Conservation management options and actions: Putative decline of coral cover at Palmyra Atoll, Northern Line Islands, as a case study

•Palmyra Atoll's lagoon was modified by building of a causeway that effected flow.•Putative decline of coral cover may be due to increased temperature or turbidity.•We report no differences in temperate or turbidity at sites across the causeway.•Recommendations to modify/remove the causeway will not have the intended affect.•Our study highlights problems faced by managers of Pacific islands and atolls.

Localised loss of live coral cover at Palmyra Atoll (central Pacific Ocean) has been attributed to increased temperature and/or sedimentation arising from alterations made to the lagoon system. It has been hypothesised that a causeway spanning the lagoon hinders water circulation, resulting in warmer and/or more turbid water flowing towards a site of high coral cover and diversity (Coral Gardens). Analyses of a multi-site and multi-year data set revealed no differences in mean temperature or turbidity values on either side of the causeway and provided no evidence of significantly warmer or more turbid water at Coral Gardens. We conclude that the putative decline in live coral cover cannot be attributed to the presence of the causeway and that proposed management actions involving modification to the causeway cannot achieve the conservation outcomes suggested of them.