Biota of Lakes and Reservoirs - Hydro-Environmental Analysis: Freshwater Environments - page 437

Species diversity typically drops sharply in the profundal benthos as opposed to the littoral
zoobenthos. This is particularly the case for eutrophic waters where the hypolimnion is usually
anoxic. In those systems, the zoobenthos, where present, are often those forms indicative of highly
polluted waters (such as some oligochaetes). For example, Lathrop (1992) demonstrated a decline in
the zoobenthos of Lake Mendota, Wisconsin, from the early 1900s to the present day even though
the extent and the duration of hypoxia have not substantially changed over that period. Lantrop sug-
gested that the decline could be due to increased ammonia and sulide concentrations resulting from
increased eutrophication.

15.3.2.5 Fish
Fish are an ecologically and economically important component of the biota of lakes and reser-
voirs. Many lake management strategies for recreation are focused on optimizing the abundance
of speciic, economically important species, such as bass, lake trout, walleye, etc. These may be
locally native species, but not necessarily so. For many reservoirs, which are not considered natural
systems to begin with, the introduction of nonnative and often hatchery-raised sport ish is a com-
mon practice.
While the management of lakes has often focused on increasing angler harvest, ish are an inte-
gral component of lake ecosystems, playing important roles in energy lows, nutrient cycling, and
maintaining community balance (Baker et al. 1993). Thus, isheries management not only impacts
the ish population, but it also impacts, and is impacted by, all other aspects of the lakes ecology.

15.3.2.6 Birds and Mammals
Birds and mammals are also important components of lake and reservoir ecosystems. Birds, for
example, include those that are characteristic of open waters (e.g., ducks, geese, grebes, cormorants,
kingishers, terns, gulls, and pelicans); shoreline (e.g., stilts, greenshank, sandpipers, storks, ibises,
spoonbill, herons, and egrets); contiguous meadows and grasslands; reed beds and other vegetation;
and open air space above wetlands (e.g., rails, bitterns, coots, jacanas, moorhens, snipe, and painted
snipe). These birds not only represent important components of the lake ecosystem, but they are also
economically important (e.g., birding and hunting).

15.4 INVASIVE SPECIES
Invasive species are commonly taken as those nonnative species, which, when introduced to some
new ecosystem, often become dominant to the detriment of the native species. However, a more
general deinition by the Nature Conservancy is that an invasive species is “any species not native
to an ecosystem whose introduction does or is likely to cause economic or environmental harm or
harm to human health.” There are a wide variety of plant and animal species that by this deinition
are invasive, some of which are discussed in the following sections.
Invasive species are an enormous national problem. One response, motivated in part by the
invasive zebra mussels, was the passage of the federal Nonindigenous Aquatic Nuisance Prevention
and Control Act of 1990 amended by the National Invasive Species Act of 1996 that calls for the
development of state and regional management plans to control aquatic nuisance species and for the
secretary of the army to develop a program of research and technology development for the envi-
ronmentally sound control of zebra mussels at public facilities. The purposes of the Nonindigenous
Aquatic Nuisance Prevention and Control Act are to (Hanson and Sytsma 2001):

• Prevent unintentional introduction and dispersal of nonindigenous species into waters of

the United States

• Coordinate federally conducted, funded, or authorized research, prevention, control, infor-

mation dissemination, and other activities