The number and type of nonnative species introduced into U.S. waters. Nonnative ("alien" or "invasive") species can spread rapidly and have significant economic and ecological effects, displacing both commercially valuable species and other native species and interfering with commercial activities. (Figs. 1, 2, 3)

Rates of fish diseases and other abnormalities, because such occurrences, if frequent enough, can indicate unhealthy populations.(Figs. 4, 5)

The number and extent of harmful algal blooms, because they can have significant economic and ecological effects by reducing water clarity, harming native species, discouraging tourism, and in some cases affecting human health. (Fig. 6)

Case studies indicate that the rates of introduction of nonnative species and the occurrence of fish abnormalities and harmful algal blooms are increasing. However, no consistent and comprehensive information is available to validate these concerns.

Example: Exotic Species Established in the Great Lakes (1) Technical Note	Example: Exotic Species Established in San Francisco Bay (2) Technical Note
Source: Mills, et al, 1993; Edsall, et al, 1995; Mills, et al 1994	Source: Cohen & Carlton, 1998
Nonnative species have been introduced, either intentionally or accidentally, into areas outside of their natural ranges. The Zebra mussel and European green crab, which can be transported in ships’ ballast water, are examples of species that disrupt commerce and threaten commercially valuable shellfish. Recent invaders, such as the veined rapa whelk, are being monitored because of concerns about their effects on native species. Some 234 exotic species are established in the San Francisco Bay and delta and 145 in the Great Lakes, with many becoming dominant in portions of the system. The Asian clam occupied 100 percent of the habitat suitable for it in San Francisco Bay within two years of its introduction.

Example: Fish Abnormalities in the Gulf of Mexico and Mid-Atlantic Region (3) Technical Note	Example: Skin Tumors in Great Lakes Fish (4) Technical Note
Source: Fournie, et al, 1996	Source: Edsall, et al, 1996
Shown here is the prevalence of fish abnormalities - fin erosion, ulcers, growths, or lumps - in the Mid-Atlantic and Gulf Coast regions, and the frequency of skin tumors in fish from both pristine and contaminated areas in the Great Lakes. For fish abnormalities, the graphs include both regional averages and levels in selected major estuaries. For tumors, levels above 5 percent are considered elevated.

Harmful Algal Blooms (5)
	There is growing concern that the number, intensity, frequency, duration, and economic impacts of harmful algal blooms are increasing in the United States and globally.

STATUS OF DATA & OTHER NOTES No consistent and comprehensive information is available on the rate of invasion, the overall number, or the spread of nonnative species in coastal and marine waters. Data shown here are examples and are not from ongoing monitoring programs. No consistent and comprehensive information is available on the occurrence of fish tumors or other abnormalities or harmful algal blooms. Although monitoring programs have been established in some areas, it is not yet possible to present national summaries. Please see the Technical Notes for additional information.

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