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The kelp
cabal
After studying the ecology of Tatoosh Island for more than a decade,
Catherine Pfister and Timothy Wootton consider the tiny rise of
land off the Washington coast a second home. So when the husband-wife
team first noticed in April 1998 that more than 75 percent of the
island water’s kelp had disappeared, they felt almost as if
they had been robbed. This April they returned to Tatoosh, intent
on investigating what had happened to the seaweed.
The couple—both assistant professors in ecology & evolution
and the Committee on Evolutionary Biology—research population
dynamics and species interactions in aquatic ecosystems. As Pfister
explains, kelp is a major player in the carbon cycle. Bits of kelp
that break off as the waves crash down eventually become food for
filter feeders such as mussels and barnacles, and there are many
animals that graze directly on kelp. Its absence, she says, could
have major effects on the populations of animals, such as mussels
and otters, that depend on it for food.
During their stay on Tatoosh this past summer, the researchers
identified two chief suspects in the kelp’s disappearance:
the erratic weather duo of El Niño and La Niña. Though
a La Niña doesn’t always follow an El Niño, that
was the case in 1997–1998. While unusually warm waters in the
equatorial Pacific Ocean characterize El Niño, unusually
cold waters mark La Niña. Several clues have led the U of
C researchers to surmise that these temperature changes in the Pacific
affected the ecology of Tatoosh, located a half mile off Cape Flattery,
the northwestern-most point in the contiguous United States.
Of the dozen populations of one variety of kelp, called sea palm,
that the ecologists had been following, two have completely disappeared
since the last El Niño. In the remaining populations, the
number of plants also declined. Wave activity during the most recent
El Niño may have resulted in more frequent storms, dislodging
the adults before they had the chance to release their spores, says
Pfister.
Another possibility, say the ecologists, is that the rise in the
Pacific’s temperature during the El Niño prevented the
normal upwelling of nutrient-rich bottom waters, depriving the kelp
of essential nutrients. Alternatively, says Wootton, the warmer
waters could have increased the metabolism of the water’s animal
inhabitants. If that’s the case, he explains, kelp-eating organisms,
such as limpets and chitons, may have digested and used the energy
from their food faster, allowing them to eat kelp faster than usual.
Pfister and Wootton also saw changes associated with a La Niña
year. Wootton says the water off the island’s coast stayed
in the 40s during the summer, when it should have been into the
50s by July. Cooler waters usually are associated with more nutrients,
but, Wootton says, it may have been too cold for planktonic algae
to grow fast enough to support aquatic life.
Pfister and Wootton hope their continuing observations will enable
ecologists to better determine how environmental changes affect
coastal species.—Sharon Parmet
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