KELP FORESTS...forest 2.2 0.35 0.015 4. Only about 5-10 % of the primary production is consumed by...

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KELP FORESTS

Kelp Lecture

1. Descriptive ecology

2. Distribution

3. Morphology

4. Productivity

5. Life history and reproduction

6. Abiotic factors that influence kelp distribution and growth

7. Biological factors that regulate kelp populations

8. Kelp Forest communities

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What Charles Darwin

said…

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. 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, 1 June 1834, Tierra del Fuego, Chile

Kelps worldwide

Ecklonia Nereocystis

Laminaria Pterygophora

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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

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Giant kelp

(Macrocystis pyrifera)

1. In northern Hemisphere a) Occur on rocky bottoms (2 m to 30 m)

b) Competitive dominant alga

c) Northern limit set by hydrodynamic

forces

d) Southern limit set by poor substrate &

temperature/nutrients conditions

Kelp forests - Where do they occur?

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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

is comparable to that covered by coral reefs. Unlike

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.

Worldwide Kelp (Laminariales) Distribution

They grow in cold nutrient rich waters

From: Steneck et al. 2001

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From: The biology and ecology of giant kelp

forests. David R. Schiel & Michael S. Foster.

Distribution of Macrocystis and geographic features

3. MORPHOLOGY

Apical Meristem

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1. 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.

2. 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

3. MORPHOLOGY



Holdfast

Stipe

Blade

Canopy

Sporophylls

Sporophyll

Sorus

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Two sources of productivity in a kelp forest

- second fastest growing “plant” on earth

- bathed in nutrients

- constant production / loss of blades (leaves)

- fed on directly by grazing snails and crustaceans

- blades litter reef to create detritus food chain

Macrophyte production

Plankton influx

- phytoplankton, holoplankton, meroplankton

- great abundance and diversity of planktivores

1. 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

2. kelp forests are among the most

productive communities in the world.

Estimates of productivity comparable to

tropical rain forests.

3. 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

4. PRODUCTIVITY

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Comparisons between terrestrial forests and giant kelp forests

FOREST TYPE

ANNUAL NET

PRODUCTION

(dry kg / m2 / yr)

PRODUCER

BIOMASS

(dry kg / m2)

LITTER

MASS

(dry kg / m2)

Tropical

rain forest

2.2

45

0.2

Tropical

seasonal forest

1.6

35

0.5

Temperate

evergreen

forest

1.3

35

3.0

Temperate

deciduous

forest

1.2

30

2.0

Boreal forest

0.8

20

4.0

Giant kelp

forest

2.2

0.35

0.015

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 accumulates on the ground

and persists as litter on the forest

floor.

6. There is an order of magnitude less

litter on the floor of a kelp forest

compared to terrestrial forests

4. PRODUCTIVITY -continued

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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 matter which provides a significant 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.

4. PRODUCTIVITY - continued

Percentage of Kelp-Derived Carbon in Kelp Forest Consumers Suspension Feeders % kelp carbon Mussel (Mytius edulis) 25 - 40 Soft coral (Alcyonaria. sp.) 40 - 70 Barnacle (Balanus nubilus) 75 – 85 Sea anemone (Metridium senile) 15 - 40 Rock jingle (Pododesmus cepio) 40 - 55 Mysid (Proneomysis sp.) 45 - 60 Detritivores Amphipod (Anonyx sp.) 70 - 95 Crab (Dermaturus mandtii) 20 - 35 Predators Rock greenling (Hexagrammos lagocephalus) 40 – 65 Sea star (Leptasterias spp.) 30 - 55 Cormorant (Phalacorcorax peligicus) 35 - 70

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1

2

3

4

Nereocystis Macrocystis

Sorus - Specialized

zoospore producing

tissue

Sorus

1. Blade

2. Stipe

3. Holdfast

4. Pnuematocyst

5. Life history and reproduction

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alternation of generations between a macroscopic spore producing

stage = sporophyte, and a microscopic gamete producing stage =

gametophyte

growth

Zoospores

Gametophytes

m

f

syngamy

Embryonic

sporophyte

Juvenile sporophyte

growth

Adult sporophyte

settlement

release

Mac

rosc

opic

Mic

rosc

opic

recruitment

Life history and reproduction

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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.

5. This is particularly important when you think about the habitat

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.

5. LIFE HISTORY AND REPRODUCTION – cont.

6. ABIOTIC FACTORS THAT INFLUENCE KELP

DISTRIBUTION & GROWTH

. • 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.

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central California

N = 5879

southern California

N = 9119

Baja California

N = 4137

0

20

10

40

30

50

7 5 11 17 15 9 13 19 23 25 21

Temperature (°C)

Nit

rate

(m

g /

L)

0

20

10

40

30

50

0

20

10

40

30

50

Nutrient-limited


DISTRIBUTION & GROWTH

. • Temperature – generally considered a cool water species

– 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

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Growth as a function

of temperature and

nitrate concentration

1970 1975 1980 1985 1990 1995 2000

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Year

Fra

ction o

f P

atc

hes O

ccupie

d (

%)

Figure 2

Kelpbeds in Southern California

2015

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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)


DISTRIBUTION & GROWTH - continued



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Growth as a function of irradiance and nutrient limitation

Nutrients limiting

Nutrients replete

Dispersal

• Kelp populations are very dynamic and frequently undergo

local extinctions and recolonizations.

• 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, seems incompatible with rapid

and widespread recolonization of kelps that is frequently

observed.

7. BIOLOGICAL FACTORS THAT REGULATE

KELP POPULATIONS

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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??

Dispersal

Nutrients limiting

Nutrients replete

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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.

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.

2. Urchins don’t always display an active grazing behavior. They are

typically sit and wait herbivores much like abalone that catch detached

pieces of kelp as they drift by.

Questions:

• What causes their change in behavior passive sit and wait to active

grazing??

• How long are barrens maintained?

• What controls urchins??

.

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Control of grazers (predation, disease, storms, recruitment)

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. 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.

Sea urchins graze on kelp

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Kelp forest changes


NORTH ATLANTIC

• Sea urchins and kelp, but

no sea otters, but very

large predatory fish!

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Cod fishery intense for centuries

Urchins rise again

• Fishing technology

decreases cod pop. by

1930s

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Gulf of Maine


Kelp

Urchins

Nova Scotia


Kelp

Urchins

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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)

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Sea otters control urchin populations

by eating them

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.

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Otters and urchins Alaska


Kelp

Urchins

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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

Kelp Forest Communities

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Habitat structure

Kelp forest ecosystems

- subcanopy

- surface canopy

- turf

Juvenile finfish

Adult finfish Marine mammals

Understory algae

Invertebrates

Invertebrates

Giant kelp communities

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"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

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Kelp forests in Northern Hemisphere

(south – north)

Sub-canopy species



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Katlian Bay

Pirate Cove

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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

• One possible solution – Marine Protected Areas established

explicitly for conservation

Sea Grasses

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Seagrasses

Part of a larger coastal system…

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WHAT ARE SEAGRASSES?

• Aquatic angiosperms (flowering plants)

• Monocotyledenous

• a flowering plant with an embryo that bears a single cotyledon (seed leaf).

• Polyphyletic with 4-5 families, ~12 genera and 50-70 species

• Foundation species

• Autogenic ecosystem engineers

• Found in subtidal AND intertidal (i.e. Zostera marina)

SEAGRASSES AS ECOSYSTEM ENGINEERS

• Foundation species & autogenic ecosystem engineers

For example…

Less light attenuation=higher

photosynthetic rate

Improves water

clarity

Sediment-laden water flows

across seagrass meadow/bed

Trap sediment

Vegetative

structure provides

habitat to

invertebrates and

fishes

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MORPHOLOGY OF SEAGRASSES

• Varies by species

• Rhizomatous growth pattern • Rhizome extends horizontally in

the sediment near the surface

• Also develop adventitious

roots

• Vertical rhizomes develop

leaves from a basal meristem

• RAMET=vertical unit of

aboveground leaves and below

ground roots; modular unit of

seagrass growth • Nutrients are translocated from

ramet to ramet via horizontal

rhizome

• GENET=all ramets that are

genetically identical

WHERE SEAGRASSES OCCUR

LOCAL DISTRIBUTION

• depth limit=restricted by light availability

• shallow depth range limit=restricted by

desiccation

GLOBAL DISTRIBUTION

• Found in both tropical and

temperate coastal systems

Increased light attenuation

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SEAGRASSES PROVIDE ECOSYSTEM SERVICES & FUNCTIONS

Regulatory and Economic value Cultural value

SEAGRASS GOODS & SERVICES Commercial & artisanal fisheries

Nursery Habitat for offshore fisheries

Food

Fodder or bedding for animals

Fiber

Packing material

Fertilizer and mulch

Building dikes

Coastal protection from erosion

Water purification

Interaction with adjacent ecosystems

Maintenance of biodiversity and threatened

species

Carbon dioxide sink

Cultural, esthetic and intrinsic values

Stabilizing sediments

CO

2

decomposition

microbial activity

O

2

O2 (anoxic sediment)

C

C C

C

C

C

C

C

C

C

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