The Scientist November 2019

28 THE SCIENTIST | the-scientist.com

A

singular scene from last year’s

red tide event in the Gulf of

Mexico sticks in the mem-

ory of phytoplankton ecolo-

gist Vincent Lovko. “I got to go up in a

helicopter with a news crew,” Lovko says.

“ Yo u could see the front of the bloom

right along the coast”—a reddish cloud of

millions of microscopic organisms called

dinoflagellates floating in the water. “The

striking part was all the little white dots,

which were the dead fish.”

Red tides are caused by the dramatic

reproduction of Karenia brevis, a species

of dinoflagellate that is common in Gulf

waters. Every year when conditions turn

favorable, populations of the unicellu-

lar alga grow rapidly, dyeing undulating

patches of water a brown, green, or rusty

hue. Sometimes these events come and

go in a matter of weeks or months. But

the bloom that Lovko, a researcher at the

Mote Marine Laboratory in Sarasota, saw

dotted with the corpses of fish lingered in

the Gulf for more than a year. It started

sometime in October 2017 and didn’t dis-

sipate until early this year. And the fish—

most likely killed by potent neurotoxins

called brevetoxins produced by K. bre-

vis—weren’t the red tide’s only victims.

According to statistics kept by the

Florida Fish and Wildlife Conservation

Commission (FFWCC), the bloom killed

more than 1,000 sea turtles, about 200

manatees, and nearly 190 bottlenose dol-

phins, in addition to countless fish and

some economically important inverte-

brates, such as stone crabs. Humans may

have also felt the effects of Florida’s most

recent red tide, with the Florida Depart-

ment of Health noting a small uptick in

the number of weekly emergency depart-

ment visits statewide in July through

November 2018 for people reporting

respiratory symptoms and red tide expo-

sure. Although a causal relationship was

not formally established in these cases,

brevetoxins are known to cause respi-

ratory irritation when the compounds

become airborne as wind and waves

whipped the water into sea spray.

Currents first swept the 2017–2019 red

tide near the Florida panhandle and then

around the Florida Keys and up the Atlan-

tic coast, dumping swaths of ruddy water

into nearshore ecosystems as far north as

Orlando. (See map on the opposite page.)

The bloom “was in so many places at the

same time,” remembers Kate Hubbard,

head of the harmful algal bloom (HAB)

research and monitoring program at the

FFWCC’s Fish and Wildlife Research

Institute (FWRI). Phytoplankton biol-

ogist Cynthia Heil, director of the Mote

Marine Laboratory’s newly formed Red

Tide Institute, adds, “Local currents do

impact these blooms.”

Red tides are nothing new to the Gulf.

They’ve plagued the area for hundreds of

years, and since the 1940s, when researchers

linked K. brevis (then called Gymnodinium

breve) to the Gulf ’s red tide events, the sci-

entific community has been trying to learn

more about the biology of the dinoflagellate

species, hoping to more accurately predict

blooms and mitigate the damage to local

ecosystems and human health. But many

critical questions remain. Scientists have

not yet fully described K. brevis’s life cycle

or plausibly hypothesized why the species

evolved to produce brevetoxins, nor do they

have a complete understanding of the envi-

ronmental and ecological drivers of bloom

formation, maintenance, and termination.

The factors at play are so numerous

and dynamic that anticipating shifts in

local conditions that might promote a

bloom has proven difficult, to say the

least. Broader concerns about how cli-

mate change might alter Florida’s red

tides add to the uncertainty. All of this

makes for a vexingly complex soup of

unknowns surrounding K. brevis.

But new insights are emerging all

the time, and the scientists who study

the phytoplankton and its blooms are

getting closer each year to decoding the

phenomenon. Hubbard, Lovko, sev-

eral of his Mote colleagues, and other

researchers throughout the state and

beyond are taking advantage of new

technologies—such as self-propelled

underwater robotic gliders that sam-

ple water and track conditions in situ,

and advanced genetic tools for detect-

ing the presence of K. brevis cells—to try

to understand what triggers the phyto-

plankton to undergo rapid population

growths, why they make brevetoxins at

all, and how best to mitigate red tides

once they begin ramping up in the Gulf.

“The implementation of those tools

is going to really help us address some

of those key questions,” Hubbard says.

“I feel pretty optimistic that we are going

to be able to make some new discoveries

... to help us in our predictive models.”

The bloom trackers

Historical accounts suggest that popula-

tions of K. brevis in the Gulf have been

undergoing annual population booms

since at least the 15th and 16th centu-

ries, when Spanish explorers in Florida

described fish kills in Gulf waters that

bore a striking resemblance to the scene

that Lovko noted last year.^1 In 1882, the

first official, though anecdotal, docu-

mentation of fish kills, bird deaths,

and human sickness caused by red tide

blooms in the Gulf of Mexico—as far

back as 1844—was published in the Pro-

ceedings of the U. S. National Museum.

I honestly do not know if K. brevis blooms

can be “prevented” based on the level of

our current knowledge.

—Karen Steidinger, retired phytoplankton ecologist

after whom Karenia brevis is named