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Abstract The existence of highly productive coral reefs within oligotrophic gyres is in part due to intensive recycling of macronutrients and organic matter by microbes. Therefore, characterizing reef bacterioplankton communities is key for understanding reef metabolism and biogeochemical transformations. We performed a high‐resolution survey of waters surrounding Mo'orea (French Polynesia), coupling 16S metabarcoding with biogeochemical and physical measurements. Bacterioplankton communities differed markedly among reef ecosystems on three sides of the island, and within each system distinct communities emerged in forereef, backreef and reef pass habitats. The degree of habitat differentiation varied among the island sides according to current speeds inferred from wave power. Oceanic‐associated taxa were enriched in forereefs and throughout western reefs with highest wave power and lowest productivity. Reef‐associated taxa were enriched in backreef and pass habitats most strongly on northern reefs with lowest wave power and highest productivity. Our results offer insight into dynamics regulating reef microbial communities. 

Evidence of metamorphism at ultrahigh‐pressure (UHP) conditions is documented by the presence of coesite, diamond and/or majoritic garnet. However, the growth of UHP‐stable phases such as majoritic garnet is often volumetrically low, and overprinting during exhumation can obscure evidence of UHP growth, making it difficult to positively identify UHP rocks. In this study, we selected garnet‐kyanite schists from three microdiamond‐bearing localities within the Rhodope Metamorphic Complex, located in eastern Greece. Samples from Xanthi, Sidironero, and Kimi have similar bulk rock compositions, but the pressure–temperature (P–T) paths differ. Because the major phases record vanishingly little evidence of metamorphism at UHP conditions, we analyzed zircon grains with complex textures to evaluate if zircon preserves a record of UHP metamorphism. Zircon grains from all localities have cores and rims separated by a characteristic interface domain, as revealed by cathodoluminescence (CL) imaging. The detrital igneous cores range in age from c. 2.5 Ga to 220 Ma and exhibit a negative Eu* anomaly, a Yb/Gd of 10–100, and variable Th/U (0–1.2). Rims yield dates of 150–125 Ma with Yb/Gd of 0.1–10 and Th/U of 0–0.2. Interface domains yield dates 165–145 Ma with Yb/Gd ranging between 0–1000 and Th/U < 0.2. We interpret the distinctive CL textures and Yb/Gd of the interface domains as evidence of zircon that reacted at UHP. The interface domain in zircon from all petrographic contexts yields variable Yb/Gd ratios that are significantly higher than both cores and rims. We therefore interpret that zircon recrystallized via interface‐coupled dissolution–reprecipitation reaction; this process preferentially partitioned heavy rare earth elements within the interface domain, which explains the higher Yb/Gd ratios. The rim domains equilibrated with the matrix, producing a relatively homogeneous and low Yb/Gd ratio in these domains. The spatial extent and degree of preservation of interface domains are interpreted as a function of the P–T path and minor variations in bulk composition. Interface domains are best preserved in rocks from Xanthi and Sidironero; in these samples, thin, homogeneous, garnet‐stable rims only partially overprint and crosscut the interface domain. In contrast, rocks from Kimi followed a higher‐temperature trajectory and the zircon grains grew large rim domains that overprinted much of the interface domain and the detrital core. Zircon grains from plagioclase‐rich versus quartz‐rich domains within samples from Sidironero show differences in texture, which indicates that local bulk composition can affect what evidence of UHP metamorphism is preserved. Collectively, these samples provide a new, durable marker of metamorphism in UHP rocks and yield new insight about which factors affect the preservation of UHP textures. 

ABSTRACT Debates over whether and how populations are regulated have recently shifted away from detecting and instead towards quantifying the strength of density dependence and its variation among systems. Yet, the degree of variation in density‐dependent mortality and the factors driving this variation remain poorly understood. Here, we conducted a meta‐analysis of 38 reef fish species across 56 studies, which yielded 147 estimates of intraspecific density‐dependent mortality, primarily during early or small life stages. The magnitude of density‐dependent mortality (the increase in the per capita mortality rate due to one fish per unit area of habitat) was surprisingly inconsistent both within and among species. Several factors emerged as drivers of variation. Predators amplified the negative effects of density, and density‐dependent mortality was greater for species that typically colonize at low densities or achieve larger maximum sizes. However, even within a single species, the strength of density‐dependent mortality varied dramatically—often by several orders of magnitude—and sometimes changed sign. This heterogeneity likely reflects multiple processes acting together, including environmental context (e.g., predator density or refuge availability), traits of the focal organism (e.g., size) and methodological differences (e.g., study design) among studies. Our results underscore the need for future efforts to quantify and report ancillary variables and strive to identify how much these factors contribute to population regulation. 

ABSTRACT Community or volunteer participation in research has the potential to significantly help mobilize the wealth of biodiversity and functional ecological data housed in natural history collections. Many such projects recruit community scientists to transcribe specimen label data from images; a next step is to task community scientists with conducting straightforward morphological measurements (e.g., body size) from specimen images. We investigated whether community science could be an effective approach to generating significant body size datasets from specimen images generated by museum digitization initiatives. Using the community science platform Notes from Nature, we engaged community scientists in a specimen measurement task to estimate body size (i.e., intertegular distance) from images of bee specimens. Community scientists showed high engagement and completion of this task, with each user measuring 43.6 specimens on average and self‐reporting successful measurement of 98.0% of the images. Community scientist measurements were significantly larger than measurements conducted by trained researchers, though the average measurement error was only 2.3%. These results suggest that community science participation could be an effective approach for bee body size measurement, for descriptive studies or for research questions where this degree of expected error is deemed acceptable. For larger‐bodied organisms (e.g., vertebrates), where modest measurement errors represent a smaller proportion of body size, community science approaches may be particularly effective. Methods we present here may serve as a blueprint for future projects aimed at engaging the public in biodiversity and collections‐based research efforts.