Nature Today | Krill shrimp in the Netherlands!
On November 11, 2022, the divers Lilian Schoonderwoerd and Mattie Trommelen saw some shrimp-like animals at the Bergse Diepsluis in the Oosterschelde at a depth of eight meters that they could not name. They swam just above the bottom and resembled shrimp, but still diverged. Despite the fact that they were very mobile, Lilian managed to photograph one. After the previous of this photo came the enthusiasm. The third author of this post (Marco Faasse) has identified the animal in the photo as a so-called ‘krill shrimp’. Krill is a collective name for small crustaceans that are mainly found in cold water, especially in Antarctica. There they occur in huge numbers, with many tens of thousands per cubic meter. Among other things, krill is the staple food of baleen whales, including the Blue Whale, the largest animal on earth. It was not known that krill also occurs in the Oosterschelde.
Two species known from the Netherlands
Krill belongs to the order Euphausiacea. More than ninety species occur worldwide. All kinds of marine life; they occur in all oceans. More than forty species can be found in European waters (in the Northeast Atlantic and the Mediterranean). Some species also occur in the North Sea, even near the Dutch coast. So far, two known species have been recorded from Dutch waters. The most commonly found species is the small krill shrimp (Nyctiphanes couchii). There are mainly reports of this from further offshore in the Dutch part of the North Sea, but also from the Voordelta and once in the Western Scheldt near Borssele, in 1995. This is an unpublished observation by Marco Faasse. Until now, no animals were known from the Oosterschelde and the other Zeeland streams. The other species is the Norway krill shrimp (Meganyctiphanes norvegica). This unique krill shrimp is only further from the coast.
Identify krill
A difference with shrimps is that krill shrimps swim their entire life and do not have real walking legs, shrimps do. Also, krill species do not have a kinked body. The animals have a carapace (head-breast shield) that includes all segments of the thorax, but the gills are not entirely male. Many krill species have luminescent organs. In the photo they are visible as red dots, including on each segment of the abdomen at the bottom of the side, and at the base of the eyes. The female of the small krill shrimp keeps the eggs in a special brood bag until she emerges. The animals mainly eat small plant plankton. During the day Small krill shrimps are close to the bottom, while at night they can be found more on the surface. So that’s in line with where Lilian found them.
As for the naming: this species is also often referred to as N. couchi. However, the correct spelling is N. couchii, with two times the letter i at the end. As a Dutch name Small krill shrimp seems acceptable: this reflects the small size (up to about 17 millimeters) compared to other species, including the other species known from the Netherlands: Meganyctiphanes norvegica (up to 45 millimeters in size). For the latter, Norway krill shrimp seems appropriate, after its scientific name (norvegian = originated from Norway).
Known and famous
The largest whale – at the same time also the largest living animal on earth – is the Blue Whale. Together with other baleen whales, these giants of up to 25 meters in size feed on krill shrimp, of which they eat up to 4000 kilos per day.
Millions of children worldwide distributed the animated films about the clown fish Nemo and the dancing penguins in Happy Feet. As a result, in many cases they have also gained knowledge about the food of whales. For example, in the movie ‘Finding Nemo’ the phrase appears: ‘Don’t worry. Whales don’t eat clownfish. They eat krill. In the second Happy Feet movie, entire scenes are even devoted to krill, including with the deceased famous krill shrimps Will and Bill (in English with the voices of Brad Pitt and Matt Damon: ‘So this is all we are, lunch! Goodbye krill world’). The films concern species other than the species now found near the Bergse Diepsluis and the others from our well-known North Sea.
Observations
Reports of marine and brackish water organisms and of terrestrial, freshwater and marine molluscs are welcome at ANEMOON Foundation and platforms like Observation.nl.
Text: Lilian Schoonderwoerd, Rob Leewis and Marco Faasse, all ANEMOON Foundation and Biological Working Group
Photos: Lilian Schoonderwoerd (lead photo: Small krill shrimp from the Oosterschelde, 11-11-2022)
Drawings: Holt & Tattersall, 1905