One of the major projects that I've been involved with during our present field season is what we usually refer to as "the substrate experiment." One of the things we are trying to understand is how light limitation (i.e., having too little light for maximum growth) influences the production of defensive chemicals in macroalgae that have ample nitrogen for growth. Antarctic macroalgae virtually always have ample nitrogen for growth but that usually isn't true over broad scales elsewhere in the world. Doing this type of experiment is one of the unique things about Antarctica that brought us here to study chemical defenses.

"Substrates" is a term applied broadly in marine ecology for artificial (or at least, artificially located) surfaces placed into the ocean for experimental purposes. Sometimes one is studying what naturally settles and grows on the substrate. Other times one attaches specific organisms to the substrates to study their growth or other aspects of their biology.

Our substrates fall into the later category. They are concrete squares 40 cm on a side and about 5 cm deep. They weigh about 50 lbs on land. They were made with "high tech" plastic rods at each of the 4 corners. The rods are threaded so that plastic nuts can be screwed down on them, and they extend 25 cm above the top of the substrates. These are used to attach racks of plants to the substrate and to hold Plexiglas panels above them.

The plants are attached to the racks by being threaded through the strands of polypropylene line, the plastic kind of rope that floats and is often used in boating. The lines are then attached to the racks by plastic cable ties through loops in each end of the rope. Maggie, with help from Jim, spent many hours weaving the loops into those rope ends.

There are three Plexiglas panel treatments. One treatment cuts out 80 percent of the light getting to the plants below. To do that, I sandwiched three layers of window screening between two of the plastic sheets. A second treatment has only a single, unshaded plastic panel and the final treatment has no panel at all.

There are four sets of these three treatments that were deployed into the waters right off the station at about 3-3.5 meters depth. To do that, we waited for a calm day with no sea ice. We had a platform with a winch and davit (swing arm) put into the boat so that the tenders, Jim and Kevin, could lower the substrates into the water -- there is a large stainless steal eye bolt in the center of each substrate that allows this.

Once they got the substrate into the water, Chris and I attached a lift bag to the eye bolt and released the wire from the winch. Chris and I then guided each substrate to the bottom, adding air to the lift bag to maintain buoyancy as we went down. Lift bags are nothing more than floats you can add or remove air from to allow you to move heavy objects around underwater. I had previously scouted out the four spots we wanted to put the substrates -- one group of three in each spot. We sent up a small buoy from each spot to allow the boat to bring the substrates close in so we didn't have to swim them very far. It took us four dives, but we got them all put in place in a single day.

Next I started threading the plants onto the strings in the lab and arranging them on the racks. This took about two and a half days. We used four different species of macroalgae that have interesting defensive chemistry that we wanted to follow. Identifying these species was a major goal of our last field season.

After the racks were threaded, we again waited for a good dive day. The next day was too bad to dive, but by noon of the day after that we were able to get to work. Chris and Bill each accompanied me on one of the two afternoon dives necessary to attach the racks of plants to the substrates. Maggie went back out with me after dinner to bolt down the plexiglas panelson on each of the eight substrates that needed them.

So the experiment was complete! Now we dive on it every few days to clean sediment off the plexiglas and do any other needed repairs. We had hoped to have the whole experiment running for a month but knew that icebergs might damage some or all before that, so we had contingency plans to run part or all of the experiment for shorter times if necessary. The algae from two sets of the substrates were harvested after 11 days when they were damaged by an iceberg but the rest (hopefully) will remain in place for 30 days before Maggie and Chris harvest them (I'll be home at UAB by then).

Only time will tell what our scientific results from the experiment will be. That will be many months after the final plants are harvested but I am already anxious to know how it all works out.