THE CONCEPT OF ECOSYSTEM DEVELOPMENT
by Antonio C. Antonio
June 10, 2014
QUESTION:
How will an abandoned shrimp pond evolve using a generalized concept of
ecosystem development?
When left undisturbed, an abandoned shrimp
pond will undergo progressive change in a phenomenon called ecosystem
development. Ecosystem development is a
broad term which includes both biotic and abiotic changes in the environment
and is the outcome of all the processes in the system. It includes the following parameters: (1) the kinds and number of species that
colonized an ecosystem; (2) the changes in the climate or microclimate in the
ecosystem; (3) the distribution of energy in the ecosystem; (4) the different
organic matter found in the soil and/or water, etc.
Ecological succession, on the other hand, is
the sequential, gradual and directional change in the structure and composition
of the biotic community in an ecosystem.
There are two types of ecological succession: (1) primary succession
where a new ecosystem develops in a particular area and (2) secondary
succession where changes occur from a disturbed ecosystem. The “re-evolution” of an abandoned shrimp
pond, like most ecological successions we witness, could be considered a
secondary succession.
Shrimp ponds productivity has proven to be
unsustainable, largely because of (a) disease problems, (b) defects in pond
infrastructure and inappropriate construction methods, (c) overstocking and (d)
poor environmental conditions. After a
few production cycles, shrimp ponds become unproductive and become idle then
abandoned. Unofficial estimates suggest
that as many as 70% of shrimp ponds are left unattended after they are deemed
unproductive. The eventual non-productivity
of shrimp ponds is attributed mainly to (1) hydrological conditions, (2) the
flora and fauna composition of the pond, and (3) alterations to the physical
and chemical properties of the soil.
It should be noted that
many shrimp ponds were conversions from mangroves and mangroves forest areas. The problem of unproductive and abandoned
shrimp ponds magnifies further as shrimp pond producers endeavor to recover
and/or maintain their business. They often
consider moving to sites, normally within the same periphery of the original
pond, and pursue shrimp production. This
practice eventually expands the problem.
In time, the area of abandoned shrimp ponds expands wider and wider.
Shrimp farming creates
environmental problems such as:
a)
Salinisation of the soil;
b)
Increase in coastal soil erosion;
c)
Discharge of undesirable chemicals causing coastal water pollution and
reduced nutrient enrichment;
d)
Activation of acid sulphate soils;
e)
Contamination of ground water;
f)
Reduction of habitat and reduction of shoreline protection;
g)
Reduction of agricultural land and mangrove deforestation; and,
h)
Introduction of exotic species and depletion of wild prawn and fish
larvae stocks.
The question now and
challenge is what to do with abandoned shrimp ponds. There are several alternative courses of
action:
1.
Rehabilitate the abandoned shrimp ponds so they could be re-utilized to
shrimp ponds again;
2.
Rehabilitate the abandoned shrimp ponds so they could be put to some
other alternative and sustainable use like production of salt; and,
3.
Restore the environmental conditions within the abandoned shrimp ponds
and adjacent areas by re-establishing a productive mangrove ecosystem.
These options, however,
are quite expensive. But abandoning the
shrimp pond without the benefit of intervention whatsoever will have a
environmentally disastrous consequence.
Cost and benefit ratio will have to be established but since the issue
at hand involves the environment, the environment must always be given
preferential attention and priority.
Another success-probable
option is to leave the shrimp pond alone with minor infrastructure intervention
such as tearing down floodgates, barriers, impounding dikes, etc. to allow
water/seawater to flow in and out with the rising and lowering of the
tide. This way, although it may take a
longer period of time, the shrimp pond will have a chance to re-generate and
evolve into a secondary succession. It
should also be noted that no other shrimp pond is established in adjacent
areas… the entire periphery of the shrimp pond should be left alone and
considered in any measure to rehabilitate the entire area.
Most, if not all,
knowledgeable personalities on the environment agree that the most and only
plausible alternative at present is to convert or restore the abandoned shrimp
ponds into mangrove forests. The
mangrove is the natural hatchery for shrimp larvae and provides the food
chain. The roots, trunks fallen branches
and leave are food for shrimps. The
absence of a certain degree of mangrove reforestation is a must to accomplish
the restoration of abandoned shrimp ponds.
In summary, the following events
occur prior to the abandonment of the shrimp pond:
1.
A shrimp pond is established by scraping-off soil to construct an
impounding dike and increase the pond’s capacity by deepen the pond. Oftentimes, some mangrove trees are
sacrificed in the effort to widen the pond for a bigger production;
2.
Salt and seawater is allowed into the pond;
3.
The mangrove, being a natural hatchery for shrimps, will spawn shrimp
nauplius that then grown into adult shrimps;
4.
Shrimp farmers have a tendency to overpopulate (for business and
profitability reasons) and overfeed (thinking that shrimps will grow faster
when fed abundantly);
5.
Unconsumed feed settles at the bottom of the pond that allows other
organisms to grow and contribute to the soil’s toxicity and acidity. This is the main contributor to eventual
undersized harvest and diseases that often causes the widespread death of the
shrimp population;
6.
When it is no longer profitable to continue operating the shrimp pond
for shrimp production purposes, it is now abandoned.
The shrimp pond can only
regenerate back to its original condition if and when the following measures
are undertaken:
a)
INFRASTRUCTURE INTERVENTION – Impounding dikes are broken down at
strategic point to allow sea water to come in and go out to conform with the
daily tides. Marine organisms will
accompany the sea water as it regularly flows into the pond. Screen materials are installed in these
inlets and outlets to prevent these organisms from leaving the pond. These organisms will eventually settle on the
bed of the pond and (in time) consume the acids in the soil. The eventual elimination of acids in the pond
will bring it back to its original productive state.
b)
MANGROVE REFORESTATION – To aid and hasten the regeneration of the
shrimp pond, additional mangrove species of trees (such as bakawan) will have
to be planted.
Infrastructure
intervention, mangrove reforestation and the assumption that the pond is left
undisturbed, therefore, no other human activity is present, will allow the
shrimp pond to evolve back to its original state. The period involved in the restoration
process will largely depend on the degree of degradation and the shrimp pond’s
proximity to the coastline. Researchers
and environment management practitioners put this from 15 to 30 years
Just my little thoughts…
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