Impact on Marine Ecosystem
Moger, Kishor K.T., Rajeish Moger, Harshavardhan Joshi, Milind
Katare, Chandrashekar B. H., Mahesh V., Pradeepkumar N.
KVAFSU, College of Fisheries, Mangalore, Karnataka,
Corresponding auther: Narasimha Moger
Humans have used
and had an impact on marine ecosystems throughout history. As human
populations and their economic activity increased the impact
intensified, but our awareness of the long-term, pervasive effects on
marine life is relatively recent and very incomplete. This chapter
introduces some of the ethical and utilitarian values which underlie
our relationship with marine ecosystems and gives a brief overview of
historic evidence concerning past states of marine ecosystems and
intensification of human impacts. It describes impacts of fishing and
other human pressures on the demography and biomass of exploited
species and on loss of vulnerable species and habitats. Fishing and
climate interact to cause observed change to ecosystems, including
their trophic structure, with consequences for resilience and
productivity. Emerging conclusions about human impacts, future human
stewardship and utilization of marine ecosystems are presented.
Human activity over the centuries has
depleted 90% of marine species, eliminated 65% of seagrass and
wetland habitat, degraded water quality 10-1,000 fold, and
accelerated species invasions in 12 major estuaries and coastal seas
around the world, according to a study published in Science Magazine
on Friday, June 23d, and supported in part by the Lenfest
However, in areas where
have been implemented in the 20th century, signs of recovery are
Entitled "Depletion, Degradation,
and Recovery Potential of Estuaries and Coastal Seas," the study
is the most comprehensive quantitative assessment of the state of
estuaries and coastal ecosystems ever conducted. Initiated by the
National Center for Ecological Analysis and Synthesis and co-authored
by ten international experts, it shows that human impact on estuaries
and coastal waters dates back to ancient times (e.g. Roman Empire in
the Adriatic Sea). However, damage to marine ecosystems has
accelerated over the past 150-300 years as populations have grown,
demands for resources have increased, luxury markets have developed,
and industrialization has expanded.
"Throughout history, estuaries and
coastal seas have played a critical role in human development as a
source of ocean life, habitat for most of our commercial fish catch,
a resource for our economy, and a buffer against natural
Dalhousie University in Halifax, Canada and lead author of the study.
"Yet, these once rich and diverse areas are a forgotten
resource. Compared to other ocean ecosystems such as coral reefs,
they have received little attention in the press and are not on the
national policy agenda. Sadly, we have simply accepted their slow
Most mammals, birds and
estuaries were depleted by 1900 and declined further by 1950 as the
demand for food, oil, and luxury items (such as furs, feathers and
ivory) grew. Among fish, the highly desirable and easily accessible
salmon and sturgeon were depleted first, followed by tuna and sharks,
cod and halibut, and herring and sardines. Oysters were the first
invertebrate resource to degrade because of their value and
accessibility as well as destructive harvesting methods.
The primary cause of estuarine damage is
human exploitation, which is responsible for 95% of species
depletions and 96% of extinctions, often in combination with habitat
destruction. In the coming years, however, invasive species and
play a larger role in stressing estuarine resources.
According to the study, the fastest path
to recovery has been through mitigating the cumulative impacts of
human activity. Seventy-eight percent of recoveries have happened by
reducing at least two human activities, including resource
exploitation, habitat destruction, and
Despite severe degradation in these 12
very different estuarine and coastal water environments, there is
good news. "Only 7% of species went regionally extinct, and some
are rebounding (birds and seals in particular). Clearly, recovery is
achievable. As we expand our conservation efforts, we will see more
evidence of healthier, abundant marine ecosystems." said Roger
Bradbury, a resource management scientist at Australian National
In developed countries, trends suggest
that estuaries may have passed the low point and are on the path to
recovery, according to the study. In developing countries, however,
population growth, which puts pressure on coastal areas, may further
"The 2004 Asian Tsunami and 2005
Hurricane Katrina helped us recognize how important healthy estuaries
are in our lives," stated Jeremy Jackson, a paleontologist at
Scripps Institution of Oceanography. "Thanks to this study, we
can now see much more clearly what coastal ecosystems looked like
before humans interfered with them, which has given us a historical
baseline and a vision for how to regenerate diverse, resilient
ecosystems that can thrive in the centuries to come."
The study quantifies the magnitude and
causes of ecological change in 12 estuaries and coastal seas in
Europe, North America, and Australia from the onset of human
settlement to the present day. They are Massachusetts Bay, Delaware
Bay, Chesapeake Bay, Pamlico Sound, Galveston Bay, Francisco Bay,
Western Baltic Sea, Wadden Sea, Northern Adriatic Sea, Southern Gulf
of St. Lawrence, Outer Bay of Fundy, and Moreton Bay. The researchers
combined palaeontological, archaeological, historical, and ecological
records to trace changes in important species, habitats, water
quality parameters and species invasions.
Commercial fishing boat
existence we have relied on the oceans for food, as a waste dump,
for recreation, for economic opportunities and so on. However, it's
not only our activities in the marine environment that affect life in
the sea it's also the things we do on land.
With more than half the
world's population now living within 100 kilometres of the coast,
it's not surprising that our activities are taking their toll.
Human impacts have increased along with our rapid population growth,
substantial developments in technology and significant changes in
land use. Over-fishing, pollution and introduced species are
affecting life in the seas and New Zealand is no exception!
Humans living near the
coast have probably always used the ocean as a source of food.
However, with advances in fishing equipment, larger ships and new
tracking technologies, many fish stocks around the world have reduced
significantly. Fish stocks on continental shelf areas are now widely
considered to be fully or over exploited. Aside from reducing fish
stocks, unsustainable fishing practices can have other negative
impacts on the marine environment. For example, some fishing
techniques such as dredging and trawling can cause widespread damage
to marine habitats and organisms living on the sea floor. These
techniques also often capture non-target species (known as bycatch)
that are then discarded.
In New Zealand,
fisheries are managed by a quota system that sets catch limits for
commercially important species and aims at sustainable management of
our fish stocks. The Royal Forest and Bird Protection Society (NZ)
publishes the Best Fish Guide to try and encourage us to make more
sustainable choices when purchasing seafood. The list evaluates fish
stocks and bycatch levels and the fishing methods used.
Phytoplankton bloom — Our
oceans have long been used as an intentional dumping ground for all
sorts of waste including sewage, industrial run-off and chemicals. In
more recent times, policy changes in many countries have reflected
the view that the ocean does not have an infinite capacity to absorb
our waste. However, marine pollution remains a major problem and
threatens life in the sea at all levels.
Some marine pollution
may be accidental, for example, oil spills caused by tanker
accidents. Some may be indirect, when pollutants from our communities
flow out to sea via stormwater drains and rivers. Some effects may
not be immediately obvious, for example, bioaccumulation, the
process where levels of toxic chemicals in organisms increase as they
eat each other at each successive trophic level in the food web.
All marine pollution has
the potential to seriously damage marine habitats and life in the
sea. Scientists are concerned that marine pollution places extra
stress on organisms that are already threatened or endangered.
Eutrophication is the
result of a particular type of marine pollution. It is caused by the
release of excess nutrients into coastal areas via streams and
rivers. These nutrients come from fertilisers used in intensive
farming practices on land. Additional nutrients in the sea can lead
to excessive phytoplankton growth that results in "blooms". When
these large numbers of organisms die, the sharp increase in
decomposition of the dead organisms by oxygen-using bacteria depletes
oxygen levels. In some cases, this can result in the death by oxygen
starvation of large numbers of other organisms such as fish.
Since the arrival of
humans in New Zealand, introduced species in our terrestrial
ecosystems have contributed to a significant loss of biodiversity.
Introduced species also present a threat to our marine environment.
It is not always easy to monitor or prevent the introduction of
unwanted marine organisms, and visiting ships may introduce them
accidentally on their hulls, in ballast water or on equipment.
Not all introduced
species will spread or even survive, but once established, they may
be difficult or impossible to remove. For example, the Japanese
seaweed, Wakame Undaria pinnatifida, which probably arrived in 1987,
is now widespread. Scientists are still monitoring its impact on our
native marine organisms.
Biosecurity New Zealand
provides information about the prevention of marine pests and
maintains a list of high-risk organisms.
NATURE OF SCIENCE
sometimes uncovers environmental problems that are linked to human
lifestyles. This research shows that the way we live needs to be
balanced with environmental needs, which sometimes puts scientists in
a difficult position in defending their work.
There is evidence to
suggest that human activities have caused the amount of carbon
dioxide in our atmosphere to rise dramatically. This impacts on the
marine environment as the world's oceans currently absorb as much
as one-third of all CO2 emissions in our atmosphere. This absorption
of CO2 causes the pH to decrease, resulting in the seawater becoming
Scientists have long
understood that an increase in carbon dioxide in the atmosphere will
result in higher levels of dissolved CO2 in seawater. However, a
relatively recent discovery is that even small changes in water pH
can have big impacts on marine biology. Ocean acidification is a
worldwide issue, but as CO2 is more soluble in colder water, it is of
particular concern in New Zealand's temperate oceans.
It is difficult to
predict the overall impact on the marine ecosystem but many
scientists fear that ocean acidification has the potential to
decrease marine biodiversity on a very large scale.
Seafood — Fish — Crustacea
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