Meeting Abstract
Sea spiders vary over five orders of magnitude in body size; temperate species are small whereas polar and abyssal species can be huge. They are thus a useful model for identifying ecological factors that drive observed biogeographical distributions of gigantism and for testing the adaptive significance, if any, of being large in polar waters. Our recent research into the bending strength of the legs of sea spiders led us to hypothesize that the distribution of large species is limited by oceanic current. We tested this hypothesis by measuring: drag that large sea spiders would experience in temperate waters using a submerged, 3D printed model attached to a force transducer, clinging strength of live sea spiders in their natural habitats in response to induced current, and the effects of flow velocity on locomotion in a water flume. We tested for potential selective advantages of large body size by measuring walking speed during escape and sinking rate in water. Consistent with our current-limitation hypothesis, flow velocities during a large-flux tide cycle in temperate sea-spider habitat were 3-5x greater than velocities that significantly reduced locomotion in large sea spiders, and peak drag upon our 3D model was >150x body weight. This peak drag was 5x the force required to break the legs of sea spiders. Small sea spiders live within boundary layers and thus appear to be sheltered from high velocity and drag. Induced current caused large sea spiders to detach from their substrates, but their clinging strength depended upon surprise and substrate type. Escape speed and sinking rate increased with body size. Gigantism may thus allow sea spiders to exploit ephemeral, patchy food resources and to control their body position after disturbance such that they select and remain in desirable habitat. NSF PLR- 1341485.
