Publications [#228568] of Sonke Johnsen

Papers Published

1. Jackson, E; Johnsen, S, Orientation to Objects in the Sea Urchin Strongylocentrotus purpuratus depends on apparent and not actual object size., The Biological bulletin, vol. 220 no. 2 (April, 2011), pp. 86-88, ISSN 0006-3185 [doi]
   (last updated on 2026/01/14)

   Abstract:
   Sea urchins are known to move toward large visual targets, indicating that they have limited visual acuity. There is a minimum target size that elicits this response. However, it is not known whether the actual or apparent size of the target is the determining factor in whether urchins will respond. The present study builds on the results of previous work by independently altering actual and apparent target sizes. Thirty-five specimens of Strongylocentrotus purpuratus (Stimpson, 1857) were presented with circular targets of 6-cm and 11-cm diameter, placed at distances such that their diameters circumscribed arcs of 7.5° or 12°. Urchins oriented significantly only toward targets with an apparent diameter of 12° (P = 0.005 and P = 0.02), regardless of actual target diameter. Thus, it was concluded that these urchins respond on the basis of the apparent size and not the actual size of targets. © 2011 Marine Biological Laboratory.