Transcript KELP FORESTS: past, present and future

sea otter - review of last lecture
The last of the otters
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150 years after excessive hunting, by late 1800s, only 3000 otters left
International Fur Treaty established in 1911: illegal to kill sea otters,
even for indigenous Alaskans
Otters repopulate
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In 1980s, census conducted: 150,000 otters on earth, mostly in Alaska
2000 otters found in California, population was thought to be extinct there
Sea otters give birth to 1 infant per pregnancy, 6 month gestation
A new threat emerges
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In 1991, first killer whale attack on Alaskan otter is
witnessed
Sequential overharvesting of marine mammals
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Killer whales may have switched to otters because their
normal food (whales and seals) has become rare.
KELP
FORESTS
What Charles Darwin
said…
“I can only compare these great
aquatic forests…with the
terrestrial ones in the
intertropical region. Yet if in any
country a forest was destroyed, I
do not believe nearly so many
species of animals would perish
as would here, from the
destruction of the kelp. Amidst
the leaves of this plant
numerous species of fish live,
which nowhere else could find
food or shelter…”
Charles Darwin, 1 June 1834, Tierra del
Fuego, Chile
Outline
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Kelp structure and function
Kelp ecosystem biodiversity
Change of kelp through time
Human destruction of kelp
Kelp forests in the future
Role of sea otters as keystone species
Urchin barrens
Kelp (Brown Algae)
Brown Algae (Phaeophyta)
 1000 species, almost all
marine
 Includes Sargassum, Padina,
kelps
 Most common in cold,
temperate seas
 Two pigments for
photosynthesis:
1) Chlorophyll a (like all plants)
2) Fucoxanthin (brown color)
Kelp: Division Phaeophyta
(Brown Algae)
Parts of a kelp
 Gas-filled pneumatocysts
 Rootlike holdfast to
attach to substrate
 Long hollow stem or
stipe
 Leaflike blades
 Complex life cycle
FUNCTION AND FORM
Kelp “life history”
Kelp alternates between a large
sporophyte and a tiny
gametophye
- sporophyte = “plant that makes
spores”
(diploid, 2N, large plant-like stage)
- gametophyte = “plant that makes
gametes”
(haploid, 1N, small inconspicous
stage - can be a tiny thread)
http://www.mbari.org/staff/conn/
botany/browns/james/Web/life
his.htm
Kelp forest zonation
Giant Kelps - largest of all algae
Kelp Forests
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One plant can grow 2530 m in one season
Can reach 45 m long
Among most
productive of all plant
communities
Subtidal to 20 meters
Like cold water
Kelp forests - Where do they
occur?
Cold, temperate water
Kelp forests are more
common off West Coast of
N. America than E. Coast
Why?
Kelp forests - Where do they
occur?
Giant kelp forests
More common off West
Coasts of N. America than
E. Coast
because of cool California
current off Ca coast
vs.warm Gulf Stream on East
Coast
Kelp forests occur in cool water
Figure 13.21
Kelp diversity
Low taxonomic diversity
(few species of kelp)
 High structural and
functional diversity
(many shapes and creates
many different
architectural habitats that
promote diversity of
associated organisms)
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The ecological role of kelp
The ecological role of kelp
•Dampen wave action
•Reduce coastal erosion
•Enhance recruitment of fish and invertebrates
•High productivity and turnover of plant matter puts
many nutrients into system
•High structural diversity (like a forest on land)
provides shelter and habitat for many species
•Habitat complexity created:
- understory with filtered light
- canopy at surface
Animals of the kelp forest
Kelp forests come and go…
Kelp forests vs terrestrial forests
Similarities and differences to
terrestrial forests
Both forest types:
Recruitment and growth depends upon canopy breaks for available light
Structure similar - different canopy levels, varied understory
Form foundation for large diversity of animals and plants
Both are primary producers, get their energy from the sun
Kelp forests have shorter life spans, shorter heights
Kelp forests are faster growing, shorter-lived:
Few kelp sp. last more than 25 years
Terr. forest trees can live for thousands of years
Kelp forests are more diverse in terms of number of animal phyla, less in terms of animal
species?
Terrestrial forests are habitat for roughly 3 phyla
Kelp forests are habitat for 10 or more phyla
Kelp forests are deforested by
natural causes
Salinity, temperature
change, storms,
seasons
Can recover fairly
quickly under
natural conditions
Sea urchins graze on kelp
Sea otters control urchin
populations by eating them
Rise of urchins through time
CALIFORNIA
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CA kelp forests
considered most
diverse in world
Exploited for past 1213,000 yrs
Shell middens from
aboriginal people show
decrease in animal size
with hunting
Animals begin to disappear from
kelp forests
Otters functionally gone by early 1800s
Kelp forest ecosystem persisted
for next 150 years
Probably because other predators,
like fish, compensated by increasing
in numbers and eating urchins
White sea bass landings
CA kelp begins to change
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CA kelp forest so diverse,
other predators keep
urchins in check even with
few otters
Continues to persevere
for another 150 years
Now in trouble - not so
diverse
Kelp forest changes
Kelp conservation status
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Climate change (global temp. increase), human pop. growth,
coastal development, oil spills, overfishing impacts, non-native
sp. invasions all predicted to increase over next 25 years
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Currently, in some areas fisheries for urchins coincide with
fisheries for urchin predators – a delicate balance
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Not all areas will be affected in future by temperature changes,
but – mean annual global temperature predicted to increase (last
century 1 degree C increase in global air temp)
NORTH PACIFIC/ALASKA
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Sea otters, sea
cows, sea
urchins and
humans
History of fishing in N. Pacific
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Colonization 30,000
years ago, boats used
off Japan coast for past
25,000 years
Stellar’s sea cow
hunted to extinction
(35 feet long, several
tons)
History of fishing in Alaska
Humans in Alaska for 9000-10,000 years.
Indigenous tribes began to hunt otters
~ 2500 years ago.
Otter hunting intensified with European
arrival in 1700s.
Ecosystem changed to urchin dominated.
Otters and urchins
NORTH ATLANTIC
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Sea urchins and
kelp, but no sea
otters, but very
large predatory fish!
Cod fishery intense for centuries
Urchins rise again
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Fishing technology
decreases cod pop. by
1930s
A sign of things to come
CONCLUSION
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Kelp forests are home and nurseries for much
marine life
Kelp forests could disappear or become
functionally extinct within decades in absence of
effective management that takes complex
ecosystem into effect, including direct and
indirect effects (eg, overhunting of whales leads
to killer whale predation on sea otters, leads to
rise of urchins and death of kelp)
References
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Dayton, PK, Tegner MJ, Edwards PB, et al Sliding baselines, ghosts, and reduced expectations in kelp forest communities
ECOL APPL 8 (2): 309-322 MAY 1998
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Estes, JA, Duggins, DO, Rathbun, GB. The ecology of extinctions in kelp forest communities. CONSERV BIOL 3 (3): 252264 SEP 1989
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Jackson, JBC, Sala E Unnatural oceans SCI MAR 65: 273-281 Suppl. 2 SEP 2001
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Jackson, JBC, Kirby, MX, Berger, WH, et al. Historical overfishing and the recent collapse of coastal ecosystems SCIENCE
293 (5530): 629-638 JUL 27 2001
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Jackson, JBC What was natural in the coastal oceans? P NATL ACAD SCI USA 98 (10): 5411-5418 MAY 8 2001
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Simenstad CA, Estes JA, Kenyon KW. Aleuts, sea Otters, and alternate stable-state communities SCIENCE 200 (4340): 403411 1978
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Steneck RS, Graham MH, Bourque BJ, et al. Kelp forest ecosystems: biodiversity, stability, resilience and future ENVIRON
CONSERV 29 (4): 436-459 DEC 2002
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Tegner, MJ, Dayton, PK Sea-urchins, El-Ninos, and the long-term stability of southern California kelp forest communities
MAR ECOL-PROG SER 77 (1): 49-63 OCT 1991