Dolphins disappear, and mangroves give life hope to Guanabara Bay

When the first promises of cleaning up the Guanabara Bay, in Rio de Janeiro, were in their infancy, around four hundred Guiana dolphins were still circulating in the polluted waters.

The mangroves, which covered the entire coast before the explosion of urban growth around it, amounted to about 60 square kilometers — less than a quarter of what they once were.

After 40 years of failed clean-up promises, the two symbols of what was once an unspoiled bay had different fates.

There are currently no more than 30 dolphins, heading towards disappearance in the coming decades. The mangroves, in turn, have already filled their protected area and are expanding to other regions.

The difference reflects the diversity of the environmental quality of the 328 square kilometers of the bay’s water surface, whose image is completely associated with sewage. It also shows the impact of pollution and nature’s ability to recover.

The main area of ​​remaining mangroves is in the APA (environmental protection area) of Guapimirim, at the bottom of the bay. Created in 1984, it guaranteed the survival of the ecosystem threatened by the extraction of wood for burning in the pottery ovens that operated around the bay.

In the 37 years of preservation, the entire area has been regenerated naturally or reforested. Currently, there is no space for replanting.

“Just stopping the action of removing the mangrove was enough to start the recovery. Some wounds were left where, from 2008, a direct intervention was made to recover”, said Maurício Muniz, an environmental analyst at the APA for 12 years.

Mangroves are important points for marine species. About three-quarters of them depend on this ecosystem at some stage in their lives.

A census carried out between 2008 and 2015 identified 167 species of fish, 34 of reptiles and 32 of mammals in the APA in the protected area at the bottom of the bay.

The preservation of the site is the result of a combination of low urban occupation around the rivers that flow into the APA and the natural flow of these water bodies. The volume of water from the five that reach the area represents about 60% of the total freshwater that flows into the bay through 55 rivers.

In addition, the conservation unit is close to the end of the central channel of the bay, through which intense exchange of water with the sea takes place. About half of Guanabara’s water is changed every 12 days.

“These two factors explain why we have more than 50 years of intense pollution in this ecosystem and yet it is still possible to see biological diversity,” said Muniz.

The better water quality around the APA attracted the approximately 30 Guiana dolphins that still live in Guanabara Bay.

According to José Laílson Brito Junior, coordinator of the Maqua Laboratory (Aquatic Mammals) at the Faculty of Oceanography at Uerj, the cetaceans are gradually no longer circulating throughout the bay, as they used to, to concentrate for longer near the protected area.

“They always circulated throughout the bay, leaving the bottom and going to the entrance. Currently, they spend more time in the APA area. It’s a change in behavior,” he said.

The presence of dolphins in the bay was so great that they have been part of the official coat of arms of the city of Rio de Janeiro since 1896. In the 1980s, a study indicated that there were still 400 of them in the bay.

Lailson and two colleagues decided to recount the cetaceans when cleanup promises resumed. In 1995, a year after the launch of the Guanabara Bay Depollution Program, they found about 100. Currently, there are only 26 identified and it is estimated the presence of about 30.

“This is what we call a vestigial population. At this rate, it is likely that by 2050 we will no longer have dolphins,” said the researcher.

The disappearance of the dolphins does not just represent the loss of a historic symbol of the city, says the coordinator of Maqua.

“The porpoises are sentinels of the bay. As they have a fixed residence, they feed on the animals that are there and are a good indicator of environmental health. And they are warning us that business is not good”, says Lailson.

One of the worst indicators of contamination is the presence of ascarel, a product used in transformers whose production and use have been controlled since the 1980s, but persists in the environment. It reduces fertility and practically condemns the first female offspring to death.

“When they have puppies, almost 80% of the contaminating load goes through breastfeeding. From the second, there is a smaller load, but still present”, says Lailson.

Symbol of a bay that no longer exists, the dolphin was forgotten in the dispute to be one of the mascots of the 2016 Olympics, held in Rio de Janeiro. The promise to treat 80% of the sewage discharged into Guanabara Bay by the time of the Games also fell by the wayside.

The international questioning about the conditions of the bay to host the sailing competitions in the Games led marine biologist Ricardo Gomes to dedicate himself to showing that, despite the problems, the bay was still alive.

“In 2015, those reports started saying that Guanabara Bay was dead, that it would be a shame to hold the Olympic Games there. I thought: ‘This message from her dead is not having any effect.’ dump,” he said.

Gomes filmed about 70 marine species both in points with reasonable water quality and in more polluted places, such as Praça 15.

“Right on the first dive I saw an incredible diversity. What surprised me the most were the stingray species. Despite all the problems, Guanabara is the fifth bay in the world with the greatest elasmobranch biodiversity because of the seven species of stingrays identified by UFRJ “, he says.

Life in the bay remained possible thanks to the intense exchange of water with the sea, mainly through the central channel through which the large vessels pass.

The most degraded area is around Ilha do Governador, where the most polluted rivers in the hydrographic basin are located. The best is in the central channel, in the areas close to the sea and in the APA de Guapimirim. Still, they live with problems.

Ocean engineering professor Paulo Rosman, from Coppe/UFRJ, says that, once the new clean-up promises are fulfilled, “in one year we can see a spectacular improvement in the bay”.

“Unbelievably, the bay has a lot of life. It is biologically very rich. In a year [sem esgoto] completely changes its figure”, he says.

José Lailson, from Maqua/Uerj, is more reticent.

“If one day the organic load reduces, it is likely that we will have an interaction of the new water with the contaminated sediments, which can postpone the depollution. It would be a long way. We do not use DDT [tipo de pesticida] there is a long time and the sign [dele nos botos] don’t download. It is very persistent in the environment”, says the researcher.

For Maurício Muniz, from the Guapimirim APA, the conservation unit could become a “Noah’s Ark” for the repopulation of species in the bay. He states that it is not necessary to wait for the conclusion of the sanitation projects to start improving the environmental condition.

“The processes of depollution of urban bays in the world show that, when it goes from very low levels to about 50%, a threshold that helps the self-purification of the environment, the leap in quality is already enormous”, he says.

“Improving the environmental condition of the bay is closer than we believe. The problem is that nothing was done. We stayed at medieval levels of sewage treatment for decades”, says Muniz.​