Download Invasion of alien species: an impending threat

Indian Journal of Geo Marine Sciences
Vol. 45 (11), November 2016, pp. 1409-1411
General Article
Invasion of alien species: an impending threat
Seema B. Sharma 1*, Thivakaran A. Gobi 2 & Mahesh G. Thakkar3
1,3
Department of Earth and Environmental Science, KSKV Kachchh University, Mundra Road,
Bhuj, Kachchh, Gujarat, Pin code 370001 India.
2
Gujarat Institute of Desert Ecology, Bhuj, Kachchh, Gujarat India
* [Email: [email protected]]
Received 01 September 2016; revised 07 November 2016
With increased globalization, biological
invasion of exotic species into native biodiversity
of any country1, 2 is a threat ecologist and natural
resource managers have to cope with. In
agriculture sector alone billions of US dollars are
being spent3 to check or neutralize the detrimental
impact of some of the biological invaders. While
in agriculture systems their invasion is detected
earlier, in forest ecosystems, wetlands and
common lands such invasion is evident only at a
later stage. In terrestrial ecosystem, the best case
in point is Prosopis juliflora (common name
Vilayati babul) which was introduced deliberately
during later part of 1800 in arid and semi arid
regions of India as it was thought to provide green
cover in an area which is otherwise sparse in
vegetation and control desertification. While this
species is known to provide livelihood option in
arid settings, its impact in negating local floral
biodiversity is apparent. Similarly, in marine
ecosystems, ballast waters and ship hulls are the
prominent sources of alien species invasion.
While pros and cons of this controversy are
raging and inconclusive, it is imperative to gain
some insight into some salient points of biological
invaders and ways and means to cope with it. This
article highlights some of such points which will
further our understanding of the science of
biological invasion.
It appears almost all introductions of non
indigenous species in some way are facilitated by
human activities. The shrimp, Litopenaeus
vannamei was introduced in Indian shrimp culture
from foreign waters4 since this species is highly
disease resistant and tolerates and grows better in
higher salinity ranges. One could often hear
reports of individual aqua farms clandestinely
introducing this species without adequate
scientific screening even before it was legalized5.
These kind of clandestine activities pose major
threats of inadvertent introduction of alien species
in Indian waters. Gulf of Kachchh alone handles
nearly 70% of the crude oil requirement of the
country leading to heavy vessel (ship) transport.
Visiting vessels are potential source of alien
marine species. Ballast waters and ship hulls are
the prominent source of alien species invasion in
coastal waters6. Ballast is any material used to
weigh down and/or balance the ships. It helps in
submergence of propeller and rudder for steerage.
For thousands of years, ships carried rocks and/or
metal as solid ballast. Ships of modern times use
sea water for ballasting. When a ship empties its
cargo, it takes in water as ballast to maintain its
stability and structural integrity. Conversely,
when it loads cargo, the ballast water is
discharged usually in the vicinity of ports just
prior to loading the cargo from an exporting
country. Sea water loaded for ballast purposes
contains a gamut of organisms and their
propagules. In the wild, natural processes control
their sustenance. However, their hostage status in
the dark ballast waters leads to alterations in
physiological and population structure of these
organisms1. Especially species of foreign origin
with a meroplankonic stage could get introduced
easily. One of the authors encountered a new
mussel in Gulf of Kachchh waters during one of
the routine field visits which did not match with
the description of any Indian mussel species. This
further strengthens the possibility of introduction
of marine species through ship traffic in Gulf of
Kachchh waters. Comparison of the pre-1960
faunal survey data for the Indian Seas with that
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INDIAN J. MAR. SCI., VOL., 45, NO.11, NOVEMBER 2016
for the post-1960 period showed that 205 nonindigenous taxa were introduced in the post-1960
period; shipping activity is considered a plausible
major vector for many of these introductions7.
In terrestrial ecosystems, besides the best known
example
of
P.juliflora,
Parthenium
hysterophorus, has been introduced through
commercial food grains during this century and
declared as weed of national significance in India.
Increasing trade and commerce through land and
sea routes provide perfect means of spread for
these invasive plants. Their ability to remain
dormant for prolonged period of time and
resilience and plasticity to new environmental
conditions enable them to get established and
spread quickly. There have been few attempts in
India to identify and quantify the origin, number
and possible impacts of biological invaders that
inadvertently arrive at our ports and borders while
in countries like US preliminary screening is in
place to track such biological invaders albeit with
limitations. However, it is to be noted that among
the introduced species, only minority of them
become invasive and again there is no much effort
to monitor their arrival and establishment. This is
further eased by the fact that many of the plant
species introductions in the country are
intentional (best example being the Bt. Cotton in
agriculture and many plants for landscaping and
gardening). Countries of Africa and southern
America and Middle East are possible sources of
invasive/non indigenous species into India with
which there has been a spurt in trade and
commercial activity recently. This is one area of
research priority to safeguard biological integrity
of the country.
Introduction of invasive plant species in
small numbers are not likely to survive due to
many environmental, biological and genetic
factors. However, multiple and sequential
introduction of species which have got the
plasticity and elasticity to survive and establish in
new environment could easily become invasive in
nature in due course of time. Most of the invasive
species are hardy and capable of withstanding
harsh environmental condition such as those of
arid and semi arid regions, which renders such
regions more susceptible to biological invasions
of plant as well as animal species. Here again
abiotic and biotic factors governing an exotic
species’ survival and establishment is so varied
and little understood that each species will have to
be studied to arrive at conclusions regarding their
life history and invasive nature. Some basic traits
like long flowering and fruiting period, short time
between seed germination and flowering, prolific
seed production, prolonged period of dormancy
enable them to establish successfully; traits shown
by P.juliflora.
Almost no data exist to show that how
invasive an introduced plant species could be in a
new terrestrial environment. Tracking seed and
propagules movement could provide some clues
as to how invasive the plant could be. It is known
some dispersal mechanisms like wind and cattle
transport could be potential source of spread in
arid treeless ecosystems like Kachchh, western
India. Some traits of the non indigenous plant
species that render them invasive include a deep
and dense root system to capture water in arid
zones, abundant nectar that attract pollinators,
high nitrogen fixing capacity that alters soil
chemistry and high fire resisting and heat yielding
capacity; traits none of the native species possess
disabling them less competitive and rendering
them to become extinct in the run. Strong genetic
make-up is another trait to the advantage of
invasive plant species.
Assessing the impact of invasive plant
species is challenging indeed; a task further
complicated by the seemingly better advance they
provide in terms of livelihood options by way of
fuel and other benefits especially in resource
scarce arid zones. Present management dilemma
vis-a-vis P.juliflora largely stems from these so
called advantages they provide. By and large
investigators largely disagree on the measurement
of consequences. Effects at different levels like
genetic, population, community, ecosystem and
economic levels further complicate the impact
assessment. Lack of data on the structure and
function of previous ecosystem before invasion
makes it further difficult for comparison. An
invasion is recognised only after it has occurred
and the ecosystem has changed unrecognisably.
The threat to biodiversity due to invasive alien
species is considered second only to that of
habitat destruction8.
India lacks a credible institutional set up to
watch introduction of alien species both in
terrestrial and marine environment. On the
terrestrial front, though numerous economic
benefits are being attributed to the all pervasive P.
juliflora, its impact on native plant species in
particular and arid biodiversity in general should
be re-evaluated in the light of already carried out
studies and new studies with the sole objective of
assessing its impact on biodiversity. Similarly,
efforts to reconstruct ecosystem in its pre-invasive
period could be done to the maximum possible
extent through the available literature for better
comparison with the present conditions.
SHARMA et al.: INVASION OF ALIEN SPECIES
A common accepted procedure to measure
the impact of invasive plant species with
P.Juliflora as reference species should be
formulated by the scientific community. Scientific
studies based on this procedure would address
many of the outstanding questions on its
perceived benefits and detrimental impacts on the
social, economic and ecological spheres. The
formulated procedure will have far reaching
utility in solving many of the issues pertaining
biological invasions of other species as well. This
common procedure would also help the widely
accepted management solution of site specific
control/promotion vis-a-vis P. juliflora by giving
a concrete indication.
On the marine front, though the Ministry of
Environment, Forest and Climate and Change
(MoEFCC) is known to have a cell to watch alien
species introduction, it is again crippled by the
common problems of lack of adequate scientific
staff and funding and clear cut policy guidelines.
While the introduced species get noted earlier in
terrestrial ecosystems such as agricultural land,
forests and other ecosystems, it takes time to
notice such alien species in marine/coastal waters
partly due to lack of monitoring programmes and
partly due to oversight. Lack of trained
taxonomist in marine ecosystems further
accentuates the problem since the introduced
species are overlooked. This problem is so acute
in maritime states like Gujarat where the science
of marine biology is still in its rudimentary stage
and there are no proper mechanisms to keep a
vigil for invasive marine species. In addition to
strict enforcement of a national quarantine policy
on ballast water discharges, long-term
multidisciplinary research on ballast water
invaders is crucial to enhance our understanding
of the biodiversity and functioning of the
ecosystem2. Hydrodynamic modelling can help in
reasonable and reliable prediction of ballast water
discharge9 and further policies suited to Indian
environments5.
There is a general lack of awareness even
among scientific communities about alien species
invasion. Especially, in vibrant maritime states
like Gujarat where aggressive maritime activities
are going it poses major threat. It is high time that
scientists and policy makers of the country are
awakened to this impending threat of alien
species invasion in Indian forests, agriculture
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lands and coastal ecosystems before it is too late.
Prosopis juliflora and Parthinium histirophorus
as a case in point amply demonstrate the
consequences of alien species getting entrenched
in Indian ecosystems. Despite a widespread
outcry on invasive plant species, studies on the
various facets of its ecology and biology are
either inadequate or irrelevant to frame a solid
management approach on this species. Priority
areas for research should be identified to fill this
gap. Multi disciplinary studies involving
researchers of population ecology, soil chemistry,
simulation modelling etc should be undertaken to
fill this gap.
Acknowledgement
The first author is thankful to DST, New Delhi for
WOS-A fellowship and Science and Engineering
Research Board-DST (SERB-DST), New Delhi
for National Post-Doctoral Fellowship. The
second author is thankful to Gujarat Institute of
Desert Ecology, Bhuj for providing facilities.
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