I promised (threatened?!) you would hear more about how amphipods rule and govern our lives down here and more importantly the benthic environment here at Palmer Station, Antarctica. Craig has and will keep you posted on how important amphipods are in regard to the myriad of lush algae that carpet our local underwater turf. His work may end up suggesting that amphipods are the goats or sheep keeping underwater vegetation mowed and tidy.
Kevin Peters, a former Palmerite and UAB graduate student currently completing his PhD dissertation, conducted work here that indicates that amphipods might also have an important relationship with a group marine animals commonly called sponges. Think flat, blue kitchen sponge – a synthetic version – or the (real but dried) yellowish soft globular one used to wash your car (before detailing drive-ins became vogue).
Sponges have holes and absorb water. Biologically, sponges are animals without backbones, hence invertebrates. Most are marine but a few live in freshwater. All are biologically categorized in the phylum Porifera – referring to the many pores or holes that make up the sponge. The pores are lined with special cells that pull water into the pore and filter out tiny little nutritious goodies that are drawn in with the water.
Remember those amphipod bags I sweated a day over? I needled Craig and Jim to help me on the ship helping with finishing touches. Check out our sewing circle on the bridge during our crossing. We have been using these bags while diving to carefully collect sponges and simultaneously ensnare any of the small amphipods associated with them. It seems that various types of amphipods like to hang out on the surface of the sponge, and others will actually be inside the sponge. One of my missions here is to survey many different types of sponges and determine which amphipods are present and why. Do these sponge pods use their host sponge simply as a home, a safe nursery for their many babies (twins are a small pod family – think at least septuplets!), or as food?
One of the first sponges we collected for this investigation was Artemisina sp. This sponge is characterized as having long orange, prickly ‘fingers’. Do you think my photo of this sponge holds true? The PSC07-9 label to the right of the sponge refers to our record keeping system to identify samples. This sponge was collected and logged sequentially in the Palmer Station Collection (20)07 log book as unique collection number 9.
Often scientific names have a reference to Latin or Greek mythology. Our sponge may have been namedfor the Greek goddess Artemis. Her virtues are recorded as including protector of the natural environment and of the young and presiding over childbirth. Read on and consider the similar ecological role our Artemisina sponge may playing in Antarctica.
Lots of sponges can be called prickly. This is because many sponges have special skeletal structures called spicules that help give support and a framework for the mass of cells that comprise a sponge. In Antarctica particularly, spicules are often made of silica, a.k.a. glass and can be needle shaped as in the case of Art – my short hand for the scientific name Artemisina. Spicules can also be more elaborate with 3, 4 or 6 needles or rays radiating from a single point. My sponge, “Art”, is in its spicule simplicity, Artful!
Art is also rather artsy in the amphipods that have been drawn to it. In my introductory investigation of this sponge, I found primarily 3 pods associated with it. You may recall that I previously wrote that some amphipods reach a length of a small jelly bean. Art’s pod community unfortunately does not include such big dwellers. To find the pods in and on Art, I had to place sections of the sponge under the microscope and carefully remove the pods with fine dissecting tools so as to not injure (crush!) the tiny amphipods.
Some of the pods associated with Artemisina were itty and bitty but ever so cute, which I have tentatively identified as Ausatelson sp. This diminutive pod (less than 1mm length) reminds me of a little boy wearing a football jersey that comes down to his ankles. The white jersey with red speckles is really the carapace or exoskeleton of the amphipod. In Ausatelson the exoskeleton is longer than in most pods- extending to their ‘toes’ rather than ‘knees’ or “thighs’ and one of the sections is exaggeratedly wide and oval.
Ausatelson or whoever it really is, are fun to watch trudge up and down the prickles on Art’s surface with their short legs, somewhat confined by the carapace. Often they would march right into a pore in the surface of Art and disappear into the catacomb of spicules. Don’t be fooled by their unstreamlined appearance – they put up a good chase when they decide to swim!
One of the larger amphipods I missed at first because it looked so much like the sponge itself. Paradexamine fissicauda is spiny and splotchy orange-red hued. Don’t you think Dex (my short hand for the long name) blends in well with Art (see photo)?? This pod is more like the average jelly bean lengthed pod. It would not fit too comfortably inside any of the sponge pores but maybe it gets the food or shelter it needs just by proximity to a similarly spiked and hued sponge.
It is said you are what you eat and the pigmentation of Leucothoe spinicarpa certainly reflects its possible diet. All the Lukes, as I call this pod, appear intricately engraved with orange hieroglyphics. However, the Lukes are armed with some pretty serious feeding appendages. The large, opaque claw you can see is in amphipod-speak called a gnathopod. ‘Gnath’ is a Greek root referring to the jaw. ‘Pod’ in this word dissection case refers to foot (podiatrist). So a gnathopod is a jaw-foot appendage – food gathering tool. Considering the armature, Lukes might prefer to eat something meatier than sponge and may have taken on coloration to match the host and remain undetected by potential predators.
Identifying the players on the various sponge fields we plan to investigate is sort of the easy part. Determining why the pods are on particular sponges and how sponges are impacted, if at all, by these associations is what will keep me in the game at Palmer this season. So stand by for another part of Pods Rule at Palmer coming to this website soon…..