The Substrate Experiment, which I have written about earlier, is a major part of what I am doing this season at Palmer Station- but I also have another experiment running. The Bucket Experiment involves lots of buckets, a large tank, lots of plastic tubing and some critters. More scientifically, it is testing some hypotheses about induction of chemical defenses.
Induction of defenses means that the algae do not contain high levels of the defensive metabolites all the time- but that they produce these chemicals in response to a cue, such as grazing by snails (i.e. the production of the chemical is induced by snail grazing). This idea is part of the Induced Defense Model (IDM) which is an extension of the Optimal Defense Theory (ODT).
The ODT is pretty simple- it says that organisms (algae in this case) will protect the parts of their body (the “thallus” for algae) which are most important for their survival, and also that they will protect parts of the thallus which are most vulnerable to attack (such as the outer layers or tips). This means that the algae is maximizing the use of the resources available for defense (which it works hard at producing through photosynthesis, and especially hard in the Antarctic where there is sometimes not much light around).
The IDM extends from that idea and states that the production of defensive metabolites should be correlated with the risk of attack. For example, algae are not under risk of attack by snails all the time. Some individuals have snails grazing on them, others don’t. So if the algae that have no snails on them do not waste energy defending themselves from (absent) snails then that is a good thing in terms of energy use.
But if they are able to then produce the defensive chemicals when snails do start grazing on them this would be called an induction response. This theory only applies to small relatively immobile grazers, like snails and amphipods, which will remain on the algae for a long time (unlike fish which might come along and take a quick bite and move away before an induction response can occur).
So the Bucket Experiment is testing for an induction of phlorotannin production in response to grazing by two species of amphipods, one species of snail and also artificial grazing (by me with a razor blade). I removed 5 tips from Desmaretsia menziesii individuals and put each in a bucket with one of the different treatments (snails and amphipods & artificial grazing) and a control bucket. I did this to a total of 5 individuals so I ended up with 25 buckets.
These buckets are in a large tank in the aquarium room which has seawater flowing in from Arthur Harbour. Each bucket has it’s own inflow pipe and outflow holes to ensure that there can be no communication between the buckets (algae can send chemical messengers through the water which can cause neighboring members of the species to respond- just like corals release chemical cues that trigger release of eggs and sperm at the same time during spawning). I have some lights above the tank which are on a timer so that the algae get 18 hours of light a day. Each day I rotate the buckets around so that every bucket gets to sit in every position in the tank (in case there is a difference in the amount of light or water flow in one particular position). So each day I get to put on my rubber boots and play with buckets and hoses- sounds like child’s play I know! It is really quite fun.
The experiment is running for about 6 weeks and at the end of that time I will run phlorotannin assays and amphipod bioassays on the samples. I’ll tell you about how much fun (?) that is in later entry.