Category Archives: Crustacea

Evolutionary history of cave shrimps

Machumvi Ndogo - preparing for a dive in the dark

Machumvi Ndogo – preparing for a dive in the dark

In 2008 UiB colleagues Kenneth Meland and Endre Willassen surveyed karst caves in Zanzibar together with Hajj M. Hajj in search for aquatic crustacea. Many of these localities have so-called anchialine conditions in which marine water penetrates inland and can mix more or less with fresh ground water.

 

Atyid shrimps were sampled in salt water about 300 m inland from the coast.

Atyid shrimps were sampled in salt water about 300 m inland from the coast.

One of these sites had three species of small shrimps of the family Atyidae. The phylogenetic relationships of these shrimps have now been analysed by an international team of “cave men” based on full mitochondrial genome sequencing performed at the University of the Balears.

Molecular clock estimates date the relationship of the Zanzibarian species to other known species in the Atlantic and Indo-pacific  to the Cretaceous period.

Shrimps from Osine Cave

Shrimps from Osine Cave

The paper is available from this link:

https://www.nature.com/articles/s41598-017-03107-y

Species divergence history of the study group.

Species divergence history of the study group. Click for details.

AmphipodThursday: IceAGE-amphipods in the Polish woods

img_2610This adventure started 26 years ago, when two Norwegian benthos researchers (Torleiv Brattegard from University of Bergen and Jon-Arne Sneli from the University in Trondheim) teamed up with three Icelandic benthos specialists (Jörundur Svavarsson and Guðmundur V. Helgasson from University of Iceland and Guðmundur Guðmundsson from the Natural History Museum of Iceland) to study the seas surrounding the volcanic home of the Nordic sages. 19 cruises and 13 years later – and not least lots of exciting scientific findings and results the BioICE program was finished.

But science never stops. New methods are developed and old methods are improved – and the samples that were stored in formalin during the BioICE project can not be used easily for any genetic studies. They are, however, very good for examinations of the morphology of the many invertebrate species that were collected, and they are still a source of much interesting science.

Participants of the IceAGE workshop. Photo: Christian Bomholt (www.instagram.com/mcb_pictures)

Participants of the IceAGE workshop. Photo: Christian Bomholt (www.instagram.com/mcb_pictures)

The dream about samples that could be DNA-barcoded (and possibly examined further with molecular methods) lead to a new project being formed – IceAGE. A large inernational collaboration of scientists organised by researchers from the University of Hamburg (and still including researchers from both the University of Iceland and the University of Bergen) have been on two cruises (2011 and 2013) so far – and there is already lots of material to look at!


This week many of the researchers connected with the IceAGE project have gathered in Spała in Poland – at a researchstation in woods that are rumoured to be inhabited by bison and beavers (we didn´t see any, but we have seen the results of the beavers work). Some of us have discussed theories and technical stuff for the papers and reports that are to come from the project, and then there are “the coolest gang” – the amphipodologists. 10 scientists of this special “species” have gathered in two small labs in the field-station, and we have sorted and identified amphipods into the wee hours.

It is both fun and educational to work together. Everybody have their special families they like best, and little tricks to identify the difficult taxa, and so there is always somebody to ask when you don´t find out what you are looking at. Between the stories about amphipod-friends and old times we have friendly fights about who can eat the most chocolate, and we build dreams about the perfect amphipodologist holiday. Every now and then somebody will say “come look at this amazing amphipod I have under my scope now!” – we have all been treated to species we have never seen before, but maybe read about. We also have a box of those special amphipods – the “possibly a new species”- tubes. When there is a nice sample to examine, you might hear one of the amphipodologist hum a happy song, and when the sample is all amphipods but no legs or antennae (this can happen to samples stored in ethanol – they become brittle) you might hear frustrated “hrmpfing” before the chocolate is raided.

 

Isopodologists (Martina and Jörundur) visiting the amphipodologists... Photo: AH Tandberg

Isopodologists (Martina and Jörundur) visiting the amphipodologists… Photo: AH Tandberg

The samples from IceAGE are all stored in ethanol. This is done to preserve the DNA for molecular studies – studies that can give us new and exciting results to questions we have thought about for a long time, and to questions we maybe didn´t even know we needed asking. We can test if what looks like the same species really is the same species, and we can find out more about the biogeography of the different species and communities.

The geographical area covered by IceAGE borders to the geographical area covered by NorAmph and NorBOL, and it makes great sense to collaborate. This summer we will start with comparing DNA-barcodes of amphipods from the family Eusiridae from IceAGE and NorAmph. They are as good a starting-point as any, and they are beautiful (Eusirus holmii was described in the norwegian blog last summer).


Happy easter from all the amphiods and amphipodologists!

Anne Helene


Literature:

Brix S (2014) The IceAGE project – a follow up of BIOICE. Polish Polar Research 35, 1-10

Dauvin J−C, Alizier S, Weppe A, Guðmundsson G (2012) Diversity and zoogeography of Ice−
landic deep−sea Ampeliscidae (Crustacea: Amphipoda). Deep Sea Research Part I: 68: 12–23.

Svavarsson J (1994) Rannsóknir á hryggleysingjum botns umhverfis Ísland. Íslendingar og hafiđ.
Vísindafélag Íslendinga, Ráđstefnurit 4: 59–74.
Svavarsson J, Strömberg J−O,  Brattegard T (1993) The deep−sea asellote (Isopoda,
Crustacea) fauna of the Northern Seas: species composition, distributional patterns and origin. Journal of Biogeography 20: 537–555.

Aliens amongst us?

It certainly does not take a great leap of imagination to get from these Isopoda collected by the MAREANO programme to various science fiction monsters!

isopoda_images_resized

click to embiggen!

I just completed photographing and tissue sampling 95 specimens that will be submitted for barcoding through NorBOL  – we’ll send them to the CCDB-lab in Canada for sequencing, and upload the metadata and sequences in the BOLD database – fingers crossed for successful sequencing!

Door #22 A jolly, happy family?

Musculus discors hidden in Securiflustra securifrons. Photo: AHS Tandberg

Musculus discors hidden in Securiflustra securifrons. Photo: AHS Tandberg

At first glance, it can look like a seaweed. The depth, however, should start your alarm-bells for flora and point you towards fauna: the plantlike animal Securiflustra securifrons (Pallas, 1766) is a bryozoa – a collection of colonial filterfeeders less than 1 mm in size each. We are at 80-120 m depth in the cold Heleysundet – the sound between the two islands Spitsbergen and Barents Island in the eastern part of the Svalbard Archipelago. This is a sound famous among captains for its fast tidal streams, and the fast-flowing waters give the bryozoans a nice place to live. The colonies branch out to catch the most water-flow and the most food from the water.

Musculus discors. Photo: AHS Tandberg

Musculus discors. Photo: AHS Tandberg

Where the “branches”  form we see what might look like small hairy balls – these are the bivalve Musculus discors (L., 1767). The hairy look comes from their byssus threads – they produce and then use these threads to attach to the Securiflustra (and being packed in the threads they might get some camouflage from them).

 

Moving inside the molluscs we might find not only one, but two species of amphipods. In our samples from Heleysundet 14% of the Musculus had the carnivorous amphipod Anonyx nugax Ohlin, 1895 inside, and an astonishing 3 out of 4 Musculus had amphipods of the species Metopa glacialis (Krøyer, 1842) inside.  The system resembles a Russian doll – one species living inside another living inside yet another…

Anonyx affinis (large amphipod, upper left) and Metopa glacialis (small amphipod lower half og mussel) innside a Musculus discors. Photo: AHS Tandberg

Anonyx affinis (large amphipod, upper left) and Metopa glacialis (small amphipod lower half og mussel) innside a Musculus discors. Photo: AHS Tandberg

What reason can a small crustacean have to live inside the quite closed off world of a bivalve? The bivalve filters water actively – it pumps water over its gills, and then transports food-particles such as phytoplankton down the gills towards its mouth. Non-desirable particles are normally packed into mucus and transported out of the bivalve. Now imagine liking to eat some of those particles the bivalve finds non-desirable, and being placed on the gills of said bivalve. No need to hunt for the food – it will be coming on the conveyor-belt the gills are – and all you need to do is to eat. The bivalve does not seem to be troubled by this co-habitant – it does not eat the same food as the bivalve.

Not only does Musculus discors provide Metopa glacialis with food, the mantle cavity provides a luxury-shelter where the amphipod can raise a family! Amphipods, together with isopods, cumaceans, tanaidaeans and quite a few mysicadeans keep their offspring in a brood-pouch from the fertilisation of the eggs to the medium sized juveniles crawl out into the real world. Living inside a bivalve allows Metopa glacials to extend its child-care to young life outside the brood-pouch. Our examinations of the bivalves from Heleysundet showed us adult Metopa in the middle of the bivalve, with several juveniles “strategically placed” inbetween the two layers of gills in each shell-half. Surrounded by food, safe from most predators! (Predation of Metopa glacialis might be the main objective for Anonyx affinis, the food-source of the lysianassid needs to be established. It might also be the nice and fatty mollusk.)

 

Metopa glacialis innside a Musculus discors. Small arrows point to juveniles, large arrow to adult female. Photo: AHS Tandberg

Metopa glacialis innside a Musculus discors. Small arrows point to juveniles, large arrow to adult female. Photo: AHS Tandberg

Comparing with amphipods of the same size-range from the same areas, Metopa glacialis seems to have a safe life. Safe enough that they can manage to have several sets of offspring. We see that they don´t wait until´the first batch of kids are out of the “house” – we found one adult female with two size-groups of offspring and a fresh egg-filled brood-pouch!  Each batch can be 20 offspring, so that would mean one pregnant mom and 40 kids in one small house!

 

Many people travel to visit family during the holidays. Even when we cherish the time with our loved ones, filling the house with grandparents, aunts, uncles and cousins might cramp everybodys style slightly. Not so with Metopa glacialis. Measuring the size of all inhabitants show us that the kids stay home until they are adult and can move out to their own home. So when you can´t sleep because your younger cousin plays on her gamer all night, or because your old aunt snores when you come into your shared room, think how much more difficult life could have been if you were an amphipod. Happy holidays!

Anne Helene

PS: A slightly extended version in Norwegian (part of the TangloppeTorsdag blog) can be read here)


Literature:

Just J (1983) Anonyx affinis (Crust., Amphipoda: Lysianassidae), commensal in the bivalve Musculus laevigatus, with notes on Metopa glacialis (Amphipoda: Stenothoidae). Astarte 12, 69-74

Tandberg AHS, Schander C, Pleijel F (2010) First record of the association between the amphipod Metopa alderii and the bivalve Musculus. Marine Biodiversity Records 3:e5 doi:10.1017/S1755267209991102

Tandberg AHS, Vader W, Berge J (2010) Studies on the association of Metopa glacialis (Amphipoda, Crustacea) and Musculus discors (Mollusca, Mytilidae). Polar Biology 33, 1407-1418

Vader W, Beehler CL (1983) Metopa glacialis (Amphipoda, Stenothoidae) in the Barents and Beaufort Seas, and its association with the lamellibranchs Musculus niger and M. discors s. l. Astarte 12:57–61

Door #15 Twinkle, twinkle, little animal?

Yesterdays door of this calendar introduced the bioluminescent animals of the deep sea.
In the parts of the ocean where sunlight reaches (the photic zone), production of ones own light is not common. This is because it is costly (energetically), and when the surroundings already are light, the effect is almost inexistent. An exception to this is the use of counter-illumination that some animals have: lights that when seen from underneath the animal camouflages them against the downwelling light from above.

But what then with the ocean during the polar night? Last Thursdays blog told the story of the dark upper waters during the constant dark of the arctic winter, and how the quite scanty light of the moon is enough to initiate vertical mass movements. Another thing we see in the dark ocean is that processes that at other latitudes are limited to the deep sea come up nearly to the surface during the polar night.

So – in the Arctic winter we don´t have to use robots and remote cameras to observe biioluminescent animals: we can often observe them using normal sport diving equipment or even from above the surface. A very recent study (Cronin et al, 2016) has measured the light from different communities in the Kongsfjord of Svalbard during the polar night. They found that going from the surface and down, dinoflagellates produced most light down to 20-40 m depth, the lighting “job” was then in general taken over by small copepods (Metridia longa). Most light was produced around 80 m depth.

Bioluminescent dinoflagellates shining through the winter sea ice in Kongsfjorden. Photo: Geir Johnsen, NTNU

Bioluminescent dinoflagellates shining through the winter sea ice in Kongsfjorden. Photo: Geir Johnsen, NTNU

It is possible to recognise different species from the light they make; a combination of the wavelength, the intensity and the length of the light-production gives a quite precise “thumbprint”. If we know the possible players of the system in addition, an instrument registering light will also be able to give us information about who blinks most often, at what depths, etc. Cronin and her coauthors have made a map of the lightmakers in the Kongsfjord.

Bioluminescence profiles from Kongsfjord. Figure 3 from Cronin et al, 2016

Bioluminescence profiles from Kongsfjord. Figure 3 from Cronin et al, 2016

This is all well and good, but the next question is of course WHY. There can be several uses for light, and we can bulk the different reasons into 3 main groups: Defense, offense and recognition.

Different strategies for Bioluminescence. Fig 7 from Haddock (2010), redrawn for representation of the Polar night bioluminescence by Ola Reibo for the exhibition "Polar Night"

Different strategies for Bioluminescence. Fig 7 from Haddock (2010), redrawn for representation of the Polar night bioluminescence by Ola Reibo for the exhibition “Polar Night”

 

The bioluminescent cloud from an escaping krill. Kongfjorden, during the Arctic polar night. Photo: Geir Johnsen, NTNU

The bioluminescent cloud from an escaping krill. Kongfjorden, during the Arctic polar night. Photo: Geir Johnsen, NTNU

Defence has already been mentioned above: the counterillumination against downwelling light is helping an animal defend itself against predation. Some will leave a smokescreen, or even detach a glowing bodypart while swimming away in the dark, and others blink to startle the enemy or to inform their group-mates that an enemy is getting close.

 

 

Offense is mainly to use the light to get food (this is typical angler-fish-behaviour), and recognition is very often about flirting. Instead of flashing your eyelashes at your your chosen potential partner, you flash some light at him or her…

Thursdays are about amphipods in this blog, so here they come. Bioluminescent amphipods are present mainly in the hyperiid genera Scina (a Norwegian representative of this genus is Scina borealis (Sars, 1883).) Hyperiids are amphipods that swim in the free watermasses, like most other bioluminescent animals.

The bioluminescent amphipod Scina borealis (Sars, 1893). The added stars indicate where the bioluminescence occurs. Original figure: G.O.Sars, 1895.

The bioluminescent amphipod Scina borealis (Sars, 1893). The added stars indicate where the bioluminescence occurs. Original figure: G.O.Sars, 1895.

Crustacea use more different ways to produce bioluminescence than most other groups – this points to a possibility that the use of bioluminescence has evolved several independent times in this group. So the copepod Metridia longa will use a different chemical reaction than the krill, and the amphipods use again (several) different reactions. Some research on the bioluminescence of amphipods was undertaken already in the late 1960s, where P Herring collected several Scina species and kept them alive in tanks. There he exposed them to several luminescence-inducing chemicals and to small electrical shocks, to see where on the body light was produced and in what sort of pattern. He reported that Scina has photocytes (lightproducing cells) on the antennae, on the long 5th “walkinglegs”, and on the urosome and uropods. They would produce a nonrythmical rapid blinking for up to 10 seconds if attacked, and at the same time the animal would go rigid in a “defence-stance” with the back straight, the antennae spread out in front of the head, and the urosome stretched to the back. This definitely seems to be a defence-ligthing, maybe we should even be so bold as to say it would startle a predator?

Anne Helene


Literature:

Cronin HA, Cohen JH, Berge J, Johnsen G, Moline MA (2016) Bioluminescence as an ecological factor during high Arctic polar night. Scientific Reports/Nature 6, article 36374 (DOI: 10.1038/srep36374)

Haddock SHD, Moline MA, Case JF (2010) Bioluminescence in the Sea. Annual Review of Marine Science 2, 443-493

Herring PJ (1981) Studies on bioluminescent marine amphipods. Journal of the Marine biological Association of the United Kingdoms 61, 161-176.

Johnsen G, Candeloro M, Berge J, Moline MA (2014) Glowing in the dark: Discriminating patterns of bioluminescence from different taxa during the Arctic polar night. Polar Biology 37, 707-713.

Door #14: Where the sun doesn’t shine. Lucifer, luciferin and luciferase

Yesterday’s blog was about about Lucia, the mythical virgin who is celebrated with lights produced from combustion energy in candle lights. Lucia’s name is derived from the latin lux, meaning light. Similarly, Lucifer was one who was carrying light. We will not dwell with the ridiculous lore about Lucifer in old folk beliefs. Instead we will briefly look at real carriers of light from the organic world. Light can also be produced with other processes than fire and a range of organisms are particularly skilled in “letting there be light” in their environments. This is what we call bioluminescence. Bioluminescent substance can be used by potential prey animals to scare away predators. (Hover over picture with your mouse to see the gif.)

“Glow worm” beetles or “fire flies” of the families Lampyridae and Phengodidae are familiar to most people who have been out-door on a dark summer night. Studies of fire fly behavior have revealed how different species of these beetles communicate with their kinds using flash signals with variable frequency, intensity and duration. The biochemical mechanisms at work during bioluminescence are also relatively well studied in these beetle groups.

In the marine environments bioluminescence is known from many unrelated organisms and because different molecular reactions are involved in light production it is likely that bioluminescence must have evolved independently many times. A glowing sea may be experienced when massive densities of dinoflagellates are flashing their lights on the coast at night. Particularly Noctiluca scintillans, whose body is big enough to be visible with the naked eye, is frequently referred to in field guides to marine shore life. But many dinoflagellate species are involved in the bioluminescence that Norwegians call “morild”, – the “fire in the sea”. This phenomenon has also been called phosphorescence, however this is the process where light energy is absorbed by a substance and emitted on a different wave length. Special fluorescent proteins are responsible for glow-stick effects in organisms. (Incidentally the Greek light-carrier Phosphorus has been equated with the Latin Lucifer, and those of us who have seen white phosphorous in action understand what gave the name to this very reactive version of the element.) Studies of dinoflagellates have associated the light production with molecular bodies named scintillons and demonstrated that the biochemical activity in these objects in diatoms is governed by diurnal rhythms. This appears to make sense, because what is the point of flashing lights at day time? It may not be quite clear what use the diatoms have of producing light at night time either. However, it seems more obvious that there are functional advantages of bioluminescence in the depth of the ocean, where light does not penetrate. And it is below the so-called euphotic zone, from approximately 200 m on that bioluminescence is effective in different sorts of interactions among various animal groups. Deep water angler fish even use lit lures to attract prey.

Light emission in some animals is based on symbiosis with bacteria such as Aliivibrio fischeri.  In other cases, the animal itself may produce the active proteins. Different biochemical systems are at work in bioluminescence and the light-producing molecules are not the same in all systems. Still, as a group of oxidizing and light emitting molecules they all go by the name of luciferin.  To produce a light flash a catalyzing agent is also needed. This is provided by a group of different enzymes called luciferase.  Other active components and free ions may be involved in the reaction which may be triggered in different ways, either mechanically as with a set of oars and a rowboat when dinoflagellates are near the surface water, or by some biochemical trigger. Sometimes it must happen by some neural response in the animal.

Light organs in the lantern fish Benthosema glaciale. (from Paulsen et al. 2013

Light organs in the lantern fish Benthosema glaciale. (from Paulsen et al. 2013)

The lantern fishes are known for their photophores, – series of small organs that can produce yellow, green or blue light. Because the arrangement of photophores is different in different species, the organs are thought to play a role in communication between con-specific individuals. This may be the case for other animals as well, such as squids. It is also believed that the light organs can have a camouflaging effect by visually breaking up the silhouette of the fish, when the fish is viewed against a lighter back-ground higher up in the water column. The fish thus obtains protection from predators below by means of counter-illumination.

Several deep water animals are confusing potential predators by ejecting a luminescent substance towards the predator. Shrimps of the family Oplophoridae are particularly known to exercise this defensive technique.  The luciferine in shrimps is called coelenterazine and is presumably produced in the digestive gland called haepatopancreas. When the shrimp spews the glow through the mouth, the effect is somewhat similar to the one that cephalopods use when they disappear in a cloud of ink.  May we call it a “lucifer smoke-screen”?

Our museum collections have a rich material of these shrimps. Several species were collected during the MAR-ECO cruises over the Mid-Atlantic Ridge. One of them was Oplophorus spinosus shown in the picture below. While all of the oplophorids appear to be able to use a “lucifer smoke”, some of the species, including O. spinosus, also have light producing organs along their sides, somewhat similar to what we see in the lantern fishes. These photophores are complicated light generating organs with lenses and reflectors. They may be able to filter the wave length, and also the intensity and direction of the emitted light. In oplophorids, such organs are only found in three of the most closely related genera of the family, according to a recent study by Wong et al. (2015).  Interestingly, these animals also have two types of eye pigments. One type is shared with other oplophorids and is sensitive to the blue-green part of the light specter.  The other pigment is also sensitive to the shorter wave length in UV light. Because of the special abilities of the eyes it is tempting to think that these shrimps somehow are using the photophores in communication with individuals of their species. If so, Oplophorus spinosus and similar light talk would be a perfect case for biosemiotics. “Please shrimp, tell us about the world view from your perspective!” However, it is possible that the use of the photophores is only for counter-illumination when the shrimps are performing vertical migrations in the water column.

Oplophorus spinosus - a bioluminescent mid water shrimp (Photo: David Shale, MAR-ECO)

Oplophorus spinosus – a bioluminescent mid-water shrimp carrying large eggs (Photo: David Shale, MAR-ECO).

The “signalling abilities” of bioluminescent compounds are exploited in biotechnology and cell research. Luciferase from Oplophorus has been exploited as a so-called reporter gene in visualization of cell activities and gene transcription. May be it is not too far-fetched to see the shrimps as some kind of “light-carriers”.

 

Papers

Inoue S, Kakoi H, Goto T. (1976) Oplophorus luciferin, Bioluminescent substance of the Decapod shrimps, Oplophorus spinosus and Heterocarpus laevigatus. J.C.S. Chem. Comm. 966:1056-1057.

Poulsen JY, Byrkjedal I, Willassen E, Rees DJ, Takeshima H, Satoh TP, Shinohara G, Nishida M, Miya M. (2013).Mitogenomic sequences and evidence from unique gene rearrangements corroborate evolutionary relationships of Myctophiformes (Neoteleostei). BMC Evolutionary Biology 13:111.

Shimomura O, Masugi T, Johnson FH, Hanedal Y. (1978) Properties and reaction mechanism of the bioluminescence system of the deep-sea shrimp Oplophorus gracilorostris. Biochemistry 17:994-998.

Wong JM, Pérez-Moreno JL, Chan T.-Y, Frank TM, Bracken-Grissom HD. (2015) Phylogenetic and transcriptomic analyses reveal the evolution of bioluminescence and light detection in marine deep-sea shrimps of the family Oplophoridae (Crustacea: Decapoda). Molecular Phylogenetics and Evolution 83:278–292

Door #8: the ups and downs of a marine werewolf?

When we think about what drives the ecosystems, much of the initial responsibility is put on the sunlight. This is mainly because of the photosynthesis, and thus the basic pieces of almost all food-webs, but light is also important for the animals. Many animals use visual cues to find food, and whether you search for food or do not want to become food, the presence (or absence) of light will help you.

Themisto sp swims up into the dark night. Photo: Geir Johnsen, NTNU

Themisto sp swims up into the dark night. Photo: Geir Johnsen, NTNU

Seawater is a pretty good stopper of light. We don’t need to dive far down before we are in what we consider a dark place, and less and less light finds its way the deeper we come. We tend to call the depths between 200 and 1000 m “the twilight zone”: most light stops way before 200m and the last straggling lumens give up at 1000m.

Most places on earth has a daily division between a dark and a light period: night and day. This is the ultimate reason for what is often called “the largest motion on earth”: Millions of zooplankton hide out in the darker parts of the water column during the day, and then move up to feed on the plants living in the light-affected parts of the water during the night (when predators will have a hard time seeing them). This daily commute up and down is called Diel Vertical Migration (DVM).

Themisto sp among the many smaller particles. (The light in this picture is from a flash). Photo: Geir Johnsen, NTNU

Themisto sp among the many smaller particles. (The light in this picture is from a flash). Photo: Geir Johnsen, NTNU

But what about the waters north of the polar circle? These areas will for some time during the winter have days when the sun stays under the horizon the entire day – this is “the Dark time” (Mørketid). At higher latitudes, there will be several days, or even weeks or months when the sun is so far below the horizon that not even the slightest sunset-glow is visible at any time. In this region, we have long thought that the Dark time must be a dead or dormant time.

 

The acoustic signals that gave the first indications of LVM. Figure 2 from Last et al 2016.

The acoustic signals that gave the first indications of LVM. Figure 2 from Last et al 2016.

We could not have been more wrong! It turns out that during the polar night, the DVM moves from being on a 24 hr cycle (sunlight-induced), to a 24.8 hour cycle! What is now the driver? The moon !(The lunar day is 24.8 hrs). Another thing that shows us that the moon must give strong enough light that predators can hunt by it, is that every 29.5 days most of the zooplankton sinks down to a depth of 50m: this falls together with the moon being full. Researchers have started to call this LVM (Lunar-day Vertical Migration) to show the difference to the “normal” DVM. There are of course lots of complicated details such as the moons altitude above the horizon and its phase that influences the LVM, but in general we can say that during the polar night (the Very Dark time), the “day” as decided by light has become slightly longer than normal.

The full moon, photographed by the Apollo 11 crew after their visit. Photo: NASA, 1969

The full moon, photographed by the Apollo 11 crew after their visit. Photo: NASA, 1969

Themisto - the werewolf. Note that the whole head is dominated by eyes - this is a visual hunter! Photo: Geir Johnsen, NTNU

Themisto – the werewolf. Note that the whole head is dominated by eyes – this is a visual hunter! Photo: Geir Johnsen, NTNU

Some of the larger animals taking part in the LVM are the amphipods Themisto abyssorum and Themisto libellula. They are hunters – so their reason to migrate up in the water column is not the plants, but the animals eating the plants; their favourite food are copepods of the genus Calanus. These are nice and quite energy-rich small crustaceans that eat the microscopic plants in the upper water column. We have sampled both Themisto-species in the middle of the winter (january), and their guts were filled to the brim with Calanus, so we know that they continue hunting by moon-light. They are such voracious hunters that some researchers have started to call them marine werewolves: the moonlight transforms them from sedate crustaceans to scary killers…

 

But, if they are the hunters, why do they spend so much time in the deep and dark during the lighter parts of the day? The hunters are of course also hunted. Fish such as polar cod (Boreogadus saida),  birds such as little auk (Alle alle) and various seals like to have their fill of the Themisto species. So – life has its ups and downs, and the dance of hunter and hunted continues into the dark polar night…

Anne Helene


Literature:

Berge J, Cottier F, Last KS et al (2009) Diel vertical migration of Arctic zooplankton during the polar night. Biology Letters 5, 69-72.

Berge J, Renaud PE, Darnis G et al (2015) In the dark: A review of ecosystem processes during the Arctic polar night. Progress in Oceanography 139, 258-271.

Kintisch E (2016)  Voyage into darkness. Science 351, 1254-1257

Kraft A, Berge J, Varpe Ø, Falk-Petersen S (2013) Feeding in Arctic darkness: mid-winter diet of the pelagic amphipods Themisto abyssorum and T. libellula. Marine Biology 160, 241-248.

Last KS, Hobbs L, Berge J, Brierley AS, Cottier F (2016) Moonlight Drives Ocean-Scale Mass Vertical Migration of Zooplankton during the Arctic Winter. Current Biology 26, 244-251.

Door # 7: Always on my mind…?

Today is #WormWednesday on Twitter, and we figured that it was a good day to introduce you to this rather unlucky fellow and his sidekick…

The orange (coloured in Photoshop) is the parasite. The two long sacks are filled with eggs.

The orange part (coloured in Photoshop) is the parasite. The two long sacks are filled with eggs.

They were collected during our field work in Sletvik in October. The worm is a polychaete in the genus Terebellides, whilst the parasite is a Copepod. This species rich group of small crustaceans have many modes of life, but parasitism is a common one, with about half of the ~13 000 species being parasites.

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Door #1 Gammarus wilkitzkii – closer than Santa to the North Pole?

We greet December with our 2016 edition of the invertebrate advent calendar, and will be posting a new blog post here every day from today until the 24th of December! Be sure to check in often! All posts of this year’s calendar will be collected here: 2016 calendar, and all of the post in last year’s event are gathered here in case you would like a recap: 2015 edition. First out is Anne Helene and a Northern amphipod:

December is over us, the Advent Calendar from the invertebrate section lets you open the first door today, and many children (both small and slightly older) are eagerly awaiting the answer to their letter to Santa Claus. Mr Claus is supposed to live on the North Pole, and many letters addressed there have been coming through different post-offices the last months.

Many of us are wondering if Santa Claus might be a Species dubius (a species it is slightly doubtful exists), but if he exists, his homestead is becoming endangered. We are seeing a rapid decline of the Arctic sea ice (here is a video from NOAA showing the extent and age of the icecap from 1987 to 2014), and this will undoubtedly have a large effect on the Earths climate.

A polar bear mother and cub walking on the top of the sea ice. Photo: AHS Tandberg

A polar bear mother and cub walking on the top of the sea ice. Photo: AHS Tandberg

In addition to the theoretical possibility of Santa, there are several true and precious species that depend on the sea ice for their life. Most probably think about polar bears and seals now, but there is an even more teeming abundance of life right under the ice, many of them live as the sea ice is an upside-down seafloor. The largest animal biomass of all the many invertebrate species connected to the sea ice (we call these sympagic species), comes form the amphipod Gammarus wilkitzkii Birula 1897.

Gammarus wilkitzkii is the largest of the invertebrates that hang out (literally) under the ice; they can reach almost 3 cm length. They are whitish-grey, with red-striped, long legs. The hind legs have hooks that allow them to easily attach to the sea ice, and hanging directly under the ice instead of swimming saves a lot of energy for them. This behaviour is so necessary to them that if we keep them in an aquarium, they need something to hang on to – be it the oxygen-pump, a piece of styrofoam, the hand of a researcher or the edge of the lid. There are a few observations of swimming G. wilkitzkii sampled from the middle of the water-column, but this seems to be specimens that have lost their hold in life – we do not think they can live long swimming around (that would take too much energy).

A male (white) Gammarus wilkitzkii holding a female (yellow) Gammarus wilkitzkii. The male is also holding on to the sea-ice with his hind legs. Photo: Bjørn Gulliksen, University of Tromsø and UNIS.

A male (white) Gammarus wilkitzkii holding a female (yellow) Gammarus wilkitzkii. The male is also holding on to the sea-ice with his hind legs. Photo: Bjørn Gulliksen, University of Tromsø and UNIS.

Being such large animals, and in such large abundance, G. wilkitzkii are preyed upon mostly by diving sea-birds, but they have also been found in the stomach-content of harp-seals and to a small degree the small and stealthy polar cod. Most of these animals are mainly found in what we call the marginal ice zone – where the sea ice meets the open water. This is also the place where G. wilkitzkii can find most of its own food: algae, other small invertebrates and ice-bound detritus.

A diver under the sea ice. Photo: Geir Johnsen, NTNU

A diver under the sea ice. Photo: Geir Johnsen, NTNU

G. wilkitzkii is also found in great quantities under the multi-year ice, where it probably leads a safer life. Being at the edge of the ice presents a problem: this is the ice that melts during the summer, and that will force the amphipods to move further into the ice as its habitats disappear. The underside of the ice is not a flat field – it is a labyrinth of upside-down mountains and valleys, with several small and large caves. Many nice hiding-places, but if you swim or crawl along the ice-surface, the distance is longer than we would measure it on the top of the ice.

Where the ice is thin, or where there is no snow covering the ice, some light will shine through. This means that the edge of the ice normally lets a lot more light through than the multi-year ice. We dont know what this does for G. wilkitzkii, but they have eyes that are of similar size and shape as the other species in the genus, so they possibly use their eyes for hunting for food or checking for enemies.


G. wilkitzkii is an animal that is accustomed to a tough life. The sea temperature right under the ice normally lies around -1.8ºC, (so below what we think of as “freezing”) this is because of the high salinity of the water. As sea-water freezes, the salt leaks out, and flows in tiny brine-rivers trough the ice and down into the water below.  They have specialised their life cycle to fit with the available food – so that their young are released when there is much food to be found, and they can live up to 6 years reproducing once every of the last 5 years, probably to make sure at least some of their offspring survive.

We have 24 more days before we find out if Santa “exists”, though this might not give us the answer to him having become a climate-refugee. Hopefully, we will have to wait much longer to find out what will happen with the many ice-dependent invertebrates, but becoming climate-refugees might not be easily accomplished for them.

Anne Helene


Literature:

Arndt C, Lønne OJ (2002) Transport of bioenergy by large scale arctic ice drift. Ice in the environment – Proceedings of the 16th IAHR International Symposium on Ice, Dunedin , NZ. p103-111.

Gulliksen B, Lønne OJ (1991) Sea ice macrofauna in the antarctic and the Arctic. Journal of Marine Systems 2, 53-61.

Lønne OJ, Gulliksen B (1991) Sympagic macro-fauna from multiyear sea-ice near Svalbard. Polar Biology 11, 471-477.

Werner I, Auel H, Garrity C, Hagen W (1999) Pelagic occurence of the sympagic amphipod Gammarus wilkitzkii in ice-free waters of the Greenland Sea – dead end or part of life-cycle? Polar Biology 22, 55-60.

Weslawski JM, Legezinska J (2002) Life cycles of some Arctic amphipods. Polish Polar Resarch 23, 2-53.

Amphipod-Thursday. WoRMS – (all) about amphipods

It is a sad fact, but a fact nonetheless. Most biologists are not taxonomists. Even so – the work many biologists do is based on knowing the species studied, and knowing the correct name is part of that important knowledge.

Screenshot from WoRMS-search: Andaniopsis lupus

Screenshot from WoRMS-search: Andaniopsis lupus

But how do we know what names are valid, and what species have been formally described within a group? Taxonomic revisions tend to have name-changes as a result, and new species are described all the time – for amphipods an average of 140 species new to science are described yearly…

Screenshot from World Amphipoda Database

Screenshot from World Amphipoda Database

This is where databases will be your best friend! For marine species, the World Record of Marine Species, WoRMS, database is used widely, with more than 200 000 visits every month. Here you can find not only current accepted names, but also information about synonymised names, taxonomic literature, and for some species information about distribution, ecological traits and links to other resources. The data have all been checked and edited by a world-wide team of taxonomic and thematic editors – all responsible for their special groups of organisms.


IMG_9037This week, 22 of the 34 taxonomic editors of the World Amphipoda Database, feeding WoRMS with all Amphipod-related information, gathered at the Flanders Marine Institute in Oostende, Belgium to learn about how to best edit the information about Amphipods. It was two days full of information about the database, but also of hands-on training and with the help of the nice people in the Data Management Team of WoRMS, we managed to get quite a lot of information added and edited on the database. Needless to say, with more than 9000 amphipod species accepted (and several of them with earlier names or alternate representations), we have not completely finished yet. The work on editing a database is continuous – and we have plans for adding more info for each species, including type-information, ecological information and links to identification keys.


The second best thing about going to workshops (the first being all the exciting new things we learn), is that we get to spend time with colleagues from far away. The people working on amphipods are in many ways my extended family – this is at least how it feels whenever we meet. News about both amphipods and life in general are exchanged, possible new projects are planned, and friendships continue to be reinforced over cups of coffee, early breakfasts and late dinners. And every time we leave each other, there is a hope that our next meeting might not be too far away.  My colleagues from Poland call this “the Amphipoda way of life”  – and this friendly, collaborate life is a good life to have as a researcher.

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Participants at the workshop. Photo: AHS Tandberg (with help from ? at VLIZ)

Anne Helene


Citations:

Horton, T.; Lowry, J.; De Broyer, C.; Bellan-Santini, D.; Coleman, C. O.; Daneliya, M.; Dauvin, J-C.; Fišer, C.; Gasca, R.; Grabowski, M.; Guerra-García, J. M.; Hendrycks, E.; Holsinger, J.; Hughes, L.; Jaume, D.; Jazdzewski, K.; Just, J.; Kamaltynov, R. M.; Kim, Y.-H.; King, R.; Krapp-Schickel, T.; LeCroy, S.; Lörz, A.-N.; Senna, A. R.; Serejo, C.; Sket, B.; Tandberg, A.H.; Thomas, J.; Thurston, M.; Vader, W.; Väinölä, R.; Vonk, R.; White, K.; Zeidler, W. (2016) World Amphipoda Database. Accessed at http://www.marinespecies.org/amphipoda on 2016-04-07

WoRMS-info on workshop: http://www.marinespecies.org/news.php?p=show&id=4531