A red tide has appeared along the coast of Southern California
in recent weeks, worrying some swimmers by tinting the waves a
rusty color during the day and thrilling surfers by illuminating
the waves at night.
The occasional phenomenon occurs when a type of microorganism
multiplies enough to turn the ocean reddish-brown. At night,
billions of the one-celled creatures glow blue when disturbed.
The current bloom extends from Santa Barbara to Baja, and it
arises from different organisms than the highly toxic red tides
seen along other shores. The local red tide is safe to swim in,
officials say, although eating locally collected shellfish is
probably best avoided during the phenomenon.
"We get these amazing red tides, and we can actually enjoy them
instead of cursing them," said Peter Franks, a biological
oceanographer at Scripps Institution of Oceanography at UC San
Franks said scientists have many theories to try to explain the
red tides, but little concrete evidence to support their ideas.
The red tides are caused by one-celled organisms, called
dinoflagellates, that are a part of plankton. As weak swimmers,
they fare well in calm conditions. The red tide spreads when plenty
of sunlight is available because dinoflagellates make food via
photosynthesis like plants.
"My understanding is that it's not harmful to swimmers or
surfers," said Patrick Vergne, Del Mar's lifeguard chief. "We do
get a lot of comments, a lot of people coming up to the lifeguard
towers asking what it is."
According to the California Department of Health and Human
Services, most red tides are completely harmless. But during some
red tides, shellfish can become poisonous because they are filter
feeders that strain organisms from the water. Only testing can show
if the shellfish have accumulated toxins dangerous to people. Using
the "better safe than sorry" strategy of not eating local shellfish
during the red tide is recommended.
Surfers complain that the red tide seems to be accompanying an
upwelling of cold water from the deep ocean. Franks said the
connection might be valid because the water contains nutrients
needed by many microorganisms, including dinoflagellates.
The red tide itself changes the balance of the marine ecosystem
as the dinoflagellates take over.
"It has a pretty gnarly effect on the species diversity," said
Marco Gonzalez, chairman of the San Diego chapter of the Surfrider
Foundation, an environmental group. "It's a natural process. It's a
spike that the local processes take a little while to recover
For most of the people who visit the beach by day, the red tide
is simply a curiosity.
At night, the waves shine a beautiful blue. The dinoflagellates
glow when disturbed as a sort of burglar alarm. When a predator
attacks one of the organisms, the flash of light attracts a
policeman of sorts - a bigger predator.
Surfers watch in awe as the luminescence fills the wake of fish
"It's fun to go out there because it's like you're tripping out
on acid," said Sam Powers, a surfer who works at the Surf Ride
store in Oceanside. "It's like a natural high."
The red tide can provide residents of Southern California with
an experience similar to catching fireflies in a jar. Franks said a
fun experiment is to fill a jar of water in knee-deep surf, store
the jar in a cool place and shake the jar at night. Millions of
microscopic dinoflagellates, aroused by the motion, should flood
the jar with blue light.
Contact staff writer Katie Burns at (760) 740-5442 or