A few days ago a friend told me that he had witnessed thousands of shrimps dying at Praia Formosa.
He told me that the sea was calm that day (at 21-07-2015), only very small waves, almost like a lake. Then he noticed there was something unusual, many dead reddish shrimps were floating on the water surface (some of them were still alive), so many that people swimming could feel shrimps touching their skin.
I collected biological material to try an identification. I found out that they were not shrimps but krill. The species is Euphausia gibboides, a krill species that occur at Madeira latitudes. Here is a photo of a specimen I have collected:
The specimen was 21 mm long.
Some of the features used to identify it were its round eye, a pointed rostrum, a mid-dorsal spine and a lappet (small process extending dorsally from the end of the 1st segment of the 1st antenna) forward and outward-directed .
See Euphausia gibboides distribution map  in the Atlantic:
This species eats microplankton and is itself an important prey for fish, birds and whales .
It do not live in the coast between rocks like some shrimp species do. It is not benthic (living in the bottom of the sea), they are creatures that live in the water column.
This species lives in and below the thermocline (thermocline is the temperature transition layer between the mixed layer at the surface and the deep water layer). Lives in cool subsurface layers, and adults migrate down to 300-400 m by day .
So, I would not expect to find this species near the coast.
What could have happen to make the krill die in mass at the beach?
What made the krill die in mass?
Was this a natural die-off, a natural phenomenon, maybe as consequence of sea changes? Is it related to fishing activities or to a pollution event?
Was the krill captured offshore by fishing boats and released near Praia Formosa where they would not find the cool layers they need to survive?
In Madeira there is no continental shelf, the bottom of the ocean gets very deep not far away from the shore. Maybe somehow they end up near the beach by night, brought by the waves, and when the day came they were not able to go back to higher depths where the temperature is colder. If so, they were stuck there at Praia Formosa at a depth of only a few meters where the quite waters of that day, warmed by the sun, would prove fatal to them.
Did the krill die as a consequence of some pollution event? Was the water contaminated that day, like some people had claimed? It would only make sense if it was a specific kind of pollution that would affect only this species. I did not hear of dead fish or the death of any other kind of shrimp (I think none of the benthic shrimp species were found dead that day). Personally I think it was not a case of pollution.
Maybe it was only some natural phenomenon related to sea streams and water temperature changes.
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