passage to more than one billion tonnes of merchandise.

“When the port and the industrial complex were built, ecology was not a concern,” comments Luiz Miranda, coordinator of the team that analyses how sea waters flow in the region. Therefore, as early as the sixteenth century, a port had already appeared in the channel of the Santos estuary, thanks to its calmer waters, which were free of pirates such as those that recently ransacked an Oceanographic Institute boat during its night work at the entrance to the bay, causing collections to be restricted to daytime.

The chosen site is safe for the boats in the port, but puts nature at risk. The estuary canal connects the bay to the mangrove swamp that used to stretch along the rivers and canals throughout the flatlands that reach all the way to the foot of the Serra do Mar hills, nowadays taken over, in part, by towns and shantytowns. “This occupation is problematic, since the mangrove swamp is the ocean’s nursery”, says Rosalinda Montone, an expert on sewage pollution. As several species of fish, crustaceans, and molluscs, creatures of economic importance, reproduce in the less salty waters of the estuary, its pollution causes the population of these animal to fall in the bay and even in the open sea.

Nurseries in the dark
And Ecosan results have shown that pollution is concentrated in this area. Luiz Miranda found that when the high tides reach their peak and the low tides their lowest point (the spring tides), more particles are carried into the bay than are carried out of it. The problem is aggravated by the sewage carrier into the ocean, which forms a barrier that hinders water circulation in the bay and retains the residues. Thus, the ocean outfall is not diluted in the sea, which is what was intended when the pipe was built. “The effluents are discharged in the worse position”, regrets the oceanographer; “in developed countries, pipes take the outfall as far as 15 or 20 km away from the shore, not just the four km we see here”. The physical properties of the seafloor help to keep the waste there: 43% of the seafloor is mud, which absorbs whatever is in the water, including pollutants.

The consequence is that the bay is becoming shallower and shallower. “There’s no way to re-establish depth; the bay would have to be dredged”, concludes Miranda. That is exactly what the port administration does to ensure the area’s navigability. However, dredging is not that easy.

Stirring up the seafloor releases pollutants and spreads them again all over the bay. Moreover, a consensus as to the best place for discarding the dredged up material has not been reached. “They throw it into the open sea, beyond the bay”, says Rosalinda, “and the water becomes full of iridescent bubbles that look like little jellyfish”. These are gases released by the stirred up organic matter. One of the effects of this pollution is to interrupt fish migration routes. According to the researcher, mullets are no longer able to enter the Santos bay.

Analyzing the fish, June Ferraz Dias has found a diversity similar to that of other regions in Brazil’s Southeast. Some species prevail, such as the cangoá and the yellow-catfish. In the better conserved regions, such as Cananéia, in São Paulo’s southern coast, 80% of the fish captured belong to eight species. In Santos, the number of prevailing species is just three. June’s team is now analyzing heavy metals in fish muscle, but the team has been surprised to find a high aluminum content, whose origin the researchers are unable to identify precisely. Though fairly resistant to the adverse circumstances, the fish are not safe. Márcia Bicego, an expert in organic contaminants, tells us that pollution affects the morphology of the zooplankton, the microscopic fauna that composes most of the diet for small fish, which suffer from food shortage and may be contaminated. She emphasizes the importance of this in guiding public policies to limit the volume of pollutants emptied into the bay. “Even contaminant levels considered low may have severe effects”, she ponders.

The excess of organic matter is not harmful for all sea animals. José Eduardo Martinelli Filho finished his Master’s degree in 2007 at the laboratory of Rubens Lopes, one of the people responsible for the study of the zooplankton in the Santos estuary and the bay, and found the Vibrio cholerae bacterium, which causes cholera, in a substantial proportion of the species examined. “The sea is the natural environment for the bacterium; but organic pollution makes the bay especially suitable for its multiplication”, explains. There are no reasons to avoid the sea, since not all forms of the V. cholerae cause the disease. Theoretically, a bather who inadvertently swallows water infected with the zooplankton might develop cholera. However, no cases have been reported to date, probably because the aggressive form of the bacterium is rare.

Another organism that takes advantage of the increase in organic matter was found by the team of Ana Maria Vanin, Ecosan’s general-coordinator. A student of the organisms known as benthon that live on the seafloor, Ana Maria has found an animal that looks like moss, a bryozoan, and which forms a 2.5 cm thick carpet. “It creates microenvironments that serve as shelter for other organisms, such as small crustaceans”, she says. The species was already known, but the existence of so much of it was unexpected. In spite of the anomalous density, this carpet on the bottom of the sea, extending from near the beach all the way to a depth of 40 meters, seems to have no negative impact.

In general, the researcher detected less biodiversity in the region of Santos than that found on the northern shore of the state, in São Sebastião or Ubatuba. “Samples collected near the outfall smell bad”, she says. “This pollution inhibits diversity and fish and crustacean abundance.” At the more polluted points, the dominant specie is the blue-crab, probably unfit for human consumption. Ana Maria does not yet know how to explain why there are fewer crabs in the Santos bay than might be expected, given the diversity of species in the surrounding areas. The accumulation of sediment and pollutants in the estuary is most likely to blame for this lack of ecological richness.

The project members still have a lot of data to analyze, but a detailed picture has already emerged of the status of this part of the coast, a picture that can only be obtained through a large and diverse team of experts working together for several years. This should be reproduced in other areas. The team plans to prepare a book with a diagnosis of the Santos bay and the adjacent ocean platform to encourage researchers, authorities, and laypeople to find solutions.

The Project
The influence of the Baixada Santista estuary on the ecosystem of the adjacent platform (Ecosan) (nº 03/09932-1); Type Thematic Project; Coordinator Ana Maria Vanin – IO/USP; Investment R$ 753,782.89 (FAPESP and CNPq)