Getting home from a relaxing Holiday is one thing,
enjoying the rain and a slightly burned skin the days after another! The
weather can be quite strange and I heard some rumors that the sun was very
strong last week across the whole of Europe, hence my itching skin. My
destination for this Holiday was Almuñécar in Andalusia, Spain.
One of the very first days I made a remarkable
discovery. My partner and I were walking past the coastline, enjoying our walk,
watching the seagulls, all the cliché things that we love to do while not at
work. But sometimes work follows you to the other side of Europe... On the coast
of Almuñécar I found a small red tide.
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| Red tide ranging over 30-50 meters across the coast of Almuñecar, Spain |
A red tide is a phenomenon that is caused by algal blooms. These microscopic algae are so massive in numbers during a bloom, that they color the water red. These blooms are mostly caused by dinoflagellates (phytoplankton). Some species are even capable of emitting a blue-green light by means of bioluminescence when disturbed; unsettling and most beautiful at the same time. The video below shows the red tide - bioluminescent in San Diego 2011 by Logan Call. I haven't seen it happening in Spain.
A red tide occurs several times a year. It can cause problems, in particular when
these algae are capable of producing harmful toxins. These toxins may cause
illness in humans and other animals, particularly when consuming shellfish.
In the Summer of 2011, a fishing ban was in place on
some fishing grounds of the Málaga coastline, Andalusia. Increased levels of
PSP toxins were found in bivalve moluscs during the red tide season. PSP stands
for Paralytic Shellfish Poisoning. This disease is caused by the production of saxitoxin by the Alexandrium species (dinoflagellate, type of algae).
The algae are eaten by grazers, like krill and shellfish. Krill and shellfish are not affected by the saxitoxins. They form a kind of depot in body mucilage, concentrating toxins to high PSP levels. In turn the toxins will not circulate in their body liquid system, keeping them safe from harm. When such contaminated shellfish is consumed, the PSP toxins are released and taken up in the blood circulation of the consumer. The toxins are able to disrupt the nerve system and even cause paralysis in the consumer. Large fish kills and numerous mammalian diseases have been recognized to result from the consumption of shellfish during red tide algal blooms.
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| Red tide concentrating in one corner at the beach of Nerja near the Balcon de Europa |
Red tide events can result from warming ocean surface
waters, low salinity, calm seas, high levels of nutrients and rainfall before
sunny days, especially in warm Summer months. Wind, currents, storms and ships
can distribute floating areas and spread it out.
I concluded that the red color at the coast of Almuñcar
was in fact a small red tide, especially because it is known in this particular
area. Of course I didn’t bring a big microscope with me during a relaxing (!)
Holiday, and taking samples would be of no use in such heat (only a lab will be
able to cool samples and analyze them soon after). Besides, the red tide is potentially toxic: even breathing in the tiny droplets from the spray may accumulate illness. I also believe that customs at the airport wouldn't agree with taking potential poisonous liquid with me to another country!
A few days later I
discovered another red tide on the coast of Nerja. There was some rubbish floating
in the tide – dead fish? The season has only just started, so I expect there
will be red tide alarms now and again the upcoming months on the Andalusian
coast.
Resources:
Microbial Life: educational Resources: Red Tide
