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Whassup with the brown stuff?

1/16/2014

 
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Some weird brown patches appeared just offshore on the wildside a few weeks ago. Wasn't sure what they were as there had been talk of a toxic red tide in the Cape Town area.

Then yesterday I spotted a few in the bay out front and decided to find out a bit more. Turns out they're most likely to be a non-harmful algal bloom, not a poisonous red tide. Shew.

Algal blooms are usually harmless and are part of the natural ocean cycle. When conditions are just right, ocean phytoplankton reproduce like bunnies, creating a thick, visible layer near the surface. These algae blooms - or what we often term as "red tide" -  might look really sketchy during the day, but if the critters are the bioluminescent (such as Noctiluca scintillans), then look out for the night show!

This particular variety of phytoplankton glows blue when agitated, transforming dark ocean into a giant lava lamp. If the bloom comes ashore, watch the waves light up as they crash onto the beach in a weird neon blue glow. Unfortunately our patches have stayed offshore so I haven't seen the disco-glow as yet. Maybe someone should go do doughnuts out there on their jetski at night?
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So why do these blooms occur? It's usually from some form of nutrient input. On the West Coast it's upwelling bringing bottom nutrients to the surface due to a combination of wind and bathymetry, combining with sunlight, and then "boom"....you get an explosion of phytoplankton production.

These critters are always in our waters, they just need the right fuel to bloom. In the Eastern Cape there are upwelling cells (mostly off Port Alfred) which can periodically bring nutrients to the surface when the winds line up correctly. Another factor which might spark a bloom is when organic nutrients are leaked into the ocean from sewerage, fertiliser, or river run-off, where the addition of these nutrients is enough to start a phyto feeding frenzy.

The blooms in our bay could arise from either one, but most likely are natural events resulting from wind-induced nutrient input from cold bottom waters. 

The most likely suspect around PE is the glow-in-the-dark-dude, Noctiluca scintillans. He's a big-ass dinoflagellate, well, big-ass in the dyno world - clocking in at about 2 mm. The blooms usually are thick and bright red/orange and cause outboard motors to choke up (OK, so there goes the idea of getting a jetski to buzz about in them to make glow trails at night)

Other than draining oxygen from surface waters when decomposing or possibly clogging motors/gills/intake pipes the blooms are not toxic. We've had no record of poisonous blooms in the East Cape area to date.

The toxic red tides which affect the West Coast happen when blooms of a specific phytoplankton species die after depleting all of the upper layer nutrients and oxygen and then become toxic.  The blooms are eaten by filter-feeders - and then that's why it becomes an issue to eat shellfish from those areas. Cos you essentially eat what they've eaten. 

Maybe if you eat our blooms you can glow in the dark when you jump?! 

(Um no, that was a joke. Please don't eat the algae! It probably tastes kak, and you definitely won't glow)
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Red tide off St Croix island 2012. © Gavin Rishworth
Thanks to Tim Parker-Nance, Gavin Rishworth & Dr Gavin Snow for their input
Gail
1/16/2014 02:49:48 pm

Thanks for the explanation. Have been watching the luminous waves & red patches off Blue Horizon Bay. Beautiful as the waves break.

millerslocal
1/16/2014 03:39:00 pm

Be great if you can try and snap a few shots! Love to see what it looks like. None has made shore on my stretch of coast, so haven't seen any night-time pyrotechnics yet.

Peet Vermaak
1/20/2014 08:27:56 pm

Thank you for the explanation. The glow is magic at night. I have been living at Blue Horizon Bay for 14 years and have never seen the sea turn red to the extent that it has now. The sea is red along the whole coast from Sea View, Beach View and well past BHB. Hopefully it is not harmful like the 'red' tide is. It is very interesting that in today's Herald it is reported that municipal spokesman Mtubanzi Mniki and Wildlife and Environmental Society of SA Port Elizabeth senior conservation officer Morgan Griffiths had not heard of the red tide in PE.

millerslocal
1/20/2014 09:38:23 pm

I think the confusion is arising over the generic use of the word "red-tide" which most people associate with the toxic version on the West Coast. Apparently ours is benign. But would still assume that someone from NMBM would at least test it to be certain.

Kevin
1/23/2014 05:52:49 pm

Was on the beach in BHB last night at 22:00 and it was fantastic. I recommend it to everyone. Something you do not see too often.


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