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Aquatic America

Habitat degradation could threaten the stability of the world’s largest fish diversity

066_PeixesLéo Ramos, taken at the São Paulo AquariumFish diversity in South America is greater than scientists had thought. Whereas less than 20 years ago the estimate of 8,000 species was considered an exaggeration, the more than 100 new species described each year over the past decade now enable us to estimate the continent’s ichthyofauna at about 9,000 species. A relatively low 4% to 10% of these species is endangered, compared to the percentages in North America (27%) and Europe (37%). In South America, however, increasing deforestation, urbanization, river damming and other factors are threatening that relative comfort, as discussed in an article by biologist Roberto Reis of the Pontifical Catholic University of Rio Grande do Sul (PUC/RS), published in a special issue of the Journal of Fish Biology in July 2016. The article presents new data on the conservation of aquatic habitats, which include not only rivers and the ocean, but also mangroves, estuaries, coastal lagoons, lakes and streams.

Estuaries, which are more sensitive than large bodies of water to human-induced changes, are important spawning and nursery habitats for fish living in rivers or the ocean. In addition, lagoons and streams host endemic species that that exist nowhere else and, therefore, could become extinct when these habitats are altered. “Especially along the northeastern and southeastern coast of Brazil, many unmapped lagoons have turned into swamps or have dried up completely as a result of dredging and silting, making it impossible to know whether they were inhabited by endemic species,” says biologist Ana Cristina Petry of the Center for Ecology and Socio-environmental Development on the Macaé campus of the Federal University of Rio de Janeiro (UFRJ).

In collaboration with a team of researchers working from locations ranging from the northern state of Piauí to Mar del Plata, Argentina, Petry compiled data from 103 lagoons along the continent’s Atlantic coast that encompassed 5,400 square kilometers of surface area and hosted numbers of species that varied from one to 76. One alarming point of information is that about 80% of the lagoons investigated lies outside of conservation units. “Coastal lagoons provide important ecosystem services such as spawning and growth habitats, not only for marine and freshwater fishes, but also for insects, amphibians, reptiles and birds, besides being fishing sites,” she explains. Several of the lagoons studied over a period of decades suffered profound changes in area and species diversity.

One threat is the introduction of exotic species, which compete with native species for food and spawning areas and cause imbalances in the system. In the small northeastern coastal lagoons of less than one square kilometer in size, these intruders represent 50% of all species.

Streams are another aquatic environment that is sensitive to human activity. They are smaller than rivers, normally located near forests, and the organisms living in them depend on the food they provide in the form of leaves, fruits and insects. Some streams form micro-basins independent of the large watersheds and are even more threatened by deforestation and pollution. Such is the case for the Mato Grosso River, which despite its name is a stream located in the state of Rio de Janeiro. Biologist Rosana Mazzoni of Rio de Janeiro State University (UERJ) analyzed the fauna from three different sections of the stream: one well preserved, with transparent water and no light penetration through the dense tree canopy; a second section with partially removed forest; and a third, completely deforested, with considerable light penetration and turbid water due to excessive amounts of algae and erosion of the banks.

Pirarucu: managed fishing in the Amazon, but no one knows how many species are endangered

Léo Ramos, taken at the São Paulo Aquarium Pirarucu: managed fishing in the Amazon, but no one knows how many species are endangeredLéo Ramos, taken at the São Paulo Aquarium

Mazzoni and her colleagues found significant differences between the sites in terms of fish density and feeding patterns. Although five fish species are present in each location, the deforested area favored the occurrence of sediment-tolerant animals, such as Suckermouthed Catfish (Hypostomus punctatus) and Red Fin Otocincluse (Parotocinclus maculicauda), another catfish species. While the principal food source for the fish in the preserved area consisted of invertebrates such as larvae, in the deforested area, that diet was replaced by detritus, organic matter and algae–which become abundant in the absence of forest coverage due to greater penetration of light for photosynthesis. “At least in this case, forest removal did not eliminate species; they were able to adapt,” Mazzoni says. “Nevertheless, the density of some species varies considerably according to local conditions.” Just as catfish are present in greater quantity in degraded areas, the lambari species Astyanax taeniatus and Characidium vidali, which are abundant in the preserved area, are becoming rarer with increasing deforestation.

Biologist Mário Barletta, editor of the special issue of the Journal of Fish Biology and a professor at the Federal University of Pernambuco (UFPE), calls attention to the need to base conservation policies on scientific data, which is not always done. “Economic development is necessary, but it should always take the environmental impact into account,” he advises. Barletta is referring mainly to large infrastructure works, which are not always undertaken with the benefit of prior research. In one case where that occurred, he was able to do the fauna survey in a section of estuary before, during and after a dredging operation for construction of a port terminal in the estuary complex of Paranaguá Bay in the state of Paraná. The salinity gradient of estuaries, which provide a transition between river and ocean, favors fish and crustaceans.

Dredging to remove bottom sediments is done in port areas to increase channel depth and enable large ships to anchor. “The accumulation of sediments at the bottom happens in part because the riverbanks are deforested. A forest does the work of securing this material and preventing it from moving into the water,” Barletta explains. Without vegetation in the surrounding areas, dredging may again be needed sometime later, because sediment will again tend to accumulate in the riverbed.

During the study of the Paranaguá Bay estuary, which is an important area for artisanal fishing as well as a spawning and nursery habitat for marine and estuarine fish, economically important species such as Southern Kingfish (Menticirrhus americanus) and Smooth Weakfish (Cynoscion leiarchus) practically disappeared during and soon after the work. At the same time, the density of sea catfish species Cathorops spixii and Aspistor luniscutis increased as much as tenfold during the work. Barletta and other researchers involved in the study concluded, therefore, that dredging should be done from the late rainy season to the early dry season, when there is no spawning activity in the area. “Thanks to the prior study, we determined the best time for doing the work and reducing the impact,” he says.

Tambaqui: genetic diversity may be affected by encroachment in the Amazon Basin

Léo Ramos, taken at the São Paulo Aquarium Tambaqui: genetic diversity may be affected by encroachment in the Amazon BasinLéo Ramos, taken at the São Paulo Aquarium

Even when spawning season is respected, there is a growing threat to the early life of these animals: the presence of plastic in the waterways. In another paper published in the same issue, Barletta sought to determine which species were present in the mangrove stands in the estuary of the Goiana River along the coast of Pernambuco State, relative to moon phases. He points out that studies of fish populations normally take into account timescales of months to years, but rarely consider lunar cycles or periods of days and weeks. It is during these short intervals, however, that a more direct relationship can be seen between the environment and its resources (food, shelter, protection from predators and other behaviors).

In addition to quantifying the species, researchers found micro and macroplastics (pieces smaller and larger than five millimeters, respectively) in all of the areas studied, in densities similar to those of the eggs and larvae of sardines (Rhinosardinia bahiensis), the third most abundant species. The waning phase of the moon, when there are fewer zooplankton (larvae and very small organisms), is precisely the time when more microplastics are found, caused by degradation of plastic bottles, bags, and fishing line and nets due to the action of sun and water.

The presence of this detritus in the mangroves is especially worrisome because larvae and the offspring of fish and of other aquatic organisms live in these environments until they reach a safe enough age to migrate to a river, an estuary or the ocean. “Since microplastics share the habitat with fish and larvae, they can be ingested and enter the food chain, along with any pollutants they contain, such as cadmium, copper and zinc,” Barletta explains. This means that pollutants will not only reside in the beings that eat the microplastics, but they will be passed on to their predators, and continue up the predator chain until they reach humans.

Pirarara (Redtail Catfish): diet includes other fishes, which raises the risk for mercury contamination

Léo Ramos, taken at the São Paulo Aquarium Pirarara (Redtail Catfish): diet includes other fishes, which raises the risk for mercury contaminationLéo Ramos, taken at the São Paulo Aquarium

For this reason, conservation projects need to take the human factor into account. Although fishing is prohibited for bonytongue fish, or pirarucu (Arapaima sp.), in the state of Amazonas, for example, they are widely commercialized in that state. One possible solution lies in what is known as community-based management. Biologist Thiago Petersen, currently a doctoral researcher at the National Institute for Research on the Amazon (INPA), closely monitored the recovery of the pirarucu population at the Piagaçu-Purus Sustainable Development Reserve, one of the few places where this lake-dwelling fish can be caught in Amazonas.

“The pirarucu population in each lake is counted, and then a management plan is created with community involvement to determine which lakes will allow fishing for commercial purposes and/or community consumption, and which will ban fishing,” Petersen says. In places where this management model has existed longer, such as the Mamirauá Sustainable Development Reserve, also located in Amazonas, up to 30% of the fish population per year may be removed. Areas beginning to use management, such as Piagaçu-Purus, stipulate a more conservative limit of 8% to 10%. The effort has paid off in this case: between 2008, when a management model was implemented, and 2014, fish populations increased between 62% and 99%.

Although there have been a few successful attempts at preservation, Leandro Castello, who is a coauthor of an article on pirarucus and a professor at Virginia Polytechnic Institute and State University, cautions that there is not enough information to more accurately determine how many species are endangered. “In the Amazon, for example, there is relatively little degradation of these ecosystems, but the situation is changing quickly, and it’s only a matter of time before the landscape is completely altered,” he points out. One factor that directly affects Amazonian fish is hydroelectric power plants. “The fish even swim over the dams to lay their eggs in the upper part of the river,” says Roberto Reis. “When the eggs move down the river and reach a hydroelectric plant, however, the current dies down and they sink to the lower depths, which are devoid of oxygen, and they die. The remaining ones end up being eaten by the millions of piaba fish that live in the reservoirs.”

Scientific articles
REIS, R. E. et al. Fish biodiversity and conservation in South America. Journal of Fish Biology. V. 89, p. 1-16. July 2016.
LOBÓN-CERVIÁ, J. et al. Effects of riparian forest removal on the trophic dynamics of a Neotropical stream fish assemblage. Journal of Fish Biology. V. 89, p. 50-64. July 2016.
BARLETTA, M. et al. Effects of dredging operations on the demersal fish fauna of a South American tropical-subtropical transition estuary. Journal of Fish Biology. V. 89, p. 890-920. July 2016.
LIMA, A. R. A. et al. Changes in the composition of ichthyoplankton assemblage and plastic debris in mangrove creeks relative to moon phases. Journal of Fish Biology. V. 89, p. 619-40. July 2016.
PETERSEN, T. A. et al. Recovery of Arapaima sp. populations by community-based management in floodplains of the Purus River, Amazon. Journal of Fish Biology. V. 89, p. 241-48. July 2016.
PETRY, A. C. et al. Fish composition and species richness in eastern South American coastal lagoons: Additional support for the freshwater ecoregions of the world. Journal of Fish Biology. V. 89, p. 280-314. July 2016.