HOW ARE PINNIPEDS AFFECTED BY CHANGES IN THE FOOD CHAIN?

El Niño not only affects large visible animals like seals and sea lions, but it also effects all living things in the sea. Normally the California coast has a cold water environment with upwelling. The animals and plants that are part of the off-shore habitat have adapted to live in water that is normally much cooler at this time of year. The giant kelp,Macrocystis sp.., is a good example. It's optimal temperature range is 68-74 degrees Fahrenheit or 20-23 degrees Celsius. Kelp grows best in the cold winter months and in the early spring when waters are the coolest. It tends to decline in the warmer summer months and the fall when the water is warmer. If reproduction occurs when the water temperature is above 68 degrees, the tiny male and female plants die, interrupting the cycle of reproduction.

Additionally, the unusually warm water of El Niños changes normal ocean movements. Upwelling decreases and the nutrients that are normally brought to the surface become limited in number. Without nutrients, phytoplankton productivity drops off. The zooplankton that feed on the phytoplankton subsequently start to decline. The fish and squid populations that feed on the plankton decrease. At the top of the food chain, seals and sea lions no longer can find enough fish to sustain their normal weights. The adult animals with a lot of experience are not affected too much. They have learned to adapt by diving deeper and foraging longer. Adults are physically strong enough to outlast El Niño's effects. It is the very young and the very old that are affected severely. The young do not have much experience , nor can they dive to the increased depths where fish and squid can now be found. The old are often weak and the increased physical stress places them in further jeopardy.

 

These thin sea lion pups show effects of lack of food resources in the ocean.

To test your understanding, complete the following:

• List the organisms below as either producers or consumers in a kelp forest food web. Upon what organisms do pinniped populations depend How are the different species both dependent and interdependent? Why is there such dependence on the producers?

sponges, sea anemones, hermit crab, kelp crab, barnacle, macrocystis, coralline algae, sea stars, brittle stars, sea urchins, octopi, squid, abalone, turban snail, leopard shark, rockfish, kelpfish, sculpin, sheephead, garibaldi, anchovy, herring., sea lion, harbor seal, white shark, phytoplankton, zooplankton.

• How is the processes that occur during an El Niño similar or dissimilar to the destructive processes that occur on land in an event such as a drought?

Additional activities for students:

• Kelp Forest food chain, food web, and food pyramid activities.
• Upwelling, current exercises

WHY ARE THERE DIFFERENCES OF EL NINO IMPACT

Otariids often bear the brunt of El Niño conditions, especially the California sea lion population. Sea lion pups are born in June. They normally nurse from their mother for 8 to 14 months. The mother sea lion must feed during the prolonged nursing period. The quality of food she consumes affects the quality of her milk. Because of the length of pup dependence on the mother and because the mother is feeding on inadequate fish resources or must spend increased time and energy to obtain food, the mother's milk is lower in fat and does not provide adequate nutritional value for the pup. Furthermore, a severe El Niño will escalate its impact on the food supply during the time that the pup is demanding more nutritional support from the mother. If the mother is unable to obtain enough food, she quits producing milk altogether and subsequently abandons her young. Also hungry pups tend to wander. If the mother is gone too long in her attempts to forage, the pup may wander away from the rookery and the mother may be unable to find it upon her return. Pups entering the ocean in search of their mother can be swept by the currents off the Channel Islands. The luckier pups end up stranding on mainland beaches where they may be transported to a rescue center. The unlucky ones perish in the ocean or are not found until their condition is so debilitated that they do not survive. In El Niño years sharks and killer whales flourish. Sea lions are surface feeders, relying on fish and squid populations that swim close to the surface. Adult sea lions can dive to a maximum of 800 feet and stay submerged for 10-12 minutes.

Fur seals suffer a similar fate. The pups are born in June and have a 6 month nursing period. Fur seals feed offshore in deeper water and do not hunt in the kelp forest. Fur seal mothers also have difficulty finding food for themselves and subsequently the pups are undernourished and also abandoned early.

In contrast, the effect of El Niño conditions on the phocid population is much different. Elephant seal pups are born in January. The Northern elephant seal mother does not feed during nursing, so she has to rely on the resources stored in her body. She usually has enough fat reserves to feed her baby. The nursing period is very short, only about 4 weeks. Babies are able to live on their fat reserves for several more months after being weaned by the mother. During a severe El Niño, pups enter a debilitated ocean and are impacted when they must feed themselves. If there are not enough food resources to support them, the pup population faces increased mortality compared to years with abundant resources.

The effect on harbor seals should be somewhat varied. Pups are born during a longer period, from late February into June. They spend 4 to 7 weeks nursing from the mother. The mother feeds during nursing. She puts the pup on the beach and goes into deeper water to find food. During mild El Niño events, the pups may be born late enough to escape most of the hardships imposed on other animals. If ocean conditions have been restored, the mother is able to feed herself adequately and nurse her baby. During major events, the animals suffer much like the sea lions. The mother does not find adequate food, and, therefore, cannot produce milk. The pups are abandoned in poor condition. Furthermore, these animals are subjected to the effect of strong, late-season storms. If the pup is pulled off the beach into swift water when it is too young, it may drown. It is not known if the harbor seals have smaller babies or a higher abortion rate during El Niño events.

Under normal conditions, life is difficult for a pinniped pup. After the nursing period, the mother weans the pup by leaving it to fend for itself. Under normal circumstances, about 50% of all pups are not alive by age one; under El Niño conditions many more pups die. It is often the case that 90%-100% of the pup population does not survive during an El Niño year.

High mortality during storm

DATA FROM MARINE MAMMAL CARE CENTER

Below is the stranding data from the Fort MacArthur site for the year 1993-1997. Construct similar graphs with this data. Again you should print out the data so that you can leave this program and work with a spreadsheet.

In constructing the spreadsheet, continue entering the data from the next charts to the right of the previous set, creating one continuous apreadsheet. Do not reenter the months in the center of the spreadsheet.

GRAPH C: Graph each year, all four species

For a more complete discussion of this topic refer to:

• ·"Seasons of the Kelp Forest," Teachers Guide to the Kelp Forest,MARE, Marine Activities, Resources and Education, Lawrence Hall of Science, University of California, Berkeley, CA 94720-5200
• ·University Corporation for Atmospheric Research, "El Niño and Climate Prediction," Reports to the Nation, National Oceanic and Atmospheric Administration, Spring 1994
• ·Abbott, Isabella and Hollenberg, George, Marine Algae of California, Stanford University Press, Stanford, CA, 1976
• ·Greene, Thomas, Marine Science, Amsco School Publications, 1998.
• ·Monterey Bay Aquarium, Sea Searcher's Handbook, Roberts Rinehart Publishers, Boulder, CO, 1996
• ·The Center for Marine Conservation, The Ocean Book, John Wiley and Sons, New York, 1989
• ·Sumich, James and Dudley, Gordon, Laboratory and Field Investigations in Marine Life, Wm. D. Brown Publishers, Dubuque, IA, 1996
• ·Hill, Amy, Marine Biology, An Introduction to Marine Ecosystems, J. Weston Walch, Portland, Maine, 1995
• ·Van Cleave, Janice, Oceans for Every Kid, John Wiley and Sons, Inc. New York, 1996
• ·Niesen, Thomas, The Marine Science Coloring Book, Harper Perennial, Oakville, CA, 1982
• ·Videodiscovery, The Water Planet, Videodiscovery, Inc., 1995
• Cabrillo Marine Aquarium, Coastal Marine Environment Previsit Materials, 1997

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