Severe Bleaching Events Research Articles

Dissecting coral recovery: bleaching reduces reproductive output in Acropora millepora

AbstractIncreasingly frequent and severe bleaching events driven by climate change are decreasing coral populations worldwide. Recovery of these populations relies on reproduction by the survivors of such events including local and upstream larval sources. Yet, corals that survive bleaching may be impaired by sublethal effects that suppress reproduction, reducing larval input to reefs, and consequently impeding recovery. We investigated the impact of the 2020 mass-bleaching event on Acropora millepora reproduction on inshore, turbid reefs in Woppaburra sea Country (the Keppel Islands), to improve our understanding of the effects of bleaching on coral populations. A. millepora experienced high bleaching incidence but low mortality across the island group during this event and thus constituted an ideal population to investigate potential sublethal effects on reproductive output. Six months after the heat wave, and just prior to spawning, we collected, decalcified, and dissected samples from 94 tagged A. millepora colonies with a known 2020 bleaching response, to investigate the relationships between stress severity and reproduction. Despite having regained their pigmentation, we detected a significant reduction in fecundity in colonies that had bleached severely. Considering the impact of the bleaching event on the coral population sampled (i.e., mortality, bleaching severity and colony size), coupled with reductions in fecundity, we estimated a total decrease in population-level reproductive output of 21%. These results suggest that reduced reproductive output may impact recovery of coral populations following bleaching and should be considered alongside traditional estimates of coral mortality.

A gauge of coral physiology: re-examining temporal changes in Endozoicomonas abundance correlated with natural coral bleaching.

Bacteria contribute to many physiological functions of coral holobionts, including responses to bleaching. The bacterial genus, Endozoicomonas, dominates the microbial flora of many coral species and its abundance appears to be correlated with coral bleaching. However, evidences for decoupling of bleaching and Endozoicomonas abundance changes have also been reported. In 2020, a severe bleaching event was recorded at reefs in Taiwan, providing a unique opportunity to re-examine bleaching-Endozoicomonas association using multiple stony corals in natural environments. In this study, we monitored tissue color and microbiome changes in three coral species (Montipora sp., Porites sp., and Stylophora pistillata) in Kenting National Park, following the bleaching event. All tagged Montipora sp. and Porites sp. recovered from bleaching within 1 year, while high mortality occurred in S. pistillata. Microbiome analysis found no correlation of Endozoicomonas relative abundance and bleaching severity during the sampling period, but found a stronger correlation when the month in which bleaching occurred was excluded. Moreover, Endozoicomonas abundance increased during recovery months in Montipora sp. and Porites sp., whereas in S. pistillata it was nearly depleted. These results suggest that Endozoicomonas abundance may represent a gauge of coral health and reflect recovery of some corals from stress. Interestingly, even though different Endozoicomonas strains predominated in the three corals, these Endozoicomonas strains were also shared among coral taxa. Meanwhile, several Endozoicomonas strains showed secondary emergence during coral recovery, suggesting possible symbiont switching in Endozoicomonas. These findings indicate that it may be possible to introduce Endozoicomonas to non-native coral hosts as a coral probiotic.

Natural recovery of corals after severe disturbance.

Ecosystem recovery from human-induced disturbances, whether through natural processes or restoration, is occurring worldwide. Yet, recovery dynamics, and their implications for broader ecosystem management, remain unclear. We explored recovery dynamics using coral reefs as a case study. We tracked the fate of 809 individual coral recruits that settled after a severe bleaching event at Lizard Island, Great Barrier Reef. Recruited Acropora corals, first detected in 2020, grew to coral cover levels that were equivalent to global average coral cover within just 2 years. Furthermore, we found that just 11.5 Acropora recruits per square meter were sufficient to reach this cover within 2 years. However, wave exposure, growth form and colony density had a marked effect on recovery rates. Our results underscore the importance of considering natural recovery in management and restoration and highlight how lessons learnt from reef recovery can inform our understanding of recovery dynamics in high-diversity climate-disturbed ecosystems.

Marine Heatwave Caused Differentiated Dysbiosis in Photosymbiont Assemblages of Corals and Hydrocorals During El Niño 2015/2016.

Reef corals have been threatened by climate change, with more frequent and intense bleaching events leading to extensive coral mortality and loss of coral cover worldwide. In the face of this, the corals' photosymbiont assemblages have received special attention as a key to better understand the bleaching process and its recovery. To assess the effects of thermal anomalies, the coral Mussismilia harttii and the hydrocoral Millepora alcicornis were monitored through the El Niño 2015/2016 at a Southwestern Atlantic (SWA) coral reef. A severe bleaching event (57% of colonies bleached) was documented, triggered by a < 3 °C-week heatwave, but no mortality was detected. The hydrocoral was more susceptible than the scleractinian, displaying bleaching symptoms earlier and experiencing a longer and more intense bleaching event. The composition of photosymbionts in the M. alcicornis population was affected only at the rare biosphere level (< 5% relative abundance), with the emergence of new symbionts after bleaching. Conversely, a temporary dysbiosis was observed in the M. harttii population, with one of the dominant symbiodiniaceans decreasing in relative abundance at the peak of the bleaching, which negatively affected the total β-diversity. After colonies' complete recovery, symbiodiniaceans' dominances returned to normal levels in both hosts. These results highlight critical differences in how the two coral species cope with bleaching and contribute to the understanding of the role of photosymbionts throughout the bleaching-recovery process.

Optimized spatial and temporal pattern for coral bleaching heat stress alerts for China's coral reefs

Most studies on coral bleaching alerts use common Degree Heating Week (DHW) thresholds; however, these may underestimate historical patterns of heat stress for coral reef ecosystems. Taking an optimized DHW threshold for coral bleaching alerts for Coral Reef Watch (CRW) and Coral Reef Temperature Anomaly Database (CoRTAD) products, we analyzed the precise spatial and temporal pattern of heat stress on China's coral reefs from 2010 to 2021 in the South China Sea (SCS) and the Beibu Gulf (BG). We compared acute heat stress using common and optimized thresholds. Results indicated that the ocean warming rate in 2010–2021 was approximately 0.43 ± 0.22 °C/10a, showing a significant increase in the northern SCS and the BG. More severe bleaching events were predicted by the optimized thresholds and the high-frequency areas were mainly in the northern SCS. The number and intensity of years with severe heat stress anomalies was in the order 2020 > 2014 > 2010 > 2015. Heat stress duration was the longest in the Xisha Islands among offshore archipelagos, and longest in 2020–2021 in Weizhou Island in BG in the relative high-latitude inshore reefs. These abnormal events were mainly caused by El Niño, but La Niña was also involved in 2020.

Inconsistent Coral Bleaching Risk Indicators Between Temperature Data Sources

AbstractCoral reefs are facing severe threats and are at risk of accelerated decline due to climate change‐induced changes in their environment. Ongoing efforts to understand the mechanisms of coral response to warming rely on multiple sources of temperature data. Yet, it remains uncertain whether the Sea Surface Temperature (SST) data used for coral reef studies are consistent among different data products, despite potential implications for conservation. A better understanding of the consistency among the different SST data applied to coral reefs may facilitate the fusion of data into a standard product. This will improve monitoring and understanding of the impact of global warming on coral reefs. Four types of SST data across North‐Western and South‐Western Australia are compared to assess their differences and ability to observe high thermal stress during historical coral bleaching events. The four SST data sources included those derived from Global Circulation Models, NOAA CoralTemp SST product, ESA CCI SST product, and coral core derived SST. Coral bleaching risk indicators, Degree Heating Week (DHW), and Degree Heating Month (DHM) were calculated using these sources and compared for consistency. DHW and DHM were inconsistent among data sets and did not accurately reflect high thermal stress metrics during moderate and severe bleaching events. Some reefs did not experience bleaching in spite of high DHWs and DHMs, suggesting a mismatch in data scales, or perhaps other oceanographic factors and coral adaptation. By exploring the differences and similarities among these four data sources, this study highlights the need to compare existing indicators of thermal stress from different data sets.

Increased dominance of heat-tolerant symbionts creates resilient coral reefs in near-term ocean warming

Climate change is radically altering coral reef ecosystems, mainly through increasingly frequent and severe bleaching events. Yet, some reefs have exhibited higher thermal tolerance after bleaching severely the first time. To understand changes in thermal tolerance in the eastern tropical Pacific (ETP), we compiled four decades of temperature, coral cover, coral bleaching, and mortality data, including three mass bleaching events during the 1982 to 1983, 1997 to 1998 and 2015 to 2016 El Niño heatwaves. Higher heat resistance in later bleaching events was detected in the dominant framework-building genus, Pocillopora, while other coral taxa exhibited similar susceptibility across events. Genetic analyses of Pocillopora spp. colonies and their algal symbionts (2014 to 2016) revealed that one of two Pocillopora lineages present in the region (Pocillopora "type 1") increased its association with thermotolerant algal symbionts (Durusdinium glynnii) during the 2015 to 2016 heat stress event. This lineage experienced lower bleaching and mortality compared with Pocillopora "type 3", which did not acquire D. glynnii. Under projected thermal stress, ETP reefs may be able to preserve high coral cover through the 2060s or later, mainly composed of Pocillopora colonies that associate with D. glynnii. However, although the low-diversity, high-cover reefs of the ETP could illustrate a potential functional state for some future reefs, this state may only be temporary unless global greenhouse gas emissions and resultant global warming are curtailed.

Rapid recovery of coral communities from a mass bleaching event in the summer of 2016, observed in Amitori Bay, Iriomote Island, Japan

Devastating bleaching of coral communities at Amitori Bay, Iriomote Island, Japan, occurred in 2016 during the third global mass bleaching event in 2014–2017. The present study documented changes in coral communities in Amitori Bay from just before until after the 2016 bleaching event (2016–2020), by measuring coral cover and recruitment at nine sites (with two additional sites in 2018) in the bay. Spawning rates of acroporid corals were also monitored from 2017 to 2019 by visual observation and using bundle collectors to observe how long the effect of bleaching persisted. Reductions of 64.7 and 89.5% from 2016 to 2017 were observed in cover and recruitment of all coral families, respectively. Coral cover of all coral families recovered to pre-bleaching levels by 2020 and recruitment in 2020 was about two times greater than the pre-bleaching level. These results mirrored those of acroporids. Spawning rates of Acropora corals increased significantly from 40.6% in 2017 to 90.0% in 2019. Recovery of coral cover 4 years after the severe bleaching event was likely related to regrowth of remnants and of surviving juveniles of < 5 cm. The sudden increase in recruitment was likely driven by a combination of larval supply from other populations, increased numbers of reproductive adults, increases in spawning rates, and increased larval retention in the bay due to wind conditions in 2020. This study suggests that coral communities as in Amitori Bay will be critical for local-scale community persistence, serving as both source and sink populations.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00227-022-04091-2.

Observations of coral and cryptobenthic sponge fluorescence and recruitment on autonomous reef monitoring structures (ARMS)

Fluorescence imaging of benthic communities is a widely used tool for determining the rate of hard coral recruitment in tropical reefs. Whilst fluorescent proteins are well-studied in scleractinian corals, less is understood about their distribution and function in other sessile reef invertebrates. This short study examines fluorescence images of benthic communities on Autonomous Reef Monitoring Structures (ARMS) from a remote and protected Indian Ocean reef system. We compare the abundance of adult and juvenile hard corals across three sites and between the topside and underside of ARMS recruitment plates. We also discuss observations of skeletal fluorescence in sponges, as well as uneven green fluorescent protein (GFP) concentrations across adult coral colonies. Our findings provide an insight into the recovery of shallow reefs previously hit by severe bleaching events and highlight the potential of ARMS fluorescence imaging for the analysis of cryptobenthic communities.

Macroalgal canopies provide corals limited protection from bleaching and impede post-bleaching recovery

Coral bleaching, the result of loss of endosymbiotic dinoflagellates, as well as post-bleaching recovery can be exacerbated or mitigated by a range of local factors such as depth, turbidity, and natural or artificial shading providing protection for corals during thermal anomalies. On many reefs, losses in coral cover coincide with increases in upright macroalgae growth. Such shifts in benthic communities are generally viewed as negative, whereby macroalgae can outcompete corals for space, and affect adult coral health and fitness. However, the canopy provided by upright macroalgae could reduce solar irradiance and provide refuge for understorey corals during heat events, decreasing coral bleaching and subsequent mortality. To test this hypothesis, this study manually removed macroalgae from experimental plots on a macroalgae-dominated fringing reef at Magnetic Island in the central inshore region of the Great Barrier Reef, comparing the subsequent bleaching during and recovery following a severe heat stress event. In March 2020, sea surface temperature at Magnetic Island reached 31.4 °C, leading to bleaching. Surveys of coral communities undertaken at the peak of accumulated severe heat stress (DHW of 9.3 °C-weeks) in control and macroalgae removal plots showed that, averaged across coral morphological groups, there was no overall difference in bleaching prevalence in algal-removal and control plots (21.1% and 20.8% of the community bleached; respectively). However, bleaching prevalence varied within morphological groups, with massive morphology corals demonstrating higher probability of bleaching in removal plots compared to controls (0.26 and 0.09, respectively). Bleaching severity (i.e. percent of the colony tissue bleached) was consistent across control and removal plots (83.2% and 80.4% of colony area, respectively, averaged across morphologies), with branching corals demonstrating the lowest severity. Surveys were repeated in July after heat stress had dissipated, with coral communities in algal-removal plots displaying greater recovery than controls (i.e. 86.1% and 75.6% healthy, respectively, model estimated mean averaged across morphologies). Encrusting corals in control plots were the slowest to recover. We conclude that macroalgae provided limited refuge for branching and encrusting corals at the height of the thermal event, likely due to the severity of the accumulated heat stress, while massive corals enjoyed some degree of protection from the canopy. Greater recovery of coral communities in removal plots may potentially be explained by reduced competition with adjacent macroalgae. This study provides important insights into the interactions between these two dominant benthic groups and supports previous work finding macroalgae inhibits coral recovery after severe bleaching events.

Thermal stress triggers productive viral infection of a key coral reef symbiont.

Climate change-driven ocean warming is increasing the frequency and severity of bleaching events, in which corals appear whitened after losing their dinoflagellate endosymbionts (family Symbiodiniaceae). Viral infections of Symbiodiniaceae may contribute to some bleaching signs, but little empirical evidence exists to support this hypothesis. We present the first temporal analysis of a lineage of Symbiodiniaceae-infecting positive-sense single-stranded RNA viruses ("dinoRNAVs") in coral colonies, which were exposed to a 5-day heat treatment (+2.1 °C). A total of 124 dinoRNAV major capsid protein gene "aminotypes" (unique amino acid sequences) were detected from five colonies of two closely related Pocillopora-Cladocopium (coral-symbiont) combinations in the experiment; most dinoRNAV aminotypes were shared between the two coral-symbiont combinations (64%) and among multiple colonies (82%). Throughout the experiment, seventeen dinoRNAV aminotypes were found only in heat-treated fragments, and 22 aminotypes were detected at higher relative abundances in heat-treated fragments. DinoRNAVs in fragments of some colonies exhibited higher alpha diversity and dispersion under heat stress. Together, these findings provide the first empirical evidence that exposure to high temperatures triggers some dinoRNAVs to switch from a persistent to a productive infection mode within heat-stressed corals. Over extended time frames, we hypothesize that cumulative dinoRNAV production in the Pocillopora-Cladocopium system could affect colony symbiotic status, for example, by decreasing Symbiodiniaceae densities within corals. This study sets the stage for reef-scale investigations of dinoRNAV dynamics during bleaching events.

The importance of 1.5°C warming for the Great Barrier Reef.

Tropical coral reefs are among the most sensitive ecosystems to climate change and will benefit from the more ambitious aims of the United Nations Framework Convention on Climate Change's Paris Agreement, which proposed to limit global warming to 1.5° rather than 2°C above pre-industrial levels.Only in the latest Intergovernmental Panel on Climate Change focussed assessment, the Coupled Model Intercomparison Project phase 6 (CMIP6), have climate models been used to investigate the 1.5° warming scenario directly. Here, we combine the most recent model updates from CMIP6 with a semi-dynamic downscaling to evaluate the difference between the 1.5 and 2°C global warming targets on coral thermal stress metrics for the Great Barrier Reef (GBR). By ~2080, severe bleaching events are expected to occur annually under intensifying emissions (shared socioeconomic pathway SSP5-8.5). Adherence to 2° warming (SSP1-2.6) halves this frequency but the main benefit of confining warming to 1.5° (SSP1-1.9) is that bleaching events are reduced further to 3 events per decade. Attaining low emissions of 1.5° is also paramount to prevent the mean magnitude of thermal stress from stabilizing close to a critical thermal threshold (8 Degree Heating Weeks). Thermal stress under the more pessimistic pathways SSP3-7.0 and SSP5-8.5 is three to fourfold higher than the present day, with grave implications for future reef ecosystem health. As global warming continues, our projections also indicate more regional warming in the central and southern GBR than the far north and northern GBR.

Habitat degradation increases interspecific trophic competition between three spiny lobster species in Seychelles

Spiny lobsters (P. penicillatus, P. longipes and P. versicolor) are heavily dependent on habitats like coral reefs, known to be highly vulnerable to climate change-driven degradation. Yet, little is known about their trophic ecology and their adaptive capacity to a changing environment. In this study, we used fatty acids (FA) analysed in the hepatopancreas and δ13C and δ15N stable isotopes analysed in the tail muscle of three spiny lobster species from the Seychelles coastal waters to (1) infer habitat use, dietary patterns and potential for resource competition and (2) investigate the effects of reef type and coral bleaching on their trophic niche metrics. We found that there was a potential for interspecific competition between the three species, shown by their high dietary overlap (mean FA niche overlap ranging from 71.2% to 99.5% for P. longipes and P. versicolor in P. penicillatus) and similar habitat use (δ13C value ranges). P. penicillatus, the largest of the three species, was more a generalist than the two other species (i.e., had a larger FA niche) and P. versicolor seemed to feed on smaller/earlier life stage prey than P. longipes (based on differences in δ15N values). The potential for resource competition of Seychelles spiny lobsters appeared higher in granite than carbonate reefs, and in post-2016 coral bleaching reefs. Our results suggest that P. penicillatus could have a greater adaptive capacity to climate change due to its higher dietary plasticity and that competition between Seychelles spiny lobsters may increase in the future as the frequency and severity of bleaching events is predicted to increase with climate change.

Metabolomic signatures of coral bleaching history.

Coral bleaching has a profound impact on the health and function of reef ecosystems, but the metabolomic effects of coral bleaching are largely uncharacterized. Here, untargeted metabolomics was used to analyse pairs of adjacent Montipora capitata corals that had contrasting bleaching phenotypes during a severe bleaching event in 2015. When these same corals were sampled four years later while visually healthy, there was a strong metabolomic signature of bleaching history. This was primarily driven by betaine lipids from the symbiont, where corals that did not bleach were enriched in saturated lyso-betaine lipids. Immune modulator molecules were also altered by bleaching history in both the coral host and the algal symbiont, suggesting a shared role in partner choice and bleaching response. Metabolomics from a separate set of validation corals was able to predict the bleaching phenotype with 100% accuracy. Experimental temperature stress induced phenotype-specific responses, which magnified differences between historical bleaching phenotypes. These findings indicate that natural bleaching susceptibility is manifested in the biochemistry of both the coral animal and its algal symbiont. This metabolome difference is stable through time and results in different physiological responses to temperature stress. This work provides insight into the biochemical mechanisms of coral bleaching and presents a valuable new tool for resilience-based reef restoration.

The past century of coral bleaching in the Saudi Arabian central Red Sea.

Accurate knowledge of the spatial and temporal patterns of coral bleaching is essential both for understanding how coral reef ecosystems are changing today and forecasting their future states. Yet, in many regions of the world, the history of bleaching is poorly known, especially prior to the late 20th century. Here, I use the information preserved within skeleton cores of long-lived Porites corals to reconstruct the past century of bleaching events in the Saudi Arabian central Red Sea. In these cores, skeletal “stress bands”—indicative of past bleaching—captured known bleaching events that occurred in 1998 and 2010, but also revealed evidence of previously unknown bleaching events in 1931, 1978, and 1982. However, these earlier events affected a significantly lesser proportion of corals than 1998 and 2010. Therefore, coral bleaching may have occurred in the central Red Sea earlier than previously recognized, but the frequency and severity of bleaching events since 1998 on nearshore reefs is unprecedented over the past century. Conversely, corals living on mid- to outer-shelf reefs have not been equally susceptible to bleaching as their nearshore counterparts, which was evident in that stress bands were five times more prevalent nearshore. Whether this pattern of susceptible nearshore reefs and resistant outer-shelf reefs continues in the future remains a key question in forecasting coral reef futures in this region.

Observations and a Model of Net Calcification Declines in Palau's Largest Coral Reef Lagoon Between 1992 and 2015

AbstractNet ecosystem calcification (NEC) rates of Palau's largest lagoon and barrier reef system between 1992 and 2015 are estimated from sparse total alkalinity (TA) and salinity measurements and a tidal exchange model in which surface lagoon water transported offshore on the ebb tide is replaced by saltier (denser) ocean water that sinks to the bottom after entering the lagoon on the flood tide. Observed lagoon salinities are accurately reproduced by the model with no adjustable parameters. To accurately reproduce observed lagoon TA, NEC for the lagoon‐barrier reef system was 70 mmols m−2 day−1 from 1992 to 1998, 35 mmols m−2 day−1 from 1999 to 2012, and 25 mmols m−2 day−1 from 2013 to 2015. This indicates that Palau's largest lagoon and barrier reef system has not recovered, as of 2015, from the 50% decline in NEC in 1998 caused by the loss of coral cover following a severe bleaching event. The cause of the further decline in NEC in 2012–2013 is unclear. Lagoon residence times vary from 8 days during spring tides to 14 days during neap tides and drive substantial spring‐neap variations in lagoon TA (~25% of the mean salinity‐normalized ocean‐lagoon TA difference). Sparse measurements that do not resolve these spring‐neap variations can exhibit apparent long‐term variations in alkalinity that are not due to changes in NEC.

Leptoria phrygia in Southern Taiwan shuffles and switches symbionts to resist thermal-induced bleaching

Symbiodiniaceae communities in some corals often shuffle or switch after severe bleaching events, one of the major threats to coral survival in a world with climate change. In this study we reciprocally transplanted five Leptoria phrygia colonies between two sites with significantly different temperature regimes and monitored them for 12 months. Our ITS2 amplicon deep sequencing demonstrated that L. phrygia acclimatized to maintain a strong and stable association with Durusdinium D17, D. trenchii, and D. glynnii, but also remained flexible and formed a short-term association with different Cladocopium. Most interestingly, two colonies shuffled between Durusdinium and Cladocopium without the occurrence of bleaching; one colony even switched its dominant Cladocopium after generic shuffling. Both dominant Cladocopium were originally rare with relative abundances as low as 0.024%. This is the first record of adult corals switching dominant symbiont without bleaching.

The past, present, and future of coral heat stress studies.

The global loss and degradation of coral reefs, as a result of intensified frequency and severity of bleaching events, is a major concern. Evidence of heat stress affecting corals through loss of symbionts and consequent coral bleaching was first reported in the 1930s. However, it was not until the 1998 major global bleaching event that the urgency for heat stress studies became internationally recognized. Current efforts focus not only on examining the consequences of heat stress on corals but also on finding strategies to potentially improve thermal tolerance and aid coral reefs survival in future climate scenarios. Although initial studies were limited in comparison with modern technological tools, they provided the foundation for many of today's research methods and hypotheses. Technological advancements are providing new research prospects at a rapid pace. Understanding how coral heat stress studies have evolved is important for the critical assessment of their progress. This review summarizes the development of the field to date and assesses avenues for future research.

Response of reef corals and fish at Osprey Reef to a thermal anomaly across a 30 m depth gradient

Coral bleaching causes coral mortality that has knock-on effects on reef ecosystems, including reductions of some fish species. However, the extent of coral bleaching varies considerably among habitats. For example, deeper areas of reefs typically bleach less than areas in the shallows. However, rates of coral mortality at depth and the knock-on effects on other reef species are rarely documented. Here, we quantified the extent of coral bleaching and resulting mortality following a marine heat wave at Osprey Reef in the Coral Sea, Australia, along a depth gradient from 2 to 30 m. We also quantified the response of the associated reef fish assemblages. We found taxon-specific patterns in both bleaching and mortality, with some taxa bleaching less at depth, some bleached most at intermediate depths, and others exibiting no difference among depths. Similarly, bleaching-induced mortality varied among taxa and with depth. However, in the more abundant taxa (e.g. Acropora, Montipora and Porites), mortality was lower at greater depths. Reef fish assemblage structure had not changed 1 yr after bleaching. The relatively high incidence of bleaching at depth compared to other studies is likely due to high light penetration in the clear waters of the Coral Sea, suggesting corals in these habitats have a higher risk of bleaching during thermal anomalies. Nonetheless, corals capable of living in deeper waters appear more likely to have persisted through this severe bleaching event, while the fish assemblage did not change in response to the loss of live coral cover.

Effective co-management and long-term reef fish recovery from severe coral bleaching: Insights from Misali Island, PECCA, Tanzania

Misali, an uninhabited islet along the east coast of Pemba Island off the mainland Tanzanian coast, is a biodiversity hotspot and Marine Protected Area (MPA), consisting of a core non-extraction zone (NEZ) surrounded by a larger area where some artisanal fishing is allowed. Within a year of receiving official protection under a co-management agreement, the island underwent a catastrophic bleaching event in 1998, and funding and enforcement in the protected area have been inconsistent since a restructuring of management in 2006. In this study, we investigate current health of the island's fish community, and report 186 observed fish species. We estimate that, including unseen species and those outside the study area, the total species richness may be comparable to the historical baseline of 244 species; however, this represents a decline from the 270 species estimated in 2001 and the 350 species observed in 2004, after several years of successful protections. Patterns of species richness over time likely reflect changes in management effectiveness and engagement of Misali's fishing communities. Diversity of indicator (Chaetodontidae) and keystone (Scarinae) taxa were comparable to historical levels and greatest inside the NEZ, suggesting continued reef health and resilience. However, we found no other significant differences between fish communities inside and outside the NEZ, which observations indicate is poorly enforced, and the disproportionate loss of large predatory fish species may indicate overfishing. The case study of Misali suggests that a temporary reduction in fishing pressure while the island was recovering from a severe bleaching event may have had long-lasting benefits for reef health and resilience. For future management, we recommend consideration of species-specific protections, a possible re-designation of NEZ boundaries to include more unique habitat types, and reintegration of local fishing communities into MPA co-management.