For many organisms, early life stages experience significantly higher rates of mortality relative to adults. However, tracking early life stage individuals through time in natural settings is difficult, limiting our understanding of the duration of these 'mortality bottlenecks', and the time required for survivorship to match that of adults. Here, we track a cohort of juvenile corals (1-5 cm maximum diameter) from 12 taxa at a remote atoll in the Central Pacific from 2013 to 2017 and describe patterns of annual survivorship. Of the 537 juveniles initially detected, 219 (41%) were alive 4 years later, 163 (30%) died via complete loss of live tissue from the skeleton, and the remaining 155 (29%) died via dislodgement. The differing mortality patterns suggest that habitat characteristics, as well as species-specific features, may influence early life stage survival. Across most taxa, survival fit a logistic model, reaching > 90% annual survival within 4 years. These data suggest that mortality bottlenecks characteristic of 'recruitment' extend up to 5 years after individuals can be visually detected. Ultimately, replenishment of adult coral populations via sexual reproduction is needed to maintain both coral cover and genetic diversity. This study provides key insights into the dynamics and time scales that characterize these critical early life stages.

AbstractTropical reef communities contain spatial patterns at multiple scales, observable from microscope and satellite alike. Many of the smaller-scale patterns are generated physiologically (e.g., skeletal structures of corals at <1-m scale), while some of the larger patterns have been attributed to scale-dependent feedbacks (e.g., spur and groove reefs at 10-100-m scales). In describing the spatial patterning of reef benthic communities at landscape levels, we uncovered unique spatial patterning among living marine algae. Populations of the calcifying green alga Halimeda were observed to form a consistent polygonal pattern at a characteristic scale of 3-4 m. The pattern showed no clear evidence of having been formed through biologically created shifts in hydrodynamical conditions or related mechanisms. In considering the specifics of Halimeda growth patterns, a model of self-organization involving separation and patterned extension is proposed, a mechanism revealed in some geological pattern formation. This observation reinforces the diversity of pathways by which striking spatial patterns can occur in ecosystems.