What Charles Darwin said…
KELP FORESTS
I know few things more surprising than to see this
plant growing and flourishing amidst those
breakers of the western ocean, which no mass
of rock, let it be ever so hard, can long resist.
Charles Darwin, 1 June 1834, Tierra del Fuego,
Chile
Kelp Lecture
1.
2.
3.
4.
5.
6.
Descriptive ecology
Distribution
Morphology
Productivity
Life history and reproduction
Abiotic factors that influence
kelp distribution and growth
7. Biological factors that regulate
kelp populations
8. Kelp Forest communities
Laminaria
Pterygophora
Kelps worldwide
Nereocystis
Ecklonia
1
Kelp (Brown Algae)
Giant kelp
(Macrocystis pyrifera)
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
• Occur on rocky bottoms (2 m to 30 m)
• Competitive dominant alga
• Northern limit set by hydrodynamic
forces
• Southern limit set by poor substrate
& temperature/nutrients conditions
Kelp Lecture
1.
2.
3.
4.
5.
6.
Descriptive ecology
Distribution
Morphology
Productivity
Life history and reproduction
Abiotic factors that influence
kelp distribution and growth
7. Biological factors that regulate
kelp populations
8. Kelp Forest communities
2
Kelp forests - Where do they occur?
Worldwide Kelp (Laminariales) Distribution
They grow in cold nutrient rich waters
Laminaria
Macrocystis
y
and Nereocystis
Macrocystis
and Lessonia
Ecklonia and
Macrocystis
Macrocystis, Ecklonia and Laminaria
From: Steneck et al. 2002
II. DISTRIBUTION
1. kelp forests are found in shallow rocky habitats along
temperate coasts throughout the world
2. the area of the world’s oceans covered by kelp forests
i comparable
is
bl to that
h coveredd by
b corall reefs.
f Unlike
lik
corals, however, kelp thrives in cool nutrient rich water
3. this explains why the most extensive kelp forests are
found on western continental margins, which are areas
where extensive upwelling occurs.
3
Santa Cruz
Giant kelp’s range
~1450 km
Apical Meristem
N
Asunción
Pacific Ocean
Canopy
3. MORPHOLOGY
1.
2.
simple plants consisting of a holdfast, stipe of variable length, vegetative blades,
and reproductive blades called sporophylls that produce spores. The primary
function of the holdfast is to anchor plant. Thus it differs from a root in that it is
not specially adapted to absorb nutrients. Very little in the way of tissue
specialization in kelps, or in algae in general. All parts of the plant serve in
nutrient absorption and photosynthesis.
most photosynthesis occurs in the upper portions of the plant. A plant that extends
throughout the water column it has a need to transport some of food derived from
photosynthesis to support growth of lower portions. It does this using specialized
cells in the stipe that form a primitive conductive tissue that is unique among the
kelps
Blade
Sporophylls
Stipe
Sporophyll
Sorus
Holdfast
4
4. PRODUCTIVITY
1.
2.
3.
FOREST TYPE
ANNUAL NET
PRODUCTION
(dry kg / m2 / yr)
PRODUCER
BIOMASS
(dry kg / m2)
LITTER
MASS
(dry kg / m2)
among the fastest growing plants in the
world in either marine or terrestrial habitats.
maximum elongation rates in the giant kelp
Macrocystis pyrifera are on the order of 12
-18 inches per day
Tropical
rain forest
2.2
45
0.2
Tropical
seasonal forest
1.6
35
0.5
kelp forests are among the most productive
communities in the world. Estimates of
productivity comparable to tropical rain
forests.
Temperate
e pe ate
evergreen
forest
Temperate
deciduous
forest
Boreal forest
1.3
35
3.0
1.2
30
2.0
0.8
20
4.0
2.2
0.35
0.015
Interestingly, the biomass of the primary
producers is two orders of magnitude less in
the kelp forest. which really points to the
high productivity of kelp relative to land
plants
Two sources of productivity
Macrophyte production
- bathed in nutrients
- second fastest growing “plant” on earth
Giant kelp
forest
4. PRODUCTIVITY
4. Only about 5-10 % of the primary production is consumed
by grazers in either terrestrial or kelp forests.
5. In terrestrial forests most of the biomass accumates on the
ground and persists as litter on the forest floor.
- constant production / loss of blades (leaves)
- fed on directly by grazing snails and crustaceans
6. There is an order of magnitude less litter on the floor of a
kelp forest compared to terrestrial forests
- blades litter reef to create detritus food chain
Plankton influx
- phytoplankton, holoplankton, meroplankton
- great abundance and diversity of planktivores
5
4. PRODUCTIVITY
Kelp forests vs terrestrial forests
7. Another reason for the small accumulation of kelp litter is
that kelps continually sluff organic material which
ultimately enters the nearshore food web.
8. As kelp senesces it releases particulate and dissolved
organic
g
matter which pprovides a significant
g
source of carbon
for secondary consumers.
9. Interesting study that used stable carbon isotope analyses in
the Aleutian Islands to confirm the important trophic role of
kelp derived carbon in nearshore marine communities.
Percentage of Kelp-Derived Carbon in Kelp Forest Consumers
Suspension Feeders
Mussel (Mytius edulis)
Soft coral (Alcyonaria. sp.)
Barnacle (Balanus nubilus)
Sea anemone (Metridium senile)
Rock jingle (Pododesmus cepio)
Mysid (Proneomysis sp.)
% kelp carbon
25 - 40
40 - 70
75 – 85
15 - 40
40 - 55
45 - 60
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
K l forests
Kelp
f
t are ffaster
t growing,
i
shorter-lived:
h t li d
Detritivores
Few kelp sp. last more than 25 years
Terr. forest trees can live for thousands of years
Amphipod (Anonyx sp.)
Crab (Dermaturus mandtii)
70 - 95
20 - 35
species?
Terrestrial forests are habitat for roughly 3 phyla
Kelp forests are habitat for 10 or more phyla
Predators
Rock greenling (Hexagrammos lagocephalus)
Sea star (Leptasterias spp.)
Cormorant (Phalacorcorax peligicus)
Kelp forests are more diverse in terms of number of animal phyla, less in terms of animal
40 – 65
30 - 55
35 - 70
6
5. LIFE HISTORY AND REPRODUCTION
1. alternation of generations between a macroscopic spore
producing stage = sporophyte, and a microscopic gamete
producing stage = gametophyte
Adult sporophyte
Macroscopic
Juvenile sporophyte
growth
Microscopic
recruitment
growth
Gametophytes
m
release
syngamy
f
Embryonic
sporophyte
Zoospores
settlement
7
3. fertilization occurs after spores have dispersed and settled,
which is very different from marine animals. This means that
spores need to settle at relatively high densities in order to
insure successful fertilization. The chance of this happening
declines with dispersal distance due to the rapid dilution of
spores following their release from the parent plant. The
ecological consequence of this life history feature is that it
constrains the distances over which spores can effectively
colonize.
Percent dispersing at least distance X
100%
2. kelps are very fecund - A given plant can produce over 10
trillion spores during its relatively short lifetime, which for
some species like the giant kelp is at most a couple years.
Carpinteria - June
Carpinteria - Jan/Feb
Naples - June
Naples - Jan/Feb
100%
80%
80%
60%
60%
40%
40%
20%
20%
0%
0.0001
0.001
0.01
0.1
1
Distance (km)
10
100
Percent of inter-pa
atch distances less than X
Figure 9
5. LIFE HISTORY AND REPRODUCTION
0%
Spore Dispersal
100
80
And this leads to ????
60
Percent Occurrence (cumulative)
40
20
0
1
10
100
1000
Maximum Spore dispersal (log m)
8
Selfing In Kelps
Selfing rates should increase with age
of kelp bed
100
90
Density (#*m 2)
Percent Occurrence
Medium (.05-.15)
60
Low (<.05)
50
Time
40
30
20
10
0
0
Age of Kelp Bed
High (>.15 )
70
10 20 30 40 50 60 70 80 90 100
Self-fertilization rates
Consequences of limited dispersal – Self Fertilization Costs
Fitness component
Proportional difference
between selfed (100%
treatment) and outcrossed (5% treatment)
individuals
Accumulated fitness of
selfed individuals
relative to out-crossed
individual (proportion)
1) Zygote production
0.61
0.61
2) Survival to
adulthood
1.01
0.62
3) Development of
reproductive structures
0.24
0.15
4) Fecundity
0.11
0.0165
Percent self-fertilization in
n kelpbed
.
80
100
90
80
70
Fitness
consequences
60
50
40
30
20
10
0
0.25
0.20
0.15
0.10
0.05
0.0
Plant Density (# per sq meter)
Kelp forests come and go…
9
6. ABIOTIC FACTORS THAT INFLUENCE KELP
DISTRIBUTION & GROWTH
Pe
ercent self-fertilization
Generalized Life History of a Macrocystis Population
Kelpbed senescence through self-fertilization?
1)
Age of Kelp Bed
100
90
80
70
60
50
40
30
20
10
0 0.25
Fitness
consequences
0.20
0.15
0.10
0.05
0.0
Density
Plant Density (# per sq meter)
Nutrients- plants obviously need nutrients to grow and
reproduce.
Concentrations of nitrogen and phosphorus vary spatially
and temporally in coastal waters. In California, nutrient
concentrations generally greater in the north than in the
south. They typically peak in the spring when most
upwelling occurs and are at a low in the fall. Nutrient
concentrations can vary greatly from year to year owing to
oceanographic events such as El Nino during which time
they tend be in very short supply.
Time
50
5. LIFE HISTORY AND REPRODUCTION
central California
N = 5879
40
30
20
5 Thi
5.
This is
i particually
ti ll important
i
t t when
h you think
thi k about
b t the
th habitat
h bit t
that kelp plants recruit to. They start life as a microscopic cell on
the bottom not at the surface. It turns out that in most cases the
lower depth limit of kelp is determined by the amount of light
reaching small stages on the bottom. It has been estimated that
the depth that this occurs is where light is reduced to » 1% of that
at the waters surface.
10
Nitratte (μg / L)
4. abiotic factors such as nutrients, temperature and light on growth
and reproduction greatly affect life history stages. The
production of gametes in the microscopic stage only occurs under
certain conditions of light nutrients and temperature.
0
50
southern California
N = 9119
40
30
Nutrient-limited
20
10
0
50
Baja California
N = 4137
40
30
20
10
0
5
7
9 11
13
15
17
19
21
23
25
Temperature (°C)
10
6. ABIOTIC FACTORS THAT INFLUENCE KELP
DISTRIBUTION & GROWTH
2)
Temperature- primarily cool water plants.
The effects of temperature are difficult to assess in nature because in
many temperate areas where kelp grows temperature covaries
inversely with nutrient concentration. In southern California kelp
growth is extremely seasonal: greatest in spring when temperatures
typically are low and nutrients are high and lowest in the late summer
and fall when sea water temperatures are high and nutrient
concentrations are low. Such seasonal variation can disappear during
prolonged periods of high temperature and low nutrients such as that
that occurs during El Niños. Under these conditions growth and
reproduction remains low year round and in the most severe cases
results in death
6. ABIOTIC FACTORS THAT INFLUENCE KELP
DISTRIBUTION & GROWTH
3. Light – essential for growth and reproduction
• Provides energy for photosynthesis
• Influenced by depth, water clarity, season, latitude,
vegetation shading
• Most severe in early life history stages and transitions
(spore, gametophyte, fertilization, sporophyte)
Figure 2
Kelpbeds in Southern California
100%
Fraction of Pattches Occupied (%)
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
1970
1975
1980
1985
1990
1995
2000
Year
11
6. ABIOTIC FACTORS THAT INFLUENCE KELP
DISTRIBUTION & GROWTH
1982-83 El Niño
4. Water Motion:
• The concentration of nutrients is not the only thing that affects
nutrient absorption in kelp. For example, in calm conditions
growth can be limited by nutrients even in relatively nutrient
rich waters. This is because nutrients can become locally
d l d near the
depleted
h surface
f
off plant
l tissues
i
in
i still
ill water. Water
W
motion prevents this from happening by maintaining a
constant flux of nutrients across the tissues of the plant.
• Too much water motion, however, is not good. it can dislodge
plants from the bottom, then they end up on the beach or get
transported offshore where they die.
Figure 2
Kelpbeds in Southern California
• There is a tradeoff in being large. Light vs Drag
• High water motion associated with storms is extremely
important source of disturbance in kelp communities and can
have a profound effect on the spatial and temporal dynamics of
kelp populations. Severe storms such as the ones that occurred
during the 1982-83 El Niño can completely destroy entire
populations of kelp.
100%
90%
Fraction of Pattches Occupied (%)
• While light may set the lower depth limit for kelp, water
motion is believed to be important in determining the upper
limit for many species.
80%
70%
60%
50%
40%
30%
20%
10%
0%
1970
1975
1980
1985
1990
1995
2000
Year
12
6. ABIOTIC FACTORS THAT INFLUENCE KELP
DISTRIBUTION & GROWTH
BIOLOGICAL FACTORS THAT REGULATE
KELP POPULATIONS
Dispersal
Kelp populations are very dynamic and frequently undergo local
extinctions and recolonizations.
Hard substrate- usually a solid
substrate to anchor. Some
controversy about the nature of
rock that is best
•
Based on artificial reef
experiments
•
Colonized by kelp then
overgrown by Muricea
•
WHY????
Dispersal is a key element to the recolonization process.
Historically spore dispersal in kelps has been thought to be
limited to within a few meters of the parent plant. Such limited
dispersal, however, cannot account for the rapid and widespread
recolonization of kelps that is frequently observed.
Dispersal
Range off soft
R
f –
bottomed kelp
Pt. Conception
1. Spore dispersal in kelps may not be limited to a few
meters.
2. We have measured spore dispersal over distances as large
as several kilometers.
• Large storms
• Turbulent flow
3. Storms also cause massive release of spores
4. Together – release and dispersal during storms leads to
long distance dispersal
What else??
13
Competition
1. Competition between different vegetation layers can be important in
structuring kelp populations. Most the work that has been done has
focused on adults inhibiting juveniles. In general the recruitment of
nearly all algae is suppressed underneath dense kelp canopies. Light
reduction to 1%
2. Hormonal trickery
3. Layering - Given this high level of shading it is not surprising that
there is strong competition for light among the different vegetation
layers.
4. There has also been much work done on the effects of intraspecific
competition. In general, kelps tend to grow larger, live longer, and
produce more spores in lower density stands, though there are some
exceptions to this pattern.
San Clemente Artificial Reef (SCAR)
Experimental Design
Two types of material
• quarry rock boulders
• recycled concrete rubble
Three bottom coverages
l (~40%)
( 40%)
• low
• medium (~60%)
• high (~80%)
Stratified block design
• 7 replicate blocks of 6 reef designs
• Module size = 40 m x 40 m
Duration
• five years (2000 – 2004)
SM and B represent the
natural reefs at San
Mateo and Barn, which
are used as reference
sites.
14
Hard Substrate
B
Understory algae (% Cover)
Performance Standard - At least 90% of the
initial area of hard substrate must remain
available for attachment of reef biota.
Percent cover of understory algae on the artificial
and natural reefs
Density of adult giant kelp on the different reef designs
B
SM
Low
Med
100
SM
Low
M ed
100
R ock
80
80
60
60
40
40
20
20
0
High
C oncrete
0
2000 2001 2002 2003 2004
2000 2001 2002 2003 2004
Percent cover of sessile invertebrates on the artificial
and natural reefs
High
60
Rock
40
60
B
40
20
20
0
0
2000 2001 2002 2003 2004
SM
Low
Med
High
Concrete
Invertebrates (% coverr)
Adult density (No. 1
100 m-2)
Performance standard
2000 2001 2002 2003 2004
120
Rock
120
100
100
80
80
60
60
40
40
20
Concrete
20
0
0
2000 2001 2002 2003 2004
2000 2001 2002 2003 2004
15
Adult density (No. 100 m-2)
60
Rock
Macrocystis
Control of grazers (predation, disease, storms, recruitment)
Competition for light
SCAR
40
1.
The single most effective predator on sea urchins are sea otters which once ranged
from the Kuril Islands in Japan through the Aleutian Is and down the coast of North
America to Baja California. Otters eat ≈ 25 % of their body weight per day and can
effectively eliminate local populations of sea urchins and other shellfish.
2.
Islands with sea otters had low densities of urchins and densely vegetated kelp beds.
In contrast, islands without sea otters are basically unvegetated barren areas with
have high densities of urchins and no macro algae.
algae Thus sea otters have been given
this keystone status. The paradigm is that where there are otters you get kelp beds
where there is no otters you get sea urchin barren grounds. This paradigm seems to
apply generally in Alaska.
20
Reference Reefs
0
Invertebrates (% cover)
Understory alg
gae (% Cover)
2000 2001 2002 2003 2004
100
R ock
80
60
40
20
0
2000 2001 2002 2003 2004
120
Rock
100
80
60
40
20
0
2000 2001 2002 2003 2004
Grazing
1. Clearly the number one enemy of kelp are sea urchins. They are the single
most important grazer in kelp communities worldwide. They can form large
feeding fronts and eat everything in sight (including fiberglass transect
tapes), essentially leaving behind a barren ground devoid of macro algae.
Sea urchins graze on kelp
2. Urchins don’t always display an active grazing behavior. They are
typically sit and wait herbivores much like abalone that catch detached
pieces
i
off kelp
k l as they
h drift
d if by.
b
Questions:
• What causes their change in behavior passive sit and wait to active grazing??
•
How long are barrens maintained?
•
What controls urchins??
.
16
Sea otters control urchin populations
by eating them
Kelp forest changes
NORTH PACIFIC/ALASKA
• Sea otters, sea
cows, sea
urchins and
humans
History of fishing in N. Pacific
• 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)
17
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
• Sea urchins and kelp, but
no sea otters, but very
large predatory fish!
18
Cod fishery intense for centuries
CALIFORNIA
• CA kelp forests
considered most diverse
in world
• Exploited for past 1213 000 yrs
13,000
• Shell middens from
aboriginal people show
decrease in animal size
with hunting
Urchins rise again
• Fishing technology
decreases cod pop. by
1930s
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
19
White sea bass landings
CA kelp begins to change
• CA kelp forest so diverse,
other predators keep urchins
in check even with few otters
persevere for
• Continues to p
another 150 years
• Now in trouble - not so
diverse
other predators on sea urchins in California, which include lobster
and fish predators such as the sheephead wrasse
•
other predators on sea urchins in California, which include
lobster and fish predators such as the sheephead wrasse
•
sporadic recruitment of sea urchins
•
disease, which has been known to greatly reduce urchin
numbers over relatively wide areas. In California these outbreaks of
disease are generall
generally associated with
ith periods of warm
arm water.
ater
Expansion of kelp beds have been documented following massive
urchin die offs.
•
storms - which not only destroy kelp, but also can drastically
reduce populations of sea urchins. Perhaps the best example of this
comes from a study done at Naples Reef off Santa Barbara by Al
Ebeling
20
Kelp forest ecosystems
Kelp conservation status
Habitat structure
• 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
- surface canopy
• Currently, in some areas fisheries for urchins coincide with
fisheries for urchin predators – a delicate balance
- subcanopy
- turf
Kelp Forest Communities
Giant kelp communities
Juvenile finfish
Invertebrates
Understory algae
Invertebrates
Adult finfish
Marine mammals
21
Kelp forest zonation
"The numbers of living creatures of all Orders
whose existence intimately depends on kelp is wonderful…
I can only compare these great aquatic forests with
the terrestrial ones in the intertropical regions."
"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 kelp."
Charles Darwin (1860) The Voyage of the Beagle
Kelp Forest Ecosystems
Primary producers
Biodiversity
ca. 90 spp. macroalgae
Grazers
ca. 40 spp. fish, gastropods,
echinoderms, crustaceans
Planktivores
ca. 210 spp. fish, porifera, bivalves,
bryozoans, tunicates, crustaceans
Predators
ca. 145 spp. fish, gastropods,
echinoderms, crustaceans
Detritivores
ca. 15 spp. echinoderms,
(single Channel Is. kelp forest, species > 2 cm)
22
Kelp conservation status
• 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
• Currently, in some areas fisheries for urchins coincide with
fisheries for urchin predators – a delicate balance
23