In Situ Orientation of Fish Larvae on the Great Barrier Reef Differs with Region

Larval reef fishes have very good orientation abilities during their pelagic stage, and this has major implications for dispersal and population connectivity.  Larvae of the damselfish, Chromis atripectoralis over 1995-2011 had consistent, location-independent orientation to the south (mean = 170^o) in the Lizard Island (LI) region of the northern Great Barrier Reef (14.5 ^oS).  This was based on in situ observations of over 300 larvae by divers and by use of a Drifting In Situ Chamber (DISC).  In early 2014, in situ observations by divers of 44 C. atripectoralis larvae were made over 8 days in the region of Big Broadhurst Reef (BBR) in the central Great Barrier Reef (19^oS), over 500 km SSE of LI.  In both regions, more than 90% of larvae had significant within-individual directionality, with high precision.  However, in contrast to the LI region, larvae at BBR had significant among-individual orientation to the ENE (mean = 63^o): significantly different from orientation in the Lizard Island region (p<0.00001, Watson-Williams F Test).  This is the first time that regional differences in orientation of larval fishes have been reported.  The implications of these regional differences for dispersal and population connectivity are discussed, as are possible reasons for them.