RESEARCH IN MARINE SCIENCE

Healthy coral fragment growing on a Reefscapers coral frame (Sheraton Maldives)

Insights into Coral Spawning Patterns on Maldivian Reef Ecosystems

Coral reproductions - stages of broadcast spawning

These preliminary findings may be subject to change. None should be cited without prior written permission from Reefscapers.

Introduction

Coral reproduction is a fundamental process retaining coral reef functions and structure (PDF: Baird et al., 2015). Understanding coral reproduction timings is crucial to elucidate our knowledge on characteristics regulating populations and communities, particularly through recruitment rates and ecosystem connectivity (Kool, Moilanen & Treml, 2013; and Done, Gilmour & Fisher, 2015). This has important implications on coral reef management and conservation (Richmond, 1997).

Little remains documented about the extent of spawning synchronicity on the world’s seventh largest coral reef ecosystem, comprising 3.14 % of global reefs, here in the Maldives (Dhunya, Huang & Aslam, 2017). This lack of publicised data on histological sampling to distinguish the onset of gametogenesis in-situ to amalgamate regional spawning patterns hinders our understanding of coral reproductive biology at a regional scale and limits our ability to assess shifts in reproductive phenology over time.

Reefscapers Coral spawning research Marine Savers Maldives

Methodology

We examined baseline environmental cues, spawning patterns, timings and gametogenic cycles of Acroporidae in naturally occurring wild colonies and asexually propagated restored colonies. We analysed shallow water reefs across Landaa Giraavaru (Baa Atoll), Kuda Huraa (Kaafu Atoll), and Sheraton Full Moon (Kaafu Atoll).

Results

Differences in tide height across 4 days in November 2021, with time of spawning overlayed for 3 species of Acroporidae in Baa atoll.

Reefscapers corals spawning Maldives tides

The difference in day of species spawning is highly significant between atolls in Autumn (p<0.001) and significantly different in Spring (p<0.05). For both seasons Kaafu Atoll spawns before Baa Atoll. This is linked to significantly different environmental conditions at each latitude: low tide (p<0.001), wind speed (p<0.0) and tidal depth (p<0.001).

Reefscapers coral spawning Maldives Marine Savers results

The number of coral colonies per species spawning during Autumn 2021 in Kaafu and Baa Atolls.

The number of coral colonies per species spawning during Spring 2022 in Kaafu and Baa Atolls.

Reefscapers coral spawning Maldives Marine Savers

Key Findings

- 18 species of Acroporidae observed spawning and one species of Goniastrea
- Two spawning cycles occur each year during spring and autumn
- Multi-specific synchronous spawning and split spawning observed
- Kaafu Atoll coral species typically spawns before Baa Atoll
- Environmental cues identified that coincide with spawning windows
- Species spawning variation across atolls and seasons

Future Implications

Coral bleaching decreases reproductive potential of survivors (Leinbach et al., 2021), reduces gamete numbers (Ward, Harrison & Hoegh-guldberg, 2002) and leads to a long-term impact on reproduction over multiple spawning periods (Levitan et al., 2014).
As the persistence of Maldivian reef ecosystems rely on natural recruitment through reproduction, it is imperative we understand reproductive rates to predict population recovery following disturbance. This information will help us to understand regional spawning patterns and shifts in reproductive phenology over time.

Researchers: Margaux Monfared, Simon Dixon, Amelie Carraut, Kate Sheridan, Matthew Gledhill, Thomas Le Berre & Alejandra Woolrich

Acknowledgements: Thanks to the whole Reefscapers team, and to our Resort colleagues at both Four Seasons and Sheraton for their support.

These preliminary findings may be subject to change. None should be cited without prior written permission from Reefscapers.

Presentation of our work at the Maldives Marine Symposium 2022 (arranged by the MMRI)

What is Coral Spawning? Enjoy our short documentary ‘New Beginnings’

PUBLISHED RESEARCH PAPERS

Identifying Key Factors for Coral Survival in Reef Restoration Projects Using Deep Learning

Author(s): Gaétan Morand, Simon Dixon, Thomas Le Berre.
Journal of Aquatic Conservation: Marine and Freshwater Ecosystems
Publication date: 07 September 2022 > https://doi.org/10.1002/aqc.3878
The raw data files (SQL & CSV) are made available by SEANOE Sea scientific open data edition

Abstract

Coral restoration has emerged globally as a form of life support for coral reefs, awaiting urgent mitigation of anthropogenic pressures. Yet its efficiency is difficult to assess, as sizeable transplantation programmes handle hundreds of thousands of fragments, with survival rates inherently time intensive to monitor. Owing to limited available data, the influence of most environmental and methodological factors is still unknown.
To address this issue, machine learning and computer vision were used to track individual colonies’ survival, in a world first. Fragments from several species of Acropora and Pocillopora were transplanted over 12 sites across two Maldivian atolls. These colonies grew on coral frames, placed between 1 and 30 m deep. Analysis of monitoring pictures provided health and growth data on 77,574 individual coral colonies to inform the influence of genus, depth, initial fragment size, and substrate on their survival.
Among 77,574 fragments, individual survival rate was 31% after 2 years (21% after 4 years), which is much lower than most reported results. Deeper placement was an important success factor for Acropora transplants, but not for Pocillopora. In both genera, smaller initial fragment size was key to increased survival rates. Pocillopora fragments survived better than Acropora fragments at shallow depths (≤7 m), regardless of initial fragment size. Deeper, both genera had similar survival rates, which were influenced by initial fragment size and depth with comparable importance. During the mid-2019 heat wave, previously transplanted Acropora fragments were 38% more likely to die than Pocillopora fragments.
Overall, the total volume of live coral steadily increased over time, by more than 3.7 × 106 cm3 per year, as the volume increase in surviving fragments more than compensated for the volume loss due to mortality. This finding supports the use of targeted coral restoration to accelerate reef recovery after mass bleaching events.

Coral Restoration Effectiveness: Multiregional Snapshots of the Long-Term Responses of Coral Assemblages to Restoration

Author(s): Margaux Y. Hein, Roger Beeden, Alastair Birtles, Naomi M. Gardiner, Thomas Le Berre, Jessica Levy, Nadine Marshall, Chad M. Scott, Lisa Terry, Bette L. Willis.
Publication date: 17 April 2020, Diversity 2020, 12(4), 153; https://doi.org/10.3390/d12040153

Abstract

Coral restoration is rapidly becoming a mainstream strategic reef management response to address dramatic declines in coral cover worldwide. Restoration success can be defined as enhanced reef functions leading to improved ecosystem services, with multiple benefits at socio-ecological scales. However, there is often a mismatch between the objectives of coral restoration programs and the metrics used to assess their effectiveness. In particular, the scales of ecological benefits currently assessed are typically limited in both time and space, often being limited to short-term monitoring of the growth and survival of transplanted corals.

In this paper, we explore reef-scale responses of coral assemblages to restoration practices applied in four well-established coral restoration programs. We found that hard coral cover and structural complexity were consistently greater at restored compared to unrestored (degraded) sites. However, patterns in coral diversity, coral recruitment, and coral health among restored, unrestored, and reference sites varied across locations, highlighting differences in methodologies among restoration programs. Altogether, differences in program objectives, methodologies, and the state of nearby coral communities were key drivers of variability in the responses of coral assemblages to restoration. The framework presented here provides guidance to improve qualitative and quantitative assessments of coral restoration efforts and can be applied to further understanding of the role of restoration within resilience-based reef management.

ONGOING RESEARCH

Reefscapers at Sheraton Maldives coral reef propagation

Reefscapers Diaries

During the global coral bleaching event of 2016, we started recording detailed observations of the natural reefs and our coral frames.
These monthly diaries document our efforts to mitigate the effects of coral bleaching, and increase biodiversity of marine species.

Coral Spawning in the Maldives

Read about our pioneering research, studying coral spawning events both on the wild reef and on our propagated coral frames.
We have also transferred coral gametes to our Lab, and successfully settled coral larvae to produce coral polyps (a first in the Maldives).

Maldivian Corals Database

What are the most commonly observed species of corals in the Maldives?
Which species of corals are recommended for coral propagation and reef regeneration?
How can we differentiate between the different species of corals in the Maldives?

Propagating Coral Microfragments

Scleractinian “massive” stony corals are essential to reef ecosystems, but are neglected by global restoration research (fewer than 5% of studies). Propagation tends to focus on a small group of faster-growing coral species for ease of proliferation and rapid results.

National Turtle ID Project

We invite citizen scientists from around the Maldives to submit turtle photos to us for inclusion in our national database.
The turtle facial scutes (scales) form a unique pattern (similar to fingerprints in humans) enabling identification of individuals.