Biology subjects

Doropoulos, C.

Publications and source records attributed to Doropoulos, C..

10 recordsLinked to original sources

bioRxiv2025

Larval seedboxes: a modular and effective tool for scaling coral reef restoration

Natural recovery of degraded coral reefs is constrained by low larval recruitment, limiting restoration at ecologically meaningful scales. While propagule-based approaches have proven effective in plant-dominated systems, scaling larval restoration for sessile invertebrates like corals remains challenging. Traditional coral larval methods rely on net enclosures, restricting impact to small areas (<75 m2). We developed and tested a modular, passive larval delivery system - the larval seedbox - to overcome these spatial constraints. Each unit (600 x 500 x 300 mm; 11 kg) enables delayed release of competent larvae near the benthos, enhancing substrate encounter rates over broader areas. At Lizard Island (Great Barrier Reef), five seedboxes delivered [~]14 million larvae across [~]2 ha of degraded reef. Larval release coincided with slack currents to facilitate local retention and subsequent dispersal. Settlement was assessed on 234 tiles placed in concentric arrays around each seedbox. After 48 hours, 85% of tiles had settlers (up to 1,041 per tile), with mean densities 24-times greater than background levels. Enhanced settlement was directly quantified across >470 m2, with spatial modelling estimating >3,000 m2 via tidally driven dispersal. The larval seedbox enables unrestrained, scalable coral larval seeding and represents a practical advance toward broad-scale reef restoration.

ecology↗

bioRxiv2025

Proximity and current alignment drives fertilisation success in a broadcast-spawning coral

As coral populations decline under climate change and other stressors, surviving corals will become increasingly isolated. While Allee effects that reduce gamete encounters and fertilisation success may lead to reproductive and recruitment failure, the critical population densities and distances between individuals required to maintain viable populations remains uncertain. Here, we investigate the links between colony isolation and fertilisation patterns using an experimentally manipulated patch of the broadcast spawning tabular coral, Acropora hyacinthus. Corals were arranged in a clustered radial design, with colonies arranged at increasing distances radiating downstream from a central spawning aggregation. Fertilisation and paternity assignment analyses were used to examine the influence of parental distance, current alignment, colony size, and genetic relatedness. Fertilisation success declined sharply with increasing distance among corals, and paternity assignments indicated most parents were located within 3 m of each other, underscoring the importance of colony proximity. Additionally, fertilisation success was highest for colonies positioned downstream of the central cluster, and 84% of sequenced progeny were sired by colonies located directly upstream. Simulations of natural reef spatial population distributions projected onto a virtual grid, incorporating empirically derived parentage distances, indicated that populations remained well-mixed at typical adult densities in nearby reefs. However, as densities decreased to 1 colony per 100 m-2 (i.e. 0.01 colonieslllm-2), reproductive isolation and the formation of patchy breeding units became prevalent. Overall, our findings highlight that the spatial arrangement and isolation of corals on reefs, and subsequent Allee effects on fertilisation, can jeopardise the reproductive success of broadcast spawning corals. Conservation efforts are needed to help maintain viable coral populations and successful reproductive aggregations for degraded reef systems.

ecology↗

bioRxiv2025

Optimising fertilisation kinetics models for broadcast spawning corals in the genus Acropora

Synchronous spawning is a specialised adaptation to maximise fertilisation success in free spawning sessile invertebrates. There are many factors that drive and limit reproduction in such benthic invertebrates including localised hydrodynamic forcing, adult density dependence, and fine-scale gamete interactions, all of which are difficult to measure in situ. Therefore, measures to manage or restore reproductive populations of sessile invertebrates rely in part on adequate modelling of spawning processes at localised scales. Fertilisation kinetics of spawning events has been modelled for many free spawning marine invertebrate taxa, yet little work has been done to parameterise such models for hermaphroditic corals. This study used experimentally derived coral-specific parameters and optimisation protocols to improve model predictions of fertilisation outcomes for Acropora kenti (formerly A. "Maggie" tenuis) and A. digitifera. Three fine scale parameters that are difficult to measure experimentally - fertilisation efficiency (Fe), egg concentration (E0), and polyspermy block strength (tb) - were estimated using optimisation, and medians and 95% confidence intervals were derived for each parameter and species. For A. kenti the median optimised Fe value was 0.0194 (0.0027-0.0776), and tb was 0.1000 (0.1000-0.1000). For A. digitifera, the median optimised Fe value was 0.0013 (0.0002-0.0030), and tb was 10.0000 (2.4703- 10.0000). Further, sensitivity analyses suggest that kinetics models are the most sensitive to changes in Fe parameter values, as well as species-specific metrics like sperm swimming speed and egg size. Results will inform biophysical coral fertilisation models to better predict reproductive outcomes and support management decisions that safeguard natural reef recovery.

systems biology↗

bioRxiv2025

Impacts of wind-driven hydrodynamics on the early stages of coral development

Coral spawning has evolved to occur during relatively calm hydrodynamic conditions. However, moderate to high surface winds are often present on spawning nights in specific regions, with many unknown impacts to the early life-history stages of corals. Here, we mechanistically examine the sensitivity of fertilisation and larval development to increasing wind speeds for four common species of hermaphroditic corals on the Great Barrier Reef: Acropora kenti, A. millepora, A. spathulata, and Platygyra daedalea. Wind intensities relevant to coral spawning seasons were simulated by downscaling location-specific, historical wind speeds to laboratory flumes. Generally, fertilisation success declined as duration of exposure increased and was often lowest at the highest wind intensity equating to 15 knots in situ. Embryo damage, deformity, and fragmentation increased with exposure time, but varied across species. Four days following spawning, damaged and fragmented embryos had the highest mortality rates (76-82% and 70-73%) compared to intact embryos (26% and 52%) for A. kenti and A. spathulata, respectively. Experimental parameters were used to fit a 3D Fluid Dynamics model with outputs confirming that water surface elevations, velocity, and turbulence energy increased by up to 10%, 40%, and 50% respectively as winds intensified, likely explaining the physical drivers of the deleterious effects observed. Overall, results from this study indicate that suboptimal spawning conditions reduce propagule production, which may diminish recovery potential, thus require consideration when planning management strategies to safeguard coral reproduction.

systems biology↗

bioRxiv2025

The influence of larval retention on coral recruitment

Marine broadcast spawners typically exhibit bipartite life-histories with distinct pelagic larvae and benthic phases. The transition between phases shapes benthic populations, but the rate of larval arrival to a reef is largely unknown due to challenges in accurately measuring supply. Once larvae arrive to a reef, reduced current flow and velocity, facilitate the transition from the water column to the benthos for inefficient swimming larvae. Yet, for coral reefs characterised by complex hydrodynamics and tides, slack current conditions typically last 1.5-3 hours and it remains unclear if such short retention periods drive significant recruitment. This study mechanistically examined the effects of water retention on the settlement of coral larvae from the water column to the benthos and subsequent longer-term recruitment over 15-months. Brief periods of slack currents (<3-hours) retained larvae in unconstrained larval supply treatments, resulting in settlement rates 40-times higher than natural, background rates. Constrained and longer retention of larvae under nets for 2.5- and 24-hours resulted in 4-7-times higher initial settlement than the unconstrained treatment and 305-times higher than background rates. However, after 15-months, similar numbers of surviving recruits were observed across all larval supply treatments, highlighting the effects of density-dependent population regulation. Observations from recruitment tiles show survival rates of coral recruits after 15-months were low (<0.25), even though gregarious settlement behaviour and settlement close to tile edges improved survival. In contrast, observations from the natural substrate show survival rates were 2.5-3.5-times higher than tiles after 15-months, indicating density-independent survival due to optimal niche space and less space limitation. Therefore, when larval supply is high and gregarious behaviour prominent, key vital rates including recruitment and mortality derived from settlement tiles are likely overestimated, as substrate and microhabitat properties between tiles and natural reef environment vary. Overall, our study highlights the prominent role of slack current conditions and local retention of larvae in facilitating the supply-to-settlement transition, and how this interacts with density-dependent processes post-settlement. Our findings underscore the need to investigate how the interaction strengths of pre-and post-settlement processes modulate early coral recovery to best model recovery trajectories for conservation and restoration prioritisation.

ecology↗

bioRxiv2024

Allee effects, spawning asynchrony, and mixed reproductive modes in a common mass spawning coral

Understanding strategies of organisms that utilise multiple modes of reproduction presents a complex challenge for evolutionary biologists. Platygyra daedalea, a common reef-building coral with unclear reproductive boundaries between morphological species, illustrates these complexities. Here, we evaluate the contribution of these reproductive modes in the coral P. daedalea at Heron Island, on the southern Great Barrier Reef. We tagged and sequenced eighteen coral colonies, representing various degrees of spatial clustering, along a 130-m stretch of shallow reef slope. During spawning, divers collected eggs from each colony and placed them in mesh containers within the spawn slick, allowing free movement of sperm for fertilisation. High levels of spawning asynchrony were observed, potentially indicating distinct genetic clusters within the putative species, which resulted in low fertilisation success (1.5%). Notably, of those fertilised eggs, paternity assignments revealed that all resulting embryos were self-fertilised, with no cross-fertilisation occurring. The adult population showed evidence of two genetically distinct subpopulations, along with levels of spatial autocorrelation and inbreeding. This evidence supports the notion of small breeding populations within larger assemblages, density-dependent population effects, and localised recruitment. Selfing may serve as a reproductive assurance mechanism in such populations, which may be more hierarchically structured than previously thought. Given the lack of evidence for in situ outcrossed fertilisation in this natural coral population during split spawning, it appears that P. daedalea may rely on limited high-density patches of adults for successful cross-fertilisation, utilise atypical modes of reproduction when at low densities, and/or sustain its population through limited progeny.

ecology↗

bioRxiv2024

Going with the flow: leveraging reef-scale hydrodynamics for upscaling larval-based restoration

Anthropogenic pressures are impacting coastal marine ecosystems, necessitating large-scale interventions to accelerate recovery. Propagule-based restoration holds the potential for restoring shallow coastal systems at hectare scales by harnessing natural dispersal. However, predicting propagule dispersal remains challenging due to the complex hydrodynamic nature of coastal marine ecosystems and the complex behaviours of marine propagules. To improve predictions of fine-scale larval dispersal patterns, we developed a 3D reef-scale ([~]30 m resolution) dispersal model for Lizard Island, Australia, with the aim to predict the effect of island scale hydrodynamics on the distribution of coral spawn slicks and larvae. Using in situ field observations, and dispersal simulations, we assessed the models capability to (1) forecast hydrodynamic conditions, (2) predict coral spawn slick convergence zones for collection efforts, and (3) identify optimal locations and timeframes where high particle residence time may enhance local settlement following larval delivery to damaged reefs. Predictions of convergence zones in the upper water column aligned well with field observations of coral spawn slicks. At the reef benthos, the model captured variability in current speed and direction at [~]58% of studied locations. At other locations, the model did not resolve hydrodynamic conditions due to sheltering effects and associated hydrodynamic processes occurring at a scale below 50 m. At locations where the model performed well, propagules could remain within a one-hectare area around the delivery site for 5 to 15 hours depending on locations and the timing of larval release. These high retention conditions were infrequent but occurred at least once at 15 of the 25 studied sites. Observations of local currents a posteriori confirmed model predictions, showing periods of little water movement lasting from 6.5 to 15 hours. Overall, our study highlights fine-scale dispersal modelling as a key tool for scaling up larval-based reef restoration, while also acknowledging the need for better predictions of local conditions in complex, shallow environments. Applications of fine-scale modelling, coupled with local knowledge of reproductive timing and larval behavioural ecology, assist with the mass collection of propagules upon release and in identifying areas and times of optimal larval deployment to achieve the greatest impact.

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↗

bioRxiv2022

Colouring coral larvae for tracking dispersal

O_LIEcologists have long sought to understand larval dispersal characteristics of benthic marine invertebrates. Direct quantification of coral larvae dispersal has proven challenging, in part due to their complex life-history, minute size, and widespread dispersal at the scale of kilometres. Instead, indirect methods such as particle modelling, chemical signatures, and genetic correlation are often used in dispersal studies. C_LIO_LIHere, we develop a direct method of quantifying larval dispersal by applying vital stains to coral larvae, allowing differentiation and direct tracking of millions of larvae from the pelagic dispersal stage through to the sedentary stages of attachment and metamorphosis on coral reefs. C_LIO_LINeutral red and Nile blue stains were extremely effective at staining coral larvae, while alizarin red and calcein blue showed no visible results. Differences in toxicity to vital stains was noted among species, with Acropora spp. exhibiting decreased larval survival and settlement, while Merulinidae spp. were unaffected. By experimenting with different incubation times and concentrations, our results indicate that neutral red can be effectively applied for short periods (<20 minutes) at low concentrations (1-100 mg l-1), whereas Nile blue requires longer stain times (>60 minutes) at higher concentrations (100-1000 mg l-1). C_LIO_LIThe strong colour of both neutral red and Nile blue stains was retained by newly settled larvae in lab settings upwards of five days following settlement, providing a direct method of differentiating between newly settled larvae on reefs. Field-validation of Nile blue applied to coral larvae from wild-captured coral slicks demonstrates the efficacy of staining across a diverse range of coral taxa. C_LIO_LIVital staining provides a simple, rapid (<60 mins), and low cost (<AUD$0.00001 per larva) method of colouring coral larvae that allows for direct tracking of dispersal and recruitment in studies of reef connectivity and restoration. C_LI

ecology↗

bioRxiv2021

Selecting species for restoration in foundational assemblages

O_LIHumans have long sought to restore species, but little attention has been directed at how to best select a subset of foundation species for maintaining rich assemblages that support ecosystems, like coral reefs and rainforests that are increasingly threatened by environmental change. C_LIO_LIWe propose a two-part hedging approach that selects optimized sets of species for restoration. The first part acknowledges that biodiversity supports ecosystem functions and services, and so it takes precaution against loss by ensuring an even spread of phenotypic traits. The second part maximizes species and ecosystem persistence by weighting species based on characteristics that are known to improve ecological persistence--e.g., abundance, species range and tolerance to environmental change. C_LIO_LIUsing existing phenotypic trait and ecological characteristic data for reef building corals, we identified sets of ecologically persistent species by examining marginal returns in occupancy of phenotypic trait space. We compared optimal sets of species with those from the worlds southern-most coral reef which naturally harbors low coral diversity to show these occupy much of the trait space. Comparison with an existing coral restoration program indicated that current corals used for restoration only cover part of the desired trait space and may be improved by including species with different traits. C_LIO_LISynthesis and applications. While there are many possible criteria for selecting species for restoration, the approach proposed here addresses the need to insure against unpredictable losses of ecosystem services by focusing on a wide range of phenotypic traits and ecological characteristics. Furthermore, the flexibility of the approach enables the functional goals of restoration to vary depending on environmental context, stakeholder values, and the spatial and temporal scales at which meaningful impacts can be achieved. C_LI

ecology↗