• Energy Research

Global climate change includes rising temperatures and increased pCO2 concentrations in the ocean, with potential deleterious impacts on marine organisms. In this case study we conducted a four-week climate change incubation experiment, and tested the independent and combined effects of increased temperature and partial pressure of carbon dioxide (pCO2), on the microbiomes of a foundation species, the giant kelp Macrocystis pyrifera, and the surrounding water column. The water and kelp microbiome responded differently to each of the climate stressors. In the water microbiome, each condition caused an increase in a distinct microbial order, whereas the kelp microbiome exhibited a reduction in the dominant kelp-associated order, Alteromondales. The water column microbiomes were most disrupted by elevated pCO2, with a 7.3 fold increase in Rhizobiales. The kelp microbiome was most influenced by elevated temperature and elevated temperature in combination with elevated pCO2. Kelp growth was negatively associated with elevated temperature, and the kelp microbiome showed a 5.3 fold increase Flavobacteriales and a 2.2 fold increase alginate degrading enzymes and sulfated polysaccharides. In contrast, kelp growth was positively associated with the combination of high temperature and high pCO2 'future conditions', with a 12.5 fold increase in Planctomycetales and 4.8 fold increase in Rhodobacteriales. Therefore, the water and kelp microbiomes acted as distinct communities, where the kelp was stabilizing the microbiome under changing pCO2 conditions, but lost control at high temperature. Under future conditions, a new equilibrium between the kelp and the microbiome was potentially reached, where the kelp grew rapidly and the commensal microbes responded to an increase in mucus production.

Microbialization refers to the observed shift in ecosystem trophic structure towards higher microbial biomass and energy use. On coral reefs, the proximal causes of microbialization are overfishing and eutrophication, both of which facilitate enhanced growth of fleshy algae, conferring a competitive advantage over calcifying corals and coralline algae. The proposed mechanism for this competitive advantage is the DDAM positive feedback loop (dissolved organic carbon (DOC), disease, algae, microorganism), where DOC released by ungrazed fleshy algae supports copiotrophic, potentially pathogenic bacterial communities, ultimately harming corals and maintaining algal competitive dominance. Using an unprecedented data set of >400 samples from 60 coral reef sites, we show that the central DDAM predictions are consistent across three ocean basins. Reef algal cover is positively correlated with lower concentrations of DOC and higher microbial abundances. On turf and fleshy macroalgal-rich reefs, higher relative abundances of copiotrophic microbial taxa were identified. These microbial communities shift their metabolic potential for carbohydrate degradation from the more energy efficient Embden-Meyerhof-Parnas pathway on coral-dominated reefs to the less efficient Entner-Doudoroff and pentose phosphate pathways on algal-dominated reefs. This 'yield-to-power' switch by microorganism directly threatens reefs via increased hypoxia and greater CO2 release from the microbial respiration of DOC.

Une conservation efficace nécessite des bases de référence rigoureuses de conditions vierges pour évaluer les impacts des activités humaines et évaluer l'efficacité de la gestion. La plupart des récifs coralliens sont modérément à sévèrement dégradés par les activités humaines locales telles que la pêche et la pollution ainsi que par le changement global, il est donc difficile de séparer les effets locaux des effets globaux. À cette fin, nous avons étudié les récifs coralliens sur des atolls inhabités dans le nord des îles Line pour fournir une base de référence de la structure de la communauté récifale, et sur des atolls de plus en plus peuplés pour documenter les changements associés aux activités humaines. Nous avons constaté que les prédateurs supérieurs et les organismes de construction de récifs dominaient Kingman et Palmyra non peuplés, tandis que les petits poissons planctonophages et les algues charnues dominaient les atolls peuplés de Tabuaeran et Kiritimati. Les requins et autres grands prédateurs ont submergé les assemblages de poissons sur Kingman et Palmyre, de sorte que la pyramide de la biomasse était inversée (haut-lourd). En revanche, la pyramide de la biomasse à Tabuaeran et Kiritimati présentait le motif typique fond-lourd. Les récifs sans population présentaient moins de maladies coralliennes et un plus grand recrutement de coraux par rapport aux récifs plus habités. Ainsi, la protection contre la surpêche et la pollution semble augmenter la résilience des écosystèmes récifaux aux effets du réchauffement climatique. La protección efectiva requiere líneas de base rigurosas de condiciones prístinas para evaluar los impactos de las actividades humanas y evaluar la eficacia del manejo. La mayoría de los arrecifes de coral se degradan de moderada a severamente por las actividades humanas locales, como la pesca y la contaminación, así como por el cambio global, por lo que es difícil separar los efectos locales de los globales. Con este fin, estudiamos los arrecifes de coral en atolones deshabitados en las Islas Lineales del norte para proporcionar una línea de base de la estructura de la comunidad de arrecifes, y en atolones cada vez más poblados para documentar los cambios asociados con las actividades humanas. Descubrimos que los principales depredadores y organismos formadores de arrecifes dominaban Kingman y Palmira despoblados, mientras que los pequeños peces planctívoros y las algas carnosas dominaban los atolones poblados de Tabuaeran y Kiritimati. Los tiburones y otros depredadores principales abrumaron los conjuntos de peces en Kingman y Palmira, de modo que la pirámide de biomasa se invirtió (parte superior pesada). Por el contrario, la pirámide de biomasa en Tabuaeran y Kiritimati exhibió el típico patrón de fondo pesado. Los arrecifes sin personas exhibieron menos enfermedades de coral y un mayor reclutamiento de coral en relación con los arrecifes más habitados. Por lo tanto, la protección contra la sobrepesca y la contaminación parece aumentar la resiliencia de los ecosistemas de arrecifes a los efectos del calentamiento global. Effective conservation requires rigorous baselines of pristine conditions to assess the impacts of human activities and to evaluate the efficacy of management. Most coral reefs are moderately to severely degraded by local human activities such as fishing and pollution as well as global change, hence it is difficult to separate local from global effects. To this end, we surveyed coral reefs on uninhabited atolls in the northern Line Islands to provide a baseline of reef community structure, and on increasingly populated atolls to document changes associated with human activities. We found that top predators and reef-building organisms dominated unpopulated Kingman and Palmyra, while small planktivorous fishes and fleshy algae dominated the populated atolls of Tabuaeran and Kiritimati. Sharks and other top predators overwhelmed the fish assemblages on Kingman and Palmyra so that the biomass pyramid was inverted (top-heavy). In contrast, the biomass pyramid at Tabuaeran and Kiritimati exhibited the typical bottom-heavy pattern. Reefs without people exhibited less coral disease and greater coral recruitment relative to more inhabited reefs. Thus, protection from overfishing and pollution appears to increase the resilience of reef ecosystems to the effects of global warming. يتطلب الحفظ الفعال خطوط أساس صارمة للظروف البكر لتقييم آثار الأنشطة البشرية وتقييم فعالية الإدارة. تتدهور معظم الشعاب المرجانية بشكل معتدل إلى شديد بسبب الأنشطة البشرية المحلية مثل صيد الأسماك والتلوث وكذلك التغير العالمي، وبالتالي يصعب فصل الآثار المحلية عن العالمية. ولتحقيق هذه الغاية، قمنا بمسح الشعاب المرجانية في الجزر المرجانية غير المأهولة في جزر الخط الشمالي لتوفير خط أساس لهيكل مجتمع الشعاب المرجانية، وعلى الجزر المرجانية المكتظة بالسكان بشكل متزايد لتوثيق التغييرات المرتبطة بالأنشطة البشرية. وجدنا أن الحيوانات المفترسة العليا وكائنات بناء الشعاب المرجانية تهيمن على كينجمان وتدمر غير المأهولة بالسكان، في حين أن الأسماك الصغيرة آكلة العوالق والطحالب السمين تهيمن على الجزر المرجانية المأهولة في تابويران وكيريتيماتي. طغت أسماك القرش وغيرها من الحيوانات المفترسة العليا على تجمعات الأسماك في كينجمان وتدمر بحيث تم قلب هرم الكتلة الحيوية (الثقيل من الأعلى). على النقيض من ذلك، أظهر هرم الكتلة الحيوية في تابويران وكيريتيماتي النمط النموذجي الثقيل القاع. أظهرت الشعاب المرجانية التي لا يوجد بها أشخاص أمراضًا مرجانية أقل وتجنيدًا أكبر للشعاب المرجانية مقارنة بالشعاب المرجانية الأكثر سكانًا. وبالتالي، يبدو أن الحماية من الصيد الجائر والتلوث تزيد من مرونة النظم الإيكولوجية للشعاب المرجانية في مواجهة آثار الاحترار العالمي.

Seamounts are considered important sources of biodiversity and minerals. However, their biodiversity and health status are not well understood; therefore, potential conservation problems are unknown. The mesophotic reefs of the Vitória-Trindade Seamount Chain (VTC) were investigated via benthic community and fish surveys, metagenomic and water chemistry analyses, and water microbial abundance estimations. The VTC is a mosaic of reef systems and includes fleshy algae dominated rhodolith beds, crustose coralline algae (CCA) reefs, and turf algae dominated rocky reefs of varying health levels. Macro-carnivores and larger fish presented higher biomass at the CCA reefs (4.4 kg per frame) than in the rhodolith beds and rocky reefs (0.0 to 0.1 kg per frame). A larger number of metagenomic sequences identified as primary producers (e.g., Chlorophyta and Streptophyta) were found at the CCA reefs. However, the rocky reefs contained more diseased corals (>90%) than the CCA reefs (~40%) and rhodolith beds (~10%). Metagenomic analyses indicated a heterotrophic and fast-growing microbiome in rocky reef corals that may possibly lead to unhealthy conditions possibly enhanced by environmental features (e.g. light stress and high loads of labile dissolved organic carbon). VTC mounts represent important hotspots of biodiversity that deserve further conservation actions.

Coral reefs, one of the world's most complex and vulnerable ecosystems, face an uncertain future in coming decades as they continue to respond to anthropogenic climate change, overfishing, pollution, and other human impacts [1, 2]. Traditionally, marine macroecology is based on presence/absence data from taxonomic checklists or geographic ranges, providing a qualitative overview of spatial shifts in species richness that treats rare and common species equally [3, 4]. As a consequence, regional and long-term shifts in relative abundances of individual taxa are poorly understood. Here we apply a more rigorous quantitative approach to examine large-scale spatial variation in the species composition and abundance of corals on midshelf reefs along the length of Australia's Great Barrier Reef, a biogeographic region where species richness is high and relatively homogeneous [5]. We demonstrate that important functional components of coral assemblages "sample" space differently at 132 sites separated by up to 1740 km, leading to complex latitudinal shifts in patterns of absolute and relative abundance. The flexibility in community composition that we document along latitudinal environmental gradients indicates that climate change is likely to result in a reassortment of coral reef taxa rather than wholesale loss of entire reef ecosystems.

Caribbean reefs have undergone large-scale losses in coral cover in past decades, sparking a search for species that are resilient under stress. Porites astreoides has been considered a “winner” and a key player in sustaining coral cover in the Caribbean as more sensitive species struggle. However, P. astreoides has recently declined in abundance, raising concern about its status as a winner. Here, we reviewed the ecophysiology of P. astreoides in response to environmental stress to elucidate whether this species could thrive in the future of Caribbean reefs. We examined ecophysiological variables of P. astreoides related to photosynthesis, growth, recruitment, tissue condition, and microbiome in response to temperature, pH, macroalgal competition, depth, and sedimentation. Overall, P. astreoides was sensitive to environmental stress and each physiological feature showed varying levels of sensitivity. Coral-algal photosynthesis and coral tissue condition could withstand single events of thermal stress but reflected a metabolic imbalance that hinders recovery from repeated bleaching events, compromising long-term success. Colony growth was particularly vulnerable to low pH and macroalgal competition. Recruitment was unaffected, or even favored, by depth and could tolerate high temperatures, but it was sensitive to exposure to macroalgae, especially in combination with abiotic stressors. The response of the microbiome of P. astreoides to stressors is still poorly understood. In relation to other corals, P. astreoides was frequently reported as the most sensitive species in the reviewed literature. The success of P. astreoides is tightly integrated into the future of Caribbean reefs, which could be losing an old winner.

Life in the ocean will increasingly have to contend with a complex matrix of concurrent shifts in environmental properties that impact their physiology and control their life histories. Rhodoliths are coralline red algae (Corallinales, Rhodophyta) that are photosynthesizers, calcifiers, and ecosystem engineers and therefore represent important targets for ocean acidification (OA) research. Here, we exposed live rhodoliths to near-future OA conditions to investigate responses in their photosynthetic capacity, calcium carbonate production, and associated microbiome using carbon uptake, decalcification assays, and whole genome shotgun sequencing metagenomic analysis, respectively. The results from our live rhodolith assays were compared to similar manipulations on dead rhodolith (calcareous skeleton) biofilms and water column microbial communities, thereby enabling the assessment of host-microbiome interaction under climate-driven environmental perturbations.Under high pCO2 conditions, live rhodoliths exhibited positive physiological responses, i.e. increased photosynthetic activity, and no calcium carbonate biomass loss over time. Further, whereas the microbiome associated with live rhodoliths remained stable and resembled a healthy holobiont, the microbial community associated with the water column changed after exposure to elevated pCO2.Our results suggest that a tightly regulated microbial-host interaction, as evidenced by the stability of the rhodolith microbiome recorded here under OA-like conditions, is important for host resilience to environmental stress. This study extends the scarce comprehension of microbes associated with rhodolith beds and their reaction to increased pCO2, providing a more comprehensive approach to OA studies by assessing the host holobiont.