Basic Concepts and Management Issues of Rivers - River Dynamics and Integrated River Management - page 27

(Tomlinson, 1986).
Mangroves are exposed to saltwater inundation, low oxygen levels around their roots, high light and
temperature conditions, and periodic tropical storms. Despite these harsh conditions, mangroves may form
luxuriant forests, which have significant economic and environmental value throughout the world—they
provide coastal protection and underpin fisheries and forestry operations, as well as a range of other human
activities. The red mangrove has tangled, reddish roots. The mangrove appears to be standing or walking
on the surface of the seawater with muddy bed, and therefore, has a nickname of working tree.
Mangroves can only live on muddy coast and not able to grow on sand beaches. Reproduction in red
mangroves is primarily accomplished through embryo production. Mangroves have floating seeds that
germinate while still attached to the mother plant. An embryo may be embedded in the mud as it falls
and thus, it soon germinates. Figure 1.21 shows a mangrove forest in Deep Bay in the Pearl River estuary
with embryo attached on the mother tree in the left picture and seedling of mangrove growing on the
muddy coastal beach in the right picture.
(a) (b)
Fig. 1.21 (a) Mangrove forest in the muddy Deep Bay in the Pearl River estuary; (b) Seedling of mangroves growing
on the muddy beach
Riparian area —Riparian areas are the areas contiguous to and affected by surface and subsurface
hydrological features of perennial or intermittent lotic and lentic water bodies (rivers, streams, lakes, and
drainage ways). Riparian areas have one or both of the following characteristics: ķ distinctly different
vegetative species than adjacent areas; and ĸ species similar to adjacent areas but exhibiting more vigorous
or robust growth forms. Riparian areas are usually transitional between wetland and upland.
Aquatic plants —Aquatic plants usually consist of algae and mosses attached to permanent stream
substrates. Rooted aquatic vegetation may occur where substrates are suitable and high currents do not
scour the stream bottom.
Benthic invertebrate —The benthic invertebrate community of streams may contain a variety of biota,
including bacteria, protists, rotifers, bryozoans, worms, crustaceans, aquatic insect larvae, mussels, clams,
crayfish, and other forms of invertebrates. Aquatic invertebrates are found in or on a multitude of
microhabitats in streams including plants, woody debris, rocks, interstitial spaces of hard substrates, and
soft substrates (gravel, sand, and muck). Generally speaking, there are more benthic invertebrates in gravel
bed than a sand bed. Figure 1.22 shows some species of macro-invertebrates from gravel bed streams.
Invertebrate habitat at all vertical strata including the water surface, the water column, the bottom surface,
and deep within the hyporheic zone.