NUTRIENTS - Marine Pollution: What Everyone Needs to Know - page 32

What are some harmful algal species?
HABs have occurred periodically along the coast of southwest
Florida for over a century, causing the death of many species
including turtles, manatees, dolphins, and crabs. Decreased
abundance of shrimp and several fish species have also been
noted, and shellfish farms have been forced to shut down.
Mass mortality of birds after eating fish that had consumed
toxic algae has been reported. The microscopic dinoflagellate
that causes these blooms ( Karenia brevis ) produces a powerful
toxin, brevetoxin, which paralyzes animals that ingest it. It not
only kills fish, but this lipid-soluble toxin can biomagnify up
the food chain to top carnivores like dolphins. It can also cause
skin irritation and burning eyes among swimmers; people who
are not even in the water may cough and sneeze when winds
blow its toxic aerosol onshore. Along the Gulf Coast, K. bre-
vis blooms directly affect human health. Eating shellfish with
brevetoxins causes neurotoxic shellfish poisoning. In addition,
brevetoxin levels in dead fish and fish-eating birds collected
from beaches and rehabilitation centers during blooms sug-
gest that brevetoxin can cause bird mortality. These blooms
are stimulated when seasonal changes in wind patterns move
nutrients east from the Mississippi River. The N-rich river
water spurs the growth of the algae, which are pushed by
winds toward Florida, concentrating them into larger blooms.
In the spring of 2013 a record number of manatee deaths
(more than 500) was attributed to this HAB, plus other causes.
Scientists thought that toxins in the bloom settled onto the sea-
grasses that manatees eat, causing them to become paralyzed
and eventually to drown. Bottlenose dolphins are also vulner-
able to the toxin. In 1999-2000, 152 dolphins in the area died
following extensive K. brevis blooms; brevetoxin was detected
in 52% of the animals. Dolphin stomachs frequently contained
brevetoxin-contaminated menhaden fish. In 2005-2006, 90
bottlenose dolphins died when there were high densities of
K. brevis . Most (93%) of them tested positive for brevetoxin.