One of my favorite things to tell my oceanography students at the University of Alaska Anchorage is: we know less about the bottom of our own ocean than we do about the surface of Mars. We are out here exploring the Aleutian Trench to add to our knowledge of the ocean’s depths. I am part of the EpiBenthic Sled, or EBS, group, and my particular interest is a group of crustaceans called cumaceans, or comma shrimp. One of the best things about the EBS (for me anyway!) is that a good proportion of cumaceans come to the surface with their delicate legs intact, which is a challenge when you are sampling at 3500-7200 m below the surface.
Makrokylindrus sp. with long, delicate first walking legs. These long legs are frequently broken off, so it is wonderful to see an intact specimen.
Small crustaceans like cumaceans can be important food sources for fish, seabirds and even whales, because there can be up to 90,000 individuals per square meter in shallow waters. The deep depths at which we are sampling are out of range for birds and whales, but fish are still around. There are also lots of worms and other predators that might want small crunchy mouthfuls. Being covered in long spines, like Vemakylindrus, probably helps defend against predators. Being covered in tiny spines seems to help with camouflage, as species like Bathycuma sp. act like Velcro and everything (mud, mucus, miscellaneous bits) sticks to them.
Bathycuma sp. 2 covered in short spines that act like Velcro, probably for attaching camouflage.
Cumaceans are related to isopods and amphipods, sharing the brooding of their young in a brood pouch. In this photo, you can see the babies in the transparent brood pouch. The young grow in the pouch until they are released as small versions of the adults. This means the brood pouch can get quite large, as you can see.
Nannastacidae sp., a female with her offspring in her brood pouch, or marsupium.
In this area, very little is known about the cumaceans so the questions are quite basic, such as what is the biodiversity, is their distribution limited, and if so, by physical features such as the trench or by other features such as food supply, sediment chemistry or grain size? In some places, cumaceans are very sensitive to depth and temperature, so one question is if the trench will act as a barrier, keeping different species on each side, or not. Most of the cumacean species I have seen so far are new to science, including some surprises like Chalarostylis sp., which I did not expect to see here. While Chalarostylis is only found in the deep sea, very few species are known from around the world, and it has never been reported before from the North Pacific.
Chalarostylis sp., a rare deep sea cumacean not known previously from the North Pacific.
A great thing about being out at sea with a big group of scientists is we all get excited to see the special animals we are encountering. It is common to hear a gasp while sorting, followed by “Wow”, then “come look at this!” when someone finds something exceptional in the sample. We are all learning from each other, because we all specialize in different types of organisms. There is some good natured teasing, as we each think the organisms we study are the best. Of course, comma shrimp ARE the best! 😉
