back to data
glossary
Photo courtesy of UCSC
Many fish species, like herring, rely on the kelp as a surface for their larvae to use as settlement habitat. Meanwhile adult fish feed and hide in the kelp fronds.

Invertebrates such as crabs, snails, bryozoans, ascidians, sea urchins, clams, and shrimp are also found in kelp forests. Some use the blades as living habitat, while others feed on the kelp itself.

Sea otters also find safety and food in kelp forests. They feed on the sea urchins, clams, and crabs that live in this undersea forest. The long stands of kelp provide good protection from predators.

Humans have also begun to commercially harvest kelp. Kelp can be processed into nutritional supplements for direct human consumption, or into fertilizer

( www.biology.ucsc.edu/people/raimondi/readdie/ecology.htm)
Tall stands of giant kelp attach to rocky substrate to form dense forests that create a three-dimensional habitat. The ocean is truly a 3-D world where there are no hiding places. An animal swimming in the water column can be attacked from every direction. Kelp forests offer a haven for protection as well as hard surface for settlement.
Sea otters and sea urchins in the kelp forest.

Sea urchins are voracious herbivores. They climb up the holdfast and graze on the stipe, as well as eat drift algae that accumulate on the ocean bottom. Studies have found urchins responsible for completely removing kelp from an area, leaving it an urchin barren. Sea otters feed primarily on sea urchins, and thus are an important predator in the kelp forest. Aleutian Islands that have been recolonized by sea otters now have thriving kelp forests where extensive urchin barrens once dominated.

(www.biology.ucsc.edu/people/raimondi/readdie/ecology.htm; Estes and Palmisano, 1974)

Figure 1. Picture of an urchin barren. Purple and red sea urchins cover most of the outcropping. Only a few stipes and stands of kelp remain.
 
Figure 1. Total kelp density around Adak Island in 1987 and 1997.
Figure 2. Grazing intensity as measured by percent kelp loss per day around Adak Island in 1991 and 1997.

This study surveyed kelp forest density and sea urchin biomass at Adak Island. The graphs contrast the changes in kelp density and urchin biomass during a ten year period (1987 - 1997):

  • Kelp density declined by a factor of 12 (Figure 1).
  • Average rate of kelp tissue loss to herbivory increased from 1.1% per day in 1991 to 47.5% per day in 1997 (Figure 2).
  • Sea urchin size and density produced an eight-fold increase in biomass (Figure 3).
  1. Notice the time frame correlation between the kelp forest degradations and sea otter decline.
  2. What is happening to the kelp forest as a result of the declining sea otter population?
(Figures modified from data presented in Estes et al, 1998)
Figure 3. Sea urchin biomass around Adak Island in 1987 and 1997.
back to data
glossary
 

This web site was created by Lynn Tran at the North Carolina State University, Department of Mathematics, Science, and Technology Education on 7/12/03. Faculty advisor Dr. David Eggleston, NCSU, Department of Marine, Earth, & Atmospheric Sciences. Last updated December 29, 2003 .