The Ecological Mysteries of Latin America’s Rivers

Monti Aguirre
Thursday, December 8, 2011

Latin America’s watersheds are rich in biodiversity, yet it is remarkable how much we don’t know about the ecology of these rivers. Aquatic and terrestrial species interact in still-mysterious ways, their relationships dependent on rivers’ patterns of flood and drought, of slow and fast currents, of sediment deposit and wetlands and mangroves creation.

With the disruption of healthy riverine ecosystems from deforestation and damming, scientist’s opportunity to understand and appreciate these interactions is rapidly disappearing. Yet, plans to dam most Latin American rivers are proliferating like an infestation of termites.
We interviewed a few key scientists working in the area to reflect on the work they do, and the challenges they see. Here is what they told us.

On Extinction and Orchids

American botanist Lou Jost works as a mathematical ecologist, plant biogeographer and conservation scientist. A fellow of the Population Biology Foundation in Ecuador, he is also one of the world's top orchid hunters. In the past decade, Dr. Jost discovered 60 new species of orchids and five other new plant species.

Extinction is the worst crime that humans can inflict on nature. Once a species is gone, it can never come back, and its unique genetic information, accumulated during millions of years of evolution, is erased from the planet. Luckily most water projects do not commit this ultimate crime, but when a project comes along that does put the survival of a species at risk, the world should react.

The animals and plants most vulnerable to this kind of extinction are the species found only in one river and nowhere else in the world. This kind of local endemism is relatively rare.

However, in the eastern Andes of Ecuador, where I live, the hydroelectric projects planned for the Upper Rio Pastaza and for its tributary, the Rio Topo, threaten several locally endemic species. The Abitagua Dam will affect the only place in the world where the orchid Epistephium lobulosum has been found. This mysterious plant was discovered in 1959.

An even more mysterious plant, the critically endangered Myriocolea irrorata, is endemic to the Rio Topo. The extinction of such a distinctive species is a crime even worse than the extinction of a species that has other close relatives. None of this apparently matters to the Ecuadorian government, which has made a conscious decision to approve all hydroelectric projects in the country.

What happens when these species disappear? We really don’t know. The Epistephium orchid on the Rio Pastaza is so rare that it probably plays no role in the local ecosystem, but it nevertheless represents a significant segment of evolutionary history, with unique features and biochemistry that we know nothing about. The Myriocolea, on the other hand, is locally abundant along the Rio Topo, and may well be part of an intricate set of relationships with other organisms. Because it has no close relatives, its biochemistry may be very interesting, but again we know nothing about it.

When we destroy these unique species and their associated ecosystems, we throw away their evolutionary secrets forever. We are like ignorant people burning books before we have even learned to read them. No civilized society would dream of massive government-supported public book-burnings these days. Why then do we so freely destroy the much more remarkable, irreplaceable works produced by nature and evolution?

Mysterious Catfish

Peruvian ichthyologist Norma Salcedo works at the Grice Marine Laboratory, College of Charleston in South Carolina. Much of her field research is in the tropical Andes.

For the past 10 years I have been working on a group of armored catfishes commonly known as “rubbernose plecos.” These fish only live in highlands, like the slopes of the Andes, where the turbulence of the waters and the low temperatures make the water very oxygenated, where the slope is not too high (otherwise it is salmon territory), not too low (where the sediment is too fine and the oxygen low). These fish feed by rasping the algae that grow on the surface of rocks in regions where cold water runs very fast, so fish diversity is not very high. This fragile ecosystem, known as the tropical Andes, is the largest, most continuous one they inhabit.

There is so much we don't know about the fish I study! How far do they migrate? Do they migrate at all? How do they reproduce? All the species in this genus depend on well-oxygenated, coarse bottom streams and rivers, as they use their mouths to attach themselves to the rocks. Little is known about the hydrology of these regions and how it correlates with the aquatic fauna in it.

Aquatic invertebrates are very good indicators of water quality. Think about it: larvae and adults of beetles, butterflies, mayflies, dragonflies, gnats, horse flies – all these feed the vertebrate fauna and pollinate plants. In other words, the whole forest depends on the water and the organisms in it at different levels.

I have worked mainly in higher elevation regions, the regions known as cloud forests. The water in the streams comes from the melting of the snow in the high peaks. The whole forest depends on the water in one way or another. The evaporation of this water keeps the vegetation moist. Fish, of course, live in it. Other vertebrates, like birds and mammals drink the water and feed on organisms that grew using the water in the streams and rivers. So, it is all connected.

Migration and Dams

Bill McLarney is an aquatic biologist working with Costa Rican nonprofit organization Asociacion ANAI, which has pioneered some of the world’s most successful and highly participatory community based development initiatives in tropical zones. Dr. McLarney has dedicated many years to work hand in hand with the inhabitants of Costa Rica’s Talamanca region, a UNESCO World Heritage Site and Biodiversity Hotspot.

In Mesoamerica we know very little about key river species. For example we don’t have a complete life history for any of the fish and shrimp species of La Amistad International Park, a World Heritage Site shared by Costa Rica and Panama. And what we do know, we fail to place in the context of a dynamic system. We fail to recognize that the change we choose to make at one point on the river changes the river over its entire length.

The threat to La Amistad has become more serious with the disclosure of multiple dam plans on the Atlantic slope of the La Amistad area in Costa Rica.

Diadromes (fish and shrimp which migrate between fresh and salt water) are a mechanism for transporting organic matter between the continental mass and the sea. The water also performs this function, in a downstream direction, but only diadromous animals transport organic matter back upstream in their bodies. Extermination of diadromous fish and shrimps from the upper reaches of streams in the La Amistad area would effectively remove most of these “bioturbators,” resulting in greater retention of accumulated sediments at high altitudes, with unpredictable but significant effects on sedimentation patterns, channel dynamics and biotic interactions both within and downstream of the World Heritage Site.

Certain species are more sensitive to certain stresses, and so will be the first to be lost when those stresses occur. Often a loss of species doesn’t harm or even get noticed by anybody, other than those few of us who care about species for their own sake (and of course the other species that depend on it). What is scary is when we grossly alter ecosystems, as when we dam a river across a migratory route.

Rivers and forests are a continuum, and if you change the composition of the riverine fauna, you change the forest. And vice versa. The changes can only be partially predicted, and mainly on a case-by-case basis.

In the Caribbean National Forest in Puerto Rico, when Atyid shrimp were eliminated from rivers above dams, the river got wider and eroded into the forest. Atyids burrow constantly in the rocky substrate, in search of food and shelter. In so doing, they mobilize sediments that are carried downstream. Researchers in Puerto Rico demonstrated that sites without Atyids tended to accumulate sediments, whereas sites with Atyids flushed them. Filling of pools with sediment naturally results in water expanding to the sides, thus stressing stream banks during high flows. There are lots of other effects, too, especially related to processing of leafy detritus, and changes in algal cover. Similar effects have been attributed to Loricariid catfish in Panama, Sicydium gobies in Costa Rica, and others.

The central point is that mucking around with central elements of ecosystems is risky business.

The idea behind Environmental Impact Assessments (EIAs) is a good one and would work well if we as a society made decisions based on rational discussions. In the real world, they are usually treated as merely a formality in the licensing process. If I have to build a dam, I am required to hire a consultant to do an EIA. Do you suppose that consultant doesn’t know who signs his check? If the consultant is a good one, he may offer alternatives leading to a less damaging project, but he is not going to say “Don’t build the dam, society will be better off without it.” Even if we had some sort of independent review body for EIAs, we don’t have a rational or democratic process in place for dealing with such a review. More often than not the projects which get seriously proposed are heavily favored by the governments in question and the ultimate decision is made by a very few people. In my experience, the chief value of EIAs is that debate over them can buy time.

Migration and Seed Dispersers

Flavio Lima is an ichthyologist at the University of Sao Paulo in Brazil. He has worked on the natural history and conservation of South American freshwater fishes since 1993.

I have worked with the taxonomy of several groups of South American freshwater fishes, especially the large characid fishes, the genera Brycon.

Brycon are middle- to large-sized fishes whose preferred habitat range from small forested rivers at headwater areas to large rivers with extensive floodplains in lowland areas. The larger species living on large rivers undertake long-range migrations to the spawn areas and are extremely prolific, large females being able to release almost a million eggs in a single reproductive bout.

The genus Brycon is the most widespread fruit-eating fish lineage of the Neotropics. Brycon species are actually omnivores that ingest a broad range of food items, including smaller fish, and occasionally even terrestrial vertebrates as frogs and rats. Predominantly their diet consists of terrestrial vegetal matter, most notably fruits and seeds. It has been assumed that Brycon species are important seed dispersers of trees in large periodically flooded forests of the Central Amazon, and they probably also play a similar role in riverine ecosystems all over their geographical range.

Species of Brycon were always considered to be good indicators of healthy aquatic ecosystems due to their dependence of good-quality water, riparian forest and natural flow regimes. They can certainly be thought of as "canaries in the coal mine."

Fishes living in rapids all over South America should be considered indicators of the quality of aquatic ecosystems. Species belonging to all these families are expected to decline substantially or even disappear completely if the pace of disturbance of the riverine ecosystems of South America proceeds unabated, especially in regard to the building of large dams.

The Brycon vermelha are endemic from small coastal river systems from eastern Brazil that have historically suffered from deforestation, siltation, and pollution. More recently, damming has become an additional, ultimate impact to affect these species. The conservation status of these species is really a matter of high concern. For example, a hydroelectric dam is currently being built at the core area of occurrence of Brycon vermelha, at a river stretch of the Rio Mucuri, a small coastal drainage of eastern Brazil – in spite of the fact that this fish is considered officially threatened with extinction in Brazil since 2004.

In my experience of several years observing how Environmental Impact Assessments are made and what benefits they produce, they fail almost completely in serving any purpose in conservation. At best, they provide an opportunity to make good samples of areas that were poorly known previously. Even those opportunities are commonly lost, however, because the specimens collected are not adequately preserved or never sent to zoological/natural history scientific collections.

Also, EIAs often are biased to views palatable to the contractors of the study, and too often omit or de-emphasize a project’s impacts. For example, the recent EIA for the Belo Monte dam barely mentioned that there are two fish species officially considered as threatened. These are only known from the stretch of the Rio Xingu, which will have its flow dramatically reduced if the project is built. And this is only the tip of the iceberg, since we barely know the fish diversity and natural history of the area, and the EIA has done very little to change this situation. In fact, our knowledge of fish diversity and ecology is extremely out of pace with the environmental disturbance predicted to happen due to the construction of several dams, both small and large, all over Brazil.

To provide adequate conservation measures, it would be fine if we already possessed the current level of knowledge on South American freshwater fishes. But we are 50-60 years delayed in this scientific quest, and no doubt we are going to pay dearly for this, with possibly hundreds of species vanishing before anything can be done for their conservation. In my view, only a huge change in mentality, a change in the economic and development paradigm, as the one now being asked by groups all over the world, can avert this gloomy prediction from taking place.