Volume 26, Issue 24, Pages R1266-R1267 (December 2016) A magnetic compass that might help coral reef fish larvae return to their natal reef  Michael Bottesch, Gabriele Gerlach, Maurits Halbach, Andreas Bally, Michael J. Kingsford, Henrik Mouritsen  Current Biology  Volume 26, Issue 24, Pages R1266-R1267 (December 2016) DOI: 10.1016/j.cub.2016.10.051 Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 1 Settlement-stage cardinal fish O. doederleini can use a magnetic compass to orient. Center: a hydrodynamic model of the tidal and NNW drift currents prevailing at Capricorn Bunker Reef Group, Australia illustrates the expected distribution of passively dispersing particles (red dots) 8 days after release from the One Tree Reef (modified after Figure 1D in [2]). The purple patches in the map indicate lagoons, the whitish color depicts the 20 m isopleths on the reef slopes, and the islands inside the Heron and One Tree reefs are depicted in brown. The bluish background is inter-reefal waters. Settlement-stage O. doederleini were individually tested in an orientation bowl. For sun compass experiments during the day, the fish were tested under clear sunny skies. At night, the fish were placed inside the 99% homogenous center of one of the two sets of Helmholtz coils used for these experiments (insert, top right). The headings of the fish were recorded by an overhead infrared video camera. The circular diagrams at the top of the figure show the spontaneous compass orientation of the fish under clear skies during the day (Sun), and at night in the absence of any celestial cues in the natural magnetic field (NMF) and in a changed magnetic field turned 120° clockwise (CMF). Each dot at the circle periphery indicates the mean orientation based on 3–5 tests of one individual fish in the given condition. Arrows indicate the group mean vectors. Lines flanking the group mean vector indicate the 95% confidence intervals for the group mean direction. The dashed circles indicate the radius of the group mean vector needed for significance according to the Rayleigh test for p < 0.05. ‘mN’ and ‘gN’ at the top of the circular diagrams indicate the direction of magnetic North and geographic North, respectively. Current Biology 2016 26, R1266-R1267DOI: (10.1016/j.cub.2016.10.051) Copyright © 2016 Elsevier Ltd Terms and Conditions