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Recovery trajectories of oceanic reef ecosystems following multiple mass coral bleaching events

February 2022
Marine Biology 169(2)

DOI:10.1007/s00227-021-04013-8

Authors:

Charles Marsh

University of Oxford

Jude Bijoux

Private University Consortium Ltd

Gilberte Gendron

Sustainable Ocean Seychelles

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Climate-induced mass bleaching events are one of the greatest threats to coral reefs, causing widespread loss of coral cover. Drivers of recovery and adaptation for coral reefs in the face of repeated large-scale disturbances are unclear, with marked differences across geographies. Using a monitoring dataset lasting from 2005 to 2018, we documented the response of coral reefs of northwest Mahé in the granitic Seychelles islands following the 1998 and 2016 mass bleaching events. We analysed trends in coral cover, coral community composition and key fish trophic group densities for 24 sites. Coral cover increased almost fourfold from 2005 to 2015 with 42.1% mean coral cover in 2015, highlighting a recovery from the 1998 bleaching event dominated by Acropora growth forms. Impacts of the 2016 bleaching event were less acute than the 1998 one. However, following the 2016 bleaching event, coral cover significantly decreased to 16.1% mean cover in 2017, marked by a sharp decrease of Acropora corals and branching growth forms. Corallivorous, herbivorous and piscivorous fish densities were positively correlated with coral cover from 2005 to 2016. These findings highlight the dominant role of Acropora in recovery from mass coral bleaching events. It also shows the importance of time-series datasets in understanding coral recovery dynamics and their use in an integrated management approach to building reef resilience.

Location of the Seychelles north of Madagascar, location of Mahé within the Inner Seychelles Islands, and the location of the survey sites along the northwest Mahé coastline. Dark symbols represent granitic sites and light grey symbols carbonate sites, triangles represent sites outside bays and circles sites inside bays. Site numbers are linked with names in table S1. The two marine parks areas of Baie Ternay and Port Launay are shaded light grey

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Predicted total coral cover (c, d) and Acropora coral cover (e, f) from 2005 to 2018, at sites with carbonate (c, e) and granitic (d, f) substrates, and for sites located in protected (dark grey) and unprotected (black) areas. Predictions are the summed effects of mixed generalised additive models (± s.e.) with random effects excluded. Monthly mean sea-surface temperatures (a; SST) and precipitation (b) during the same time-series are presented for comparison above. Vertical polygons represent the duration of a bleaching event between February–July 2016

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Average cover of coral growth forms; ACB—Acropora branching, ACD—Acropora Digitate, ACE—Acropora encrusting, ACT—Acropora tabular, HCB—Hard Coral Branching, HCE—Hard Coral Encrusting, HCM—Hard Coral Massive, HCS—Hard Coral Sub-massive from 2005 to 2018. Growth forms displayed were sampled all years, other categories and missing growth forms are included in other

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Changes in coral assemblages (growth forms composition) over the years visualised with non-metric multidimensional scaling (nMDS). Data square root transformed, stress 0.037. The star diagram shows the vectors for the growth form categories

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Predicted fish abundance for corallivores (a), herbivores (c) and piscivores (b, d) from 2005 to 2018 for sites located in protected (dark grey) and unprotected (black) areas. Predictions are the summed effects of mixed generalised additive models (± s.e.) with random effects excluded. All other predictors were held at mean levels and for deep sites. For piscivore abundance predictions are for sites inside bay areas, and results for carbonate (b) and granitic (d) sites are presented. Predictions illustrating all significant model terms are presented in the Online Resources 3–5. Vertical polygons represent the duration of a bleaching event between February–July 2016

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Marine Biology (2022) 169:23

https://doi.org/10.1007/s00227-021-04013-8

ORIGINAL PAPER

Recovery trajectories ofoceanic reef ecosystems followingmultiple

mass coral bleaching events

FannyVessaz1,4· CharlesJ.Marsh7,8· JudeBijoux2· GilberteGendron3,5· ChristopheMason‑Parker4,6

Received: 14 December 2020 / Accepted: 14 December 2021 / Published online: 18 January 2022

Abstract

Climate-induced mass bleaching events are one of the greatest threats to coral reefs, causing widespread loss of coral cover.

Drivers of recovery and adaptation for coral reefs in the face of repeated large-scale disturbances are unclear, with marked

diﬀerences across geographies. Using a monitoring dataset lasting from 2005 to 2018, we documented the response of coral

reefs of northwest Mahé in the granitic Seychelles islands following the 1998 and 2016 mass bleaching events. We analysed

trends in coral cover, coral community composition and key ﬁsh trophic group densities for 24 sites. Coral cover increased

almost fourfold from 2005 to 2015 with 42.1% mean coral cover in 2015, highlighting a recovery from the 1998 bleach-

ing event dominated by Acropora growth forms. Impacts of the 2016 bleaching event were less acute than the 1998 one.

However, following the 2016 bleaching event, coral cover signiﬁcantly decreased to 16.1% mean cover in 2017, marked by

a sharp decrease of Acropora corals and branching growth forms. Corallivorous, herbivorous and piscivorous ﬁsh densi-

ties were positively correlated with coral cover from 2005 to 2016. These ﬁndings highlight the dominant role of Acropora

in recovery from mass coral bleaching events. It also shows the importance of time-series datasets in understanding coral

recovery dynamics and their use in an integrated management approach to building reef resilience.

Keywords Climate change· Coral bleaching· Coral reefs· Fish trophic guilds· Community structure· Recovery

trajectories· Western Indian Ocean· Protected areas

Introduction

Over the last several decades, global changes (ocean warm-

ing, acidiﬁcation) exacerbated by local human impacts (e.g.

pollution, sedimentation, coastal development, overﬁshing)

have intensiﬁed, leading to degradation of coral reef eco-

systems (Gardner etal. 2003; Hoegh-Guldberg etal. 2007;

Hughes etal. 2018). The rate of ocean warming has likely

increased twofold since 1993, and the occurrence of marine

heat waves has doubled in frequency since 1982 (Bindoﬀ

etal. 2019). Climate change is now recognised as the pri-

mary threat to the world’s tropical coral reef ecosystems,

with temperature-induced mass coral bleaching events pre-

dicted to become more frequent and severe (van Hooidonk

etal. 2016; Hughes etal. 2018). Repeated and more intense

mass coral bleaching disturbances undermine coral reefs

resilience, impairing their ability to function and recover

from such events (Hughes etal. 2010; Hodgson etal. 2015).

One of the most noticeable eﬀects of reef degradation is

the loss of live coral cover and reef rugosity (Hoegh-Gul-

dberg etal. 2007; Hughes etal. 2018; Magel etal. 2019).

Responsible Editor: S. Harii.

* Christophe Mason-Parker

c_mason_parker@hotmail.com

1 Blue Ventures, London, UK

2 Island Biodiversity andConservation Centre, University

ofSeychelles, Victoria, Seychelles

3 Seychelles National Parks Authority, Victoria, Seychelles

4 Global Vision International Seychelles, Victoria, Seychelles

5 Sustainable Ocean Seychelles, Victoria, Seychelles

6 Marine Conservation Society Seychelles, Victoria, Seychelles

7 Department ofEcology andEvolutionary Biology, Yale

University, NewHaven, CT, USA

8 Center forBiodiversity andGlobal Change, Yale University,

NewHaven, CT, USA

Content courtesy of Springer Nature, terms of use apply. Rights reserved.

ResearchGate has not been able to resolve any citations for this publication.

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