Dr. Sarah Benedict was stumped.
Alex Ballon, an otherwise healthy
and energetic 24-year-old, said that about an hour ago he dropped
a cold soda can because it felt as though it were burning hot.
Tingles radiated down his arms and legs, he said, but parts of
his face felt numb. He'd been vomiting for hours with knifing
pains in his abdomen.
Dr. Benedict closed the emergency
room curtain and reviewed the case. She had ruled out all
of the basics. No allergies. No exposure to chemicals
at work. No changes in daily routine. Alex said he
had just returned from a fishing trip in the Florida Keys with
some of his buddies. That was all. On their last day
he even caught an enormous grouper that had been lurking around
one of the reefs the whole week they were there. Of course
he ate part of it with his buddies, he said. He couldn't
resist sampling the sweet victory of the catch.
Aha! Dr. Benedict always did
love fitting together the puzzle pieces of challenging cases.
Eating the grouper was the part of Alex's story that completed
the puzzle. Alex was probably suffering from ciguatera (pronounced
sig-wa-TEH-ra) fish poisoning, a commonly misdiagnosed ailment
caused by tiny toxic plants in tropical waters such as those that
straddle the Keys.
Alex's "prized" grouper had probably
ingested a type of toxic algae that made him sick.
This scenario faces many doctors, especially
those in coastal areas of the United States or other countries where
seafood is a local favorite. The culprits are toxic single-celled
floating plants called phytoplankton that are so small
that up to 400 of them can fit on the width of a human hair!
You need a microscope to watch these guys in action, but the effects
that they can have on the marine environment, and even humans (as
Alex learned the hard way), are anything but difficult to see.
The toxic phytoplankton make up
just a small fraction of the total phytoplankton population.
In fact, there are thousands of different species of microscopic
algae in the world's oceans, but less than 100 produce toxins.
The whole group of phytoplankton makes up the base of the food
chain in the oceans so they're like the "grass of the sea" and
a lot of other marine animals depend on them for food. In
a process called photosynthesis, they use light
to produce carbohydrate and oxygen from carbon dioxide and water.
Without phytoplankton, we wouldn't have air to breathe!
Now let's talk about the toxic variety
that are known more for their adverse effects rather than their
role in the functioning of the ecosystem at large.
The toxic phytoplankton, along with
some of the nontoxic species, often grow in such large numbers
that they form blooms, or population explosions
of these tiny cells. Some blooms can discolor the seawater,
and some are bioluminescent, producing a mystifying light that
is visible in the water at night. Blooms can last from days
to months - and sometimes longer than a year. They occur
in waters all over the globe, and have been called red tides,
brown tides or yellow tides. Because these descriptors tend
to vary, it's more accurate to call these natural phenomena harmful
algal blooms (HABs).
Many blooms recur in some areas
more than others. An example is the organism responsible
for red tides in Florida called Gymnodinium breve (or G.
breve for short; pronounced jim-no-DIN-ee-um brev-ee).
This tiny plant is especially notorious along the Florida Gulf
coast, often showing up in the late summer or early fall months.
G. breve is a special type of phytoplankton called a dinoflagellate
(dine-o-FLA-jell-et), which means it has two whiplike tails called
flagellae to help it move and spiral up and down
in the water column. During a bloom, the cells divide within
a few hours to a few days, and the population doubles every time.
An initial G. breve population of 700 cells would grow
to about 10,000 within one week, which is enough cells to cover
a one-inch line. Many blooms have millions of cells per
liter of seawater, which would be enough to discolor the water
and make it look "patchy."
A combination of the organisms'
life cycle (what a biological oceanographer studies) and the currents,
winds and tides (what a physical oceanographer studies) causes
harmful algal blooms to form. In other words, if the environmental
conditions are right, and the cell is at the right stage of the
life cycle, you can get a bloom. For example, HABs in Spain
and California might be linked to a physical ocean process called
upwelling (when deep ocean water comes up to the
surface near the coast of a continent). In the Gulf of Maine,
blooms occur where water from coastal currents and a host of rivers
come together. The phytoplankton cells like these convergence
zones, or fronts, because that's where nutrients
tend to accoumulate. And how do blooms dissipate?
Sometimes the wind and waves can push the fragile cells onshore
to their deaths. Bacteria and viruses, the microscopic "hit-men,"
even smaller than the tiny algae can also attack a cell, exploding
it from the inside out.
HABs can harm marine organisms in
many ways. The effects vary from species to species, and
organism to organism. For example, some fish can die from
ingesting certain tiny toxic plants; other HAB-forming species
are nontoxic to fish but kill other marine animals. Some
types of non-toxic algae called diatoms have tiny
spines made of silica on the outside of the cell that look pretty
neat under a laboratory microscope, but which sreak havoc on a
fish's gills in the water and make it difficult for the fish to
HABs also affect marine mammals
such as manatees and dolphins. Manatees, which breathe air
at the sea surface, can suffer from lung problems and even die
from inhaling airborne toxins released by HABs. Dolphins
might accumulate the toxin in their organs after eating fish contaminated
by the toxic algae in a process called bioaccumulation.
And finally, when the algal cells in a bloom begin to die and
decompose, they can rob the water of its life-sustaining dissolved
oxygen (a condition called anoxia), which causes
a variety of sea life to basically suffocate.
As Alex Ballon learned the hard
way, humans can get sick from these HABs too. HABs can cause
five types of diseases in humans: Paralytic Shellfish Poisoning
(PSP); Diarrhetic Shellfish Poisoning (DSP); Amnesic Shellfish
Poisoning (ASP); Neurotoxic Shellfish Poisoning (NSP); and Ciguatera
Fish Poisoning (CFP), the one with which Alex became familiar.
Common symptoms of all five of these sicknesses include numbness,
dizziness and nausea. What often happens is that people
eat large fish that have bioaccumulated the toxins. The
grouper Alex ate grew big and fat from years of "toxic snacks"
of smaller reef fish. Toxic algae can also be stripped from
the water by filter-feeding animals like clams or oysters, and
people who eat these shellfish (cooked or raw) can become ill.
You cannot detect many of these toxins in fish and shellfish and
cooking the shellfish doesn't neutralize the toxins, so it's tough
to avoid getting sick. Sometimes the HAB toxins are released
into the air when waves break up the cells near the beach, which
may cause beachgoers to experience asthma-like symptoms such as
coughing and eye irritation.
HABs have been documented back to
the days of the earliest Indian settlers who noticed that every
once in a while patches of water were discolored - it looked like
a splotchy sea. However, the number of known HAB species
has increased dramatically in the United States in the past three
decades. The reasons remain unknown, but possibilities include
The lingering mysteries of the HAB
story keep scientists hard at work. Dr. Karen Steidinger,
senior research scientist at the Florida Department of Environmental
Protection and world-renowned red tide researcher, said that some
of the most important unanswered questions include figuring out
how the life cycles of toxic algae influence the recurrence of blooms
in the same geographic area, determining if there are toxic dinoflagellates
in Florida waters that are not being studied, but that can cause
health risks to the public or to marine resources.
- more scientists looking for
HAB species (so more are found)
- better record keeping and information
exchange (so more are documented)
- transport to new environments
in ship ballast water (see sidebar)
- global climate changes:
sea temperature, ocean currents, winds
- pollution in our coastal waters
(can make a bloom last longer)
- world population increase (which
means more crowded coastal areas)
- increases in aquaculture
(commonly known as "fish farming), where the effects of blooms
are readily witnessed because of the more "enclosed" atmosphere
The bottom line is that a lot of
questions remain unanswered. But don't hate the feisty HAB
species just because they seem to be responsible for so many nasty
things. Like every organism, they serve a functional purpose
in nature. Even if human influences such as pollution might
make them worse, HABs are natural events. You might think
of them as the forest fires of the sea; they temporarily shake
things up in the ocean environment, but a certain overall "balance"
in the ecosystem is restored down the road.
In the last two decades there have
been several unusual marine mammal mortality events that were
most likely caused by different types of toxic phytoplankton:
The Mystery of the Magically-Appearing
- The 1980 mass mortality of monk seals on Laysan Island in
Iawaii was thought to be caused by ciguatoxin (the toxin that
causes ciguatera fish poisoning).
- Bottlenose dolphins that died along the Atlantic coast of
the U.S. in 1987 and 1988 probably suffered from a toxin called
brevetoxin and heavy metal poisoning before succumbing to a
secondary bacterial or viral infection. In 1987, humpback whales
in Cape Cod Bay died from eating mackerel containing another
type of toxin (the one that causes paralytic shellfish poisoning).
- Major manatee die-offs that occurred in Florida in 1982 and
1996 are thought to be caused by red tides. The population of
the Florida manatee is about 2200, and because manatees only
produce a single calf every 2.5-5 years, they might be dying
quicker than they can produce new animals.
The year was 1903
and Professor Ostenfeld was baffled. Dense plankton blooms
of the diatom Odontella were suddenly appearing in the
North Sea. This species was well known from the waters of
the Indo-Pacific, but had never been reported in European waters
before. It was not possible for currents to carry it to
this region, and since it was such a large diatom (another type
of phytoplankton) it probably had not been previously overlooked.
So where did it come from? Ostenfeld concluded that this
species had been introduced via the water or sediment in ships'
ballast tanks. Almost 90 years later, Gustav Hallegraeff
confirmed this theory by culturing a related species found in
ballast water brought from Japan to Australia.
When a ship is carrying
cargo, the large empty spaces (ballast tanks) need to be
filled with water to stabilize the ship while out at sea.
When the ship reaches its destination and the cargo is removed,
the ballast water is emptied and equilibrium is restored.
Resting spores (one stage in the phytoplankton life cycle)
are well suited to survive the long dark voyage in ballast tanks,
while planktonic stages do not fare as well. One ballast
tank can contain more than 300 million toxic spores!
One notable and recent
example of contamination by ballast water transport occurred in
the late 1980s when a non-indigenous toxic dinoflagellate species
was introduced into Tasmanian waters. Unfortunately, it
contaminated sensitive aquaculture areas and many commercial shellfish
farms suffered financially. Australia was again affected
when the first outbreaks of paralytic shellfish poisoning appeared
in this area. The responsible dinoflagellate had most likely
been introduced in the last ten to twenty years from ballast water
from Korea and Japan. This organism is now well established
in southern Tasmania, and has been the cause of many subsequent
shellfish bed closures.
As a result, the International
Maritime Organization has introduced guidelines for ballast water-handling
procedures. Practices such as reballasting at sea, ballasting
in deep water, disposal of ballast tank sediments away from sensitive
marine areas, and possibly treating the ballast water with heat
or chemicals are suggested to reduce the risk of harmful introductions.