Biology subjects

Haller-Bull, V.

Publications and source records attributed to Haller-Bull, V..

4 recordsLinked to original sources

bioRxiv2025

A rapidly closing window for coral persistence under global warming

Summary paragraphCoral reefs around the world are threatened by recurrent marine heatwaves causing mass coral bleaching and mortality1. Mitigating future warming impacts requires strategic management2 that adopts a long-term lens. Global analyses of projected heatwaves3,4 are critical for decision-making but how disturbance refugia, coral life-histories and adaptation interact with warming is unknown. Here, we simulate coral eco-evolutionary dynamics across >3,800 individual reefs of Australias iconic Great Barrier Reef under the current suite of climate projections5. We forecast a rapid coral decline before mid-century regardless of emissions scenario. Under the most likely warming6, corals may continue to decline throughout the century. However, corals may recover after mid-century provided that warming is sufficiently slow, allowing thermal adaptation to keep pace with temperature changes - as projected if warming does not exceed 2{degrees}C. Higher emission scenarios would drive most reefs to a near collapse. Future resilient reefs were mostly found in bleaching refugia, which also possessed a greater diversity of thermal phenotypes. Although cool-adapted corals disperse to thermal hotspots, there was no evidence of gene swamping undermining thermal adaptation. While opportunities exist to build management strategies that promote adaptation in thermal refugia and warm spots, curbing the rate of warming by 2050 is crucial for coral persistence.

ecology↗

bioRxiv2024

Reproducing within-reef variability in coral dynamics with a metacommunity modelling framework

Reef systems span spatial scales from 10s to 100s and even 1000s of kilometres, with substantial spatial variability across these scales. Managing and predicting the future of coral reefs requires insights into reef functioning at all spatial scales. However, investigations of reef functioning often consider individual reefs as the smallest unit (10s of kilometres), despite substantial spatiotemporal variability occurring within-reefs (100s of meters). We developed C[~]scape, a coral metacommunity modelling framework that integrates the demography of corals with population-level responses to physical and environmental spatial layers, to simulate a mosaic of interacting coral communities across a heterogenous seascape. Coral communities are linked using biophysical connectivity modelling. Coral community growth is modelled with a logistic growth model, with the intrinsic growth parameter determined from taxa-specific Integral Projection Models to incorporate demographic mechanisms. Site-specific coral habitat parameters, derived from satellite-based geomorphic and benthic habitat maps, define the maximum coral cover and are used to modulate community growth spatially and temporally as a function of the available space suitable for corals. These parameters are a proxy for the many interacting physical and environmental factors -- e.g., depth, light, wave exposure, temperature, and substrate type -- that drive within-reef variability in coral demography. Using a case study from the Great Barrier Reef, we show that modulating community growth using site-specific habitat parameters enables more accurate hindcasts of coral cover dynamics, while overlooking within-reef variability may lead to misleading conclusions about metacommunity dynamics. More generally, C[~]scape provides a valuable framework for predicting spatiotemporal dynamics of coral communities within and between reefs, offering a mechanistic approach to test a range of management and restoration options.

ecology↗

bioRxiv2019

Optimizing functional groups in ecosystem models: Case study of the Great Barrier Reef

Uncertainty is inherent in ecosystem modelling, however its effects on modelling results are often poorly understood or ignored. This study addresses the issue of structural uncertainty or, more specifically, model resolution and its impact on the analysis of ecosystem vulnerability to threats. While guidelines for node assignments exist, they are not underlined with quantitative analysis. Different resolutions of a coral reef network are investigated by comparing the simulated network dynamics over time in various threat scenarios. We demonstrate that the error between a higher-resolution and a lower-resolution models increases, first slowly then rapidly with increased degree of node aggregation. This informs the choice of an optimal model resolution whereby a finer level of a food web representation yields only minimal additional accuracy, while increasing computational cost substantially. Furthermore, our analysis shows that species biomass ratio and the production ratio are important parameters to guide node aggregation to minimize the error.

ecology↗

bioRxiv2019

Superadditive and subadditive dynamics are not inherent to the types of interacting threat

Species and ecosystems usually face more than one threat. The damage caused by these multiple threats can accumulate nonlinearly: either subadditively, when the joint damage of combined threats is less than the damages of both threats individually added together, or superadditively, when the joint damage is greater than the two individual damages added together. These additivity dynamics are commonly attributed to the nature of the threatening processes, but conflicting empirical observations challenge this assumption. Here, we use a theoretical model to demonstrate that the additivity of threats can change with different magnitudes of threat impacts (effect of a threat on the population parameter, like growth rate). We use a harvested single-species population model to integrate the effects of multiple threats on equilibrium abundance. Our results reveal that threats do not always display consistent additive behavior, even in simple systems. Instead, their additivity depends on the magnitudes of the impacts of two threats, and the population parameter that is impacted by each threat. In our model specifically, when multiple threats have a low impact on the growth rate of a population, they display superadditive dynamics. In contrast, threats that impact the species carrying capacity are always additive or subadditive. These dynamics can be understood by reference to the curvature of the relationship between a given population parameter (e.g., growth) and equilibrium population size. Our results suggest that management actions can achieve amplified benefits if they target low-amplitude threats that affect the growth rate, since these will be in a superadditive phase. More generally, our results suggest that cumulative impact theory should focus more than previously on the magnitude of the impact on the population parameter, and should be cautious about attributing additive dynamics to particular threat combinations.

ecology↗