Loss of North American Freshwater Biodiversity

By Chris Schenker, SRC intern

Despite garnering less attention than their marine counterparts, freshwater species are diverse, important, and also under threat. Despite covering only 0.8% of the world’s surface and accounting for about 0.01% of the world’s water, freshwater contains at least 100,000 distinct species (Dudgeon et al. 2006). Comparisons to other environments are difficult because of the variation surrounding estimates of the total number of species on Earth. However, given freshwater’s disproportionately small share of total volume and surface area, it is beyond doubt to assert that its species density is staggeringly high. Although the interrelationships are not completely understood, freshwater biodiversity plays a crucial in ecosystem function as a whole. Despite the value that freshwater flora and fauna add from a scientific, commercial, aesthetic, cultural, and recreational perspective, the species extinction rate is far higher than that for their terrestrial counterparts (Dudgeon et al. 2006).

Figure 1: Freshwater fish are under threat worldwide, but the trend is especially pronounced in North America. (

This dynamic is especially clear in North America, where aquatic environments are well-studied. Although freshwater biodiversity is higher in the tropics, North America has the highest nontropical species diversity (Lundberg et al. 2000), totaling 1,213 as of 2010 and accounting for 8.9% of the world’s freshwater fish species (Nelson et al. 2004). There is a long history of species documentation in North America, with the first observed extinctions occurring in the early twentieth century. Since then, 39 species of North American freshwater fish have been declared extinct (IUCN 2011), yielding a continental extinction rate of 3.2% (Burkhead 2012). This is a higher total than is observed globally, but that is only because of North America’s longer history of continuous faunal study in comparison to the tropics. Regions with similar histories of scientific documentation display similar trends, with 3.4% of species considered extinct in Europe (Freyhof and Brooks 2011), and 3.2% of species considered extinct in the European basin (Smith KG and Darwall 2006).

The metric that really matters is the modern extinction rate in comparison to the background extinction rate. The background extinction rate, often abbreviated BER, is the taxonomic extinction rate over geologic timescales before the introduction of human pressures. Knowing both values allows scientists to calculate the ratio of modern extinction rate to background extinction rate (M:BER). There are difficulties in calculating both rates, so numbers should be interpreted with a grain of salt, but this ratio gives a rough estimate of how much faster extinction is occurring due to humanity’s global remodeling. The M:BER ratio for North American freshwater fishes has been calculated to be as high as 877 (Burkhead 2012), making it the highest number for any contemporary vertebrate group (Barnosky et al. 2011). Despite the large number of estimates and assumptions underlying this number, it highlights the severity of the problem species are facing. Fishes labeled as threatened, endangered, and declining will be subjected to the most intense pressure, especially those that are endemic and lie in the path of future human expansion.

Figure 2: This table compares the modern extinction rates for world vertebrates to their estimated background extinction rates. (Burkhead 2012)

As imperiled as freshwater fishes are, they are only the beginning when it comes to declining freshwater flora and fauna. Many molluscs, such as snails and mussels, are going extinct at a rate that is an order of magnitude greater than that of freshwater fishes (Burkhead 2012). The main cause of this plight is human alteration of rivers and lakes, along with runoff, pollution, and the introduction of invasive species, such as zebra mussels (Cope et al. 2008). Mussels play an important role in their aquatic communities, such as providing habitat, filtering the water column, and depositing nutrients into the sediment. There is much scientific interest in what will happen to freshwater ecosystems as mussel species diversity and biomass declines.

The effect that mussels have on water filtration and waste recycling can vary widely based on the species, abundance, and environmental conditions present at the time. When water flow is low, such as in late summer, mussel communities can filter the entire volume. When water flow is high during times of melting and drainage, however, their effect is greatly reduced (Vaughn et al. 2004). Filtration performance is further affected by water temperature, with each species having its own optimal temperature. This means that in aquatic environments with multiple species of mussels, the ecosystem wide impacts of their filtration will vary widely based upon the relative dominance of each species, water flow, and temperature. Further complicating the equation is the fact that mussels also excrete ammonia, and their excretion rates can move in tandem with filtration rates, in the opposite direction, or not at all. It is all temperature dependent  (C.C. Vaughn 2010). The ammonia excreted by mussels plays an important role in lake and riverine ecosystems, boosting primary production and also benefiting consumers down the line (Spooner and Vaughn 2006). Even if excretion and filtration rates can be modeled for a set of known variables, it is important to remember that mussel communities can change in biomass and species dominance over time, and hydrological conditions are also dynamic.

Figure 3: This conceptual model demonstrates the complicated interplay between mussel species density, community structure, and ecosystem processes. (C.C. Vaughn 2010)

This example serves an important point. Attempting to understand how an aquatic environment will respond to changes in species composition is difficult. With so much uncertainty about the effects of biodiversity loss in North American freshwater ecosystems, we as a society have no idea what we may be getting ourselves in for. It is therefore prudent to prioritize the conservation of at-risk populations so that we do not have to contend with the damage that their losses may entail.

Works Cited

Dudgeon, David & Arthington, Angela & Gessner, Mark & Kawabata, Zen-Ichiro & Knowler, D & Lévêque, Christian & J Naiman, Robert & Prieur-Richard, Anne-Hélène & Soto, D & Stiassny, Melanie & A Sullivan, Caroline. (2006). Freshwater Biodiversity: Importance, Threats, Status and Conservation Challenges. Biological reviews of the Cambridge Philosophical Society. 81. 163-82. 10.1017/S1464793105006950.

Lundberg JG Kottelat M Smith GR Stiassny MLJ Gill AC. 2000. So many fishes, so little time: An overview of recent ichthyological discovery in continental waters. Annals of the Missouri Botanical Garden  87: 26–62.

Nelson JS Crossman EJ Espinosa-Pérez H Findley LT Gilbert CR Lea RN Williams JD. 2004. Common and Scientific Names of Fishes from the United States, Canada, and Mexico, 6th ed.

American Fisheries Society. Special Publication no. 29.

[IUCN] International Union for Conservation of Nature. 2011. IUCN Red List of Threatened Species, version 2011.2. IUCN. (13 June 2012;

Freyhof J Brooks E. 2011. European Red List of Freshwater Fishes. Publications Office of the European Union.

Smith KG Darwall WRT eds. 2006. The Status and Distribution of Freshwater Fish Endemic to the Mediterranean Basin. International Union for the Conservation of Nature. (14 June 2012;

Noel M. Burkhead, Extinction Rates in North American Freshwater Fishes, 1900–2010, BioScience, Volume 62, Issue 9, September 2012, Pages 798–808,

Barnosky AD et al. .2011. Has the Earth’s sixth mass extinction already arrived? Nature 471: 51–57.

Cope WG et al.  2008. Differential exposure, duration, and sensitivity of unionoidean bivalve life stages to environmental contaminants. Journal of the North American Benthological Society 27: 451–462.

C.C. Vaughn. Biodiversity losses and ecosystem function in freshwaters: emerging conclusions and research directions. Bioscience, 60 (2010), pp. 25-35, 10.1525/bio.2010.60.1.7

Vaughn CC Gido KB Spooner DE. 2004. Ecosystem processes performed by unionid mussels in stream mesocosms: Species roles and effects of abundance. Hydrobiologia 527: 35–47.

Vaughn CC Spooner DE. 2006. Unionid mussels influence macroinvertebrate assemblage structure in streams. Journal of the North American Benthological Society  25: 691–70

The imperiled fish fauna in the Nicaragua Canal Zone

By Nicole Suren, SRC intern

Plans for a new canal through the isthmus of Nicaragua have just been approved by the Nicaraguan government with little to no restrictions on what preexisting waterways can be used as part of this potential new shipping route. The currently proposed route was planned based on economic and technical considerations, but ecological concerns were not factored into the planning, leading to a variety of potential ecological problems due to the construction of the canal. These ecological detriments include overexploitation of the environment, increased water pollution, water flow modification, destruction or degradation of habitat, and the establishment and spread of non-native species. The currently proposed route is of special concern because it not only passes through Lake Nicaragua, a freshwater ecosystem of very high socioeconomic importance, but also because it connects two currently isolated drainage basins, the San Juan drainage basin and the Punta Gorda drainage basin.

Proposed route (solid line) and alternative routes (dashed lines) of the Nicaragua Canal. The 3 drainage basins involved are San Juan (red), Punta Gorda (blue), and Escondido (yellow). Fish-sampling locations are marked with open diamonds. (Härer et al. 2016)

Proposed route (solid line) and alternative routes (dashed lines) of the Nicaragua Canal. The 3 drainage basins involved are San Juan (red), Punta Gorda (blue), and Escondido (yellow). Fish-sampling locations are marked with open diamonds. (Härer et al. 2016)

This study was conducted in order to establish a baseline of biodiversity in the two potentially affected drainage basins, as well as the surrounding basins, so that changes in biodiversity due to the construction of the new canal can be accurately measured and compared against previous levels. The researchers measured biodiversity by taking surveys of the fish in each ecosystem in question with nets, and then sampling two species each from three families of fish that are common in the area. These samples were then used in a DNA analysis, where common sequences of DNA from each species were analyzed for differences. In general, the more similar the DNA sequences, the more closely connected two populations are, and the less similar the DNA sequences, the less closely connected the populations are. Based on the DNA analysis, “populations within the same basin showed almost no genetic differentiation, whereas comparisons across basins exhibited higher differentiation.” This means that populations of fish within the same drainage basin are very similar to each other, while they are quite different from fish in other, unconnected drainage basins. They also found that Punta Gorda and San Juan have 27 species in common, but they also have 24 and 31 species, respectively, that only occur in one basin.

Diagrams showing connectivity between basins (A-C) and within different locations in the San Juan drainage basin (D-F). The sizes of the circles are proportional to the sample sizes, and the proximity of the circles to each other represent how closely connected they are genetically. (Härer et al. 2016)

Diagrams showing connectivity between basins (A-C) and within different locations in the San Juan drainage basin (D-F). The sizes of the circles are proportional to the sample sizes, and the proximity of the circles to each other represent how closely connected they are genetically. (Härer et al. 2016)

Measures of biodiversity are important because they can be a direct indicator of how healthy an ecosystem is. In other words, a diverse ecosystem is a healthy ecosystem. Since the San Juan and Punta Gorda ecosystems contain populations that are so distinct from one another (which is one of the ways biodiversity is defined), the proposed connection between the two is potentially detrimental to the health of those environments because the physical barriers maintaining their diversity would be removed, thereby reducing their diversity and health. Because of these effects, the authors strongly recommend that the precautionary principle be used, and that a more ecologically sound route for the canal be chosen before starting construction.

Works Cited
Andreas Härer, Julián Torres-Dowdall, Axel Meyer. “The Imperiled Fish Fauna in the Nicaragua Canal Zone.” Conservation Biology, vol. 00, no. 0, 2016, pp. 1-10, doi:DOI: 10.1111/cobi.12768

The Zoo Debate: Educators or Entertainers?

Evidence for the Positive Contributions of Zoos and Aquariums to Aichi Biodiversity Target 1

 By Emily Rose Nelson, RJD Intern

 The UN Strategic Plan for Biodiversity 2011-2020, adopted by the Convention on Biological Diversity in 2010, is a ten-year model aiming to protect biodiversity and the benefits it provides. The plan is essential in global efforts to halt and, optimistically, reverse the current loss of biodiversity. 20 target goals, known as the Aichi Biodiversity Targets, have been put in place with intent to increase value people put on biodiversity, maintain ecosystem services and support global action for a healthy planet. The first of these targets is as follows, “ by 2020, at the latest, people are aware of the values of biodiversity and the steps they can take to conserve and use it sustainably.” Achieving such an ambitious goal as this will not be possible without work from zoos and aquariums.

UN Biodiversity

The United Nations General Assembly has declared this the “Decade on Biodiversity.”

Annually zoos and aquariums around the world receive over 700 million visitors (Gusset and Dick, 2011) providing them with the potential to make a huge impact in achieving Aichi Target 1. A 2007 study found that 131 out of 136 zoo mission statements reference education and 118 out 136 specifically mention conservation (Patrick et al, 2007). However, many of these institutions market themselves for entertainment and weaken messages of environmental education.

Moss and collaborators (2014) set out to evaluate the educational impacts of zoos and aquariums. 5,661 visitors to 26 zoos in 19 different countries all over the world were given the same open-ended surveys before and after their visit. Participants were asked to list up to five things that came to mind when they thought about biodiversity and list two actions they could take to help save animal species. Content analysis was used to provide quantitative data from these responses.

Results of the study showed that understanding of biodiversity and knowledge of actions to help protect biodiversity both significantly increased over the course of zoo and aquarium visits, providing evidence that zoos and aquariums are largely serving their role as educators as well as entertainers. The outcome shown by Moss et. al calls attention to the importance of zoos and aquariums in achieving Aichi Target 1.

PrePost Visit Bar Graph

Both dependent variables, biodiversity understanding and knowledge of actions to protect biodiversity, show significant difference between surveys before and after visiting a zoo or aquarium.

However, an increase in knowledge regarding biodiversity is not necessarily an indicator of a related change in behavior to protect biodiversity. Zoos and aquariums face the challenging task of moving people to action. One way in which they are already doing this is providing people with a connection to nature. If one feels attached to something they are more likely to care about its conservation (Falk et al, 2007). Additionally, zoos and aquariums can play a part in pro-conservation action by advocating for policy changes that protect land and wildlife, targeting and providing alternatives to threatening social norms, and serving as a role model for their visitors and other institutions.

Works Cited:

 Falk, J. H., E. M. Reinhard, C. L. Vernon, K. Bronnenkant, N. L. Deans, and J. E. Heimlich. 2007. Why zoos and aquariums matter: assessing the impact of a visit to a zoo or aquarium. Association of Zoos & Aquariums, Silver Spring, MD.

Gusset, M., and G. Dick. 2011. The global reach of zoos and aquariums in visitor numbers and conservation expenditures. Zoo Biology 30:566–569.

Moss, Andrew, Eric Jensen, and Markus Gusset. “Evaluating the Contribution of Zoos and Aquariums to Aichi Biodiversity Target 1.” Conservation Biology (2014).

 Patrick, P. G., C. E. Matthews, D. F. Ayers, and S. D. Tunnicliffe. 2007. Conservation and education: prominent themes in zoo mission statements. Journal of Environmental Education 38:53–60.