Environmental Engineering Reference
In-Depth Information
physiological and electron microscopic studies are
as follows: (a) photosynthetic pigments, (b) storage
food products, (c) cell wall component, (d)
main function is for support of the blade for
photosynthesis and for absorption of nutrients
from surrounding sea water. The blade may
resemble leaves of the higher plants and have
variable forms (smooth, perforated, segmented,
dented, etc.). The important functions of the blade
are photosynthesis and absorption of nutrient. The
blades may be
ne
structure of the cell and (e)
fl
agella. Accordingly,
algae are classi
ed into three main groups, i.e.
green (Chlorophyta), brown (Phaeophyta) and red
(Rhodophyta).
Marine biologists have documented that the
distribution of seaweeds is limited by the avail-
ability of sunlight at various depths. The evolution
of a variety of accessory pigments that absorb those
wavelengths of light that are able to reach the
deeper zones of the ocean allows the algae to sur-
vive in these bottom habitats. Sea water selectively
absorbs light with longer wavelengths, such as the
reds and yellows, so the light that penetrates to the
greatest depths is the short-wavelength blues and
greens. Pigments such as fucoxanthin and phyco-
erythrin, which absorb blue and green light, allow
algae to grow at greater depth than those algae that
do not possess these or similar accessory pigments.
The distribution of macroalgae is also affected
by temperature. The greatest diversity of algal
species is in tropical waters. Farther north or
south of the equator, the number of species
decreases, and the species themselves are differ-
ent. Many marine macroalgae found at the colder
altitudes are perennials, which means they live
longer than 2 years. During survival, a few cells,
but most often a mass of stem-like structures
appear. When the temperature warms up in the
spring, this body part initiates new growth.
Temperature is not usually a limiting factor for
algae that live in tropical and subtropical seas,
although for some species, the temperature in
intertidal areas may be too warm.
Seaweeds are similar in the form with the
higher vascular plants but the structure and func-
tion of the parts signi
ed, feathery or even
encrusted with calcium carbonate. The most sig-
ni
fl
at, ruf
fl
cant difference of seaweeds from the higher
plants is that their sex organs and sporangia are
usually one celled or if multicellular, their gametes
and spores are not enclosed within a wall formed
by a layer of sterile or non-reproductive cells.
Carbohydrates produced by these
oral com-
munities provide nutrition to faunal members of
the benthic habitats. The large biomass of sea-
weeds in the intertidal zone (Fig.
2.9
) makes it an
important primary producer of the marine and
estuarine ecosystems.
The macroalgae are noted for their primary
production. Ef
fl
ciencies of solar energy trapped
showed a maximum in Enteromorpha intestinalis
(0.64 %) and
(0.43 %) with an
average of 0.35 % by this group. A research
conducted on this aspect
Ulva lactuca
indicates that
in the
deltaic complex of Indian Sundarbans,
Entero-
morpha intestinalis
and
Ulva lactuca
are the
most productive species, followed by
Entero-
morpha prolifera
Rhizoclonium grande
(Chaudhuri and Choudhury
1994
). The gross and
net primary productions and energetics of ben-
thic macroalgae in this mangrove-dominated
ecosystem are highlighted in Tables
2.4
and
2.5
.
and
2.1.3 Seagrass and Salt Marsh Grass
Seagrass
refers to the marine flowering plants
(angiosperm) that grow luxuriantly in tidal and
subtidal marine environment. They belong to the
families Hydrocharitaceae and Potamogetona-
ceae. There are about 13 genera and 58 species of
seagrass available all over the world. Of these,
six genera (
cantly differ from the higher
plants. Seaweeds do not have true roots, stem or
leaves, and whole body of the plant is called
thallus that consists of the holdfast, stipe and
blade. The holdfast resembles the root of the
higher plants, but its function is for attachment and
not for nutrient absorption. The holdfast may be
discoidal, rhizoidal, and bulbous or branched
depending on the substratum it attaches. The stipe
resembles the stem of the higher plants, but its
Amphibolis
,
Heterozostera
,
Phyllo-
spadix
)
are mostly restricted to temperate seas and the
remaining seven genera (
,
Posidonia
,
Pseudalthenia
and
Zostera
Cymodocea
,
Enhalus
,
