Remote marine protected area reveals unusual social behaviour in Chaetodon trifascialis

Abstract

Phoenix Islands Protected Area (PIPA) in the Republic of Kiribati is one of the largest marine protected areas in the world (408,250 km[superscript 2]). These reefs are extremely remote (Fig. 1a) and, therefore, escape many anthropogenic impacts. While snorkelling in the shallow lagoon at Kanton Island (2°47′25″S 171°42′48″W) in September 2015, we came upon unusually high cover (∼100 %) of tabular Acropora (A. hyacinthus and/or A. cytherea) (Fig. 1b) and strikingly high numbers of Chaetodon trifascialis. Up to 25 individuals were observed coexisting within a relatively small area of ∼4 m[superscript 2] (Fig. 1c). Moreover, there were additional individuals present under the coral colonies out of view. Based on size, all individuals within the group were adults or sub-adult and clearly displayed overlapping ranges with minimal conspecific aggression.