Understanding marine biodiversity and
its threats are very important for a
number of reasons. One could argue
that marine biodiversity has innate
importance, as life has value on its own.
Anthropogenic impact on the oceans is
already there to a considerable degree,
especially in the coastal areas but
increasingly in the open ocean as well.
Some threats are: Pollution,
4. Habitat Destruction (loss), Introduction of alien
species, Overexploitation, Climate change and
Declining marine biodiversity worldwide is a
major and on going environmental dilemma.
Attention to biodiversity changes in the oceans
is limited and these threats are due to
development related activities along almost half
of the world's coasts. The impact of
unsustainable developmental activity has
caused loss of habitat and massive reductions in
our aquatic species biodiversity. Pollution
affects many marine organisms.
5. Increment in CO2 results in the
decrease of pH of the ocean, due to
which acidification causes destruction of
corals and coral reefs.
Major threats to marine diversity are:
7. The exploitation of marine species has
caused large scale changes in populations
of both predator and prey species
throughout the world's oceans.
Effects of fishing activities extend beyond
the target species.
The effects of fishing activities are as
diverse as the number of fishing
techniques used and include: bycatches of
marine mammals, seabirds, fish and
invertebrates; 'ghost fishing' by lost nets;
8. habitat disruption; changes in predator-prey
relationships; and resuspension of surface
sediments and contaminants.
Bycatches, although undesirable, are an
unavoidable consequence of fishing in multi-
Currently, it is estimated that the equivalent of
one-quarter of global fish catches is discarded
either dead or dying back into the sea.
Some fishing techniques are very specific and
have few effects on the habitat, e.g. traps, static
nets and baited lines.
9. Artisanal fishers in the tropics use poisons,
drive netting and explosive fishing that
causes direct physical damage to reefs.
Towed bottom fishing gears affect the
largest areas of sea bed world-wide.
1 Direct effects on benthic fauna and habitats
Fishing gear used to capture benthic species
is specially designed to remain in close
contact with the sea bed.
10. Some fishing gears, such as beam trawls and
scallop dredges, are adapted so that parts of the
gear dig into the sea bed to dislodge either
flatfish, such as sole and plaice, or bivalves,
such as scallops. Not surprisingly, the catches of
such fishing gears contain a large proportion of
non commercial benthic species other than
those sought by fishers .
The discarded bycatch , on the digging action of
bottom fishing trawls and dredges leaves a trail
of exposed and damaged animals.
11. Incidental catches and 'ghost fishing'
Advances in technology and the advent of man
made materials such as nylon have led to a
revolution in some sectors of the fishing
Despite their relative selectivity both purse
seining and set netting take incidental catches
of marine mammals reptiles and sea birds.
12. The lost gear has the potential to continue
fishing indefinitely depending upon its
condition-a phenomenon known as 'ghost-
Gear lost in shallow waters soon loses it
ability to fish as it becomes tangled up and is
overgrown with algae and encrusting animals
However, when nets are lost in deep,
relatively calm water, or are held open by
snags on rocks or wrecks, they can continue
fishing for many months or years.
13. Non-target species population changes
Fishing activities are often aimed at a particular
trophic level within a community or at one
Fishing caused the removal of the main urchin
predators, triggerfish Balistapus and Chelinus
trilobatus. This led to an ecological release of
sea-urchins and the competitive exclusion of
weaker competitors such as herbivorous fish.
14. • Urchins also erode the coral reef matrix
through their feeding activities. Thus
denser populations of larger sea-urchins,
fewer and smaller fish and reduced coral
cover were found in heavily fished Kenyan
Whaling activity earlier this century greatly
reduced baleen whale populations in the
Antarctic, reducing the consumption of krill.
Supposedly, the release of krill
corresponded to a subsequent increase in
populations of penguins and seals.
15. Dredging and mineral extraction
As humans have depleted terrestrial mineral
resources, it has become economically feasible
to begin mining the marine habitat.
These effects are evident in the marine
environment, where extraction leads to habitat
alteration, faunal removal and contaminant
However, whereas fishing affects only the
superficial layers of the sediment (0-20 cm
16. the process of aggregate extraction completely
removes the substratum to depths in excess of 1 m. In
this case, the issue is not recovery of the fauna, rather
recovery of the habitat. Dredging reduces both
habitat and species diversity within the drugs track
creating a trench in the sediment and produces a
sediment plume. Sedimentation at these deaths occur
at the rate of a few mm every thousand years. As a
result, dredge tracks will persist for many years and
filter-feeding organisms may be adversely affected by
the unnaturally large pulse of sediment that settles
out of the plume
A wide array of objects and substances are
discharged either deliberately or
accidentally into the sea: oil and other
petrochemicals, solvents, insecticides and
herbicides from agricultural run-off, heavy
metals, domestic waste, radionuclides,
sewage and other organic materials, plus a
host of others.
18. Oil spillage
An oil spill is the release of a
liquid petroleum hydrocarbon into the
environment, especially the marine
ecosystem, due to human activity, and is a
form of pollution.. Oil spills may be due to
releases of crude oil from tankers, offshore
platforms, drilling rigs and wells, as well as
spills of refined petroleum products
19. Oil penetrates into the structure of the plumage
of birds and the fur of mammals, reducing their
insulating ability, and making them more
vulnerable to temperature fluctuations and
much less buoyant in the water.
Animals who rely on scent to find their babies
or mothers cannot due to the strong scent of
the oil. This causes a baby to be rejected and
abandoned, leaving the babies to starve and
20. Oil can impair a bird's ability to fly, preventing it
from foraging or escaping from predators.
As they preen, birds may ingest the oil coating
their feathers, irritating the digestive tract,
altering liver function, and
causing kidney damage.
Together with their diminished foraging
capacity, this can rapidly result
in dehydration and metabolic imbalance.
Some birds exposed to petroleum also
experience changes in their hormonal balance,
including changes in their luteinizing protein.
21. The majority of birds affected by oil spills die
from complications without human
intervention. Some studies have suggested
that less than one percent of oil-soaked birds
survive, even after cleaning, although the
survival rate can also exceed ninety percent,
as in the case of the MV Treasure oil spill.
Oil spills and oil dumping events have been
impacting sea birds since at least the
1920sand was understood to be a global
problem in the 1930s.
22. Heavily furred marine mammals exposed to oil
spills are affected in similar ways. Oil coats the
fur of sea otters and seals, reducing its
insulating effect, and leading to fluctuations
in body temperature and hypothermia.
Oil can also blind an animal, leaving it
The ingestion of oil causes dehydration and
impairs the digestive process. Animals can be
poisoned, and may die from oil entering the
lungs or liver.
23. There are three kinds of oil-consuming
bacteria. Sulfate-reducing bacteria (SRB) and
acid-producing bacteria are anaerobic, while
general aerobic bacteria (GAB) are aerobic.
These bacteria occur naturally and will act to
remove oil from an ecosystem, and their
biomass will tend to replace other populations
in the food chain. The chemicals from the oil
which dissolve in water, and hence are available
to bacteria, are those in the water associated
fraction of the oil.
24. Chemicals in crude oil are mostly hydrocarbons
that contains toxic chemicals such
as benzenes, toluene, poly-aromatic
hydrocarbon and oxygenated polycyclic
25. Tbt poisoining
Tributyltin (TBT) is an umbrella term for
compounds which contain the (C4H9)3Sn group,
with a prominent example being tributyltin
oxide. As TBT is most often used as a biofouling
The TBT slowly leaches out into the marine
environment where it is highly toxic toward non
The effects of antifouling paint go beyond the
organisms that it is intended to kill.
26. By poisoning barnacles, algae, and other
organisms at the bottom of the food chain, the
bioaccumulation of TBT increases over time
affecting more and more of the bottom feeders
of the aquatic food web environment, which are
mainly invertebrates and are effected from TBT.
, it bioaccumulates in marine wildlife such as
molluscs, with levels being higher in organisms
and sediments in and around areas of high
maritime activity, such as ports and harbours.
27. The bioaccumulation increases over time,
leading to a biomagnification in organisms
higher up the food chain, although the
biomagnification is not that considerable in size.
As TBT can remain in the environment for up to
30 years due to often bonding to suspended
material and sediments.This can lead to very
high amounts of TBT being accumulated,
especially in smaller organisms lower down the
food chain, which in turn has various health
28. Exposure to organotin compounds causes the
development of male accessory sex organs in
female prosobranch gastropods. This
phenomenon has been termed imposex.
Vertebrates become affected by the waters
contaminated with TBT as well as by consuming
organisms that have already been poisoned.
TBT can enter the diet of humans and other
mammals. TBT has been shown to lead to
immunosuppression in sea-otters and dolphins.
TBT has also been linked to hearing loss in
mammalian predators such as toothed whales.
29. Radioactive waste
From 1946 through 1993, thirteen
countries used ocean disposal or ocean
dumping as a method to dispose of
30. Certainly radiation can enter the food chain
though plankton and kelp and then go on to
contaminate fish. Radioactive caesium and
plutonium has already been found in seals and
porpoises in the Irish Sea.
The waste materials included both liquids and
solids housed in various containers, as well as
reactor vessels, with and without spent or
damaged nuclear fuel.
31. Plastic pollution
Over 300 million tons of plastic are produced
every year for use in a wide variety of
At least 14 million tons of plastic end up in the
ocean every year, and plastic makes up 80% of
all marine debris found from surface waters to
Marine species ingest or are entangled by
plastic debris, which causes severe injuries and
32. Researchers “conservatively” estimate that 14
million tons of microplastics can be found on
the world’s ocean floor, according to
a study published last year in Frontiers in
Marine Science. They can be harmful to ocean
and aquatic life.
Eutrophication is a process driven by the
enrichment of water by nutrients, especially
compounds of nitrogen and/or phosphorus,
leading to: increased growth, primary
production and biomass of algae; changes in
the balance of organisms; and water quality
35. Nitrogen and phosphorous are the primary
inorganic nutrients responsible for the
eutrophication of marine waters. Nitrogen and
phosphorous occur naturally in marine waters,
transferred from land via streams, rivers and
runoff of rainwater and also from degradation
of organic material within the water. However,
human inputs of nutrients to the environment
has increased the load of nitrogen and
phosphorous to the oceans.
36. Primary Impacts
Algal growth in marine waters is regulated by
the level of nitrogen and phosphorous and to
a lesser extent other inorganic compounds.
Eutrophication leads to an increased algal
growth (because the level of nutrients
increases). It can lead to a shift in species
composition to fast growing algae species
(including toxic species) and a shift from long
lived macroalgae to more nuisance species
37. Secondary Impacts
The reduced amount of sunlight received by
bottom waters can lead to the reduction in the
depth distribution of macroalgae and sea
Increased decomposition of organic matter
(dead algae) can lead to oxygen deficiency in
bottom waters. Lowered oxygen concentrations
can then impact the fish and benthic fauna
(animals living on the bottom of the sea or a
lake), which either flee or die from the area.
38. In the end, eutrophication can cause a shift in
the biodiversity and ecosystem balance.
Oxygen depletion can reduce fish and shellfish
stocks and thereby have an economic impact on
the fishery industry.
Algal toxins from harmful algal blooms can
cause shellfish poisoning in humans and be of
danger to live stocks in coastal water.
The water quality can be reduced due to
decaying algae with foul odours and foam on
beaches, or toxins from blooms, impacting the
The tremendous volume of sewage humans
discharge into the ocean kills marine life,
degrades critical habitats, and harms the
ecosystems upon which humans depend, while
remaining a threat to human health. Sewage
pollution can be linked to the following impacts:
Eutrophication due to nutrient overload that
depletes oxygen, kills marine flora and fauna,
and disrupts ecological processes.16
41. Harmful algal blooms that can produce toxins
or physical material (i.e., sargassum) that kill
marine life, close beaches, and can cause
human disease through direct exposure and
indirectly through consumption of
Physical and biological damage to coral reefs,
seagrasses, and salt marshes, lead to high levels
of local acidification, and increase risk of
42. Loss of coastal ecosystem services, like erosion
control, buffers from storms, and nurseries for
Animal and human diseases resulting from
pathogens, heavy metals, and toxic chemicals
that can cause acute disease, as well as long-
term disruptions to biological processes.26-28
Contamination of fisheries and fish
mortality as well as reductions in species
diversity in polluted areas because of decreased
dissolved oxygen (due to increases in nutrient
levels) and algal toxins.
43. Climate change
As greenhouse gases trap more energy from the
sun, the oceans are absorbing more heat,
resulting in an increase in sea surface
temperatures and rising sea level.
Coastal Flooding. Flooding is becoming more
frequent along the U.S. coastline as sea level
rises. Every site measured has experienced an
increase in coastal flooding since the 1950s. The
rate is accelerating at most locations along the
East and Gulf coasts.
44. The East Coast suffers the most frequent coastal
flooding and has generally experienced the
largest increases in the number of flood days.
The ocean has become more acidic over the
past few decades because of increased levels of
atmospheric carbon dioxide, which dissolves in
the water. Higher acidity affects the balance of
minerals in the water, which can make it more
difficult for certain marine animals to build their
protective skeletons or shells.
47. • Additional coral diseases
Dark spots Disease
• Rapid Wasting Disease
• Red Band Disease
• White Plague
• Yellow Band Disease.
Marine habitat is under great threat by human
exploitation. Conservation of marine habitat is
necessary for the maintenance of marine
organisms, thereby reestablishing the balance
of earth since ocean covers the largest portion
of earths surface.
Thank you <3
An Introduction to Marine Ecology by R. S. K.
Barnes & R. N. Hughes