Eurisus sp.  

Aleutian Trench - Aleutian Amphipod Heaven

Our cruise examining the Aleutian Trench will soon be over, we have finished the last station, packed up the labs, and now even stacked everything into the shipping containers. What is left then? All the rest of the science!

We have lots and lots of samples preserved in different ways (ethanol, frozen, RNA-later, formalin or dried) and we already have DNA-extracts of some. We have associated data from each station (water temperature and salinity, sediment information, and bathymetric info), and for many specimens we have a live (or “almost live”) photo. The rest of the work will have to be done at home – in our labs on land, where we have access to other infrastructure, and not least – where the lab does not move.

We can also start to draw the first preliminary conclusions. Preliminary is an important word here, as it is impossible to get the full picture before we can look at the entire samples – and both time-constraints (there are only so many hours in each day) and technical constraints (that moving deck in the labs on the ship, for instance) prevent us from doing that on board.
One of the preliminary conclusions we can draw is that the Aleutian Trench seems to be an Amphipod Heaven. In the samples we have worked with so far, we have approximately 70 different species of these (mainly) small crustaceans, and they outnumber the closely related Isopoda – both in species and number of specimens. This is rather unusual in the deep sea. Not that the amphipods are there and thrive, but that they outnumber the other small crustaceans so much.
Why could there be so many amphipods in this specific trench? We don’t know for sure, but we can speculate. It might be that the amphipods “came here first” – and then filled up available habitats before other species who might inhabit the same habitats came around. Or it might be that they take better to the soupy sediments we have found in the bottom of the trench. Or most possibly some other reason we have not thought about yet.
Amphipods (like isopods, tanaids, cumaceans and mysids – other crustacean groups we have also had in our samples) are peracarid crustacea. They are grouped together because they have a brood-pouch where their fertilized eggs are kept through all stages during their reproduction, until they come out as small juveniles. This separates them from the other crustaceans, who let their eggs or larvae float freely with the water currents for some time during the development. Such a life-history strategy helps spreading a species to larger geographic areas, and the peracarids are more “home-bodies”. Most of them are also not very good swimmers (but a certain fraction is!).
Not being very good at spreading over wide geographic areas is one of the drivers of speciation – the “ending up as separate species” after a while because groups get geographically isolated and small genetic changes happen all the time. The Aleutian Trench is one of the older trenches, it started sometime between 150–100 million years ago. Even giving the fauna some time to get to the new trench and being able to live there, this gives the fauna here a lot of time to evolve and species to evolve locally.
So – we have a lot of different amphipods to examine when we get home. This part of the deep sea in the North Pacific has not been examined very much before, especially the deepest, hadal, areas. We are quite sure that our samples will give us several exciting species to work with. Some of them might even be new to science. That is not the same as “new for the world” – only that no scientists have examined them before. So the Aleutian Trench has been an amphipod heaven for us as well.

… and those nice scientific papers about the amphipods? If you give us a little time in our home labs, we are sure they will come as well. Amphipod heaven for everyone!


Dr. Anne Helene S. Tandberg and Dr. Anna M. Jażdżewska

Selected amphipods from the “live” sorting. A: Eusirus sp. B: Rhachotropis cf. Saskia C: Lysianassoidea D: Stegocephalidae E: Cyphocarididae F: Synopiidae G: Phoxocephalidae H: Dulichiidae  
Selected amphipods from  the “live” sorting: I: Epimeria sp. J: Pardaliscidae K: Hyperiopsis sp. L: Oedicerina cf. denticulate M: Maeridae N: Lepechinellidae O: Amathillopsidae