Biology subjects

Baum, J. K.

Publications and source records attributed to Baum, J. K..

7 recordsLinked to original sources

bioRxiv2025

Spatial variation in benthic community composition on a minimally disturbed coral reef in the years following a prolonged marine heatwave

With the increased frequency of marine heatwaves and related coral mass mortality events, it is imperative that we improve our understanding of coral reef recovery processes including how benthic community compositions can change over time. Coral reef benthic communities are influenced by many abiotic factors, but on most reefs local anthropogenic disturbances overshadow these factors thus obscuring their influence. Here, we leverage a dataset from a coral reef with very minimal local anthropogenic disturbance - the uninhabited southern coast of the worlds largest atoll (Kiritimati) - to assess spatial variation in benthic community composition three years after the mass coral mortality event driven by the 2015-2016 El Nino. Across forereef sites ranging from 7 to 22 m, scleractinian coral cover remained very low (6.9 {+/-} 0.4 % SE) while soft coral cover was < 1%. Coral cover was highest at deep sites (18-22 m compared to sites at 7-10 m depth) and exposed locations, where stress-tolerant corals likely made up a larger proportion of the coral community before the mass mortality event. Higher cover of crustose coralline algae at shallow exposed sites, fleshy macroalgae at deep sites, and turf algae at exposed locations were consistent with taxa-specific preferences for light, wave action, and sedimentation. The abundances of the most common genera of juvenile coral (Acropora and Pocillopora) were still low (< 1 juvenile colony per genus per site) and varied only with depth. These findings demonstrate how variation in pre-mortality coral composition can lead to differences in post-mortality benthic communities on low disturbance coral reefs.

ecology↗

bioRxiv2024

A blueprint for national assessments of the blue carbon capacity of kelp forests applied to Canadas coastline

Kelp forests offer substantial carbon fixation, with the potential to contribute to natural climate solutions (NCS). However, to be included in national NCS inventories, governments must first quantify the kelp-derived carbon stocks and fluxes leading to carbon sequestration. Here, we present a blueprint for assessing the national carbon sequestration capacity of kelp forests in which data synthesis and Bayesian hierarchical modelling enable estimates of kelp forest carbon production, storage, and export capacity from limited data. Applying this blueprint to Canadas extensive coastline, we find kelp forests store an estimated 1.4 Tg C in short-term biomass and produce 3.1 Tg C yr-1 with modest carbon fluxes to the deep ocean. Arctic kelps had the highest carbon stocks and production capacity, while Pacific kelps had greater carbon fluxes overall due to their higher productivity and export rates. Our transparent, reproducible blueprint represents an important step towards accurate carbon accounting for kelp forests.

ecology↗

bioRxiv2024

Impacts of a prolonged marine heatwave and chronic local human disturbance on juvenile coral assemblages

Coral reefs are threatened by climate change and chronic local human disturbances. Although some laboratory studies have investigated the effects of combined stressors, such as nutrient enrichment and heat stress, on growth and survival of early life stage corals, in situ studies remain limited. To assess the influence of multiple stressors on juvenile corals, we quantified densities of corals [≤]5 cm at 18 forereef sites with different exposure levels to underlying chronic local human disturbance before, during, and after the 2015-2016 El Nino. This marine heatwave caused prolonged heat stress and devastating losses of coral cover at our study site, Kiritimati, in the central equatorial Pacific Ocean. In total, we enumerated 7732 juvenile corals from 13 different families. Over 80% of corals were from four families: 70% from Agariciidae, Merulinidae, or Poritidae, which all have stress-tolerant life history strategies, and 11% from Acroporidae which has a competitive life-history strategy. Both local disturbance and heat stress were significantly negatively related to juvenile coral densities. Prior to the heatwave, juvenile densities were on average 72% lower at the most disturbed sites (7.2 {+/-} 1.9 m2) compared to the least disturbed ones (15.3 {+/-} 3.8 m2). Overall, juvenile corals had a lower bleaching prevalence and lower mortality during the heatwave when compared to their adult counterparts. Still, the heatwave resulted in the loss of half (50%) of all juvenile corals, with competitive and weedy life history strategy corals undergoing greater declines than stress-tolerant ones. Although juvenile coral densities increased slightly in the year following the heatwave, the effect was statistically non-significant. Our results highlight the influence of local chronic anthropogenic and climate change-driven marine heatwaves on juvenile coral densities.

ecology↗

bioRxiv2023

Marine heatwaves threaten cryptic coral diversity and erode associations amongst coevolving partners

Climate change-amplified heatwaves are known to drive extensive mortality in marine foundation species. However, a paucity of longitudinal genomic datasets has impeded understanding of how these rapid selection events alter species genetic structure. Impacts of these events may be exacerbated in species with obligate symbioses, where the genetics of multiple co-evolving species may be affected. Here, we tracked the symbiotic associations and fate of reef-building corals for six years through a prolonged heatwave. Coral genetics strongly predicted survival of the common coral Porites through the event, with strong differential survival (15 to 64%) apparent across morphologically identical -but genetically distinct- lineages. The event also disrupted strong associations between coral lineages and their symbiotic partners, homogenizing symbiotic assemblages across lineages and reducing the specificity of coral-algal symbioses. These results highlight that marine heatwaves threaten cryptic genetic diversity of foundation species and have the potential to decouple tight relationships between co-evolving host-symbiont pairs.

ecology↗

bioRxiv2023

Temperature and food chain length, but not latitude, explain region-specific kelp forest responses to an unprecedented heatwave

Kelp forests are among the most abundant coastal marine habitats but are vulnerable to the impacts of climate change. Between 2014 and 2016, an unprecedented heatwave and associated changes in trophic dynamics threatened kelp forests across the Northeast Pacific, with impacts documented from Mexico to Alaska. However, responses have varied substantially and remain poorly characterized across large stretches of coast, especially British Columbia (B.C.), which represents a significant percentage of the range of floating kelp species in the Northeast Pacific. Here, we explore variation in floating kelp (Macrocystis, Nereocystis) persistence pre- and post-heatwave across a >675 km latitudinal gradient, asking whether B.C. kelp forests are of conservation concern. We assembled and analyzed available quantitative kelp data, comparing snapshots of kelp extent before (1994 - 2007) and after (2018 - 2021) the heatwave in 11 regions spanning a range of temperature and sea otter-occupancy statuses, and contextualizing these with time series analyses, where available (n = 7 regions). We provide strong evidence that kelp forests have declined in many regions but with evidence of refugia at both local and regional scales. Kelp forest persistence was negatively correlated with summer sea temperatures in southern B.C., where temperatures varied by ~6{degrees}C across sites, at times exceeding species thermal tolerances. Kelp dynamics in northern regions appeared instead to be modulated by top-down control by urchins and sea otters. Our results demonstrate that B.C.s kelp forest have been substantially reduced in recent years but that regional and local-scale factors influence the resilience of forests to large-scale perturbations.

ecology↗

bioRxiv2022

Transformation of coral communities subjected to an unprecedented heatwave is modulated by local disturbance

Corals are imminently threatened by climate change-amplified marine heatwaves. Yet how to conserve reef ecosystems faced with this threat remains unclear, since protected reefs often seem equally or more susceptible to thermal stress as unprotected ones. Here, we disentangle this apparent paradox, revealing that the relationship between reef disturbance and heatwave impacts depends upon the focal scale of biological organization. We document a heatwave of unprecedented duration that culminated in an 89% loss of coral cover. At the community level, losses hinged on pre-heatwave community structure, with sites dominated by competitive corals--which were predominantly protected from local disturbance--undergoing the greatest losses. In contrast, at the species level, survivorship of individual coral colonies typically decreased as local disturbance intensified, illustrating that underlying chronic disturbances can impair resilience to thermal stress at this scale. Our study advances understanding of the relationship between climate change and local disturbance, knowledge of which is crucial for coral conservation this century.

ecology↗

bioRxiv2021

Inconsistent patterns of microbial diversity and composition between highly similar sequencing protocols: a case study with reef-building corals

16S rRNA gene profiling (amplicon sequencing) is a popular technique for understanding host-associated and environmental microbial communities. Most protocols for sequencing amplicon libraries follow a standardized pipeline that can differ slightly depending on laboratory facility and user. Given that the same variable region of the 16S gene is targeted, it is generally accepted that sequencing output from differing protocols are comparable and this assumption underlies our ability to identify universal patterns in microbial dynamics through meta-analyses. However, discrepant results from a combined 16S rRNA dataset prepared by two labs whose protocols differed only in DNA polymerase and sequencing platform led us to scrutinize the outputs and challenge the idea of confidently combining them for standard microbiome analysis. Using technical replicates of reef-building coral samples from two species, Montipora aequituberculata and Porites lobata, we evaluated the consistency of alpha and beta diversity metrics between data resulting from these highly similar protocols. While we found minimal variation in alpha diversity between platform, significant differences were revealed with most beta diversity metrics, dependent on host species. These inconsistencies persisted following removal of low abundance taxa and when comparing across higher taxonomic levels, suggesting that bacterial community differences associated with sequencing protocol are likely to be context dependent and difficult to correct without extensive validation work. The results of this study encourage caution in the statistical comparison and interpretation of studies that combine rRNA sequence data from distinct protocols and point to a need for further work identifying mechanistic causes of these observed differences. ImportanceAmplicon sequencing remains a popular technique for characterizing organism and environmental microbiomes. The publication of sequence data from microbiome studies on open-access repositories provides an opportunity to identify universal patterns in microbial dynamics. To this end, it has been widely accepted that sequencing output from differing protocols are comparable and can be combined for analysis, so long as the same gene region is targeted. While most protocols for amplicon sequencing follow standardized pipelines, they can differ slightly between laboratory facility and user. In this study, we compared technical replicates of coral samples to evaluate the efficacy of combining organism-associated microbial datasets derived from two differing protocols. We found inconsistencies in the differences between bacterial communities, which persisted following data manipulations intended to increase comparability. These results suggest caution must be taken in the statistical comparison and interpretation of studies that combine data derived from distinct protocols.

microbiology↗