I admit I am addicted to amphipods. I am obsessed with meeting and greeting each and every pod, short-speak for amphipod, we bring into the lab. Since amphipods seem to be associated with everything we collect, there is no shortage of these little critters to welcome.
Now you are probably wondering what exactly an amphipod is and why they would incite an obsession. Shaped somewhat like fellow crustacean the shrimp, amphipods are flattened side to side so that they have a right and left side. The name amphipod, when dissected (biologists will dissect anything!) into its parts translates into “both kinds” (from the Greek amphi) and “foot” (pod). So amphipods are crustaceans that have both kinds of feet. This refers to the fact that of their many limbs there are different kinds, some specialized for feeding, others for walking, swimming or even jumping.
Ever walk the beach and see sand fleas or beach hoppers? Those are amphipods. Some of their feet are modified to jump around and feed on tide washed in algae. They do that at night so as to avoid being seen and eaten by birds. During the day they burrow into the fine sand at the surf’s edge and are often dug up much to the surprise of bucket and spade wielding sand castle builders. No sandy beaches to walk around Palmer Station so we do not see these amphipods.
Other amphipods have limbs designed to swim all the time as they spend their entire life in the water column. Organisms that lead a mobile existence like this have what is know as a pelagic lifestyle. Pelagic is derived from another Greek word (pélagos) and means “open sea”. We don’t see many representatives of this kind of amphipod in our collections.
If you have watched Chuck’s YouTube video (“Amphipods on Antarctic Macroalgae”) you know that we see many, many, many benthic or bottom-dwelling types of amphipods. Benthic (from a Greek word meaning bottom of the sea) pods seem live in and/or on just about every alga and most invertebrates (sponges and tunicates mostly) that we study. In Antarctica alone there are over 700 different species of this type and I am like a bird watcher, obsessed with keeping a list of every new winged, now pod encounter.
The amphipods I have meet in the waters of Palmer Station come in a myriad of colors, sizes and personalities and I find their endless diversity just fascinating. One of the most common pods we collect goes by the scientific name Gondogeneia antarctica – we call it Gondo. Even though the color of this pod can vary with age and diet, it is easy to identify because its two pair of antenna are not much longer than the body and its behavior is very active!
Gondo is sort of a goat, an omnivore that eats almost everything although it does tend to favor a vegetarian diet, eating algae. So we use this species in many of our feeding experiments. Gondo is very active and can be difficult to handle in the lab with our modified slurp gun which is sort of like a large medicine dropper or turkey baster. Gondo’s frenzied activity also makes it hard to photograph so the image to the right does not do it justice. You must check out the sequel amphipod video on YouTube(“Up-close and Personal with Amphipods on Antarctic Macroalgae”) for better images and live Gondo action!
Amphipods that feed mostly on algae and smaller plant cells called diatoms are referred to as herbivores. One of the herbivores I have done some experiments with is Oradarea bidentata. Oh bident(!) for short has several relatives that look very much alike. I have trouble telling them apart still. Oh bident(!) is easy to tell though as it has two spines or teeth (bi as in two; dent as in dental) that you can see when the critter allows a profile view. Oh bident(!) and its cousins have distinctive feeding appendages which help identify them.
All amphipods have special limbs near the mouth which help deliver food. The limbs are called gnathopods (gnathos refers to jaw and you know pod already). Oradareans all have long slender gnathopods unlike Gondo which has shorter and rounder gnathopods. You can see Gondo’s gnathopods in action on the video but none of the Oh bidents(!) cooperated with a profile view to show their gnathopods.
Prostebbingia gracilis or Pgracilis is a bright red amphipod. It usually look racoonish- its dark eyes surrounded by white around where no pigment is for some reason. We will not do any experiments this year with P gracilis. Though cheery to look at it is not very active which makes it easy to photograph but sort of dull otherwise. Lack of activity means very slow feeding so this year we will just admire it as you can do in the short video clip!
The pod I have been spending the most time with is a red and white spiky/spiny critter with the long name of Paradexamine fissicauda. Though we find it sometimes on brown algae, it is more commonly associated with red algae. Of real interest to us is that Paradex not just lives on red algae as many other pods do, it also eats it. Future website entries will address this peculiar twist in chemical ecology of algae and amphipods.
Paradex is really tough to collect as it sort of plays hide and seek, wrapping itself up in algae, the spikes on its body seemingly acting as pins to ensure the branches of the alga keep it hemmed in. In Chuck’s video you saw me repeated dunking algae in seawater to encourage the pods to leave the alga. No luck doing that with Paradex, I need to inspect the algae under the microscope and unzip its spikes to free it so I can use it in experiments. See if you can find it in the video.
So, you have met 4 different amphipods. Watch the video and I think you will agree there is something addicting about amphipods and their antics. Stay with our website over the months and I will do my best to introduce you to the remaining 700 plus pods of Palmer! You too may become hooked on pods!