Aquatic biodiversity is increasingly affected and declined through various factors including increasing of temperature due to climate change, anthropogenic effects, invasive species slowly adapted in a particular environmental condition and replaced native species etc.
That is a very broad question... the effect of an invasive alien species (IAS) on a particular freshwater ecosystem will depend, not only on the introduced species' characteristics (diet, behaviour, etc...) but also on the actual state of the ecosystem and its biodiversity. Effects (or impacts) can range from direct (e.g. predation) to indirect (e.g. competition) and can have severe cascading effects at all levels of biological organisation.
If invasive species has similar/same ecological/biological needs of native species, invasives can compete with natives and can reduce its population or even the extinction, bu depends how the invaded ecosystem is structured. Ecosystems with high diversity is less suceptible in comparison with less diverse ecosystems.
Exotic and invasive species have high ecological plasticity and usually "take advantage" of empty ecological niches or "just played" to establish successfully. This situation (empty ecological niches) usually occurs in habitats altered by man, but not exclusively. Latest example, drastic environmentally, was the introduction of the Nile Perch (Lates niloticus) in Lake Victoria (Africa), ecosystem previously missing of top predators with the size and aggressiveness of the Nile Perch. Coupled with the high level of endemic fish of Lake Victoria, the introduction of the Nile Perch has made several endangered species of that particular ecosystem.
concerning aquatic plants, the invasive species are very frequently colonizing waters in the course of eutrophication, water temperature increase or when the hydraulic strains decrease.
The consequence is that most of these invasive are free floating species, which may reach huge biomasses, and limit drastically light penetration in the water column, and water oxygenation. The consequence is the collapse of aquatic biodiversity (both vegetal and animal) but very clear waters (despite the high trophic level !)
the solution is not to eradicate (in fact it is impossible) the species, but rather to decrease the nutrient input to the ecosystems and to restore hydraulic constraints, that have been frequently deleted by damming, channelization, etc.
Once an ecosystem inavded by an alien/exotic plan/animal species, the first consequence will be compettion for resources such as space, nutrients etc....between native and invasives and thus native flora/fauna gradually eliminated from an ecosystem at some point of time. In my study i found that when few ramets of eichhornia was introduced in a wetalnd, it spread over 75% of the total available area within few days by eliminating native as well as other invasive aquatic plants.
The invasive spread can be very rapid if the ecosystem community becomes farest and farest from its optimal niche, but rather isolated from the colonization of the more competitive species for the new ecological conditions. In such context, the native community is close to a fossil community, unable to resist to any species which has ecological requirements closer to the ecological conditions that prevail in the ecosystem. The very rapid exclusion described here is also related to the traits of Eichhornia, which, as a free-floating species is among the more competitive aquatic species. The rapid spread also suggests a very high nutrient availability in the water.
A study of the invasive species of Hawaii will give you an Idea as to why
it is not a good Idea to introduce new species into an eco-system.
First there were ship rats which began eating everyting, so they imported
the mongooses to eat the rats, but one was nocturanl, and the other one wasn't,
so then they imported cats to eat the rats, but all three like to eat birds and
bird eggs, which was a major part of the problem in the first place. now all of the
bird species are very tame because they evolved in a location without
predators over millions of years.
Man has a history of moving species from place to place, and suffering the
consequences later.
I agree with Irfan. There is not exact answer can be given. Relationship (impact) between an IAS and one/many native species depend on an IAS ecological characteristics (its place in an original food chain, original feeding capacity, feed preferences). Its ability to influence on physico-chemical characteristics of ecosystem is very important too (e.g. matting of water surface by duckweed species). The same characteristics of the native species have to be taking in account when predicting an influence of an IAS. Important to say that the effect of a species introduction is not always negative. It depend…..
There are many papers on this topic today.
I must say that my interest is focused on the study of invasive plants, so the information I can provide is related to this topic.
You can see below some links related to the topic. I hope you find them useful.
Linking plant invasions to global environmental change (Vilà et al., 2007): http://web.ics.purdue.edu/~jsdukes/VilaEtAl2007.pdf
Alien plant invasion and their impact on indigenous species al global scale: A review. (Dogra et al., 2010):
http://www.academicjournals.org/article/article1379601216_Kuldip%20Dogra.pdf
Impact of riparian invasive non- native plant species on freshwater habitats and species (Stockan et al., 2013):
http://www.crew.ac.uk/sites/www.crew.ac.uk/files/publications/CREW%20Invasive%20Non-natives%20Species.pdf
Alien species in fresh waters: ecological effects, interactions with other stressors, and prospects for the future (Strayer, 2010):
http://www.jlakes.org/web/alien-species-freshwaters-ecological-effects-FB2010.pdf
Best regards.
There is a great deal of literature on this topic area. Alien species in freshwater may have an impact in different ways: Competition, exclusion, disease, and impacting of the environment to make it unsuitable for native biota to survive ( by for example de-oxygenation of the hypolimnion, or deoxygenation in canals by Azolla sp.) Alien plants have been responsible for extensive growths by covering water surfaces or by forming dense growths that can form entanglements. Species such as the Asian clam or the zebra mussel can trophically alter freshwater ecosystems. Biological control can work on some aquatic plants such as the various weevils that are species specific in their diet.
Pantanal floodplain was invaded by asian clam, Limnoperna fortunnei, but due a natural oxygen depletion caused as a consequence of floodwater spread trough the plain and consequent terrestrial plant decomposition, a natural control is occuring preventing the overpopulation of this asian clam.
A lot of work has concentrated on invasive alien freshwater crayfish. These large benthic invertebrates, sometimes very long-lived, have been shown in Europe to spread disease to native crayfish, to feed selectively on invertebrates and crop down vegetation, and to compete for food and living spaces with fish and crayfish. See Richman et al. 2015 for global consequences.
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