Kelp Forest Ecosystem and Trophic Cascades

Trophic Levels• The energy flow from one trophic level to the

other is know as a food chain• A food chain is simple and direct• It involves one organism at each trophic level

– LEVEL ONE - Producers– LEVEL TWO - Primary Consumers – eat autotrophs

(producers)– LEVEL THREE - Secondary Consumers – eat the

primary consumers– LEVEL FOUR - Tertiary Consumers – eat the secondary

consumers– ALL LEVELS - Decomposers – bacteria and fungi that

break down dead organisms and recycle the material back into the environment

Trophic cascades- occur when predators in a food web decrease the abundance of their prey. This reduces the predation rate on the lower trophic levels, often resulting in an increased abundance.

Kelp

Trophic cascade in kelp forests. ?

What feeds on kelp?

Sea urchins graze on kelp- has strong effects on kelp abundance

Urchins

Kelp

Trophic cascade in kelp forests.

What feeds on Urchins?

Sea otters control urchin populations by eating them

Sea otter is well-adapted to feeding on shellfish and requires high feeding rate to maintain metabolic demands in cold water

Sea otterSkull & Teeth

Short powerful jaw

• To help it stay warm in cold water, a sea otter burns calories at nearly three times the rate you do. An otter fuels its fast metabolism by eating up to a quarter of its weight in food a day. (A 150-pound person would have to eat 35-40 pounds of food a day to match that!)

Sea otters

Urchins

Kelp

Trophic cascade in kelp forests.

So how are sea otter populations related to kelp abundance?

Sea otters

Urchins

Kelp

Increase of sea otters resultsin reduction of urchins and an increase of kelp

Trophic cascade in kelp forests.

• Result: trophic cascade. Add otters, have reduction of urchins and increase of kelp abundance. Reduce otters: kelp grazed down by abundant urchins

Sea otter, Enhydra lutris, a keystone species in Pacific coast kelp forests

Keystone Species

• A species that affects the survival and abundance of many other species in the community in which it lives.

• Its removal or addition causes a large shift in the composition of the community and sometimes even in the physical structure of the environment.

and now Orcas

DEAD

DEAD

DEAD

DEAD

DEAD

DEAD

DEAD

Ok, So what’s the problem?

Otters have beautiful Fur

Very beautiful Fur

London sea otter pelt sales from 1871 to 1910 (Source: Wikimedia Commons)

• Between 1790 and 1812, American traders sold an average of 12,000 sea otter pelts in Canton annually

• Otters hunted to near extinction• 150yrs of heavy fur hunting reduced numbers to

only about 3000 individuals

Oh no!

Sea otter’s current and historical range

International Fur Treaty established in 1911: illegal to kill sea otters, even for indigenous Alaskans

Otters repopulate• 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

Otters and urchins

A new threat emerges• In 1991, first killer whale attack on Alaskan otter is

witnessed

Sequential overharvesting of marine mammals• Killer whales may have switched to otters because their normal food (whales

and seals) has become rare.

CONCLUSION

• 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)

• Conservation• Sea otters once thrived from Baja California to the Pacific

Northwest of North America through Alaskan and Russian waters and into Japan before hunters nearly exterminated them in the 1700s and 1800s. The California population has grown from a group of about 50 survivors off Big Sur in 1938 to just over 2000 today. Although their numbers have increased, sea otters still face serious risks: oil from a single tanker spill near San Francisco or off the central coast could wipe out the entire California sea otter population.

Rise of urchins through time

Otter Fur• To stay warm in chilly ocean waters, otters wear the

world’s densest fur. At its thickest, this two-layer fur is made up of more than a million hairs per square inch. (You’ve probably got 100,000 hairs or less on your whole head!)

To keep their luxurious coats waterproof, otters spend many hours a day cleaning and grooming. Such good grooming coats their fur with natural oils from their skin and fluffs it with insulating air bubbles.