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<p>Recruitment is a critical demographic bottleneck that governs coral population persistence and reef recovery, yet the fine-scale environmental gradients that regulate settlement remain poorly resolved. Submarine groundwater discharge (SGD) creates spatially structured, multivariate biogeochemical gradients in nearshore reefs, altering salinity, carbonate chemistry, and nutrient availability. Here, we tested whether SGD regulates settlement of the brooding coral <i>Pocillopora acuta</i> through physiological effects on larvae and demographic feedbacks mediated by adult coral populations. We combined controlled 24-h settlement experiments using groundwater–seawater dilutions with an 8-month in situ deployment of settlement tiles along natural SGD gradients at two reefs in Moorea, French Polynesia, characterized by distinct groundwater chemistry and hydrodynamics. In laboratory assays, settlement responses to SGD were site dependent: Larvae exposed to groundwater from one site exhibited increased settlement with increasing SGD influence, whereas no effect of SGD was detected at the second site. In situ, SGD exhibited nonlinear relationships with both adult <i>Pocillopora</i> cover and settler abundance at one reef, peaking at intermediate groundwater influence. Across both reefs, adult coral cover positively predicted settler density, consistent with a demographic feedback linking local stock to recruitment. Together, these results demonstrate that SGD can directly alter larval settlement and indirectly regulate recruitment by restructuring adult populations. Our findings reveal that spatially heterogeneous, land-based inputs may fuel demographic feedbacks at ecologically relevant scales. As groundwater fluxes shift with climate change, understanding how multivariate environmental gradients shape recruitment will be essential for predicting reef resilience in a rapidly changing world.</p>

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Land-based inputs drive demographic feedbacks in a tropical brooding coral

  • 期刊论文

  • 发表日期：

    2026年7月24日

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  • Hannah E. Merges,
  • Danielle M. Barnas,
  • Nyssa J. Silbiger

摘要

Recruitment is a critical demographic bottleneck that governs coral population persistence and reef recovery, yet the fine-scale environmental gradients that regulate settlement remain poorly resolved. Submarine groundwater discharge (SGD) creates spatially structured, multivariate biogeochemical gradients in nearshore reefs, altering salinity, carbonate chemistry, and nutrient availability. Here, we tested whether SGD regulates settlement of the brooding coral Pocillopora acuta through physiological effects on larvae and demographic feedbacks mediated by adult coral populations. We combined controlled 24-h settlement experiments using groundwater–seawater dilutions with an 8-month in situ deployment of settlement tiles along natural SGD gradients at two reefs in Moorea, French Polynesia, characterized by distinct groundwater chemistry and hydrodynamics. In laboratory assays, settlement responses to SGD were site dependent: Larvae exposed to groundwater from one site exhibited increased settlement with increasing SGD influence, whereas no effect of SGD was detected at the second site. In situ, SGD exhibited nonlinear relationships with both adult Pocillopora cover and settler abundance at one reef, peaking at intermediate groundwater influence. Across both reefs, adult coral cover positively predicted settler density, consistent with a demographic feedback linking local stock to recruitment. Together, these results demonstrate that SGD can directly alter larval settlement and indirectly regulate recruitment by restructuring adult populations. Our findings reveal that spatially heterogeneous, land-based inputs may fuel demographic feedbacks at ecologically relevant scales. As groundwater fluxes shift with climate change, understanding how multivariate environmental gradients shape recruitment will be essential for predicting reef resilience in a rapidly changing world.