Neurotoxic algae impact dolphins

Jul 27, 2011 2 comments By


Algae blooms contain neurotoxins that may have chronic effects on the health of bottlenose dolphins.

The dinoflagellate Karenia brevis produces neurotoxic brevetoxins, which are known to be harmful to aquatic organisms and humans (as well as local economies).

Known as “Florida red tide,” wave action may cause K. brevis cells to burst, releasing the toxins into the water. When these toxins are stirred up at the water’s surface by wave action, they can cause irritation and burning of the eyes, throat, and upper respiratory tract of humans.

The airborne impact of a strong red tide can ruin a day for humans on the water or at the beach, but no human fatalities have been associated with red tide.

But dolphins, manatees, sea turtles, seabirds, and fish also can be impacted by red tides.

Newly published health assessment results from a 10-year study of live dolphins in the Sarasota Bay community show effects from algae blooms that occurred nearly annually.

Dolphins tested positive for two toxins, brevetoxin and domoic acid, with 14% of the dolphins testing positive for both.

While the full health effects on marine mammals are as yet unclear, researchers believe that brevetoxins can play an important role in marine mammal Unusual Mortality Events, that in the past have involved both dolphins and manatees.

Algal neurotoxins are known to accumulate in sediment, sea grass, shellfish, and fish, so dolphins and manatees may obtain them through the food chain.

This study is important because it points to the need for future research to understand the impact on marine mammals of chronic exposure to harmful algal blooms.

Co-authors on the research paper by our collaborator Mike Twiner include our own Drs. Brian Balmer and SDRP Director Randy Wells and SDRP alum Spencer Fire.

The Citation is: Twiner MJ, Fire S, Schwacke L, Davidson L, Wang Z, Morton, S, Roth, S, Balmer, B, Rowles,T.K., & Wells, RS. (2011) Concurrent Exposure of Bottlenose Dolphins (Tursiops truncatus) to Multiple Algal Toxins in Sarasota Bay, Florida, USA. PLoS ONE 6(3): e17394. doi:10.1371/journal.pone.0017394

The abstract is copied below. Copies of the publication may be obtained from the author ( or the online journal PLoS ONE.


Sentinel species such as bottlenose dolphins (Tursiops truncatus) can be impacted by large-scale mortality events due to exposure to marine algal toxins. In the Sarasota Bay region (Gulf of Mexico, Florida, USA), the bottlenose dolphin population is frequently exposed to harmful algal blooms (HABs) of Karenia brevis and the neurotoxic brevetoxins (PbTx; BTX) produced by this dinoflagellate. Live dolphins sampled during capture-release health assessments performed in this region tested positive for two HAB toxins; brevetoxin and domoic acid (DA). Over a ten-year study period (2000–2009) we have determined that bottlenose dolphins are exposed to brevetoxin and/or DA on a nearly annual basis (i.e., DA: 2004, 2005, 2006, 2008, 2009; brevetoxin: 2000, 2004, 2005, 2008, 2009) with 36% of all animals testing positive for brevetoxin (n = 118) and 53% positive for DA (n = 83) with several individuals (14%) testing positive for both neurotoxins in at least one tissue/ fluid. To date there have been no previously published reports of DA in southwestern Florida marine mammals, however the May 2008 health assessment coincided with a Pseudo-nitzschia pseudodelicatissima bloom that was the likely source of DA observed in seawater and live dolphin samples. Concurrently, both DA and brevetoxin were observed in common prey fish. Although no Pseudo-nitzschia bloom was identified the following year, DA was identified in seawater, fish, sediment, snails, and dolphins. DA concentrations in feces were positively correlated with hematologic parameters including an increase in total white blood cell (p=0.001) and eosinophil (p,0.001) counts. Our findings demonstrate that dolphins within Sarasota Bay are commonly exposed to two algal toxins, and provide the impetus to further explore the potential long-term impacts on bottlenose dolphin health.


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Health and Physiology

About the author

Blair Irvine, PhD, is retired and manages the SDRP website, serves as President of the non-profit Dolphin Biology Research Institute, and he volunteers as otherwise needed. He started the SDRP in 1970 with then-high school student Randy Wells. Blair led the research into the late-1970’s when Randy took over. After that, Blair's non-dolphin career was in the area of human behavioral health. With NIH support, much of his research was involved Internet interventions and training programs. His graduate degrees are in Zoology, Exercise Physiology, and Health Education.

2 Responses to “Neurotoxic algae impact dolphins”

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