Climate change and invasive species have been a challenging problem in this global change. When many stresses act in synergism they may eventually have unexpected and irreversible consequences for the native communities and also may impact economically valuable human activities such as fisheries in a particular region (Ambrogi, 2007). To avoid and minimize impact of invasive species, appropriate detection and control should be determine to achieve optimum result, include considering influence of climate change. This paper try to give general overview of the effect of climate change on invasive species, started with reviewing effect of climate change on aquatic ecosystem, then specific to aquatic invasive species (AIS) particularly the effect of altered thermal regime, and finally identify measures to be taken.
Invasive species, climate change and aquatic ecosystems
As defined in Executive Summary of the National Invasive Species Management Plan (NISMP) the term invasive species is "a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health" (NISC, 2006). Raaymakers (2007) has observed that human has contributed in the process of species dispersal as long as they have sailed across the seas; furthermore, in modern times with canal development, movement of large marine structure, marine organism attached to floating marine debris, escape of species from aquaria, and ballast water and hull fouling of commercial shipping.
Natural scientists also have determined that human activities have become dominant force in influencing climate, greatly exceeds the influence by natural process such as volcanic eruption and solar changes. Incoming solar radiation and out-going infrared (thermal) radiation that are part of Earth's energy balance are altered by greenhouse gases and aerosols. The overall effect of human activities on climate has been a warming influence (IPCC, 2007).
Ecosystem was influenced by climate in many ways; some are more vulnerable and sensitive than other. Animal, plants and microorganism lives are strongly attuned in climate, for example temperature variation; amount, timing or form of precipitation (Committee, 2008). In aquatic system, Rahel and olden (2008) state that warmer water temperatures, shorter duration of ice cover, altered streamflow patterns, increased salinization, and increased demand for water storage and conveyance structures is projected as result of climate change. As an illustration, in case of US aquatic ecosystem, Poff, Brinson & Day (2002) summarize several important points regarding potential impact of climate change, such as vulnerability of aquatic and wetland ecosystems to climate change, shift in thermal suitability of aquatic habitats for resident species by increasing of temperature, and negative effects caused by seasonal shifts in stream runoff. However, in their research, most specific ecological response to climate change cannot be predicted because of new combinations of native and non native species interaction in novel condition.
Climate change induced on ecosystem conditions also can enable spread of invasive species through both range expansion and creation of habitats and conditions suitable for newly introduced invasive species. Research on climate change and invasive species is limited; however, many studies on potential climate-change impacts to aquatic systems and AIS exist (US-EPA, 2008).
Effect of climate change on aquatic invasive species
AIS can cause wide range of ecological impacts, including loss of native biodiversity, altered habitats, changes in water chemistry, altered biogeochemical processes, hydrological modifications, and altered food webs (US-EPA, 2008).
Gritti in Hellmann (2008) noted that due to its pervasiveness and potential effect on fundamental biological process, climate change will interact with other existing stressor to affect distribution, spread, abundance and impact of invasive species.
Altered conditions such as increased atmospheric carbon dioxide, modified precipitation regimes, warming ocean and coastal currents, increased ambient temperature, and altered nitrogen distribution can increase invasive species success in some contexts. Increased temperatures and altered precipitation regimes are likely to have larger effects on AIS than increasing levels of carbon dioxide (US-EPA, 2008).
In general, figure 1 shows categorization of aquatic system characteristics that will be altered by climate change and how these changes will affect invasive species.
Figure 1. Characteristics of aquatic system that will altered by climate change and how these changes will affect invasive species (Rahel, 2008)
As identified by several researches mentioned above, there are many altered condition which possibly influence AIS; however, this paper will only concentrate to review the effect on AIS by altered thermal regime.
Effect of altered thermal regime on aquatic invasive species
Since most aquatic organisms are ectothermic, temperature is important in their physiology, bionenergetics, behavior, and biogeography. Warmer climate will expand the geographic areas with suitable temperatures for warmwater aquaculture, tropical fish culture, and outdoor water gardens (Rahel, 2008). For example, McCauley in Rahel (2008) identified that optimal temperatures for aquaculture of catfish are projected to move 240 km northward in the southeastern US for every 1ï‚°C increase in mean annual air temperature.
Change in likelihood of invasive species that will be established also caused by water temperatures warmwith climate change. Fish are often classified into thermal guilds based on temperature tolerance. Coldwater temperatures can be viewed as a filter that prevents warmwater-adapted species from establishing self-sustaining populations. This filter is diminishing, and warmwater species could spread to new areas (Rahel, 2008).
Warming water temperatures may also cause thermal lake stratification regimes, resulting in earlier mixing and phytoplankton blooms that may alter zooplankton development. Changes to timing of zooplankton reproduction and/or abundance could favor certain species over others and have potential negative consequences for aquatic ecosystems (Winder in US-EPA, 2008).
Moreover, Rahel (2008) state that "altered thermal regimes could mediate the impacts of established non-native species on native species through shifts in competitive dominance between native and nonnative species, increased consumption of native prey species by non-native predators, or increased effects of non-native parasites on native species." Water temperature raise their food consumption rate until thermally stressful conditions are reached. This condition could magnify impacts of non-native predators on native prey species. Marcogliese in Rahel (2008) also conclude that climate warming may increase virulence of nonnative parasites and pathogens to native species through allowing disease organisms completing their life cycle more rapidly and attain higher population densities.
Another effect of warming temperatures may be an increase in number of sexual versus asexual reproductive periods for plant species, resulting in increased rates of spread. Diaz-Amela in US-EPA (2008) associated the flowering cycles of a Mediterranean seagrass to warming water temperatures.
Rahel (2008) examined that most researcher focus on how climate change will increase number and severity of invasions. However, in specific case, positive effect in decreasing AIS also exist; for example, some invasive coldwater species may be unable to persist under new climate conditions.
Nevertheless, since climate change has high possibility to change ecosystems, the influence of climate change should be taking into consideration in determining detection and control measures to manage the threats.
Measures
There are several measures regarding Invasive species. It should be start with national strategy and supported by international co-operation. Then, early detection and strategies for eradication, containment, control and mitigation through mechanical, biological and chemical method should be developed (GISP, 2001).
Regarding climate change influence, monitoring survey can provide foundation for assessing combine effects of climate change and invasion by providing baseline biotic and environmental condition, though utility of a survey depends whether the result are quantitative or qualitative, and other design consideration (Lee, 2008).
Although climate change is global scale process, it has diverse regional manifestation. Ecological impact usually has local characteristics and varies from place to place (Committee, 2008). To prevent further consequence that might be occurred, more research in each specific location should be conducted to formulate measures that can be taken regarding this mater.
There are several ongoing control programs for AIS that also should be review related to climate change. For example, in case of mechanical harvesting and herbicides which used to control Eurasian watermilfoil in the littoral zone of lakes, and scrubbing or molluscicides which used to prevent clogging of water intake pipes by zebra mussels in the Laurentian Great Lakes, warmer water temperatures could allow these and other invasive species to begin growth earlier in the year and maintain growth later into the fall. Therefore, costly control actions would need to be implemented more frequently. Review also have to be done for migration barrier construction or measure with reducing solar input into streams by increasing shading from riparian vegetation (Rahel, 2008).
Conclusion
Human has contributed in causing climate change and AIS problem. Measures have been developing to overcome economic, environment and human health problem caused by AIS. Since climate change has high possibility to change ecosystem, it is an important thing to consider influence of climate change in managing risk of AIS. Specifically, altered thermal regime cause by climate change has altered pathway, change the likelihood of AIS establishment and shift competitive dominance between native and nonnative species or increased effects of non-native parasites on native species. Therefore, these changes should be integrated in strategies for detection, eradication, containment, control and mitigation of AIS.
