Transcript EnvSci CH13x

CHAPTER 13 MARINE ECOSYSTEMS
SCIENCE UNDER
THE SEA
Aquanauts explore an ecosystem on the brink
What is ocean acidification
and why is it a threat to
ocean ecosystems?
WHAT ARE OCEAN
ECOSYSTEMS?
Ocean ecosystems cover about
70% of Earth’s surface, and
house a greater variety of flora
and fauna than all land masses
combined.
WHAT KEY FACTORS SHAPE
OCEAN ECOSYSTEMS?
Ocean ecosystems are influenced by:
• depth of the water column
Sunlight supplies both heat and energy for
photosynthesis, and since 80% of sunlight is
absorbed in the top 10 meters, the upper
layers of the ocean are more productive.
• proximity to the shore
The closer to land and rivers that empty into
the ocean, the more nutrient-rich the area, and
thus more productive.
WHAT ARE THE DIFFERENT
TYPES OF OCEAN
ECOSYSTEMS?
Question
Which zone of the ocean absorbs the
greatest amount of sunlight?
A. hadal zone
B. mesopelagic
C. bathypelagic
D. epipelagic
Question
____________ are areas where
saltwater mixes with freshwater and
creates a distinct habitat.
A. wetlands
B. estuaries
C. gyres
D. ocean currents
WHY DO OCEAN
ECOSYSTEMS MATTER?
OCEANS PROVIDE
ECOSYSTEM SERVICES
• Temperature moderation
• Nutrient cycling
• Support for commercial fisheries
• Storm protection for coastal areas
• Recreational opportunities
• Source of medicines
Coral reefs are among the most
biodiverse of all ocean ecosystems.
Do Meow
WHAT IS A CORAL REEF?
WHY ARE CORALS
CONSIDERED THE ULTIMATE
KEYSTONE SPECIES?
WHAT IS A CORAL REEF?
Coral reefs are ocean ecosystems that
are found in shallow, nutrient-poor
water in tropical regions.
WHY ARE CORALS
CONSIDERED THE ULTIMATE
KEYSTONE SPECIES?
Corals are extremely important to their
ecological community as they provide the
primary structure for the reef community.
The mutualistic relationship with photosynthetic
zooxanthellae enable corals to live in nutrient-poor
marine waters.
Scientists estimate that 25% of all
ocean species spend at least some
portion of their life in a coral reef. This
outsized role in marine ecology makes
understanding coral reefs critical to
understanding what is going on in the
ocean.
WHAT IS GOING WRONG IN
CORAL REEFS AND OTHER
OCEAN ECOSYSTEMS?
Human activities that are threatening
ocean life:
FISHING PRESSURES
• overfishing – 90% of top
trophic-level fish have been
eliminated
• impacts of fishing
techniques– bottom trawling
damages sea beds; dynamite
damages coral reefs
• killing of non-target species
Human activities that are threatening
ocean life:
POLLUTION
• nutrients
• pathogens
• toxins
• oil spills
• litter and plastic waste
• sediments
Human activities that are threatening
ocean life:
INVASIVE SPECIES
• 80% of global ocean harbors
host invasive species
• invasive species may kill native
species or outcompete them
when foraging
• 80% of native species in a
coral reef may disappear if a
lionfish is introduced
Do Meow
WHAT ARE THE BIGGEST
THREATS TO
THE HEALTH OF OCEANS?
Be specific
These same threats are exacerbated
in coral reefs.
75% of the world’s
coral reefs are
threatened by human
activity.
Due their proximity to
coasts, reefs are
particularly threatened
by activities on land.
But…probably the most
significant threat to oceans
is fossil fuel combustion.
The ocean and atmosphere come into
direct contact over 75% of Earth’s surface,
and they are constantly exchanging gases
over that interface —including CO2.
Winds mix CO2 into the top few
hundred feet of water, and as
years pass, currents pull it ever
deeper into the ocean.
From the analysis of nearly 80,000 water
samples, scientists estimate some 30% of
all the CO2 released by humans in the last
two centuries has been absorbed by the
world’s oceans.
This is good news for terrestrial
ecosystems but bad news for
ocean ecosystems.
WHY?
Because it acidifies the ocean.
WHAT IS AN ACID?
HOW MUCH ARE THE OCEANS
ACIDIFYING?
WHAT ARE THE
CONSEQUENCES OF
OCEAN
ACIDIFICATION?
Today the
oceans are 30%
more acidic than
in 1800.
By 2100 the
oceans could be
150% more acidic
than in 1800.
Ocean acidification corresponds
to increase in atmospheric CO2
Declines in availability of key nutrients like
nitrogen and iron have been documented
to occur in tandem with declines in pH.
Species of
plankton more
tolerant of nutrient
declines gain an
advantage
Such a change in
species composition
can alter the food
chains and decrease
primary production in
the oceans.
Plankton
biomass may
have already
decreased
by as much
as 40%
since 1950.
As nutrients decline it could set off an
unpredictable chain of events –
POSITIVE FEEDBACK
NEGATIVE FEEDBACK
Less plankton
means less primary
production, thus
less CO2 capture
and storage
Less nitrogen
fixing means less
N2O (another
greenhouse gas)
produced
Increases in carbonic acid both eat away
at existing calcium-based materials and
interfere with their production.
This affects marine calcifiers from snails to
corals to plankton – they grow more slowly
and their bodies dissolve in the acidified
ocean water.
CAN MARINE SPECIES AND
ECOSYSTEMS ADAPT TO
THESE CHANGES (caused
by ocean acidification)?
PERHAPS
…
Acidification of oceans may also reduce
the water’s ability to absorb lowfrequency sounds, which would make at
least some regions of the ocean much
noisier and thereby disrupt whales,
dolphins, and fish.
But ocean acidification is
not the only threat to marine
ecosystems resulting from
fossil fuel combustion.
Global warming from the increased
greenhouse gases in the
atmosphere is also associated with
• rising sea levels, which may decrease
sunlight penetration, thus reducing
photosynthesis.
• rising ocean temperatures, which can increase
thermal stress, thus increasing coral bleaching.
Coral bleaching may be an adaptive response
–coral take up different species of zooks
better suited to the changed conditions.
So the effect of stress on a reef system is
influenced by past events—some reefs may
be acclimated or adapted to thermal stress or
lower pH.
Coral only survive for short periods without
zooks, and will die if not recolonized.
Multiple stresses or a stress that persists may
push a coral beyond its ability to survive or
adapt.
HOW DO WE PROTECT
MARINE ECOSYSTEMS?
“We can’t reverse the tide at this
point. But if we act quickly, we
can at least slow it down ”
- Marc Slattery