Biology subjects

Buccheri, E.

Publications and source records attributed to Buccheri, E..

4 recordsLinked to original sources

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↗

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↗