Ee. Demartini et al., INTERDECADAL CHANGE IN REEF FISH POPULATIONS AT FRENCH FRIGATE SHOALSAND MIDWAY ATOLL, NORTHWESTERN HAWAIIAN-ISLANDS - STATISTICAL POWER IN RETROSPECT, Bulletin of marine science, 58(3), 1996, pp. 804-825
Reef fish faunas were compared between surveys conducted more than a d
ecade apart at each of two isolated and nearly pristine oceanic atolls
(French Frigate Shoals [FFS] and Midway Atoll) in the northwestern Ha
waiian Islands. Species composition, assemblage structure (density ran
kings), and population densities were compared to test the hypothesis
that reef fishes had declined during a period of lower oceanic product
ivity in the central North Pacific. Within each of two principal habit
ats (barrier and patch reefs) at each atoll, species composition and r
ank densities differed little between sampling periods. Densities, how
ever, generally declined by about one-third for many numerically domin
ant species and for tars pooled into functional categories (trophic le
vels, feeding guilds). Patterns of temporal change were partly confoun
ded by distributional shifts between barrier and patch reef habitats a
t FFS, perhaps reflecting indirect effects of storm disturbance on ben
thic algal habitat. Such effects, together with related changes in cli
mate and oceanic productivity on an interdecadal time scale, might hav
e been responsible for the apparent declines in reef fish densities al
both atolls. Temporal patterns were clearer at Midway Atoll, where ch
anges in benthic algae were not evident. Our observations indicate tha
t the statistical power necessary to detect changes in the population
densities of reef fish species that exhibit large temporal fluctuation
s in numbers, particularly on oceanic islands, is generally low. Power
to detect twofold changes may be adequate, however, if taxa are poole
d into functional categories.