Environmental Engineering Reference
In-Depth Information
6
Blue Carbon in Faunal Community
…
In the blue soup the bright carbonate shell
Acidi
cation makes them gradually pale
…
The Authors
Molluscs constitute of organisms with soft
unsegmented body usually covered with calcar-
eous shell. They are the largest marine phylum,
comprising of about 23 % of all the recognized
marine organisms. About 85,000 species of
molluscs have been identi
are removed from the water column and benthos.
The readers may
nd interesting to know that
how carbon is sequestered by bivalves, as their
mind set-up is mostly based on the carbon
sequestration by autotrophs. It is true that carbon
sequestration is carried out by plants through the
process of photosynthesis, in which carbon
dioxide is converted into oxygen and plant
material (organic compounds) in presence of
light energy. The amount of carbon sequestered
can vary greatly depending on the species, site
and other external factors. The net amount of
carbon sequestered by autotrophs is evaluated
based on the balance between the changes in
aboveground vegetation, below-ground root
system, the litter layer and the soil (Hicky
2009
;
Mitra et al.
2011
,
2013
; Sengupta et al.
2013
).
The units used for this type of sequestration are
tonnes of carbon per hectare per year. These
terrestrial sequestration methods work well, but it
is the ocean that stores the vast majority of car-
bon on the planet as represented in Fig.
6.2
. The
stored carbon in the marine compartment is used
by phytoplankton, coastal vegetations (like
mangroves, saltmarshes, seagrasses, etc.) and
other shelled organisms.
The shelled organisms preferably the molluscs
are important storehouses of carbon. A number
of physical, chemical and biological processes
carry out carbon sequestration in molluscs, but
this section will focus on the biological pro-
cesses, and more speci
ed till date. Numerous
molluscs also thrive luxuriantly in freshwater and
terrestrial habitats. Organisms under phylum
mollusca are highly diverse, not only in size and
in anatomical structure, but also in behaviour and
in habitat. The phylum is typically divided into
nine or ten taxonomic classes, of which two are
entirely extinct. The two primary molluscan
classes are bivalvia and gastropoda (Fig.
6.1
).
The authors of this topic consider molluscan
community under the banner of blue carbon
primarily because of their habitat in the marshy
wetlands, mangroves, seagrass bed, saltmarsh
grass bed, coastal zones, estuaries and seas.
Carbon is also a major constituent of the cal-
careous hard shell over the body of molluscan
organisms. However, acidi
cation
—
a strong arm
of climate change
has posed a negative impact
on this community by way of dissolving and
thinning of their calcareous shell.
—
6.1
Stored Carbon in Bivalves
Filter-feeding oysters, clams or mussels sequester
signi
cant amounts of carbon by consuming
phytoplankton and absorbing dissolved organic
matter. Carbon becomes a primary component of
its shell, and it has been observed that for every
kilogram of live clams or oysters grown in
Florida waters, approximately 114 g of carbon
cally on the processes
adopted by a marine/estuarine oyster species.
The species
(commonly
known as rocky oyster) is widely seen occupying
hard substrata in the intertidal zone like walls of
lighthouse, sluice gates, pillars (Fig.
6.4
)of
Saccostrea cucullata
sh
