Local conditions magnify coral loss after marine heatwaves Donovan, Mary K; Burkepile, Deron E; Kratochwill, Chelsey ...
Science (American Association for the Advancement of Science),
05/2021, Volume:
372, Issue:
6545
Journal Article
Peer reviewed
Climate change threatens coral reefs by causing heat stress events that lead to widespread coral bleaching and mortality. Given the global nature of these mass coral mortality events, recent studies ...argue that mitigating climate change is the only path to conserve coral reefs. Using a global analysis of 223 sites, we show that local stressors act synergistically with climate change to kill corals. Local factors such as high abundance of macroalgae or urchins magnified coral loss in the year after bleaching. Notably, the combined effects of increasing heat stress and macroalgae intensified coral loss. Our results offer an optimistic premise that effective local management, alongside global efforts to mitigate climate change, can help coral reefs survive the Anthropocene.
Invasive macroalgae Eucheuma sp. and Kappaphycus spp. (E/K) became a dominant benthic feature in Kāne'ohe Bay throughout the past four decades - occurring on up to 74 ha of reef area and growing up ...to three meters thick, which prompted intensive management action. In 2013, E/K cover began decreasing at managed and unmanaged sites. This study examined the extent and timing of the E/K decline and evaluated environmental and ecological drivers beyond management contributing to the decline. E/K continued to recede into 2017 and remains sparse in Kāne'ohe Bay today. Increasing over the sampling period, herbivore biomass was negatively correlated with E/K cover, and other significant, non-linear relationships emerged between E/K cover and coral cover, sea surface temperature, wind, and rainfall. This study uncovers several possible mechanisms explaining a boom and bust in E/K abundance, emphasizes the importance of herbivory, and highlights the resilience of coral reefs in Kāne'ohe Bay.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
African savannas are experiencing anthropogenically-induced stressors that are accelerating the increase of woody vegetation cover. To combat this, land managers frequently implement large-scale ...clearing of trees, which can have a cascading influence on mammalian herbivores. Studies rarely focus on how differences in woody cover influence the herbivore assemblage, making it difficult to assess how aggressive measures, or the lack of management, to counteract increasing woody cover affect the local composition and biodiversity of herbivores. We address this knowledge gap by applying a model-based clustering approach to field observations from MalaMala Game Reserve, South Africa to identify multiple herbivore–vegetation ‘configurations,’ defined as unique sets of herbivore assemblages (i.e., groups of herbivores) associated with differing woody plant covers. Our approach delineated how tree-clearing influences the distribution and abundance of the herbivore community in relation to surrounding savanna areas, which represent a natural mosaic of varying woody cover. Regardless of season, both intensively managed areas cleared of trees and unmanaged areas with high tree cover contained configurations that had depauperate assemblages of herbivores (low species richness, low abundance). By contrast, habitats with intermediate cover of woody vegetation had much higher richness and abundance. These results have substantial implications for managing African savannas in a rapidly changing climate.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Climate change is increasing the frequency and magnitude of temperature anomalies that cause coral bleaching, leading to widespread mortality of stony corals that can fundamentally alter reef ...structure and function. However, bleaching often is spatially variable for a given heat stress event, and drivers of this heterogeneity are not well resolved. While small-scale experiments have shown that excess nitrogen can increase the susceptibility of a coral colony to bleaching, we lack evidence that heterogeneity in nitrogen pollution can shape spatial patterns of coral bleaching across a seascape. Using island-wide surveys of coral bleaching and nitrogen availability within a Bayesian hierarchical modeling framework, we tested the hypothesis that excess nitrogen interacts with temperature anomalies to alter coral bleaching for the two dominant genera of branching corals in Moorea, French Polynesia. For both coral genera, Pocillopora and Acropora, heat stress primarily drove bleaching prevalence (i.e., the proportion of colonies on a reef that bleached). In contrast, the severity of bleaching (i.e., the proportion of an individual colony that bleached) was positively associated with both heat stress and nitrogen availability for both genera. Importantly, nitrogen interacted with heat stress to increase bleaching severity up to twofold when nitrogen was high and heat stress was relatively low. Our finding that excess nitrogen can trigger severe bleaching even under relatively low heat stress implies that mitigating nutrient pollution may enhance the resilience of coral communities in the face of mounting stresses from global climate change.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The Hawaiian Archipelago experienced a moderate bleaching event in 2019—the third major bleaching event over a 6-year period to impact the islands. In response, the Hawai‘i Coral Bleaching ...Collaborative (HCBC) conducted 2,177 coral bleaching surveys across the Hawaiian Archipelago. The HCBC was established to coordinate bleaching monitoring efforts across the state between academic institutions, non-governmental organizations, and governmental agencies to facilitate data sharing and provide management recommendations. In 2019, the goals of this unique partnership were to: 1) assess the spatial and temporal patterns of thermal stress; 2) examine taxa-level patterns in bleaching susceptibility; 3) quantify spatial variation in bleaching extent; 4) compare 2019 patterns to those of prior bleaching events; 5) identify predictors of bleaching in 2019; and 6) explore site-specific management strategies to mitigate future bleaching events. Both acute thermal stress and bleaching in 2019 were less severe overall compared to the last major marine heatwave events in 2014 and 2015. Bleaching observed was highly site- and taxon-specific, driven by the susceptibility of remaining coral assemblages whose structure was likely shaped by previous bleaching and subsequent mortality. A suite of environmental and anthropogenic predictors was significantly correlated with observed bleaching in 2019. Acute environmental stressors, such as temperature and surface light, were equally important as previous conditions (e.g. historical thermal stress and historical bleaching) in accounting for variation in bleaching during the 2019 event. We found little evidence for acclimation by reefs to thermal stress in the main Hawaiian Islands. Moreover, our findings illustrate how detrimental effects of local anthropogenic stressors, such as tourism and urban run-off, may be exacerbated under high thermal stress. In light of the forecasted increase in severity and frequency of bleaching events, future mitigation of both local and global stressors is a high priority for the future of corals in Hawai‘i.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A major challenge for coral reef conservation and management is understanding how a wide range of interacting human and natural drivers cumulatively impact and shape these ecosystems. Despite the ...importance of understanding these interactions, a methodological framework to synthesize spatially explicit data of such drivers is lacking. To fill this gap, we established a transferable data synthesis methodology to integrate spatial data on environmental and anthropogenic drivers of coral reefs, and applied this methodology to a case study location-the Main Hawaiian Islands (MHI). Environmental drivers were derived from time series (2002-2013) of climatological ranges and anomalies of remotely sensed sea surface temperature, chlorophyll-a, irradiance, and wave power. Anthropogenic drivers were characterized using empirically derived and modeled datasets of spatial fisheries catch, sedimentation, nutrient input, new development, habitat modification, and invasive species. Within our case study system, resulting driver maps showed high spatial heterogeneity across the MHI, with anthropogenic drivers generally greatest and most widespread on O'ahu, where 70% of the state's population resides, while sedimentation and nutrients were dominant in less populated islands. Together, the spatial integration of environmental and anthropogenic driver data described here provides a first-ever synthetic approach to visualize how the drivers of coral reef state vary in space and demonstrates a methodological framework for implementation of this approach in other regions of the world. By quantifying and synthesizing spatial drivers of change on coral reefs, we provide an avenue for further research to understand how drivers determine reef diversity and resilience, which can ultimately inform policies to protect coral reefs.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The mass die‐off of Caribbean corals has transformed many of this region’s reefs to macroalgal‐dominated habitats since systematic monitoring began in the 1970s. Although attributed to a combination ...of local and global human stressors, the lack of long‐term data on Caribbean reef coral communities has prevented a clear understanding of the causes and consequences of coral declines. We integrated paleoecological, historical, and modern survey data to track the occurrence of major coral species and life‐history groups throughout the Caribbean from the prehuman period to the present. The regional loss of Acropora corals beginning by the 1960s from local human disturbances resulted in increases in the occurrence of formerly subdominant stress‐tolerant and weedy scleractinian corals and the competitive hydrozoan Millepora beginning in the 1970s and 1980s. These transformations have resulted in the homogenization of coral communities within individual countries. However, increases in stress‐tolerant and weedy corals have slowed or reversed since the 1980s and 1990s in tandem with intensified coral bleaching and disease. These patterns reveal the long history of increasingly stressful environmental conditions on Caribbean reefs that began with widespread local human disturbances and have recently culminated in the combined effects of local and global change.
We integrated paleoecological, historical, and modern survey data to track the prevalence of major coral species and life‐history groups throughout the Caribbean from the prehuman period to present. This extended time series reveals that Caribbean coral communities have been transformed via three distinct stages since humans: (a) declines in competitive corals by the 1960s, (b) increases in stress‐tolerant and weedy corals occurring by the 1970s and 1980s, and (c) declines or leveling‐off of stress‐tolerant and weedy corals since the 1980s or 1990s. These patterns reveal the long history of increasingly stressful environmental conditions on Caribbean reefs that began with widespread local human disturbances and have recently culminated in the combined effects of local and global change.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Evidence for managing herbivores for reef resilience Donovan, Mary K; Counsell, Chelsie W W; Donahue, Megan J ...
Proceedings of the Royal Society. B, Biological sciences,
2023-Dec-06, 2023-12-06, 20231206, Volume:
290, Issue:
2012
Journal Article
Peer reviewed
Open access
Herbivore management is an important tool for resilience-based approaches to coral reef conservation, and evidence-based science is needed to enact successful management. We synthesized data from ...multiple monitoring programs in Hawai'i to measure herbivore biomass and benthic condition over a 10-year period preceding any major coral bleaching. We analysed data from 20 242 transects alongside data on 27 biophysical and human drivers and found herbivore biomass was highly variable throughout Hawai'i, with high values in remote locations and the lowest values near population centres. Both human and biophysical drivers explained variation in herbivore biomass, and among the human drivers both fishing and land-based pollution had negative effects on biomass. We also found evidence that herbivore functional group biomass is strongly linked to benthic condition, and that benthic condition is sensitive to changes in herbivore biomass associated with fishing. We show that when herbivore biomass is below 80% of potential biomass, benthic condition is predicted to decline. We also show that a range of management actions, including area-specific fisheries regulations and gear restrictions, can increase parrotfish biomass. Together, these results provide lines of evidence to support managing herbivores as an effective strategy for maintaining or bolstering reef resilience in a changing climate.
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