Atsuko Fukunaga

Structure of Mesophotic Reef Fish Assemblages in the Northwestern Hawaiian Islands.

Mesophotic coral ecosystems (MCEs) support diverse communities of marine organisms with changes in community structure occurring along a depth gradient. In recent years, MCEs have gained attention due to their depths that provide protection from natural and anthropogenic stressors and their relative stability over evolutionary time periods, yet ecological structures of fish assemblages in MCEs remain largely un-documented. Here, we investigated composition and trophic structure of reef fish assemblages in the Northwestern Hawaiian Islands (NWHI) along a depth gradient from 1 to 67 m. The structure of reef fish assemblages as a whole showed a clear gradient from shallow to mesophotic depths. Fish assemblages at mesophotic depths had higher total densities than those in shallower waters, and were characterized by relatively high densities of planktivores and invertivores and relatively low densities of herbivores. Fishes that typified assemblages at mesophotic depths included six species that are endemic to the Hawaiian Islands. The present study showed that mesophotic reefs in the NWHI support unique assemblages of fish that are characterized by high endemism and relatively high densities of planktivores. Our findings underscore the ecological importance of these undersurveyed ecosystems and warrant further studies of MCEs.

Assessing the nature of the combined effects of copper and zinc on estuarine infaunal communities

Elevated levels of copper and zinc in sediment have been shown to adversely affect estuarine infauna. We investigated the additivity of the combined effects of copper and zinc on infaunal recolonisation through a manipulative field experiment in Orewa estuary, New Zealand, using defaunated sediment discs treated with these metals. The nature of their combined effects varied among infaunal taxa and the particular variables being examined. Additive effects were detected for species richness, for the mean log abundances of the polychaetes Prionospio sp. and Scoloplos cylindrifer and for the multivariate response of the community as a whole. Antagonistic effects were detected for the mean log abundances of total infauna and the polychaete Heteromastus sp. Characterising the potentially interactive nature of the combined effects of multiple heavy metals is essential in order to build predictive models of future environmental impacts of metal accumulation in estuarine sediments.

Use of multivariate control charts to assess the status of reef fish assemblages in the Northwestern Hawaiian Islands

A distance-based multivariate control chart is a useful tool for ecological monitoring to detect changes in biological community resulting from natural or anthropogenic disturbances at permanent monitoring sites. It is based on a matrix of any distances or dissimilarities among observations obtained from species composition and abundance data, and bootstrapping techniques are used to set upper confidence bounds that trigger an alarm for further investigations. We extended the use of multivariate control charts to stratified random sampling and analyzed reef fish monitoring data collected annually on shallow (≤30 m) reefs across the Northwestern Hawaiian Islands (NWHI), part of the Papahānaumokuākea Marine National Monument. Fish assemblages in the NWHI were mostly stable, with exceptions in the south region (Nihoa, Mokumanamana and French Frigate Shoals) in 2012 and 2015 where changes in the assemblage structure exceeded the upper confidence bounds of multivariate control charts. However, these were due to changes in relative abundances of native species, and potentially related to the small numbers of survey sites and relatively low coral covers at the sites, particularly in 2015. The present study showed that multivariate control charts can be used to evaluate the status of biological communities in a very large protected area. Future monitoring of fish assemblages in the Papahānaumokuākea Marine National Monument should be accompanied by specific habitat or environmental variables that are related to potential threats to its shallow-water ecosystems. This should allow for more detailed investigations into potential causes and mechanisms of changes in fish assemblages when a multivariate control chart triggers an alarm.