Download 2010, final Lecture 15 Human Effects

Threats to Marine Ecosystems
and Biodiversity
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General
Habitat Loss and Degradation
Resource Extraction
Species Invasions and Diseases
Climate Change
EXXON Valdez Oil Spill Trust Counciil; photolib.noaa.gov
Source: NOAA
General
• Human pressures on coastal resources are
compromising many of the ecosystem services
crucial to the well-being of coastal economies
and peoples
• The greatest threat to coastal systems is
development-related loss of habitats and
services
• Coastal ecosystems and islands face greater
numbers of threats than others, because
pressures are greater and because they are the
downstream recipients of degradation from afar
Habitat Loss and Degradation
• The most serious consequences of biodiversity
loss occur when changes are irreversible: e.g.
habitat loss, species extinctions, population
extirpations, regime shifts
• The most important driver behind these large
scale impacts on biodiversity is land conversion
(including coastal/marine habitat loss)
• The other drivers behind biodiversity loss differ
in various ecosystems, and include overexploitation, pollution, and climate change
Resource Extraction
• Many fisheries exceed
sustainable limits of use
• The removal of small-scale
heterogeneity associated with
the homogenization of habitats
is an important cause of the
loss of biodiversity
Source: T. Agardy
• Both over-exploitation beyond
sustainable levels and fishinginduced or coastal
development-related habitat
destruction are major issues
NOAA
Overfishing (= Intense Predation)
• The global marine catch has increased more than four
times in the past 40 years.
• Overfishing has pushed many fish populations into steep
declines. Catches are falling, even though fleets are
fishing harder than ever before
• The U.N. Food and Agriculture Organization (FAO)
reports that seven of ten commercially targeted fish stocks
are either fully or heavily exploited (44 percent),
overexploited (16 percent), depleted (6 percent), or
slowly recovering from previous overfishing (3 percent).
Pillaging the North Atlantic: species and the
year that > fishing effort = no increase in
yield: ‘overfishing!’
C= cod
H=haddock
P=plaice
R=redfish
Hk=hake
Hg=herring
Ocean Fisheries
• > 109 people (mostly developing nations) depend upon
marine fish for primary source of protein
• a 40 y ‘fishing boom’ has now ended: catch increasing
steadily since 1950, but since 1989 world catch has
stayed the same
• catch of ‘high value’ fish decreasing; catch of low value
fish increasing
Exploitation of global fisheries
Overfishing: Gear Impacts
• Trawlers often scrape the same area several times
each year. Sea-floor species can be crushed and
displaced, and the types and availability of nutrients
changed.
– Sediments stirred up by trawling can make water a
thousand times cloudier than normal, limiting
resettlement and feeding of plants and animals
Trawling
Beam
trawlhow to
destroy
benthic
habitats
Effects of scallop dredging
on a gravel bottom:
George’s Bank: 84 m depth
Un-fished area
Fished area 500 m away
Frequency of trawling in some
representative areas
The rapid decline of the orange
roughy fishery
Red: est. biomass
Blue: catch
Overfishing: Continued
• There is great difficulty in sustaining global fisheries
production. In response to declines of big, slower growing
species, fishers have begun "fishing down the food
chain", targeting smaller species of less value, but which
can play critical roles in food webs.
• The most glaring crises of global fisheries include:
– over-capitalization of the industry which has led to the
buildup of excessive fishing fleets, particularly of the
larger-scale vessels catching too many fish.
Overfishing: Continued
• Government subsidies enabled vessels to operate in
conditions that are uneconomic and environmentally
unsound. Fleets migrate globally to find more lucrative
fishing opportunities. Subsidies also supported a spree in
new vessel construction in recent years.
• Increased fishing pressure and competition among fishing
nations severely stresses fish stocks and the marine
environment. The use of unselective fishing gear results in
millions of tons of unwanted bycatch being dumped
overboard annually. Many millions of other animals are
incidentally killed by fishing fleets.
“Discards” in
the fishing
industry:
A.K.A.
‘BYCATCH’
Overfishing: Indirect Effects of Fishing
on Food Webs (bycatch cont.)
• Driftnets drown by-catch
– With nearly invisible filament mesh, enormous
driftnets catch and hold fish by the gills.
• Driftnets also entangle and drown birds, sharks,
whales, and dolphins.
– The by- catch problem was so dire that the UN
banned large- scale driftnetting on the high seas in
1993.
• Smaller driftnets are still used in coastal waters,
including those of the U.S
The high seas
driftnet fishery
Overfishing: Impacts on Biodiversity
• Fishing can be an agent of selection, affecting age
distribution, age and size at maturity, and growth
• Fishing can alter species composition and interactions
among fished species and their prey.
• Fisheries often begin on large predators but their
reduced numbers may lead to increased numbers of
prey species, which may themselves become fished.
• Intense fishing can lead to dominance by r-selected
species, which often become major parts of mature
fisheries. Other species can also be affected; e.g.,
fishery discards have caused long-term changes in
seabird species composition.
Overfishing: Indirect Effects
Overfishing: large marine herbivores
• Losses of herbivorous
green turtles and fishes are
thought to be partly
responsible for low levels
of seagrass grazing and
algal overgrowth of coral
reefs
Overfishing: A few success stories
• One success story,
Spanish mackerel in
the Gulf of Mexico are
no longer overfished
and, in fact, have
become a sustainable
fishery.
• Pompano are also
recovering in the Gulf
The three main “failings” of
fisheries
• Oceans are a ‘free for all’, and regulatory bodies make weak
commitments to preserve stocks and then fail to follow
through
• Fishing fleets are subsidized by nations: $20 billion globally
• Conservation measures: there are few closed seasons and
limits to total catch
• http://www.learner.org/courses/envsci/unit/text.php?unit=9
&secNum=0# Jackson video
Exotic Species in the Oceans
• Invasion of marine areas by non-native species is a major
threat. The National Research Council's study
"Understanding Marine Biodiversity: A Research Agenda
for the Nation“ says it is one of the five most critical issues
facing marine life.
• The ecological consequences of invasions include:
– habitat loss and alteration
– altered food webs
– creation of novel and unnatural habitats that may be
colonized by other exotic species
– abnormally effective filtration of the water column
– hybridization with native species
– highly destructive predators; and
– introductions of pathogens and disease
Ecosystem characteristics that may
favor successful invasions
• The invaded habitat is climatically matched with the
original habitat
• The community is an early successional one; thus, there
may be low diversity and absence of similar species.
• Lack of natural enemies
• Lack of keystone species
• Heavily polluted or disturbed environments
Possible characteristics of
successful invaders
• r-selected species with short generation times,
high fecundity, high population growth rates
– but some suggest a role for shifts between r
and K strategies
Non-native Pathways of
Introduction
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Aquaculture
Aquarium trade
Biological control
Boats and ships
Channels, canals, locks
Live bait
Nursery industry
Scientific research institutions, schools and public
aquariums
Recreational fisheries enhancement
Exotic Species: Ballast Water
T
• To maintain stability ships fill
ballast tanks with water. Large
ships often carry millions of
gallons of ballast water. As a
ship loads ballast it also loads
many organisms. Ballast water
is carried from one port to
another, where the water may
be discharged.
Exotic Species: Ballast Water (2)
• Perhaps 3,000 species per day
are transported around the
world. Most don’t survive, but
some thrive in their new
homes. These invaders can
cause disruptions to
ecosystems, economies, and
may carry human diseases.
• The Int’l Maritime Org. and
the U.S. government
recommend open ocean ballast
water exchange; however, few
countries have adopted this.
Exotic Species: Nutria
• Nutria, from South America,
were introduced into Maryland
and La. in 1940’s & 50s for fur
production. Since the 1970s,
there has been a weak demand
for fur
• Nutria burrows normally extend
4 to 6 ft. into marshes (but may
be as long as 150 ft.)
• Damage first noted in the early
1990's, and $millions in
damages have accumulated
Exotic species: Nutria (2)
• Nutria herbivory can have
dramatic impacts on coastal
landscapes , and nutria have
been implicated in large
scale losses of marsh in
Maryland.
• What was once continuous
marshland (above) now
appears as fragmented
remnants
Solutions to the Nutria Problem
• From the Dallas Morning News on July 7, 1997 “A
nutria a day helps keep erosion at bay: Louisianians
urged to eat rodents, save coast”
• "A young nutria tastes a lot like rabbit," Mr. Windom
(a La. Wildlife and Fisheries biologist) said, adding
that they can be fried, barbecued or cooked numerous
other ways.
Eutrophication
• Increased population density within watersheds has
led to dramatic increases in nutrient inputs to coastal
waters
– increases range between 2 and 20 fold over
preindustrial age
• Consequences of eutrophication
– elevated phytoplankton production coupled with
stratification of the water column leads to hypoxia
and anoxia
– fish kills, reduced light for seagrasses, increased
incidence of harmful algal blooms
Worldwide “Dead Zones”
Eutrophication: Harmful Algal
Blooms
Marine Diseases
Are much more prevalent in the world’s oceans in the
past few decades, and this has spurred a great deal of
research into the causes of these disease outbreaks.
Marine Diseases:Black Band Disease
and Coral Reef Losses
• Black band disease caused
significant coral losses
– 1973-74 in Bermuda and
Florida Keys, in 1978
Acropora corals in Florida
– 1985-86 in Florida again
– The major component is a
cyanobacterium and other
microorganisms, including
sulfate-reducing bacteria and
heterotrophic bacteria
White Band Disease
• First reports of tissue slowly
peeling off elkhorn and staghorn
corals at Tague Bay, U.S. V. I.
– The loss of tissue resulted in
a band of white skeleton and
this was named white-band
disease (WBD).
– Unlike BBD, despite
intensive study, no
microorganisms could be
found
Additional coral diseases
 Dark Spots Disease
 Rapid Wasting Disease
 Red Band Disease
 White Plague
 Yellow Band Disease
Marine Diseases: The loss of Diadema
antillarum in the Caribbean
• Black urchin plague occurred
in the Caribbean and caused
98% mortality within 10 days
of the first signs of the
disease in a new locality.
– Unlike other diseases,
which were localized, black
urchin plague spread from
Venezuela to Bermuda,
reducing populations to 17% of former levels.
Consequences of Diadema Dieoff
• Algal overgrowth of
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coral reefs
Loss reef
productivity & cover
Lost ecosystem
productivity
Marine Diseases-Seagrasses
• Labyrinthula is a slime mold that
could be responsible for mass
mortality of seagrass .
• In 1931, observers noticed
blackish-brown discolorations, a
loss of leaves and death of the
eelgrass along the U.S. east coast
• By 1933, this "disease" had
decimated 90% of all eelgrass in
the North Atlantic.
Occurrence of Labyrinthula in
Florida Bay
Climate Change
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The geographically largest scale impacts to coastal
systems are caused by global climate change
Warming of the world’s seas affects species by:
- Changing sea level faster than most can adapt;
- stressing temperature-sensitive organisms such as
corals;
- changing current patterns to interfere with important
processes like recruitment
Global warming also changes the temperature, salinity and
aciditiy of estuarine and nearshore habitats and
exacerbates the problem of eutrophication
Climate Change and Disease
• Warming can increase the transmission rates of
pathogens and hasten the spread of many forms of
human and non-human disease.
• In most if not all cases, global climate change impacts
act in negative synergy with other threats to marine
organisms, and can be the factor sending ecosystems
over the threshold levels for stability and
productivity.
Methods to Conserve Marine
Biodiversity
1. Spatial management through
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zoning and marine protected
areas
Restoration
Fisheries Management
Integrated coastal zone
management
Regional & international
agreements/treaties
Kevin Frey © CBC-AMNH
West Andros Island, Bahamas
Source: T. Agardy
Spatial management through zoning
and marine protected areas
(MPAs)
Individual sites recognized for their valuable services
are sometimes protected through zoning regulations
and other spatial management interventions such as
marine protected areas (MPAs)
Restoration
• Some key coastal habitats
such as mangrove forests,
marshes, and seagrass
meadows can be, and are
being, restored
• In general, however, the
costs of restoration far
exceed costs of protecting
the natural habitat
Fisheries Management
• Management of living marine resource use has been
practiced for several centuries
• Modern fisheries management has moved away from
stock-by-stock and single species management to
broader, ecosystem-based management
• Fisheries management tools include quotas on take,
gear restrictions, access restrictions, seasonal or other
timing restrictions, and MPAs
Integrated coastal management
• Though coastal management is spreading around the
world, management has not kept pace with
degradation
• Specific approaches have shortcomings in managing
complex issues such as biodiversity
• An integrated management response is needed to
conserve most aspects to biodiversity, especially at
the ecosystem level
Regional & intl. agreements/ treaties
• Most marine species cross the boundaries of
individual countries, making regulation beyond the
control and responsibility of any individual nation
(e.g., spiny lobsters and corals in the Fla. Keys)
• International/Regional treaties provide a legal
framework for marine conservation action, resource
regulation, and scientific research on a broad scale
Constraints to Marine Conservation
• Time Lags between perturbation to a system and the
eventual effects on the system mean that anticipating
effects is difficult
• Incomplete ecological understanding (and corollary
incomplete sociological understanding), can be a major
constraint in effective conservation
• Lack of funding (for research, for monitoring and for
enforcement of regulations) is a hindrance
• The lack of awareness and political will to change
policies is perhaps the biggest constraint
Conclusions
•Marine ecosystems are extraordinarily complex and
ecological understanding of marine ecosystems is limited,
but enough is known that better management action can be
taken
•Establishing adaptive management regimes will allow us to
gain important marine ecological information quickly
•Integrated approaches and international cooperation are
needed to conserve marine ecosystems and marine
biodiversity