Coarser taxonomic resolutions are informative in revealing fish community abundance trends for the world’s warmest coral reefs

The Arabian Gulf is a natural laboratory to examine how subtropical coral reef ecosystems might change in responding to recurring heating events because of uniquely high water temperature and relatively low fish diversity. Several statistical methods were applied to long-term (30 yrs) monitoring data in the western Arabian Gulf to extract clean signals of the fish abundances, to reveal common trends in the multivariate time series, and to test for nonlinear and lagged effects of coral coverage and sea surface temperature as predictors. Data were analyzed at three taxonomic resolutions: species (29 species out of a total of 148 species, contributing to 69% of total observations), genus (24 genera, 81%), and family (19 families, 96%), to test the taxonomic sufficiency hypothesis, which asserts that there is no significant loss of information at higher taxonomic levels for detecting changes in the fish assemblages. Multivariate abundance time series can be summarized by dynamic factor models of four common trends, which were supported by time series clustering and good model fitting performances. The taxonomic sufficiency hypothesis is supported for the first two common trends, which showed similarity among the three taxonomic resolutions. The effects of changes in coral coverage on the fish community are nonlinear and significantly lagged with lags mostly of 8 yrs, while the effects of mean sea surface temperature were significant but inconclusive. The fish communities in the coral reefs of the western Arabian Gulf are degrading in general with decreasing abundance at the three taxonomic resolutions. Analyzing data at coarser taxonomic resolutions can be informative in revealing the general trends of the abundance of coral reef fish communities, at the cost of ignoring variations at finer resolutions. This study further highlights the importance of long-term and continuous monitoring of the coral reef ecosystem at the finest possible taxonomic level to fully reveal slow but crucial changes in fish communities, as well as to detect signs of communities’ degradation to take timely restoration actions.