Biology subjects

Madin, J. S.

Publications and source records attributed to Madin, J. S..

At least 19 recordsLinked to original sources

bioRxiv2026

Adult corals enhance juvenile recruitment through cumulative ecological niche construction

Ecosystem engineers are ecological niche constructors: by modifying local environments, they alter the conditions under which organisms establish, persist and interact. Although niche construction is often framed as a population-level evolutionary feedback, it could also operate at the assemblage level when communities collectively shape their environments and filter future recruitment. Reef-building corals provide a perfect system to test this idea because adult colonies form three-dimensional carbonate structures that can persist after colony death, creating an inherited habitat for subsequent coral generations. Here, we tested whether coral recruitment to the juvenile stage was associated with local adult coral abundance, reef structure, and larval settlement supply. Combining spatially explicit coral censuses, photogrammetric reef digital elevation models and data from settlement tiles across 15 reef sites at two time points at Jiigurru, Great Barrier Reef, we found that juvenile abundance increased additively on the log scale with adult abundance and with fractal dimension, a metric of fine-scale structural complexity. Surface rugosity had weaker effects, and interactions between adult abundance and habitat structure were limited, indicating largely additive, rather than synergistic or antagonistic, effects. Our results show that both adult assemblages and the concurrent structural complexity, consistent with assemblage-level niche construction and ecological inheritance theory, shape coral recruitment.

ecology↗

bioRxiv2026

The builder's legacy: persistent reef structure creates a window for coral recovery after adult loss

Coral reef recovery depends on successful juvenile recruitment, yet which local factors govern early coral demography remains poorly resolved. Adult coral cover and reef structural complexity are widely hypothesized to regulate juvenile success, but their independent and interactive effects have not been mechanistically disentangled, nor has the relative role of living adult tissue versus persisting structural framework been clarified. Here, combining in situ coral size-structure surveys with high resolution photogrammetry across 405 reef segments spanning the main Hawaiian Islands, we quantify how adult cover and three-dimensional reef structure, measured as rugosity and fractal dimension, jointly shape juvenile coral densities. We reveal nonlinear relationships between juvenile density and adult cover, peaking at intermediate (~8%) coral cover, with fine-scale surface complexity and vertical relief exerting opposing influences across the cover gradient. Together, these reveal a structural legacy window in which reduced adult cover relaxes constraints on juvenile establishment while the three-dimensional habitat built by those adults persists. This decoupling of biological loss from structural loss creates a transient opportunity for population renewal, with intermediate-cover reefs supporting juveniles across the broadest range of structural configurations. More generally, our results show how the physical legacy of ecosystem engineers can continue to regulate population recovery after the organisms that create it have declined.

ecology↗

bioRxiv2026

Coral settlement module designs for scalable reef restoration

The global coral reef crisis has prompted restoration initiatives worldwide. Targeting the coral larval stage is among the most scalable approaches as recruitment operates over large spatial scales. It thus represents one of the best levers for coral population recovery. Active coral larval seeding has shown considerable success, and passive substrate engineering has emerged as a promising complementary strategy. Coral settlement modules featuring helix recesses have increased settlement and survival by up to 80-fold on small experimental units, but whether these results translate to tools deployable at the scale of thousands of units, remains yet an open question. Here, we transferred structural features from successful experimental coral settlement designs into production-ready concrete modules to (i) evaluate coral recruitment on five designs at four reef sites differing in flow regime and coral cover over one year; (ii) compare production-scale performance against experimental clay modules and natural reef substrate; and (iii) identify key parameters for large-scale production. The helix recess geometry of coral settlement modules outperformed the featureless control design approximately 20-fold and exceeded natural reef recruitment at least 3- to 32-fold. The helix features were successfully transferred from experimental clay to production-scale concrete modules, yielding comparable settlement densities when standardized to crevice length, which proved to be the biologically relevant unit of available habitat. Production feasibility was demonstrated by producing 690 modules for deployment on a hybrid reef on the west side of Oahu, Hawaii. The passive coral larval recruitment approach presented here could substantially improve the logistical and economic feasibility of large-scale coral reef restoration. This approach requires neither coral larval rearing, handling, nor coral fragmenting, and is compatible with active larval seeding where genetic diversity or larvae supply are limiting factors. The coral settlement modules can be cast in standardized concrete molds at precast facilities. Modules have demonstrated consistent coral recruitment enhancement across reef environments with contrasting flow and coral cover. Deploying mixed arrays of helix-recess structures with designs offering multi-level complexity and three-dimensional rugosity maximizes outcomes for coral, fish, and invertebrate communities simultaneously. Site selection is the most critical deployment decision and should consider larval supply, hydrodynamics, and substrate stability which drive recruitment outcomes more than design choice alone. The modules offer a range of application potential, ranging from integration into existing coastal infrastructure over stand-alone reef restoration approaches, to substrate-consolidating interconnected arrangements.

ecology↗

bioRxiv2026

Coral reef ecosystem functions in a human-dominated world

The metabolic processes sustaining coral reefs, from carbonate and primary production to secondary production, remain poorly integrated and rarely quantified simultaneously at global scales. This hampers our ability to predict global responses to accelerating human pressures and manage coral reef functioning. Using metabolic scaling and bioenergetic models applied to surveys from 1,100 reefs worldwide, we provide a global, standardized quantification of 14 ecosystem functions spanning benthic (corals and algae) and fish communities. Our analysis reveals a continuous functional spectrum of global coral reefs organized along four dominant axes: 1) primary production, 2) calcification and habitat structure, 3) secondary biomass production and consumption, and 4) biomass turnover. Functions mediated by fish and benthic communities show weak associations at the global scale rather than tight coupling. Climate stressors reduced calcification and local human impacts lowered secondary production. Yet these directional effects unfolded against a backdrop of substantial natural variability in reef functional configurations, such that heavily and minimally impacted reefs overlap substantially in the global functional space. Temporal analyses across three representative reef systems further revealed that functional trajectories following disturbance are context-dependent, with no universal pattern of recovery across locations. This continuous and context-dependent functional spectrum challenges the notion of universal functional benchmarks and supports locally tailored conservation strategies.

ecology↗

bioRxiv2025

Tracking morphological development in stony corals

The shape of reef-building corals largely determines how they interact with their environment and the ecosystem services they provide. However, morphology is not fixed. As corals grow and develop from singular polyps to mature adult colonies, they experience pronounced changes in their morphology. This developmental trait variation remains poorly quantified in corals, despite their importance as ecosystem engineers. To address this gap, we used photogrammetry to track the morphological development of wild coral colonies across six size-independent metrics designed to capture variation in volume compactness, surface complexity, and top-heaviness. Size-trait models and analyses of colony movement through morphological trait space revealed that small colonies shared compact morphologies and only later diverged along growth-form-specific developmental trajectories. Massive corals largely retained stable shapes as they grew, whereas non-massive colonies became less compact, more top-heavy, and in most cases, more complex. Despite these differences, there was still overlap between growth forms in their developmental trajectories through morphospace. These findings highlight that traditional categorical growth forms mask important developmental variation, particularly early in coral ontogeny. By applying a quantitative trait-based framework, this study improves understanding of coral morphological development and provides a foundation for linking individual growth trajectories to broader reef ecosystem dynamics.

ecology↗

bioRxiv2025

Demographic insights for coral restoration

O_LICoral reef decline has prompted a global surge in reef restoration initiatives. The success of initiatives that aim to sustain coral populations or assemblages will depend on demographic principles. Restoration strategies generally follow two demographic pathways: supplemental approaches, which increase population numbers through the repeated addition of recruits, fragments, or adults, without fundamentally altering long-term population dynamics; and structural approaches, which enhance vital rates-growth, survival, or reproduction- through changes that modify the demographic processes governing population growth on a sustained basis, either extrinsically (e.g., herbivory, habitat protection) or intrinsically (e.g., assisted evolution). Some interventions, such as supplemental feeding, may temporarily improve vital rates but still function as supplemental approaches because benefits persist only while interventions continue. C_LIO_LIWe synthesized 28 coral matrix population models spanning morphologically diverse coral species from the Caribbean, Hawaii, and the Great Barrier Reef to quantify supplemental and structural changes needed to increase population growth. C_LIO_LIResults highlight two consistent demographic leverage points for which population growth was most sensitive: (1) survival of reproductive adults and (2) successful recruitment. Improving adult survival or recruitment by 20% through structural means produced a 5% increase in population growth rate across population on average, assuming the whole population was affected. By contrast through supplemental means, the same increase required [~]100 recruit outplants or 5-10 adult outplants per 1,000 individuals in a population annually. For large populations typical of restoration targets (105-107 individuals), this translates to 103 adult and 104 recruit outplants per year--levels rarely logistically or economically feasible. C_LIO_LIThese findings yield two key implications. First, supplemental interventions are inefficient for large populations and demand sustained, large-scale effort, even when they temporarily enhance growth or survival. Second, strategies enhancing vital rates across broad geographic areas represent the most effective means of boosting coral abundance, including habitat protection, alleviation of environmental stressors, and interventions which promote long-term survival and recruitment. Our demographic framework underscores that if the restoration goal is sustained increases in coral cover, success depends less on repeated supplements and more on interventions that produce lasting improvements in vital rates. C_LI

ecology↗

bioRxiv2025

Cylindrical, pylon-like structures with helix recesses enhance coral larval recruitment

The decline of coral reefs requires scalable restoration strategies to enhance natural recovery processes such as coral larval recruitment. Previous research has shown that conical structures with helix recesses substantially increase settlement and early survival. However, the applicability of this microhabitat design with helix recesses in broader engineering contexts has yet to be assessed. Hereby, we tested (1) whether helix recesses can be transferred from conical dome geometries to space-efficient cylindrical pylon-like geometries, and (2) whether they can be implemented with different materials. In a field experiment in K[a]neohe Bay, Hawaii, coral recruitment was monitored over six months on cylindrical and conical structures incorporating an optimized helix profile. Cylindrical modules supported recruitment densities similar to those on conical designs, demonstrating a successful transfer of the microhabitat design to compact geometries. Planar recruit densities were [~]300 times higher across all structures, compared to those observed on nearby natural reefs. These results show that the helix recess design is functionally robust across both module shapes and materials. Cylindrical structures with integrated helix recesses, therefore, represent a practical, low-cost design element that can be incorporated in coastal engineering and restoration projects to enhance coral settlement. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=80 SRC="FIGDIR/small/680805v2_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@126b7cborg.highwire.dtl.DTLVardef@ec7c4corg.highwire.dtl.DTLVardef@1d49a78org.highwire.dtl.DTLVardef@e97189_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2024

Habitat complexity defines global biological and societal landscapes

The three-dimensional structure of land- and seascapes links biotic and abiotic processes to shape how organisms use their environments. Much effort has been dedicated to understanding this relationship between structural complexity and biodiversity. However, tailored, system-specific approaches to quantifying structural complexity preclude cross-system comparisons. Expanding a geometric framework developed for quantifying the structural complexity of local-scale surface environments, we generate high-resolution, global maps of the key complexity measures of height range, rugosity, and fractal dimension. We illustrate how patterns in these complexity attributes correspond with the distribution of ecosystems, land cover types, and the presence of people across the globe. Using geometric tools to understand how structural complexity is associated with the arrangement of natural and socio-ecosystems, we can better predict their responses to ongoing global change.

ecology↗

bioRxiv2024

Coral reef habitat complexity decreases and diversifies local availability of light

The spatial distribution of environmental conditions can determine where organisms can and cannot live. When the distribution of microhabitats within a landscape is mediated by the shape of its surface, structural complexity can indirectly affect environmental niche distributions. This study investigates how light availability patterns change along a gradient of landscape complexity measured as surface rugosity and height range in tropical shallow reefs. We used 260,000 high frequency and high spatial resolution light measurements across 903 locations to determine the proportion of light that is available at the reef surface. We find that light available on the reef surface is highly variable, with close locations within reef sites experiencing up to 25.7 mol/m2d of daily photon input difference. After accounting for light attenuation due depth, light availability decreases with increasing surface rugosity: a unit increase in local surface rugosity corresponds to an 11-29% decrease in light availability. Local surface complexity can affect the distributions of light availability at local scales, while broader extent site metrics do not capture this variability. Our results suggest that structural complexity enhances local environmental variability, and its indirect effects on other environmental variables and their interactions are essential for understanding ecosystem processes.

ecology↗

bioRxiv2024

Optimized recess design in artificial structures dramatically enhances coral settlement and survival

The worldwide decline of coral reefs, driven by climate change and local stressors, demands new, scalable restoration approaches. Coral larvae offer significant potential for reef recovery, as a single coral colony can release millions of offspring, with almost all larvae dying before finding a suitable habitat. Building upon an iterative design process, incorporating a gradient of sizes and angles based on larval settlement preferences observed in nature, we developed and tested seven 3D-printed settlement module designs, proposed to enhance coral larvae habitat. We studied the settlement and survival of coral larvae on the settlement modules integrating these designs and adjacent reef structures in K[a]neohe Bay over one year. Helix recesses dramatically outperformed other structural features, increasing settlement by [~]80-fold and post-settlement survival over a year by 20-50-fold compared to control modules. In contrast to natural reef substrates, settlement on modules with helix recesses increased by [~]70-fold. We identified the recess dimensions and light levels preferred as settlement habitat. In a parallel tank experiment, we explored the impacts of hydrodynamics on the settlement and survival of Montipora capitata larvae on modules with helix recesses. We found that settlement was more pronounced under high-flow conditions, suggesting a crucial role of micro-scale hydrodynamics in entraining settling corals. These findings highlight the potential of helix recesses to significantly improve early coral recruitment, a critical bottleneck in reef restoration. By integrating these structures into artificial reefs and coastal infrastructure, our approach offers an innovative, scalable, and cost-effective solution to enhance reef resilience and accelerate ecosystem recovery in a changing ocean.

ecology↗

bioRxiv2024

habtools: an R package to calculate 3D metrics for surfaces and objects

O_LITechnological advances in three-dimensional imaging techniques have opened the door to advanced morphological analyses and habitat mapping for biologists and ecologists. C_LIO_LIAt the same time, the challenge of translating complex 3D data into meaningful metrics that can be used in conjunction with biological data currently hinders progress and accessibility. C_LIO_LIWe introduce habtools, an R package that provides R functions to efficiently calculate complexity and shape metrics from DEMs, 3D meshes and 2D shapes as well as some helper functions to facilitate workflow. C_LIO_LIWe expect the functionality of habtools to continue to expand as new metrics and faster methods become available, and welcome new contributions and ideas. C_LI

ecology↗

bioRxiv2023

Widespread reductions in body size are paired with stable assemblage biomass.

Biotic responses to global change include directional shifts in organismal traits. Body size, an integrative trait that determines demographic rates and ecosystem functions, is often thought to be shrinking in the Anthropocene. Here, we assess the prevalence of body size change in six taxon groups across 5,032 assemblage time-series spanning 1960-2020. Using the Price equation to partition this change into within-species body size versus compositional changes, we detect prevailing decreases in body size through time. Change in assemblage composition contributes more to body size changes than within-species trends, but both components show substantial variation in magnitude and direction. The biomass of assemblages remains remarkably stable as decreases in body size trade-off with increases in abundance. One-Sentence SummaryVariable within-species and compositional trends combine into shrinking body size, abundance increases and stable biomass.

ecology↗

bioRxiv2022

Fine-scale variability in coral bleaching and mortality during a marine heatwave

Coral bleaching and mortality can show significant spatial and taxonomic heterogeneity at local scales, highlighting the need to understand the fine-scale drivers and impacts of thermal stress. In this study, we used structure-from-motion photogrammetry to track coral bleaching, mortality, and changes in community composition during the 2019 marine heatwave in K[a]ne ohe Bay, Hawai i. We surveyed 30 shallow reef patches every 3 weeks for the duration of the bleaching event (August-December) and one year after, resulting in a total of 210 large-area, high-resolution photomosaics that enabled us to follow the fate of thousands of coral colonies through time. We also measured environmental variables such as temperature, sedimentation, depth, and wave velocity at each of these sites, and extracted estimates of habitat complexity (rugosity R and fractal dimension D) from digital elevation models to better understand their effects on patterns of bleaching and mortality. We found that up to 80% of corals experienced moderate to severe bleaching in this period, with peak bleaching occurring in October when heat stress (DHW) reached its maximum. Mortality continued to accumulate as bleaching levels dropped, driving large declines in more heat-susceptible species (77% loss of Pocillopora cover) and moderate declines in heat-tolerant species (19% and 23% for Porites compressa and Montipora capitata, respectively). Declines in live coral were accompanied by a rapid increase in algal cover across the survey sites. Spatial differences in bleaching were significantly linked to habitat complexity and coral species composition, with reefs that were dominated by Pocillopora experiencing the most severe bleaching. Mortality was also influenced by species composition, fractal dimension, and site-level differences in thermal stress. Our results show that spatial heterogeneity in the impacts of bleaching are driven by a mix of environmental variation, habitat complexity, and differences in assemblage composition.

ecology↗

bioRxiv2021

Coral settlement and recruitment responses to reef fish foraging and trait diversity

The process of coral recruitment is crucial to the functioning of coral reef ecosystems, as well as recovery of coral assemblages following disturbances. Fishes can be key mediators of this process by removing benthic competitors like algae, but their foraging impacts are capable of being facilitative or harmful to coral recruits depending on species traits. Reef fish assemblages are highly diverse in foraging strategies and the relationship between this diversity with coral settlement and recruitment success remains poorly understood. Here, we investigate how foraging trait diversity of reef fish assemblages covaries with coral settlement and recruitment success across multiple sites at Lizard Island, Great Barrier Reef. Using a multi-model inference approach incorporating six metrics of fish assemblage foraging diversity (foraging rates, trait richness, trait evenness, trait divergence, herbivore abundance, and sessile invertivore abundance), we found that herbivore abundance was positively related to both coral settlement and recruitment success. However, the correlation with herbivore abundance was not as strong in comparison with foraging trait diversity metrics. Coral settlement and recruitment exhibited a negative relationship with foraging trait diversity, especially with trait divergence and richness in settlement. Our findings provide further evidence that fish play a role in making benthic habitats more conducive for coral settlement and recruitment. Because of their ability to shape the reef benthos, the variation of fish biodiversity is likely to contribute to spatially uneven patterns of coral recruitment and reef recovery.

ecology↗

bioRxiv2021

Coral niche construction: coral recruitment increases along a coral-built structural complexity gradient

Niche construction is the process through which organisms modify environmental states in ways favourable to their own fitness. Here, we test experimentally whether scleractinian corals can be considered niche constructors. In particular, we demonstrate a positive feedback involved in corals building structures which facilitate recruitment. Coral larval recruitment is a key process for coral reef persistence. Larvae require low flow conditions to settle from the plankton, and hence the presence of colony structures that can break the flow is expected to facilitate coral recruitment. Here, we show an increase in settler presence on artificial tiles deployed in the field along a gradient of coral-built structural complexity. Structural complexity had a positive effect on settlement, with an increase of 15,71% of settler presence probability along the range of structural complexity considered. This result provides evidence that coral built structural complexity creates conditions that facilitate coral settlement, while demonstrating that corals meet the criteria for ecological niche construction.

ecology↗

bioRxiv2021

Shaping coral traits: plasticity more than filtering

The structure of ecosystems is usually determined by the shape of the organisms that build it, commonly known as ecosystem engineers. Understanding to what extent plasticity and environmental filtering determine variation in ecosystem engineer physical structure is necessary to predict how ecosystem structure may change. Here, we explored coral survival and the plasticity of morphological traits that are critical for habitat provision in coral reefs. We conducted a reciprocal clonal transplant experiment in which branching corals from the genus Porites and Acropora were moved to and from a deep and a shallow site within a lagoon in the Maldives. Survival and trait analyses showed that transplant destination consistently induced the strongest changes, particularly among Acropora spp. The origin of the corals only marginally affected some of the traits. We also detected variation in the way individuals from the same species and site differentiate their shape, showing that traits linked to habitat provision are phenotypically plastic. The results suggest coral phenotypic plasticity plays a stronger role than environmental filtering, in determining zonation of coral morphologies, and consequently the habitats they provide for other taxa.

ecology↗

bioRxiv2020

Disturbance-induced changes in size-structure promote coral biodiversity

Reef-building coral assemblages are typically species-rich, yet the processes maintaining coral biodiversity remain poorly understood. Disturbance has long been believed to promote coral species coexistence by reducing the strength of competition. However, such disturbance-induced effects have since been shown to be insufficient on their own to prevent competitive exclusion. Nevertheless, Modern Coexistence Theory has revealed other mechanisms by which disturbance and, more generally, environmental variation can favour coexistence. Here, we formulate, calibrate, and analyze a size-structured, stochastic coral competition model using field data from two common colony morphologies. These two coral morphologies, tabular and digitate, differ in their size-dependent vulnerability to dislodgement caused by wave action. We confirm that fluctuations in wave action can promote coral species coexistence. However, using a recently proposed partitioning framework, we show that, contrast to previous expectations, temporal variability in strength of competition did not promote coexistence. Instead, coexistence was enabled by differential fluctuations in size-dependent mortality among competitors. Frequent and intense disturbances resulted in monocultures of digitate corals, which are more robust to wave action than tabular corals. In contrast, infrequent or weak disturbances resulted in monocultures of tabular corals. Coexistence was only possible under intermediate levels of disturbance frequency and intensity. Given the sensitivity of coexistence to disturbance frequency and intensity, anthropogenic changes in disturbance regimes are likely to affect biodiversity in coral assemblages in ways that are not predictable from single population models.

ecology↗

bioRxiv2020

A geometric basis for surface habitat complexity and biodiversity

Structurally complex habitats tend to contain more species and higher total abundances than simple habitats. This ecological paradigm is grounded in first principles: species richness scales with area, and surface area and niche density increase with three-dimensional complexity. Here we present a geometric basis for surface habitats that unifies ecosystems and spatial scales. The theory is framed by fundamental geometric constraints among three structure descriptors—surface height, rugosity and fractal dimension—and explains 98% of surface variation in a structurally complex test system: coral reefs. We then show how coral biodiversity metrics (species richness, total abundance and probability of interspecific encounter) vary over the theoretical structure descriptor plane, demonstrating the value of the theory for predicting the consequences of natural and human modifications of surface structure.Competing Interest StatementThe authors have declared no competing interest.View Full Text

ecology↗