Dune Hugger: Red Tide

Special to the PRESS

Red Tide.  An event that occasionally marks the beginning of fall for the Coastal Bend and Southern Texas Coasts that can plague the Gulf and Bay Sides of our barrier islands in Corpus Christi, Port Aransas and South Padre Island.  It causes fish kills that result in the rancid smell of rotting carcasses and cause respiratory issues and burning eye sensations in humans while either directly swimming in the water or through an aerosol that can be caused by increased wave activity and wind.  It can even result in the deaths of birds, dogs and coyotes that eat the dead fish that are saturated with the brevetoxin, a neurotoxin that Karenia brevis, the dinoflagellate that makes up Red Tide, emits.

Red Tide is one of many organisms that make up what is commonly referred to as Harmful Algal Blooms and for as often as they have been occurring over the last 20 years, little is known about what triggers them.  K. Brevis can sit dormant for years and then awake with the trigger of warm water and increased nutrients in the water.  It is assumed that this can be exacerbated by the runoff of nitrate rich water from lawns and farmland.  However, I wanted to cover some little known observations that I have come across in the past several years after I started researching the blooms during the last large months-long bloom that happened in 2011.

Many residents have observed that the evenings and mornings have been pretty mild with little noticeable effect on humans.  This makes sense after talking with a biologist from the Texas General Land Office this past week.  K. Brevis is an algae and, along with other nutrients, depends on the sun for sustenance.  According to him, the organism sinks into the depths at night to feed on nutrient rich water.  K. Brevis can propel itself through the water with one of its two whip like tails.  This reduces the surface effect of the Red Tide.  However, during the daytime hours it rises back to the surface to soak up the sun and will increase the possibility of brevetoxin aerosol in the air depending on wind and wave action.  The prime times that brevetoxin aerosol would be noticeable is 10 a.m. to 4 or 5 p.m.

The most fascinating observation that I came across though was back in 2011 through research Texas A&M University did regarding K. Brevis.  It was commonly assumed that rain would dissipate the bloom and help kill it off by diluting the salinity of the surface water.  This seems to not be the case.  According to the study, it has the opposite effect. In general, the study showed that the organism moving from saltier offshore waters to less saline coastal waters caused the K. Brevis cell to produce more brevetoxin, upwards of 14 times more, to better equalize the salt and water content within its structure.  If you were to add rain and further drop in salinity, this would be further increased.  Anecdotally this makes sense, as during that same 2011 period which was our last major bloom, the City of South Padre Island and the Surfrider Foundation was doing a dune planting with moderate surf conditions.  The aerosols were already moderate but it rained during the event and the toxicity of the air noticeably increased, becoming severe.

I have received many inquiries into the forecast of Red Tide on South Padre Island.  I have told them, and as you can see from above, that it is really an hourly event.  It is almost impossible to predict what will happen.  It can literally seem to have completely disappeared but then explode a few hours or even a few days later.  The only known thing that can negatively affect Red Tide is a long period of a severe cold front that would lower the water temperature enough to kill it off.  The other factor that would rid us of this very annoying event is a long period of wind that would push the blooms away from us.

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