Nearshore El Niño Effects:
Disturbance and Renewal

By Jack Engle

Kelp disappears! Sea stars dissolve! Subtropical fish invade! Although there has been considerable publicity about El Niño effects on marine mammals, sea birds, and migratory fishes, changes to nearshore marine communities at the Channel Islands also can be dramatic. Kelp, rocky pinnacle, and sand ecosystems all have been altered in complex ways by high temperatures, low nutrients, changing currents, and storms associated with this year's El Niño.

The lush forests of giant kelp encircling the Channel Islands depend on cool, nutrient-rich water for survival and growth. Nutrient depletion related to the influx of warm water this summer has resulted in massive declines in kelp beds, especially at the southeastern islands. Even more damage may be inflicted by the powerful El Niño storms predicted for this winter.

The loss of kelp beds is devastating for the myriad creatures dependent on this giant alga for food and shelter. Kelp-eating crabs, snails (including abalone), and fishes starve. Sea urchins, lacking drift kelp, emerge from crevices and graze away remaining kelp plants. With the kelp "trees" gone, a host of other invertebrates and fishes lose critical microhabitats, and the rich underwater forest becomes a relatively barren subtidal plain. However, many kelp forests are resilient and can re-establish themselves fairly rapidly once cooler, productive conditions return.

The nutrient-poor surface waters characteristic of El Niño also cause a marked decline in productivity of the microscopic plants and animals that form the basis of key food chains. Current-swept habitats, especially steep-sided pinnacles, are dominated by filter or suspension feeding invertebrates that specialize in consuming this plankton "soup." Sponges, sea anemones, sea fans, worms, barnacles, sand crabs, mussels, clams, bryozoans, and sea squirts all are devastated by the paucity of drift food. Higher up the food chain, carnivorous crabs, shrimp, snails, sea slugs, and fishes that prey on the sedentary plankton-feeders also suffer. Deterioration of rich pinnacle communities leads to sparse habitats dominated by bare rock, pink algal crusts, and a few opportunistic species.

A remarkable but poorly-known phenomenon associated with El Niño episodes is sea star "wasting disease." This contagious illness, apparently caused by a Vibrio bacterium, affects all species of local stars. During the warmest periods, mass mortalities occur as stars rapidly deteriorate into piles of skeletal ossicles. Widespread losses were documented during the 1982-83 El Niño.

©1997 Richard Herrmann

Bat star succumbs to "wasting disease."

Since then, sea star populations slowly recovered at the cooler northwestern islands, but recovery was minimal at the warmer southeastern islands. The 1997 El Niño has again caused catastrophic sea star mortalities at the islands. Various sea cucumbers and sea urchins have died as well. Losses of these ecologically important spiny-skinned animals have altered the intricate balance of nearshore communities.

Other cooler-water life forms are stressed or die as a result of El Niño's warming. Examples include red-bladed algae, sponges, orange cup corals, rock crabs, red abalone, tunicates, sculpins, surfperch, and rockfish. Alternatively, warm southern currents bring abundant larvae of subtropical species, including Asparagopsis seaweed, spiny lobsters, coronado urchins, and fishes such as garibaldi, blacksmith, sheephead, bluebanded gobies, and moray eels. Some unusual creatures that recently have expanded their ranges northward include mantis shrimp, orangethroat pike-blennies, Guadalupe cardinalfish, rainbow scorpionfish, finescale triggerfish, and scythe butterflyfish.

The dynamic mix of disturbance and renewal determines the composition of nearshore communities. Concerns about El Niño effects predominate now. However, in the larger perspective, El Niño years represent the peaks of a warming trend influencing life at the Channel Islands since 1976. Aside from human impacts, the species present today reflect cumulative effects of over two decades of warm-water conditions. These changes include declines in kelp forests and cool-water species, and expansion of warm-water marine life.

Jack Engle, associate research biologist at UC Santa Barbara's Marine Science Institute, conducts long-term monitoring surveys of marine resources and coordinates the Tatman Foundation's Channel Islands Research Program.

Alolkoy, Winter 1997