We are using a variety of methods to measure the strength of sea spider legs and how well they withstand different flow conditions.
Because sea spiders live in water, their body weight isn't very important to the mechanical stresses imposed on their legs. However, they may run into trouble whenever they find themselves in high currents or when they do vigorous things, like fighting, mating, or feeding. We'd like to know how strong those forces are and how well their exoskeletons are designed to handle them. To get these data, we'll do several things. One is to measure their postures in the wild, and how they walk and swim. On SCUBA, we will also measure patterns of water flow around them.
Other sea spiders we will bring back to the lab at McMurdo Station. There we'll be able to measure how much drag currents impose on them using a sensitive underwater force platform placed into a water flume, which is basically an artificial stream of sea water whose velocity we can control. We'll also watch carefully during these experiments to see how sea spiders respond to high flows. For example, we'd like to know whether they lower their bodies to get out of the main flow, or whether they reorient the positions of their legs to resist being blown away by the flow.
Another key property of sea spiders that we'd like to know is how stiff and strong their cuticles are, and how those properties vary across small-bodied and large-bodied species. To measure these properties, we will use an instrument called a materials tester. The video at right shows the machine in action measuring the stiffness of a Q-tip shaft, which is about the same size as the legs of some sea spiders. The triangular tip pushes down and the machine simultaneously measures how hard it's pushing and how much the tube has flexed. From those data you can calculate the stiffness. We want to know this so that we decide whether sea spiders are well-built and robust compared to how much drag they experience in the wild; OR whether they are on the edge and always close to breaking their legs.