Biology subjects

Gouezo, M.

Publications and source records attributed to Gouezo, M..

3 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

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

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↗