estuaries, are some of the most invaded habitats in the world (Zedler and Kercher, 2004; Cohen 
and Carlton, 1998). Some of the most notorious U.S. invaders are aquatic species such as the 
zebra mussel, purple loosestrife, tamarisk, Asian carp, Caulerpa (marine green alga), and the 
green crab. Section 1.4 describes the ecological impacts of some of these invaders and the 
potential impacts of climate change on these species. 
1.4. CLIMATE CHANGE AND ECOSYSTEM IMPACTS 
The recently released Fourth Assessment Report Summary for Policymakers from the 
Intergovernmental Panel on Climate Change (IPCC) provides a comprehensive synthesis of the 
current state of climate change science and a discussion of the projected effects that climate 
change will have in the coming decades and centuries (IPCC, 2007). Atmospheric carbon has 
increased from 280 parts per million (ppm) in pre-industrial times to 379 ppm in 2005. Other 
greenhouse gases such as methane and nitrous oxide are also on the rise. Warming is occurring 
globally, as evidenced by increases in global mean air temperatures, global mean ocean 
temperatures, melting of snow and ice in polar regions and high altitudes, and sea level rise 
(IPCC, 2007). The projected effects of climate change include warmer and fewer cold days and 
nights over most land areas, warmer and more frequent hot days and nights over most land areas, 
increased frequency of warm spells and heat waves over most land areas, increased frequency of 
heavy precipitation events over most areas, increase in areas affected by drought, increase in 
intense tropical cyclone activity, and a rise in sea level (IPCC, 2007). Figure 1-1 presents the 
conceptual model of projected effects of climate change on aquatic ecosystems, interactions with 
AIS, and adaptive management responses. Some issues that are less well understood include 
how precipitation, groundwater recharge, and streamflow will change as a result of climate 
change (IPCC, 2001). 
In addition to the physical changes, climate change is altering ecosystems and species life 
cycles. Changes include longer growing seasons in mid and high latitudes, shifts in species’ 
ranges towards the poles and higher altitudes, decline of some species, and changes in the 
reproductive cycles of plants and animals that are cued by climate and seasons (Parmesan, 2006; 
Root et al., 2003; Walther et al., 2002; IPCC, 2001). In the U.S., species restricted to southern 
habitats may move north as milder winters allow overwintering. In other cases, less heat tolerant 
species may decline in their southern ranges, allowing for new species to fill the niches left 
behind (Aerts et al., 2006). Thermal lake stratification regimes may also be affected by warming 
water temperatures, 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 and Schindler, 2004a, b). Altered hydrological regimes will also favor 
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