Abstract

Important, often abrupt, and irreversible shifts associated with the degradation of ecosystem functioning and services are increasingly commonplace. Thus, a trait-based view of communities may be more insightful than that based solely on species composition, especially when inferring ecological responses to environmental change. This underscores the importance and urgency of establishing benchmarks against which future community changes and functional structure can be evaluated. As a first step toward setting these baselines and their current spatial variability, we here describe geographic and among-habitat patterns in the functional structure of shallow hard bottom communities, including fish assemblages, across the northeast and west coasts of Rapa Nui. We also document temporal patterns of change in dominant benthic functional groups that have taken place over the past 15 years at selected sites on this isolated Pacific island. Generally weak vertical zonation patterns were observed, with most striking differences due to the paucity of branching pocilloporid corals in shallow waters(<7 m), where massive corals of Porites predominate. We identified three main 'groups' of sites in terms of the relative abundance of major functional groups and these did not follow geographic arrangement or strict coastline orientation. The similar spatial change in benthic and fish functional community structure documented here suggests there may be strong coupling with coastal oceanographic conditions that varies on scales of 1s-10s of km. Temporal patterns document relatively rapid recovery of total coral cover, largely via compensatory change in relative coral composition with an increase in Porites upon abrupt decline of Pocillopora, following extensive coral mortality caused by thermal stress (coral bleaching) in 2000. Moreover, coral abundance in shallow habitats increased beyond pre-disturbance levels (i.e., 1999-2000). In contrast to shallow habitats, corals again suffered extensive mortality and reduced cover by 2005 at mid-(10-15 m) and deep (>15 m) habitats, with contrasting recovery. These results suggest depth-dependent disturbance regimes that differ in types and frequency of events, as well as capacity to recover. Overall, our results highlight the apparent resilience of the current system and provide a first-cut benchmark as to where management subsystems might be prescribed so as to spatially match ecosystem characteristics.