Now showing items 1-20 of 1301

    • Sensitivity of Cloud Microphysics on the Simulation of a Monsoon Depression Over the Bay of Bengal

      Podeti, Srinivasa Rao; Ramakrishna, S. S. V. S.; Viswanadhapalli, Yesubabu; Dasari, Hari Prasad; Nellipudi, Nanaji Rao; Rao, B. Ravi Srinivasa (Pure and Applied Geophysics, Springer Science and Business Media LLC, 2020-08-04) [Article]
      In this study, we have examined the role of implicit and explicit representation of cloud microphysics on the simulation of a monsoon depression formed over the Bay of Bengal and the associated rainfall from 0000 UTC of 13 August to 0000 UTC of 17 August 2018 using the Weather Research and Forecast model. Five different WRF model simulations are performed by changing the Cloud Micro Physics (CMP) schemes: WSM6, Goddard, Thompson, Morrison, and Thompson Scheme with Aerosol aware options in both explicit and implicit cloud models. WRF simula15 tions are conducted by initializing the NCEP GFS analysis at 0000 UTC of 13 August 2018 and integrated up to 96-h. The boundary conditions are updated at 6-hourly intervals with the respective GFS forecasts. Our results of sensitivity simulations suggest that the Thompson Scheme with Aerosol aware scheme, followed by Goddard microphysics, captured the features of monsoon depres21 sion and associated rainfall. Microphysics schemes have an influence on the simulation of low level westerly jet, and upper level easterly jet. Implicit and explicit cloud microphysics options are able to reproduce the convection over the west-coast, but the implicit option failed in producing the prolonged convection over the east coast. The comparison of model rainfall with rain-gauge, and satellite merged rainfall estimates reveals that the large scale off-shore precipitation is better captured in CMP with the inclusion of explicit cumulus parameterization. The orographic rainfall over the wind-ward and lee-ward sides of the Eastern and Western Ghats is well predicted in the implicit CMP. The vertical distribution of the hydrometeors and rainfall analysis suggest that the Thompson Scheme with Aerosol aware scheme with the cloud-resolving explicit mode is suitable for simulating the monsoon depressions formed over the Bay of Bengal and the associated heavy rainfall over the east coast of India.
    • Treating coral bleaching as weather: a framework to validate and optimize prediction skill.

      De Carlo, Thomas Mario (PeerJ, PeerJ, 2020-07-21) [Article]
      Few coral reefs remain unscathed by mass bleaching over the past several decades, and much of the coral reef science conducted today relates in some way to the causes, consequences, or recovery pathways of bleaching events. Most studies portray a simple cause and effect relationship between anomalously high summer temperatures and bleaching, which is understandable given that bleaching rarely occurs outside these unusually warm times. However, the statistical skill with which temperature captures bleaching is hampered by many "false alarms", times when temperatures reached nominal bleaching levels, but bleaching did not occur. While these false alarms are often not included in global bleaching assessments, they offer valuable opportunities to improve predictive skill, and therefore understanding, of coral bleaching events. Here, I show how a statistical framework adopted from weather forecasting can optimize bleaching predictions and validate which environmental factors play a role in bleaching susceptibility. Removing the 1 °C above the maximum monthly mean cutoff in the typical degree heating weeks (DHW) definition, adjusting the DHW window from 12 to 9 weeks, using regional-specific DHW thresholds, and including an El Niño threshold already improves the model skill by 45%. Most importantly, this framework enables hypothesis testing of other factors or metrics that may improve our ability to forecast coral bleaching events.
    • Diversity and distribution of marine heterotrophic bacteria from a large culture collection.

      Sanz-Sáez, Isabel; Salazar, Guillem; Sánchez, Pablo; Lara, Elena; Royo-Llonch, Marta; Sà, Elisabet L; Lucena, Teresa; Pujalte, María J; Vaqué, Dolors; Duarte, Carlos M.; Gasol, Josep M; Pedrós-Alió, Carlos; Sánchez, Olga; Acinas, Silvia G (BMC microbiology, Springer Science and Business Media LLC, 2020-07-15) [Article]
      BACKGROUND:Isolation of marine microorganisms is fundamental to gather information about their physiology, ecology and genomic content. To date, most of the bacterial isolation efforts have focused on the photic ocean leaving the deep ocean less explored. We have created a marine culture collection of heterotrophic bacteria (MARINHET) using a standard marine medium comprising a total of 1561 bacterial strains, and covering a variety of oceanographic regions from different seasons and years, from 2009 to 2015. Specifically, our marine collection contains isolates from both photic (817) and aphotic layers (744), including the mesopelagic (362) and the bathypelagic (382), from the North Western Mediterranean Sea, the North and South Atlantic Ocean, the Indian, the Pacific, and the Arctic Oceans. We described the taxonomy, the phylogenetic diversity and the biogeography of a fraction of the marine culturable microorganisms to enhance our knowledge about which heterotrophic marine isolates are recurrently retrieved across oceans and along different depths. RESULTS:The partial sequencing of the 16S rRNA gene of all isolates revealed that they mainly affiliate with the classes Alphaproteobacteria (35.9%), Gammaproteobacteria (38.6%), and phylum Bacteroidetes (16.5%). In addition, Alteromonas and Erythrobacter genera were found the most common heterotrophic bacteria in the ocean growing in solid agar medium. When comparing all photic, mesopelagic, and bathypelagic isolates sequences retrieved from different stations, 37% of them were 100% identical. This percentage increased up to 59% when mesopelagic and bathypelagic strains were grouped as the aphotic dataset and compared to the photic dataset of isolates, indicating the ubiquity of some bacterial isolates along different ocean depths. Finally, we isolated three strains that represent a new species, and the genome comparison and phenotypic characterization of two of these strains (ISS653 and ISS1889) concluded that they belong to a new species within the genus Mesonia. CONCLUSIONS:Overall, this study highlights the relevance of culture-dependent studies, with focus on marine isolated bacteria from different oceanographic regions and depths, to provide a more comprehensive view of the culturable marine bacteria as part of the total marine microbial diversity.
    • Low Host Abundance and High Temperature Determine Switching from Lytic to Lysogenic Cycles in Planktonic Microbial Communities in a Tropical Sea (Red Sea)

      Abdulrahman Ashy, Ruba; Agusti, Susana (Viruses, MDPI AG, 2020-07-15) [Article]
      The lytic and lysogenic life cycles of marine phages are influenced by environmental conditions such as solar radiation, temperature, and host abundance. Temperature can regulate phage infection, but its role is difficult to discern in oligotrophic waters where there is typically low host abundance and high temperatures. Here, we study the temporal variability of viral dynamics and the occurrence of lysogeny using mitomycin C in a eutrophic coastal lagoon in the oligotrophic Red Sea, which showed strong seasonality in terms of temperature (22.1–33.3 °C) and large phytoplankton blooms. Viral abundances ranged from 2.2 × 106 to 1.5 × 107 viruses mL−1 and were closely related to chlorophyll a (chl a) concentration. Observed high virus-to-bacterium ratio (VBR) (4–79; 16 ± 4 (SE)) suggests that phages exerted a tight control of their hosts as indicated by the significant decrease in bacterial abundance with increasing virus concentration. Heterotrophic bacterial abundance also showed a significant decrease with increasing temperature. However, viral abundance was not related to temperature changes and the interaction of water temperature, suggesting an indirect effect of temperature on decreased host abundance, which was observed at the end of the summertime. From the estimated burst size (BS), we observed lysogeny (undetectable to 29.1%) at low percentages of 5.0% ± 1.2 (SE) in half of the incubations with mitomycin C, while it increased to 23.9% ± 2.8 (SE) when the host abundance decreased. The results suggest that lytic phages predominate, switching to a moderate proportion of temperate phages when the host abundance reduces.
    • Travel with your kin ship! Insights from genetic sibship among settlers of a coral damselfish

      Robitzch Sierra, Vanessa S. N.; Saenz-Agudelo, Pablo; Berumen, Michael L. (Ecology and Evolution, Wiley, 2020-07-14) [Article]
      Coral reef fish larvae are tiny, exceedingly numerous, and hard to track. They are also highly capable, equipped with swimming and sensory abilities that may influence their dispersal trajectories. Despite the importance of larval input to the dynamics of a population, we remain reliant on indirect insights to the processes influencing larval behavior and transport. Here, we used genetic data (300 independent single nucleotide polymorphisms) derived from a light trap sample of a single recruitment event of Dascyllus abudafur in the Red Sea (N = 168 settlers). We analyzed the genetic composition of the larvae and assessed whether kinship among these was significantly different from random as evidence for cohesive dispersal during the larval phase. We used Monte Carlo simulations of similar-sized recruitment cohorts to compare the expected kinship composition relative to our empirical data. The high number of siblings within the empirical cohort strongly suggests cohesive dispersal among larvae. This work highlights the utility of kinship analysis as a means of inferring dynamics during the pelagic larval phase.
    • Translational Molecular Ecology in practice: Linking DNA-based methods to actionable marine environmental management

      Aylagas, Eva; Aylagas, Eva; Pochon, Xavier; Zaiko, Anastasija; Keeley, Nigel; Bruce, Kat; Hong, Pei-Ying; Ruiz, Gregory M.; Stein, Eric D.; Theroux, Susanna; Geraldi, Nathan; Ortega, Alejandra; Gajdzik, Laura; Coker, Darren James; Katan, Yasser; Hikmawan, Tyas; Saleem, Ammar; Alamer, Sultan; Jones, Burton; Duarte, Carlos M.; Pearman, John; Carvalho, Susana (Science of The Total Environment, Elsevier BV, 2020-07-12) [Article]
      Molecular-based approaches can provide timely biodiversity assessments, showing an immense potential to facilitate decision-making in marine environmental management. However, the uptake of molecular data into environmental policy remains minimal. Here, we showcase a selection of local to global scale studies applying molecular-based methodologies for environmental management at various stages of implementation. Drawing upon lessons learned from these case-studies, we provide a roadmap to facilitate applications of DNA-based methods to marine policies and to overcome the existing challenges. The main impediment identified is the need for standardized protocols to guarantee data comparison across spatial and temporal scales. Adoption of Translational Molecular Ecology – the sustained collaboration between molecular ecologists and stakeholders, will enhance consensus with regards to the objectives, methods, and outcomes of environmental management projects. Establishing a sustained dialogue among stakeholders is the key to accelerating the adoption of molecular-based approaches for marine monitoring and assessment.
    • Light supports cell-integrity and growth rates of taxonomically diverse coastal photoheterotrophs.

      Arandia-Gorostidi, Nestor; González, José M; Huete-Stauffer, Tamara; Ansari, Mohd Ikram; Moran, Xose Anxelu G.; Alonso-Sáez, Laura (Environmental microbiology, Wiley, 2020-07-10) [Article]
      Despite the widespread distribution of proteorhodopsin (PR)-containing bacteria in the oceans, the use of light-derived energy to promote bacterial growth has only been shown in a few bacterial isolates, and there is a paucity of data describing the metabolic effects of light on environmental photoheterotrophic taxa. Here, we assessed the effects of light on the taxonomic composition, cell integrity and growth responses of microbial communities in monthly incubations between spring and autumn under different environmental conditions. The photoheterotrophs expressing PR in situ were dominated by Pelagibacterales and SAR116 in July and November, while members of Euryarchaeota, Gammaproteobacteria and Bacteroidetes dominated the PR expression in spring. Cell-membrane integrity decreased under dark conditions throughout most of the assessment, with maximal effects in summer, under low-nutrient conditions. A positive effect of light on growth was observed in one incubation (out of nine), coinciding with a declining phytoplankton bloom. Light-enhanced growth was found in Gammaproteobacteria (Alteromonadales) and Bacteroidetes (Polaribacter and Tenacibaculum). Unexpectedly, some Pelagibacterales also exhibited higher growth rates under light conditions. We propose that the energy harvested by PRs helps to maintain cell viability in dominant coastal photoheterotrophic oligotrophs while promoting growth of some widespread taxa benefiting from the decline of phytoplankton blooms. This article is protected by copyright. All rights reserved.
    • Natal philopatry increases relatedness within groups of coral reef cardinalfish

      Rueger, Theresa; Harrison, Hugo B.; Buston, Peter M.; Gardiner, Naomi M.; Berumen, Michael L.; Jones, G. P. (Proceedings of the Royal Society B: Biological Sciences, The Royal Society, 2020-07-08) [Article]
      A central issue in evolutionary ecology is how patterns of dispersal influence patterns of relatedness in populations. In terrestrial organisms, limited dispersal of offspring leads to groups of related individuals. By contrast, for most marine organisms, larval dispersal in open waters is thought to minimize kin associations within populations. However, recent molecular evidence and theoretical approaches have shown that limited dispersal, sibling cohesion and/or differential reproductive success can lead to kin association and elevated relatedness. Here, we tested the hypothesis that limited dispersal explains small-scale patterns of relatedness in the pajama cardinalfish Sphaeramia nematoptera. We used 19 microsatellite markers to assess parentage of 233 juveniles and pairwise relatedness among 527 individuals from 41 groups in Kimbe Bay, Papua New Guinea. Our findings support three predictions of the limited dispersal hypothesis: (i) elevated relatedness within groups, compared with among groups and elevated relatedness within reefs compared with among reefs; (ii) a weak negative correlation of relatedness with distance; (iii) more juveniles than would be expected by chance in the same group and the same reef as their parents. We provide the first example for natal philopatry at the group level causing small-scale patterns of genetic relatedness in a marine fish.
    • Long term exposure to increasing temperature can offset predicted losses in marine food quality (fatty acids) caused by ocean warming

      Jin, Peng; Gonzalez, Gala; Agusti, Susana (Evolutionary Applications, Wiley, 2020-07-08) [Article]
      Marine phytoplankton produce essential fatty acids (FA), which are key component of a healthy diet in humans and marine food webs. Increased temperatures can reduce lipid and FA content in phytoplankton; thus, ocean warming poses a risk for the global production of these essential FA. However, responses to warming may differ between phytoplankton species especially after long-term exposure because phenotypic plasticity, de novo mutations or genetic evolution may occur. Here, we examine the content of FA and lipids in phytoplankton following long-term selection (~2 years) to warming conditions (+ 4°C), and we observe that FA and lipids content were partly or entirely recovered following long-term exposure to warming conditions. Furthermore, this observed long-term response also offset the predicted losses of some essential polyunsaturated fatty acids (PUFA) in three of the four species tested. Our study suggests that long-term exposure of phytoplankton to warming may help to maintain marine food quality in a moderately warming ocean. The responses of FA to increasing temperatures may vary among species, and the level of this idiosyncrasy remains to be further studied.
    • Seagrass losses since mid-20th century fuelled CO 2 emissions from soil carbon stocks

      Salinas, Cristian; Duarte, Carlos M.; Lavery, P. S.; Masqué, Pere; Arias-Ortiz, Ariane; Leon, Javier X.; Callaghan, David; Kendrick, G. A.; Serrano, Oscar (Global Change Biology, Wiley, 2020-07-07) [Article]
      Seagrass meadows store globally significant organic carbon (Corg) stocks which, if disturbed, can lead to CO2 emissions, contributing to climate change. Eutrophication and thermal stress continue to be a major cause of seagrass decline worldwide, but the associated CO2 emissions remain poorly understood. This study presents comprehensive estimates of seagrass soil Corg erosion following eutrophication-driven seagrass loss in Cockburn Sound (23 km2 between 1960s and 1990s) and identifies the main drivers. We estimate that shallow seagrass meadows (<5 m depth) had significantly higher Corg stocks in 50 cm thick soils (4.5 ± 0.7 kg Corg/m2) than previously vegetated counterparts (0.5 ± 0.1 kg Corg/m2). In deeper areas (>5 m), however, soil Corg stocks in seagrass and bare but previously vegetated areas were not significantly different (2.6 ± 0.3 and 3.0 ± 0.6 kg Corg/m2, respectively). The soil Corg sequestration capacity prevailed in shallow and deep vegetated areas (55 ± 11 and 21 ± 7 g Corg m−2 year−1, respectively), but was lost in bare areas. We identified that seagrass canopy loss alone does not necessarily drive changes in soil Corg but, when combined with high hydrodynamic energy, significant erosion occurred. Our estimates point at ~0.20 m/s as the critical shear velocity threshold causing soil Corg erosion. We estimate, from field studies and satellite imagery, that soil Corg erosion (within the top 50 cm) following seagrass loss likely resulted in cumulative emissions of 0.06–0.14 Tg CO2-eq over the last 40 years in Cockburn Sound. We estimated that indirect impacts (i.e. eutrophication, thermal stress and light stress) causing the loss of ~161,150 ha of seagrasses in Australia, likely resulted in the release of 11–21 Tg CO2-eq since the 1950s, increasing cumulative CO2 emissions from land-use change in Australia by 1.1%–2.3% per annum. The patterns described serve as a baseline to estimate potential CO2 emissions following disturbance of seagrass meadows.
    • A new direction for differentiating animal activity based on measuring angular velocity about the yaw axis

      Gunner, Richard; Wilson, Rory P.; Holton, Mark D.; Scott, Rebecca; Hopkins, Phil; Duarte, Carlos M. (Ecology and Evolution, Wiley, 2020-07-07) [Article]
      The use of animal-attached data loggers to quantify animal movement has increased in popularity and application in recent years. High-resolution tri-axial acceleration and magnetometry measurements have been fundamental in elucidating fine-scale animal movements, providing information on posture, traveling speed, energy expenditure, and associated behavioral patterns. Heading is a key variable obtained from the tandem use of magnetometers and accelerometers, although few field investigations have explored fine-scale changes in heading to elucidate differences in animal activity (beyond the notable exceptions of dead-reckoning). This paper provides an overview of the value and use of animal heading and a prime derivative, angular velocity about the yaw axis, as an important element for assessing activity extent with potential to allude to behaviors, using “free-ranging” Loggerhead turtles (Caretta caretta) as a model species. We also demonstrate the value of yaw rotation for assessing activity extent, which varies over the time scales considered and show that various scales of body rotation, particularly rate of change of yaw, can help resolve differences between fine-scale behavior-specific movements. For example, oscillating yaw movements about a central point of the body's arc implies bouts of foraging, while unusual circling behavior, indicative of conspecific interactions, could be identified from complete revolutions of the longitudinal axis. We believe this approach should help identification of behaviors and “space-state” approaches to enhance our interpretation of behavior-based movements, particularly in scenarios where acceleration metrics have limited value, such as for slow-moving animals.
    • Unfamiliar partnerships limit cnidarian holobiont acclimation to warming

      Herrera Sarrias, Marcela; Klein, Shannon; Schmidt-Roach, Sebastian; Campana, Sara; Cziesielski, Maha Joana; Chen, Jit Ern; Duarte, Carlos M.; Aranda, Manuel (Global Change Biology, Wiley, 2020-07-06) [Article]
      Enhancing the resilience of corals to rising temperatures is now a matter of urgency, leading to growing efforts to explore the use of heat tolerant symbiont species to improve their thermal resilience. The notion that adaptive traits can be retained by transferring the symbionts alone, however, challenges the holobiont concept, a fundamental paradigm in coral research. Holobiont traits are products of a specific community (holobiont) and all its co-evolutionary and local adaptations, which might limit the retention or transference of holobiont traits by exchanging only one partner. Here, we evaluate how interchanging partners affect the short- and long-term performance of holobionts under heat stress using clonal lineages of the cnidarian model system Aiptasia (host and Symbiodiniaceae strains) originating from distinct thermal environments. Our results show that holobionts from more thermally variable environments have higher plasticity to heat stress, but this resilience could not be transferred to other host genotypes through the exchange of symbionts. Importantly, our findings highlight the role of the host in determining holobiont productivity in response to thermal stress and indicate that local adaptations of holobionts will likely limit the efficacy of interchanging unfamiliar compartments to enhance thermal tolerance.
    • Chromosome-scale assembly of the coral endosymbiont Symbiodinium microadriaticum genome provides insight into the unique biology of dinoflagellate chromosomes

      Nand, Ankita; Zhan, Ye; Salazar, Octavio R.; Aranda, Manuel; Voolstra, Christian R.; Dekker, Job (Cold Spring Harbor Laboratory, 2020-07-03) [Preprint]
      AbstractDinoflagellates are major primary producers in the world’s oceans, the cause of harmful algal blooms, and endosymbionts of marine invertebrates. Much remains to be understood about their biology including their peculiar crystalline chromosomes. Here we used Hi-C to order short read-based sub-scaffolds into 94 chromosome-scale scaffolds of the genome of the coral endosymbiont Symbiodinium microadriaticum. Hi-C data show that chromosomes are folded as linear rods within which loci separated by up to several Mb are highly packed. Each chromosome is composed of a series of structural domains separated by boundaries. Genes are enriched towards the ends of chromosomes and are arranged in unidirectional blocks that alternate between top and bottom strands. Strikingly, the boundaries of chromosomal domains are positioned at sites where transcription of two gene blocks converges, indicating a correlation between gene orientation, transcription and chromosome folding. Some chromosomes are enriched for genes involved in specific biological processes (e.g., photosynthesis, and nitrogen-cycling), and functionally related genes tend to co-occur at adjacent sites in the genome. All chromosomes contain several repeated segments that are enriched in mobile elements. The assembly of the S. microadriaticum genome and initial description of its genetic and spatial organization provide a foundation for deeper exploration of the extraordinary biology of dinoflagellates and their chromosomes.
    • High rates of carbon and dinitrogen fixation suggest a critical role of benthic pioneer communities in the energy and nutrient dynamics of coral reefs

      Roth, Florian; Karcher, Denis B.; Rädecker, Nils; Hohn, Sönke; Carvalho, Susana; Thomson, Timothy; Saalmann, Franziska; Voolstra, Christian R.; Kürten, Benjamin; Struck, Ulrich; Jones, Burton; Wild, Christian (Functional Ecology, Wiley, 2020-07-02) [Article]
      1. Following coral mortality in tropical reefs, pioneer communities dominated by filamentous and crustose algae efficiently colonize substrates previously occupied by coral tissue. This phenomenon is particularly common after mass coral mortality following prolonged bleaching events associated with marine heatwaves. 2. Pioneer communities play an important role for the biological succession and reorganization of reefs after disturbance. However, their significance for critical ecosystem functions previously mediated by corals, such as the efficient cycling of carbon (C) and nitrogen (N) within the reef, remains uncertain. 3. We used 96 carbonate tiles to simulate the occurrence of bare substrates after disturbance in a coral reef of the central Red Sea. We measured rates of C and dinitrogen (N2) fixation of pioneer communities on these tiles monthly over an entire year. Coupled with elemental and stable isotope analyses, these measurements provide insights into macronutrient acquisition, export, and the influence of seasonality. 4. Pioneer communities exhibited high rates of C and N2 fixation within 4 – 8 weeks after the introduction of experimental bare substrates. Ranging from 13 to 25 μmol C cm−2 d−1 and 8 to 54 nmol N cm−2 d−1, respectively, C and N2 fixation rates were comparable to reported values for established Red Sea coral reefs. This similarity indicates that pioneer communities may quickly compensate for the loss of benthic productivity by corals. Notably, between 40 and 85% of fixed organic C was exported into the environment, constituting a vital source of energy for the coral reef food web. 5. Our findings suggest that benthic pioneer communities may play a crucial, yet overlooked role in the C and N dynamics of oligotrophic coral reefs by contributing to the input of new C and N after coral mortality. While not substituting other critical ecosystem functions provided by corals (e.g. structural habitat complexity and coastal protection), pioneer communities likely contribute to maintaining coral reef nutrient cycling through the accumulation of biomass and import of macronutrients following coral loss.
    • Cell-by-cell estimation of PAH sorption and subsequent toxicity in marine phytoplankton

      Kottuparambil, Sreejith; Agusti, Susana (Chemosphere, Elsevier BV, 2020-07-01) [Article]
      Polycyclic Aromatic Hydrocarbons (PAHs) have elicited increasing concern due to their ubiquitous occurrence in coastal marine environments and resultant toxicity in organisms. Due to their lipophilic nature, PAHs tend to accumulate in phytoplankton cells and thus subsequently transfer to other compartments of the marine ecosystem. The intrinsic fluorescence properties of PAHs in the ultraviolet (UV)/blue spectral range have recently been exploited to investigate their uptake modes, localization, and aggregation in various biological tissues. Here, we quantitatively evaluate the sorption of two model PAHs (phenanthrene and pyrene) in three marine phytoplankton species (Chaetoceros tenuissimus, Thalassiosira sp. and Proteomonas sp.) using a combined approach of UV excitation flow cytometry and fluorescence microscopy. Over a 48-h exposure to a gradient of PAHs, Thalassiosira sp. showed the highest proportion of PAH-sorbed cells (29% and 97% of total abundance for phenanthrene and pyrene, respectively), which may be attributed to its relatively high total lipid content (33.87 percent dry weight). Moreover, cell-specific pulse amplitude modulation (PAM) microscope fluorometry revealed that PAH sorption significantly reduced the photosynthetic quantum efficiency (Fv/Fm) of individual phytoplankton cells. We describe a rapid and precise hybrid method for the detection of sorption of PAHs on phytoplankton cells. Our results emphasize the ecologically relevant sub-lethal effects of PAHs in phytoplankton at the cellular level, even at concentrations where no growth inhibition was apparent. This work is the first study to address the cell-specific impacts of fluorescent toxicants in a more relevant toxicant-sorbed subpopulation; these cell-specific impacts have to date been unidentified in traditional population-based phytoplankton toxicity assays.
    • Patterns, drivers, and ecological implications of upwelling in coral reef habitats of the southern Red Sea

      De Carlo, Thomas Mario; Carvalho, Susana; Gajdzik, Laura; Hardenstine, Royale; Tanabe, Lyndsey K; Villalobos, Rodrigo; Berumen, Michael L. (Wiley, 2020-06-28) [Preprint]
      Coral reef ecosystems are highly sensitive to thermal anomalies, making them vulnerable to ongoing global warming. Yet, a variety of cooling mechanisms, such as upwelling, offer some respite to certain reefs. The Farasan Banks in the southern Red Sea is home to hundreds of coral reefs covering 16,000 km and experiences among the highest water temperatures of any coral-reef region despite exposure to summertime upwelling. We deployed an array of temperature loggers on coral reefs in the Farasan Banks, enabling us to evaluate the skill of satellite-based sea surface temperature (SST) products for capturing patterns of upwelling. Additionally, we used remote sensing products to investigate the physical drivers of upwelling, and to better understand how upwelling modulates summertime heat stress on coral communities. Our results show that various satellite SST products underestimate reef-water temperatures but differ in their ability to capture the spatial and temporal dynamics of upwelling. Monsoon winds from June to September drive the upwelling in the southern Red Sea via Ekman transport of surface waters off the shelf, and this process is ultimately controlled by the southwest Indian monsoon in the Arabian Sea. Further, the timing of the cessation of monsoon winds regulates the maximum water temperatures that are reached in September and October. In addition to describing the patterns and mechanisms of upwelling, our study sheds light on the broad ecological implications of this upwelling system, including modulation of coral bleaching events and effects on biodiversity, sea turtle reproduction, fish pelagic larval duration, and planktivore populations.
    • Additive impacts of deoxygenation and acidification threaten marine biota.

      Steckbauer, Alexandra; Klein, Shannon; Duarte, Carlos M. (Global change biology, Wiley, 2020-06-26) [Article]
      Deoxygenation in coastal and open-ocean ecosystems rarely exists in isolation but occurs concomitantly with acidification. Here, we first combine meta-data of experimental assessments from across the globe to investigate the potential interactive impacts of deoxygenation and acidification on a broad range of marine taxa. We then characterize the differing degrees of deoxygenation and acidification tested in our dataset using a ratio between the partial pressure of oxygen and carbon dioxide (pO2 /pCO2 ) to assess how biological processes change under an extensive, yet diverse range of pO2 and pCO2 conditions. The dataset comprised 375 experimental comparisons and revealed predominantly additive but variable effects (91.7%-additive, 6.0%-synergistic, 2.3%-antagonistic) of the dual stressors, yielding negative impacts across almost all responses examined. Our data indicates that the pO2 /pCO2 -ratio offers a simplified metric to characterize the extremity of the concurrent stressors and shows that more severe impacts occurred when ratios represented more extreme deoxygenation and acidification conditions. Importantly, our analysis highlights the need to assess the concurrent impacts of deoxygenation and acidification on marine taxa and that assessments considering the impact of O2 depletion alone will likely underestimate the impacts of deoxygenation events and their ecosystem-wide consequences.
    • Giant clams in shallow reefs: UV-resistance mechanisms of Tridacninae in the Red Sea

      Rossbach, Susann; Overmans, Sebastian; Kaidarova, Altynay; Kosel, Jürgen; Agusti, Susana; Duarte, Carlos M. (Coral Reefs, Springer Science and Business Media LLC, 2020-06-22) [Article]
      The photosymbiosis of tropical giant clams (subfamily Tridacninae) with unicellular algae (Symbiodiniaceae) restricts their distribution to the sunlit, shallow waters of the euphotic zone where organisms are additionally exposed to potentially damaging levels of solar UV radiation. Metabolic and physiological responses of Red Sea Tridacna maxima clams, including net calcification and primary production, as well as valvometry (i.e., shell gaping behavior) were assessed when exposed to simulated high radiation levels received at 3 and 5 m underwater. The two levels of radiation included exposure treatments to photosynthetically active radiation (PAR; 400–700 nm) alone and to both, PAR and ultraviolet-B radiation (UV-B;280–315 nm). The valvometry data obtained using flexible magnetic sensors indicated that specimens under PAR ? UV-B exposure significantly reduced the proportion of their exposed mantle area, a potential photo-protective mechanism which, however, reduces the overall amount of PAR received by the algal symbionts. Consequently, specimens under PAR ? UV-B displayed a slight, although non-significant, reduction in primary production rates but no signs of additional oxidative stress, changes in symbiont densities, chlorophyll content, or levels of mycosporine-like amino acids. Net calcification rates of T.maxima were not affected by exposure to UV-B; however, calcification was positively correlated with incident PAR levels. UV-B exposure changes the valvometry, reducing the exposed mantle area which consequently diminishes the available PAR for the photosymbionts. Still, T. maxima maintains high rates of primary production and net calcification, even under high levels of UV-B. This provides experimental support for a recently described, effective UV-defensive mechanism in Tridacninae, in which the photonic cooperation of the associated algal symbionts and giant clam iridocytes is assumed to establish optimal conditions for the photosynthetic performance of the clams’ symbionts.
    • COVID-19 lockdown allows researchers to quantify the effects of human activity on wildlife

      Rutz, Christian; Loretto, Matthias-Claudio; Bates, Amanda E.; Davidson, Sarah C.; Duarte, Carlos M.; Jetz, Walter; Johnson, Mark; Kato, Akiko; Kays, Roland; Mueller, Thomas; Primack, Richard B.; Ropert-Coudert, Yan; Tucker, Marlee A.; Wikelski, Martin; Cagnacci, Francesca (Nature Ecology & Evolution, Springer Science and Business Media LLC, 2020-06-22) [Article]
      We noticed that people started referring to the lockdown period as the ‘Great Pause’, but felt that a more precise term would be helpful. We propose ‘anthropause’ to refer specifcally to a considerable global slowing of modern human activities, notably travel. We are aware that the correct prefx is ‘anthropo-’ (for ‘human’) but opted for the shortened form, which is easier to remember and use, and where the missing ‘po’ is still echoed in the pronunciation of ‘pause’ (pɔːz).
    • Standardized short-term acute heat stress assays resolve historical differences in coral thermotolerance across microhabitat reef sites

      Voolstra, Christian R.; Buitrago-López, Carol; Perna, Gabriela; Cardenas, Anny; Hume, Benjamin; Rädecker, Nils; Barshis, Daniel J. (Global Change Biology, Wiley, 2020-06-22) [Article]
      Coral bleaching is one of the main drivers of reef degradation. Most corals bleach and suffer mortality at just 1–2°C above their maximum monthly mean temperatures, but some species and genotypes resist or recover better than others. Here, we conducted a series of 18-hr short-term acute heat stress assays side-by-side with a 21-day long-term heat stress experiment to assess the ability of both approaches to resolve coral thermotolerance differences reflective of in situ reef temperature thresholds. Using a suite of physiological parameters (photosynthetic efficiency, coral whitening, chlorophyll a , host protein, algal symbiont counts, and algal type association), we assessed bleaching susceptibility of Stylophora pistillata colonies from the windward/exposed and leeward/protected sites of a nearshore coral reef in the central Red Sea, which had previously shown differential mortality during a natural bleaching event. Photosynthetic efficiency was most indicative of the expected higher thermal tolerance in corals from the protected reef site, denoted by an increased retention of dark-adapted maximum quantum yields at higher temperatures. These differences were resolved using both experimental setups, as corroborated by a positive linear relationship, not observed for the other parameters. Notably, short-term acute heat stress assays resolved per-colony (genotype) differences that may have been masked by acclimation effects in the long-term experiment. Using our newly developed portable experimental system termed the Coral Bleaching Automated Stress System (CBASS), we thus highlight the potential of mobile, standardized short-term acute heat stress assays to resolve fine-scale differences in coral thermotolerance. Accordingly, such a system may be suitable for large-scale determination and complement existing approaches to identify resilient genotypes/reefs for downstream experimental examination and prioritization of reef sites for conservation/restoration. Development of such a framework is consistent with the recommendations of the National Academy of Sciences and the Reef Restoration and Adaptation Program committees for new intervention and restoration strategies.