Ecological Overview (Why should be care about the ecological impacts of GMOs?)
The preservation of aquatic ecosystems is crucial to maintaining both land and aquatic organisms. The introduction of genetically modified organisms into an environment may alter various areas of ecology, including population dynamics, biodiversity, and the materials that sustain living organisms. The study of ecology focuses on the effects of organisms on their environments, as well as on each other. Variations in any of these categories affect the cellular and organismal levels within populations dependent upon them. One key issue to note is the decrease in biodiversity as many specialist species (species that perform one specific function in the environment) are declining, while population numbers of generalist species (species that fill many niches and perform many functions) are rising and filling the niches of specialist species.

How Do Genetically Modified Organisms Affect The Ecosystem?
One indirect effect of GMOs on aquatic ecosystems is the use of pesticides. A major use of GM crops is pesticide resistance. The allows for pesticides to be sprayed freely onto crops to kill weeds without harming the crop itself. With this "free" use of pesticides, there are many indirect effects that take place that need to be discussed. Relyea’s lab (2005) studies the severe lethal effects of Roundup on North American tadpoles. The study showed how 96-100% of larval amphibians died after being exposed to Roundup (Relyea, 2005). With that high of a percentage, it is likely that other aquatic organisms could be affected as well by the run-off of pesticides into the water where they live. This is a indirect effect of GMOs, but still can be traced back to the genetic modification of crops and the consequences they may have. The pesticides/herbicides are decreasing the population numbers of organisms, such as the North American tadpole, and may be affecting many other species as well (Relyea, 2005). This has the potential to reduce diversity in the aquatic ecosystem and consequently cause a variety of cascade effects that will cause negative impacts in species that directly consume these endangered organisms. A decline in amphibian diversity could impact the population dynamics of the ecosystem by changing which species thrive under these conditions and which are no longer able to successfully maintain their populations.

Amphibians are also at risk for toxic effects from pesticides via absorption through their skin (Brühl, 2011). Since this process is passive and cannot be strictly regulated by the organism, these pesticides can impact the organisms body systems very quickly. Another study done by Relyea (2009) showed the impacts that insecticides can have on aquatic communities. An example of an organisms suffering from these impacts is gray tree frogs. The size of the frogs that were introduced to insectices were approximately twice their normal size depending on the varying mixture of chemicals they were exposed to. By increasing their body size because of insecticide exposure, they may have a harder time finding food to eat because they can no longer reach small spaces. On the other hand, their larger size may make them an easier target for predators, which may lead to a decrease in population size and a change in the population dynamics in the ecosystem.

The North American Tadpole

As a direct effect, GMO crops have been proven to be lethal to insects. Rosi-Marshall (2007) describes how GM corn byproducts, like pollen and waste from the corn, are introduced in freshwater streams and can cause negative effects on insects, as discussed in the Organismal Effects page. These caddisflies are a very important part of the stream ecosystem and serve as prey for many aquatic predators (Rosi-Marshall, 2005). Knowing this, the mortality of caddisflies (among others that have not been studied yet), will force stream fish to either relocate to an area of the stream with a sufficient food supply, or simply decrease their population size to live off the food supply available. Reducing their population size would alter population dynamics as well, resulting in a relocation or redistribution of the species in these ecosystems. If the mortality of caddisflies continues leading them to endangerment or extinction, it will also reduce biodiversity in these ecosystems, making the ecosystem less resilient.

Aquatic insects at risk because of GMO crops introduced in headwater streams.

Genetically modified organisms have a difficult time establishing stable populations in marine environments, but if they are able to live long enough, they can potentially change the ecosystem structure and function among communities (Sobecky, 1996). This creates a time frame that should be considered for GMOs and their ability to create impacts (whether they be negative or positive) in these aquatic ecosystems. When genetically modified crops are introduced in headwater streams, there is a different decompostition rate for GM crops than non-GM crops. These changes in decompostition can impact the food supply as well as the housing for the organisms that are being altered. Axelsson’s (2010) lab discusses how genetically modified trees have slightly slower rates of decomposition. This is important because many organisms, like insects, inhabit plants as use plants as thier home. If the leaf litter quality changes because of GMO plants having increased mass than non GMO plants, this could have an effect on the species richness of insects inhabiting those plants. This, in turn, could impact the population dynamics of the ecosystem as well as surrounding ecosystems (Axelsson 2010). If we change the population density of one species of insects, this affects predators of these insects as well.

Plants in freshwater ecosystem provide habitat ares for many insects.

Further GM plant effects on organisms are studied in O'Callaghans (2005) lab. This study discusses the endotoxin (Bt) trait that is commonly used to create an insect resistant plant. If cross pollination occurs or the Bt trait is transferred to non-GMO plants in the aquatic ecosystem, the modification can happen on an uncontrollable level. This means wild (non-target) plants may become insect resistant leading to negative effects on insect population density. As discussed previously, many insects are prey to other organisms that depend on them as a food source. Little is known on the occurrence of gene transfer in the wild, so further research is needed to fully determine the impacts of these crops. Studies have been done on controlled crops where GM strains from one farm appeared in non GMO plants of a nearby farm. This is an example where cross pollination occured causing genes from the GM crops to pollinate with surrounding crops causing them to become genetically modified (Schiemann, 2003) . However, if the runoff from GMO farms ever reached aquatic ecosystems, these BT endotoxins would be transferred to the wild plats, and a drastic change in their numbers as well as their direct consumers would be expected.
If the freshwater ecosystem is to be maintained, then the preservation of population dynamics within the community needs to be stabilized. GMO’s have been shown to reduce the rate of growth as well as increase the mortality rate of different organisms such as amphibians and insects (Rosi-Marshall 2007). The Atlantic Salmon Studies will integrate how salmon is a key species whose life cycle must be preserved to maintain this balance of the freshwater ecosystem. If GMO’s reduce the growth rate and consumption of salmon, this could affect their reproduction in freshwater bodies and this will cause causes vast ecosystem-scale changes.

Integrative Case Study: How GMOs Affect Atlantic Salmon on The Ecological Level?
It is because GMO’s have cellular and organismal effects on aquatic organisms that we should be concerned about the big picture effect on the environment. Salmon are key organisms in the production of freshwater nutrients in streams, and thus affect the population dynamics of many organisms as well as their own in aquatic environments.

Looking at the population of Atlantic salmon, it is clear that their numbers are decreasing. One study done on Atlantic salmon focused on their life cycle and how small environmental factors can have major effects on the salmon's ability to regulate population density. The study found that supplementation programs used to restore population numbers only aided in short term reestablishment and do not act effectively over long periods of time (Bowlby & Gibson, 2011). Without new methods to regulate populations and increase salmon numbers, populations will further suffer and eventually cease to exist. Currently, Atlantic salmon are nearing extinction because of factors such as pollution, climate change, and exploitation (Clews et. al 2010). The introduction of runoff from genetically modified crops as a food source for salmon could further affect the population levels of these salmon in a negative way. The more environmental factors acting upon the Atlantic salmon population in negative manner, the smaller their numbers will become. This will only make it more difficult to restore these populations and keep them around in future generations.

If the reproduction and population dynamics of salmon are being effected due to GMO crops, there are greater consequences for aquatic ecosystems, starting in freshwater streams. Since salmon travel to freshwater streams to spawn, this is of great importance for maintaining population density. Salmon accumulate nutrients in their bodies as they grow in order to have the ability to travel to salt water in adulthood. These nutrients are produced and carried in the lakes and streams where they will spawn, and are then released (Bilby, 1980). Many years of research has proven that the annual deposition of salmon-carried nutrients is important for freshwater communities by directly impacting primary production(Yanai, 2005).The death of salmon after spawning further contributes to the deposition of nutrients in aquatic systems. Dead salmon deposit nutrients directly and indirectly through remineralization. These nutrients are then directly consumed by other animals (including bears, birds, and other macroinvertibrates (Bretherton, 2011)). The unconsumed salmon will then decompose via microbes which releases nutrients back into the water (Kline, 2007). These are important marine-derived nutrients that help sustain aquatic ecosystems. If this stabilizing system is disrupted by lack of nutrients from the inablilty of salmon to osmoregulate and therefore reproduce, this will have a critical impact on freshwater organisms in lakes and streams, and may limit productivity as well as decrease population densities of juvenile salmon (Holtgrieve, 2011).

Bears, among other animals like birds, consume the dead salmon after spawning occurs.