18
2 Overview of the Aquatic Ecosystem
and loss of income from water-based recreational activities. Water hyacinth is a selfpollinating, mat-forming vegetative water plant. Its structure comprises a flowering
leaves, inflorescences supported by a stolon and rhizomes with fibrous unbranched
roots reaching down to the water. They can grow up to 3 feet high.
The fact that aquatic plants are adapted to cope in the aquatic environment indicates some significant differences between their structure and that of terrestrial plants.
This abundance of water means they do not require cutin or suberin in their leaves
and roots for the prevention of water loss. They instead have other features which
address the need for buoyancy to float on water as well as survive the tides. Other
features of aquatic plants include lacunae, which are holes in the root cortex which
aid in moderating gas exchange (North and Peterson 2005). Aquatic plants can be of
three types based on their biological structure; these are:
• Phytoplanktons
• Periphytons and
• Multicellular Macrophytes
Phytoplanktons are photosynthetic microscopic plants (and animals) which drift in
water. They require light for synthesis; therefore, they are located in the littoral zones
of water. They serve as primary producers as they can convert nutrients from the water
such as zinc, nitrogen and magnesium into carbon and oxygen. Most of the oxygen
productions from photosynthesis in the oceans, lakes and rivers are carried out by
phytoplankton. Planktons which do not photosynthesize are referred to as zooplanktons. Phytoplankton also comprises algae and bacteria as well as plant phytoplanktons. There are about 43 species of phytoplankton. They serve as a nutrient source
to other aquatic organisms such as finfish and shellfish and therefore are required for
a healthy aquatic ecosystem. Their environmental and economic significance lies in
the sustenance of the other aquatic organisms of economic importance.
Periphytons are aquatic organisms which require a substrate to grow on. They could
be heterotrophic or autotrophic (Petters and Lodge 2009). Rocks and plants could
serve as such substrate as well as other surfaces. These surfaces provide the structural
support for them to survive aquatic environment. They obtain nutrients from the
water, and they serve as a food source for herbivores.
Multicellular macrophytes are more independently growing and anchored multicellular aquatic plants. They can be emergent, submerged or free-floating. Many
submerged aquatic plants do not possess cuticle as they are surrounded by abundant
water. Likewise, they partially or completely lack xylem and stomata remains open.
Roots may be present in submerged plants to anchor them to the surface or it could
be absent. While floating aquatic plants are adapted with air spaces trapped within
their structure to enable them to remain afloat, submerged aquatic plants are adapted
to survive in low light due to their distance from the surface of the water. The leaves
of the floating aquatic plants are flat to aid flotation while their roots are specially
adapted to aid oxygen uptake. Emergent aquatic plants grow in the shallowest end
of the water. Their roots are buried in the soil at the bottom of the water while the
rest of the plant grows above water. Figure 2.5 illustrates these three different types
of aquatic plants.
2 Overview of the Aquatic Ecosystem
and loss of income from water-based recreational activities. Water hyacinth is a selfpollinating, mat-forming vegetative water plant. Its structure comprises a flowering
leaves, inflorescences supported by a stolon and rhizomes with fibrous unbranched
roots reaching down to the water. They can grow up to 3 feet high.
The fact that aquatic plants are adapted to cope in the aquatic environment indicates some significant differences between their structure and that of terrestrial plants.
This abundance of water means they do not require cutin or suberin in their leaves
and roots for the prevention of water loss. They instead have other features which
address the need for buoyancy to float on water as well as survive the tides. Other
features of aquatic plants include lacunae, which are holes in the root cortex which
aid in moderating gas exchange (North and Peterson 2005). Aquatic plants can be of
three types based on their biological structure; these are:
• Phytoplanktons
• Periphytons and
• Multicellular Macrophytes
Phytoplanktons are photosynthetic microscopic plants (and animals) which drift in
water. They require light for synthesis; therefore, they are located in the littoral zones
of water. They serve as primary producers as they can convert nutrients from the water
such as zinc, nitrogen and magnesium into carbon and oxygen. Most of the oxygen
productions from photosynthesis in the oceans, lakes and rivers are carried out by
phytoplankton. Planktons which do not photosynthesize are referred to as zooplanktons. Phytoplankton also comprises algae and bacteria as well as plant phytoplanktons. There are about 43 species of phytoplankton. They serve as a nutrient source
to other aquatic organisms such as finfish and shellfish and therefore are required for
a healthy aquatic ecosystem. Their environmental and economic significance lies in
the sustenance of the other aquatic organisms of economic importance.
Periphytons are aquatic organisms which require a substrate to grow on. They could
be heterotrophic or autotrophic (Petters and Lodge 2009). Rocks and plants could
serve as such substrate as well as other surfaces. These surfaces provide the structural
support for them to survive aquatic environment. They obtain nutrients from the
water, and they serve as a food source for herbivores.
Multicellular macrophytes are more independently growing and anchored multicellular aquatic plants. They can be emergent, submerged or free-floating. Many
submerged aquatic plants do not possess cuticle as they are surrounded by abundant
water. Likewise, they partially or completely lack xylem and stomata remains open.
Roots may be present in submerged plants to anchor them to the surface or it could
be absent. While floating aquatic plants are adapted with air spaces trapped within
their structure to enable them to remain afloat, submerged aquatic plants are adapted
to survive in low light due to their distance from the surface of the water. The leaves
of the floating aquatic plants are flat to aid flotation while their roots are specially
adapted to aid oxygen uptake. Emergent aquatic plants grow in the shallowest end
of the water. Their roots are buried in the soil at the bottom of the water while the
rest of the plant grows above water. Figure 2.5 illustrates these three different types
of aquatic plants.