This is the tenth in a series of posts by Associate Curator of Invertebrate Zoology Janet R. Voight as she heads out on an expedition to Norway. There, she and colleagues will look for a wood-boring clam, Xylophaga dorsalis, to study its, well, poo. Read the first post and stay tuned for upcoming posts to find out what they discover.
Our hopes of finding live Xylophaga dorsalis clams rest on the use of the research vessel R/V Hans Brattström. Ken Halanych, Professor at Auburn University, has joined us to maximize our odds of success. Ken has far greater experience in the area, and with working at sea, than do Reuben or I. They don’t teach you to sample using boats in school (the fact that I went to grad school at the University of Arizona in Tucson is not a liability in this regard, none of them do!). You have to go out and watch and learn, then do. There are lots of knots and winches and other heavy machinery involved, but good luck is a big part of the endeavor. The R/V Hans Brattström is the smallest boat I have ever used to sample, with a crew of two, no submersibles, and only 1500 meters (1640 yards) of line on the trawl. Ken rented a car so we can drive to its berth downtown and sail north into the fjords, where we figure the odds will be improved.
I’ve had long discussions with marine station staff, the ship’s crew, and Ken about where to sample. We figured that wood gets into every fjord and floats for a while before it sinks. If the fjords here were V-shaped, wood would tend to settle into the deepest part of the V, making our job easy. However, locally, the fjord bottoms are U-shaped, meaning wood could be anywhere on the bottom. We opt to target areas with depressions, where we figure wood is more likely to accumulate.
On the first of our two days onboard the ship, we set out with a thick fog bank to the west. Our plan is to use the dredge to collect. A dredge has a triangular frame that is designed to skim the bottom—ideal for wood collecting, we figure! We steamed an hour north and a bit east of the city, deployed the dredge, and about a half-hour later brought it on deck from a depth of 250 meters, or 820 feet. Dashing our hopes, it carried only mud. We verified this by running our hands through every single bit of it. We deployed the dredge again and got the same result. We tried it a third time (the charm, you know?) and got cobble-sized rocks, without a bit of wood.
As we were getting nowhere slowly, we opted to switch to a trawl. A trawl is a net drug behind the boat; it is weighted at the bottom to sink and has floats near its top to keep the net open. There are also “doors” that weigh 80 kg (over 175 lbs) that hold it open. Again, theoretically it would work perfectly, but the first trawl came up empty. The second try was better, but no wood. By this time, we were an hour and a half steam from Bergen and needed to go back, as we would otherwise push the crew into overtime. We had to make good the next day—our only remaining day to use the boat to try to collect.
On day two, Ken didn’t make any wrong turns driving to the boat, the best omen we’d had this trip. Our first trawl came back with a piece of heavily bored wood. A huge relief! But did it have what we needed? It was covered in mud that we figured it picked up in the trawl. While it was sitting on the Hans Brattström's deck there was no way to find out; we had to get it in the lab with lights and glass aquarium walls. We weren’t about to call it a day, though; we opted to trawl just a few meters away from where we got this piece in hopes of finding another.
I was on deck hosing down some mud when the captain came aft looking concerned. I noticed the trawl line was slack, then pulled taut at 90 degrees to the boat. The net was snagged on something. It may have been an anchor from an abandoned salmon farm or a tree; whatever it was, it held the net tightly! Even my inexperienced ears could tell the winch was straining and popping as we attempted to pull free, but in due time, we did.
Nothing was in the net, but at that moment, it seemed trivial. We were just glad to recover the net, floats, and the doors! Once we resecured the weights to the bottom of the net, we were back in business. We could do only one more trawl, as time again was running short. But there was nothing notable in this last haul. All our hopes for success rest on the one piece of wood covered by muddy water in a huge bucket on the aft deck.
Read on in Part 11: It's Alive! Finding Tiny Clams Aboard Driftwood
Funding for this project was provided by the Robert A. Pritzker Center for Meteoritics and Polar Studies established by a grant from the Tawani Foundation.