Oecologia (2003) 135:532–541 DOI 10.1007/s00442-003-1220-9 POPULATION ECOLOGY Sally J. Holbrook · Russell J. Schmitt Spatial and temporal variation in mortality of newly settled damselfish: patterns, causes and co-variation with settlement Received: 10 June 2002 / Accepted: 5 February 2003 / Published online: 28 March 2003  Springer-Verlag 2003 Abstract Local abundance and dynamics of sedentary species with a dispersing life stage reflect factors that influence input and loss rates to patches of suitable habitat. For reef fishes, more attention has focused on sources of variation in input (larval settlement) than on patterns and causes of subsequent losses. We estimated spatial and temporal variation in juvenile mortality of a tropical damselfish, yellow-tail dascyllus (Dascyllus flavicaudus; Pomacentridae), using a fixed density exper- iment that was repeated 5 times at the same eight mid- lagoon localities at Moorea, French Polynesia. There was little temporal variation in the overall percent of out- planted fish lost in 48 h among five time periods (range: 32–37%), whereas there was substantial variation among the sites in the average percent lost (range: 16–56%). Differences in loss rates among the sites were highly consistent among the time periods. Densities of predators of juvenile dascyllus varied substantially among the eight sites and were highly correlated with loss rate of dascyllus. We used the empirically derived relationship between predator density and damselfish loss rate to predict the loss rate of dascyllus at four additional sites, and there was excellent agreement between the predicted and observed loss rates. There was a strong positive relationship between predator densities at the 12 sites and structural attributes of the reefs that do not change on a fast time scale, suggesting why there was strong spatial and weak temporal variation in mortality rates, with no interaction between spatial and temporal variation. Nat- ural settlement rates of yellow-tail dascyllus and of a close congener (humbug dascyllus, D. aruanus) varied among the sites, and settlement of the two species was inversely correlated (r=0.68). Settlement of these spe- cies was not statistically correlated with variation in mortality rate, but there was a weak trend for settlement of yellow-tail dascyllus to be greater at sites with higher mortality (r=0.27), and for settlement of humbug dascyl- lus to be greater at sites with lower mortality (r=0.32). We calculated that even these weak co-variances could reduce (yellow-tail dascyllus) or increase (humbug das- cyllus) the spatial variance in density of 48-h-old recruits arising at settlement by 19 and 27% respectively. Taken together, the findings suggest that the interactions between and relative contributions of input and loss processes can differ substantially over a scale of a few kilometers, resulting in a mosaic of local patches characterized by different abundances and dynamics. Keywords Dascyllus · Mortality · Patch dynamics · Settlement and post-settlement processes · Recruitment Introduction A central goal of population ecology is to understand the causes of variation in abundance of populations in space and time. Many species of freshwater, marine and terrestrial organisms have demographically open local populations, and thus the attributes of a sub-population can be influenced greatly by events that occur elsewhere. For example, most species of marine reef animals have spatially subdivided populations that are connected by planktonically-dispersed early developmental stages. Abundance and dynamics of their local populations reflect both inputs of colonists spawned elsewhere and the subsequent losses from the reef environment. Input of larvae from the plankton (i.e., settlement) frequently is highly variable both in space and time, and because of its potentially great ecological importance, considerable effort has been devoted to understanding the causes of this variation (Mapstone and Fowler 1988; Doherty 1991; Caley et al. 1996). As a result, the principal sources of variation in inputs of reef animals are known (reviewed by Underwood and Keough 2001), and they arise from a S. J. Holbrook ( ) ) · R. J. Schmitt Coastal Research Center, Marine Science Institute and Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, USA e-mail: holbrook@lifesci.ucsb.edu