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Coral bleaching and mortality can show significant spatial and taxonomic heterogeneity at local scales, highlighting the need to understand the fine-scale drivers and impacts of thermal stress. In this study, we used structure-from-motion photogrammetry to track coral bleaching, mortality, and changes in community composition during the 2019 marine heatwave in Kāneʻohe Bay, Hawaiʻi. We surveyed 30 shallow reef patches every 3 weeks for the duration of the bleaching event (August-December) and one year after, resulting in a total of 210 large-area, high-resolution photomosaics that enabled us to follow the fate of thousands of coral colonies through time. We also measured environmental variables such as temperature, sedimentation, depth, and wave velocity at each of these sites, and extracted estimates of habitat complexity (rugosity R and fractal dimension D) from digital elevation models to better understand their effects on patterns of bleaching and mortality. We found that up to 80% of corals experienced moderate to severe bleaching in this period, with peak bleaching occurring in October when heat stress (Degree Heating Weeks) reached its maximum. Mortality continued to accumulate as bleaching levels dropped, driving large declines in more heat-susceptible species (77% loss of Pocillopora cover) and moderate declines in heat-tolerant species (19% and 23% for Porites compressa and Montipora capitata , respectively). Declines in live coral were accompanied by a rapid increase in algal cover across the survey sites. Spatial differences in bleaching were significantly linked to habitat complexity and coral species composition, with reefs that were dominated by Pocillopora experiencing the most severe bleaching. Mortality was also influenced by species composition, fractal dimension, and site-level differences in thermal stress. Our results show that spatial heterogeneity in the impacts of bleaching are driven by a mix of environmental variation, habitat complexity, and differences in assemblage composition.
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Assessing the accuracy of paired and random sampling for quantifying plant–plant interactions in natural communities
Abstract Plant interactions in extreme environments are often inferred from spatial associations and quantified by means of paired sampling. Yet, this method might be confounded by habitat‐sharing effects. Here, we address whether paired and random sampling methods provide similar results at varying levels of environmental heterogeneity. We quantified spatial associations with the two methods at three sites that encompass different micro‐environmental heterogeneity and stress levels: Mediterranean environments in Canary Islands, Spain, and Sardinia, Italy, and a cold alpine environment in Hokkaido, Japan. Then, we simulated plant communities with different levels of species micro‐habitat preferences, environmental heterogeneity, and stress levels. We found that differences in species associations between paired and random sampling were indistinguishable from zero in a homogeneous space. When simulating codispersion over a decreasing abundance gradient, both sampling methods correctly identified facilitation and distinguished it from codispersion. Yet, the pairwise method provided higher facilitation estimates than the random one. At each site, there were strong differences between beneficiary species in their spatial association with nurse species, and associations became more positive with increasing stress in Spain. Most importantly, there were no differences in results yielded by the two methods at any of the different stress levels at the Spanish and Japanese sites. At the Italian site, although micro‐environmental heterogeneity was low, we found weakly significant differences between methods that were unlikely due to habitat‐sharing effects. Thus, the paired sampling method can provide significant insights into net and long‐term effects of plant interactions in spatially conspicuous environments.
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- Award ID(s):
- 1757351
- PAR ID:
- 10485197
- Publisher / Repository:
- Population Ecology
- Date Published:
- Journal Name:
- Population Ecology
- ISSN:
- 1438-3896
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/1438-390x.12161
