EXERCISE 22
The Littoral Zone
The littoral zone represents an interface between
the land ofthe drainage basin and the open water
of the lake; reservoir, or stream (Wetzel, 1990).
The extent ofthe development ofthe littoral zone
is highly variable and depends on both the
geomorphology of the basin and the rate of
sedimentation that has occurred since its
formation.
The emergent macrophytes oflittoral wetlands
and the shore regions of lakes are among the
most productive habitats of the biosphere [cf.,
Whittaker and Likens (1975)]. Productivity decreases with increasing distance from the lake, as
one passes into terrestrial conditions, and decreases as one passes toward the lake through
zones offloating-Ieaved macrophytes, submersed
macrophytes, and phytoplankton. For a number
of physiological reasons [cr., Wetzel, 1983a,
1990)], the surface area of submersed vegetation
is much greater than that for other types of
littoral macrophytes. These surfaces are
colonized densely by epiphytic algae which can
contribute much to the total productivity of the
lake. In addition, algae can grow profusely when
attached to sediments or in loosely attached
clumps among the littoral macrovegetation. All
of this primary productivity in the littoral zone
results in a large input of dissolved and particulate organic detritus to the lake system. Particulate organic detritus is deposited largely in the
sediments of the littoral zone; a portion is
transported to sediments of deeper water where
degradation continues.
The high productivity of living organic matter
and the detrital accumulations in sediments of
the littoral zone provide an abundance of
habitats and food resources for zooplankton,
invertebrates, and vertebrates such as fishes,
amphibians, birds, and muskrats. Many of the
littoral animals are specialized in their adaptation
to conditions in the littoral zone. As with the
littoral algae, the diversity oflittoral fauna is very
high.
The spatial conditions within the littoral zone
are complex. Extreme heterogeneity exists in the
distributions and productivities of the macroand microflora along the gradient from the
emergent wetland vegetation to submersed conditions. The heterogeneity and abundance of
microhabitats make quantitative sampling difficult. As a result, knowledge ofthe metabolism of
the flora and fauna is poor in comparison with
what is known of the pelagic biota. Nonetheless,
it now is known that the littoral biota are a major
component of the metabolism of the whole
ecosystem in most lakes of the world (Wetzel,
1979, 1990). An understanding of the physiological relationship of the littoral biota to the
ecology of the lake presents an imposing challenge to ecologists when evaluating the role of
this interface zone in the metabolism of the whole
ecosystem.
The following exercise is designed to introduce
some aspects of the structure and function of
littoral biota. The limitations of the various
analytical techniques will become readily apparent. The problems of extreme heterogeneity in
the distribution and metabolism of organisms
also will be obvious. However, the interrelationships of the littoral organisms to each other, to
environmental gradients, and to the rest of the
lake system can be seen in overview.
291
The Littoral Zone
The littoral zone represents an interface between
the land ofthe drainage basin and the open water
of the lake; reservoir, or stream (Wetzel, 1990).
The extent ofthe development ofthe littoral zone
is highly variable and depends on both the
geomorphology of the basin and the rate of
sedimentation that has occurred since its
formation.
The emergent macrophytes oflittoral wetlands
and the shore regions of lakes are among the
most productive habitats of the biosphere [cf.,
Whittaker and Likens (1975)]. Productivity decreases with increasing distance from the lake, as
one passes into terrestrial conditions, and decreases as one passes toward the lake through
zones offloating-Ieaved macrophytes, submersed
macrophytes, and phytoplankton. For a number
of physiological reasons [cr., Wetzel, 1983a,
1990)], the surface area of submersed vegetation
is much greater than that for other types of
littoral macrophytes. These surfaces are
colonized densely by epiphytic algae which can
contribute much to the total productivity of the
lake. In addition, algae can grow profusely when
attached to sediments or in loosely attached
clumps among the littoral macrovegetation. All
of this primary productivity in the littoral zone
results in a large input of dissolved and particulate organic detritus to the lake system. Particulate organic detritus is deposited largely in the
sediments of the littoral zone; a portion is
transported to sediments of deeper water where
degradation continues.
The high productivity of living organic matter
and the detrital accumulations in sediments of
the littoral zone provide an abundance of
habitats and food resources for zooplankton,
invertebrates, and vertebrates such as fishes,
amphibians, birds, and muskrats. Many of the
littoral animals are specialized in their adaptation
to conditions in the littoral zone. As with the
littoral algae, the diversity oflittoral fauna is very
high.
The spatial conditions within the littoral zone
are complex. Extreme heterogeneity exists in the
distributions and productivities of the macroand microflora along the gradient from the
emergent wetland vegetation to submersed conditions. The heterogeneity and abundance of
microhabitats make quantitative sampling difficult. As a result, knowledge ofthe metabolism of
the flora and fauna is poor in comparison with
what is known of the pelagic biota. Nonetheless,
it now is known that the littoral biota are a major
component of the metabolism of the whole
ecosystem in most lakes of the world (Wetzel,
1979, 1990). An understanding of the physiological relationship of the littoral biota to the
ecology of the lake presents an imposing challenge to ecologists when evaluating the role of
this interface zone in the metabolism of the whole
ecosystem.
The following exercise is designed to introduce
some aspects of the structure and function of
littoral biota. The limitations of the various
analytical techniques will become readily apparent. The problems of extreme heterogeneity in
the distribution and metabolism of organisms
also will be obvious. However, the interrelationships of the littoral organisms to each other, to
environmental gradients, and to the rest of the
lake system can be seen in overview.
291