Download 2008, finat Lecture 14 Human Effects, Aug 04

Threats to Marine Ecosystems and
Biodiversity
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5.
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 developmentrelated 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 over-exploitation,
pollution, and climate change
Average erosion rates:
30-40 tons/ha/yr
vs. 0.004-0.05 tons/ha/yr
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 (= IntensePredation)
• The global marine catch has increased more than four times in the
past 40 years -- from 18.5 million tons in 1950 to 82.5 million tons
by 1992.
• Decades of overfishings have pushed many commercially important
fish populations into steep declines. Catches are falling, despite the
expanding fleets that are fishing harder, spending more time, effort
and money than ever before.
• The U.N. Food and Agriculture Organization (FAO) reports that
seven of ten (69%) of the oceans commercially targeted marine fish
stocks are either fully or heavily exploited (44 percent),
overexploited (16 percent), depleted (6 percent), or very slowly
recovering from previous overfishing (3 percent).
The pillaging of 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
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 whipped up by trawling can make water a
thousand times cloudier than normal, limiting
resettlement and feeding of plants and animals
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
Overfishing: Indirect Effects of
Fishing on Food Webs
• Nets are not always selective: some capture everything
in their paths--the target catch, as well as many nontarget species (the by-catch).
– Unwanted or undersized animals culled from a catch
are discarded--thrown back into the sea, dead or
dying
• Shrimpers tow nets that collect shrimp, and many other
animals in their path.
– Red snapper, croaker, mackerel, sea trout, spot,
drum, and other fishes--up to nine times more than
the shrimp catch--are dumped overboard, already
dead or dying
“Discards” in
the fishing
industry: a.k.a
‘BYCATCH’
Overfishing: Indirect Effects of Fishing
on Food Webs (bycatch cont.)
• Driftnets drowned by-catch
– With nearly invisible filament mesh, enormous
driftnets (used in the open ocean) 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 being used in coastal
waters, including those of the U.S
The high seas
driftnet fishery
Overfishing: Impacts on Biodiversity
• At the genetic level, fishing can be an agent of
directional selection, affecting age distribution, age and
length at maturity, and growth rates.
• At the species level, 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, such as small pelagic fishes, which often
become major parts of mature fisheries. Other species
can also be affected; for example, fishery discards have
caused long-term changes in the species composition of
seabirds.
Overfishing: Indirect Effects
Overfishing: large marine herbivores
• Losses of herbivorous
green turtles and
fishes are thought to
be responsible for low
levels of seagrass
grazing and algal
overgrowth of coral
reefs, respectively
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.
Exotic Species in the Oceans
• Invasion of coastal and marine areas by non-indigenous
is a major threat
• Invasion of non-indigenous aquatic species, according to
the 1995 National Research Council's study
"Understanding Marine Biodiversity: A Research Agenda
for the Nation", is "one of the five most critical
environmental issues facing the ocean's 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 climatically matches the original habitat
• The existing community is in an early successional state
•
•
•
– vacant niche, low diversity of natives, absence of similar
species
• suggests a role for disturbance in the success of invaders
Lack of natural enemies
– for plants, invasions into areas with high predator densities
Low connectance in local food webs
– lack of keystone species
Heavily polluted or disturbed environment
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
Nonindigenous pathways
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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 alien species per
day are transported around the
world. Not all survive, but some
that do thrive in their new
environment. These invaders
can cause disruptions in natural
ecosystems, economic troubles,
and may carry human diseases.
• What can we do?
• The Int’l Maritime Org. and the
U.S. government recommend
open ocean ballast water
exchange; however, very few
countries have adopted this.
Exotic Species: Nutria
• Nutria, natives of 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
• Most common nutria damage
results from burrows, which
normally extend 4 to 6 ft. into
marshes (but some may be as
long as 50 to 150 ft.).
• Damage first noted in the early
1990's, and $8 M of damages
have accumulated even though
only 14% of the marsh canals
were heavily damaged.
Exotic species: Nutria (2)
• Nutria are herbivores that
can have dramatic impacts
on coastal landscapes
• The nutria has been
implicated in large scale
losses of emergent marsh in
Maryland, especially those
along the Blackwater River in
Dorchester County.
• What was once continuous
marshland (above) now
appears as fragmented
remnants
Solutions to the Nutria problem
• This 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 populations density within the nations
watersheds has led to dramatic increases in nutrient
inputs in coastal waters
– increases range between 2 and 20 fold over preindustrial age
• Consequences of eutrophication
– elevated phytoplankton production coupled with vertical
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
Marine Diseases:Black Band Disease
Associated with Coral Reef Losses
• Black band disease caused
•
significant coral losses
– 1973-74 in Bermuda and
Florida Keys.
– 1978: Acropora corals in
Florida .
– 1985-86: in Florida Acropora.
The major component of the mat
is a filamentous cyanobacterium
and other microorganisms,
including sulfate-reducing
bacteria, heterotrophic bacteria,
and other microorganisms.
Black Band Disease: Close-up
• In the 1970s Antonius reported
instances of a band of soft black
material moving over the surface
of some species of massive star
corals and brain corals in the
western Caribbean.
• The band apparently "consumed“
coral tissue as it passed over the
colony surface, leaving behind
bare skeleton. The band moved
a few millimeters per day. Thus,
a small coral head might lose all
of its tissue in a few months. The
disease became known as blackband disease (BBD).
White Band Disease
• Gladfelter first reported tissue
slowly peeling off elkhorn and
staghorn corals at Tague Bay,
U.S. V. I.
– The loss of tissue resulted in a
distinct band or line of bare
white skeleton and, as a result,
this disease was named whiteband disease (WBD).
– Unlike BBD, despite intensive
study, no assemblage of
microorganisms could be found
at the junction of sloughing
tissue and the coral skeleton.
Additional coral diseases
 Dark spots Disease
 Rapid Wasting Disease
 Red Band Disease
 White Plague
 Yellow Band Disease
Marine Diseases: The loss of
Diadema in the Caribbean
• Black-sea-urchin plague occurred
in Diadema antillarium in the
Caribbean Sea and caused high
mortalities (about 98%) within 10
days of the first signs of the
disease in a new locality.
– Unlike other urchin diseases,
which appear to be confined in
distribution, black urchin plague
spread throughout the
Caribbean Sea from Venezuela
to Bermuda (about 3.5 X 106
km2), reducing populations to
1-7% of former levels.
Consequences of Diadema Dieoff
• Algal overgrowth of
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coral reefs
Loss reef
productivity & cover
Lost ecosystem
productivity
Climate change
•
The geographically largest scale impacts to coastal
systems are caused by global climate change
•
Warming of the world’s seas affects species by:
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•
changing relative sea level faster than most biomes can adapt;
stressing temperature-sensitive organisms such as corals;
changing current patterns to interfere with important
processes; and
causing increased incidence of pathogen transmission
Global warming also changes the temperature and
salinity of estuary 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.
Most Threatened Areas
• Island systems especially sensitive; island biota
particularly vulnerable to extinction
• Nearshore areas are particularly vulnerable to multiple
anthropogenic threats, esp. pollution
• Coral reefs and the ecosystem services they provide are
especially threatened by eutrophication and warming
• Deep ocean benthos is threatened by deep sea trawling
and mining, though changes are not so readily detected
Methods to Conserve Marine
Biodiversity
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2.
3.
4.
5.
Spatial management
through 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
Management through zoning and
marine protected areas
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 once
degraded
In general, however, the costs
of restoration far exceed costs
of protecting the natural
habitat
NOAA Restoration Center, Mike Devany & Marine Resource Council
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
Sectoral approaches have been proven to have
shortcomings in management of 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 Effective 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 systems 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 systems and marine
biodiversity
Other Threats
• Radionuclides/heavy metals: now viewed as less
serious than formerly
• Emerging threat: more new and persistent organic
chemicals: have effects beyond direct toxicity
– such as: changes in structure and function of entire
communities
– disrupt reproductive behavior
– molecular effects: cancers, mutations, endocrine
disruptors (“gender bending”) e.g. TBT (tributyl
tin)
“Ghost” Fishing Gear
• More than 100,000 tonnes each year- most
is no longer biodegradable
• Biggest source: North Pacific squid gillnet
fishery: 1 million km of net set annually
Plastics
• Float, degrade slowly: highest
concentrations in northern hemisphere
• Every conceivable size, shape and color of
plastic object now in the oceans
• Now found worldwide: ‘suspension beads’:
small beads used in plastic fabrication: if
not there already, coming soon to a beach
near you!!!
Speaking of excess nutrients: The
Gulf of Mexico “Dead Zone”
• Area of hypoxic water at outflow of Mississippi
River: presumed cause: Nitrogen fertilizer
enrichment from midwest farms
• Zone has doubled in size since 1993; summer
months
• Enriched water at surface (low salinity): algae
blooms, zooplk. grazers: sink to bottom: hypoxic
(<2 ppm O2) to anoxic (0 ppm O2)
• Reached nearly 18,000 km2 after 1993 floods (not
receded much since then)- effects felt to FL Keys
More tales of the Dead Zone
• Effects not only on benthos: nekton trapped in
nearshore areas and blocked from spawning areas
• How to weigh benefits of $3 billion fishing
industry (40,000 jobs) against $98 billion farm
economy (1 million farmers)?
• Massive amount of data needed to trace marine
effects to fertilizer applications: political
ramifications
Oxygen Deficits in English
Estuaries
Oxygen depletion in the Baltic Sea
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
The buck stops here: the value of marine ecosystems
Use of the world’s fish catch:
1960-95
Exploitation of global fisheries
The plight of the Peruvian anchoveta
and associated seabirds
Trawling
Beam trawlhow to
destroy
benthic
habitats
The rapid decline of the orange
roughy fishery
Red: est. biomass
Blue: catch
The three main “failings” of fisheries
• Oceans are a ‘free for all’, a
‘hunter/gatherer’ philosophy: regulatory
bodies make weak commitments to preserve
stocks and then fail to follow through
• Fishing fleets are subsidized by nations: $20
billion worldwide
• Conservation measures: there are closed
season and limits to total catch
Overfishing: Continued
• There is great difficulty in sustaining global fisheries production at
around 82 million tons. In response to declines of commercially
valuable stocks of bigger, slower growing species, commercial fishing
fleets have turned to "fishing down the food chain", targeting
increasingly large quantities of smaller species of fish with less
commercial value but play a critical role in marine food webs.
• The most glaring manifestations of the global fisheries crisis 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. This has led to widespread overfishing (with many fish
stocks at historic lows and fishing effort at unprecedented highs);
Overfishing: Continued
• massive subsidies are being handed out by governments to fishing fleet
operators, which enables vessels to continue operating in conditions
that are uneconomic and environmentally unsound. Industrial fleets
migrate all over the world on prospecting missions to find more
lucrative fishing opportunities elsewhere. Subsidies have also
supported a spree in new vessel construction in recent years.
•
the increased fishing pressure and the competition amongst fishing
nations and their fleets severely stresses fish stocks and the marine
environment. The widespread use of unselective fishing gear and
indiscriminate practices result in tens of millions of tons of unwanted
bycatch being dumped overboard annually. Along with these, millions
of other marine animals are being incidentally captured and killed in
fishing operations.
When more means less..
The orange roughy (Hoplosthethus
atlanticus)
Food Web Alterations: Some indirect
effects of fishing on coastal food webs
• Like some birds and other fish-eating mammals in the
Bering Sea and northern Gulf of Alaska, Steller sea lions
are declining in number. Biologists think that food
shortages due to pollock fishing may be one of the major
causes of the sea lions' population decreases
• Steller sea lions fishing for pollock, Alaska Low birth
weights and less healthy adults indicate that food
shortages may be limiting Steller sea lion and harbor
seal populations in some areas of the North Pacific
Exotic Species in Marine Ecology
• Invasion of non-indigenous aquatic
species, according to the 1995 National
Research Council's study "Understanding
Marine Biodiversity: A Research Agenda
for the Nation", is "one of the five most
critical environmental issues facing the
ocean's marine life".
Exotic Species in the Marine
Environment
• Exotic Species are organisms that have been
introduced and thrive in a new marine ecosystem
– In their native environments, such organisms live in balance with
their predators, and are controlled by diseases and other
ecosystem interactions. The invaders often thrive in their new
ecosystem, where controls may not exist to keep populations in
check.
– These species can cause complex changes within the structure
and function of their new ecosystem, including restructuring
established food webs, importing new diseases and competition
with indigenous organisms for space and food.
Exotic Species in the Marine
Environment
• Exotic Species are organisms that have been
introduced and thrive in a new marine ecosystem
– In their native environments, such organisms live in balance with
their predators, and are controlled by diseases and other
ecosystem interactions. The invaders often thrive in their new
ecosystem, where controls may not exist to keep populations in
check.
– These species can cause complex changes within the structure
and function of their new ecosystem, including restructuring
established food webs, importing new diseases and competition
with indigenous organisms for space and food.
Exotic Species: Mechanisms of
Invasion
•
Aquaculture
–
Salmon, shrimp, oysters, quahogs, mussels, and algae are examples of marine aquaculture species. Unfortunately, many species
adaptable to aquaculture are not native to the area where they are cultured. These species may escape and compete with native
species, or carry diseases and parasites that can infect local populations.
•
Impacts of escaped aquaculture species
•
In Massachusetts, introductions of American oysters, Crassostrea virginica, from the Mid-Atlantic region, carried a protozoan parasite
("dermo”) infects and and eventually kills the oysters.
•
Other oyster diseases, including MSX, caused by Haplosporidium nelsoni, and juvenile oyster disease have caused widespread economic
damage to both wild fisheries the aquaculture industry, and are easily spread by moving infected seed between growing areas. For this
reason oyster planting in Massachusetts is limited to certified Northeastern hatcheries
•
Non-native oyster species have been introduced into the U.S. with variable results. The Japanese oyster, Crassostrea gigas, has outcompeted and displaced native oysters in the Pacific Northwest, and the European oyster, Ostrea edulis, has gained a foothold in the
Northeast, although occupying a different niche than the native oyster population.
•
The home aquarium trade and increased interest in garden ponds have greatly increased the importation and culture of exotic ornamental
species. Intentional and accidental releases have caused serious problems, especially in southern areas, where tropical species can
survive and reproduce.
Non-indigenous Species:
Mechanisms of Invasion
• Aquaculture
– Salmon, shrimp, oysters, quahogs, mussels, and
algae are marine aquaculture species. Unfortunately,
many species adaptable to aquaculture are not native
to the area where they are cultured. These species
may escape and compete with native species, or
carry diseases and parasites that can infect local
populations.
– Impacts of escaped aquaculture species
• In Massachusetts, introductions of American oysters,
Crassostrea virginica, from the Mid-Atlantic region,
carried a protozoan parasite ("dermo”) that infects and
Marine Diseases
• Labyrinthula is the name of a slime
mold that could be responsible for
mass mortality of seagrass .
• In 1931, observers noticed that
blackish-brown discolorations, a
loss of leaves and the death of the
eelgrass were occuring along the
northeast coast of the US.
• A little later, the Wasting Disease
was noted in Europe. By 1933, this
"disease" had decimated 90% of
all eelgrass in the North Atlantic.
Occurrence of Labyrinthula in
Florida Bay