The prokaryotic and eukaryotic microbiome of Pacific oyster spat is shaped by ocean warming but not acidification

Pacific oysters (Magallana gigas, a.k.a. Crassostrea gigas), the most widely farmed oysters, are under threat from climate change and emerging pathogens. In part, their resilience may be affected by their microbiome, which, in turn, may be influenced by ocean warming and acidification. To understand these impacts, we exposed early-development Pacific oyster spat to different temperatures (18°C and 24°C) and pCO2 levels (800, 1,600, and 2,800 µatm) in a fully crossed design for 3 weeks. Under all conditions, the microbiome changed over time, with a large decrease in the relative abundance of potentially pathogenic ciliates (Uronema marinum) in all treatments with time. The microbiome composition differed significantly with temperature, but not acidification, indicating that Pacific oyster spat microbiomes can be altered by ocean warming but is resilient to ocean acidification in our experiments. Microbial taxa differed in relative abundance with temperature, implying different adaptive strategies and ecological specializations among microorganisms. Additionally, a small proportion (~0.2% of the total taxa) of the relatively abundant microbial taxa were core constituents (>50% occurrence among samples) across different temperatures, pCO2 levels, or time. Some taxa, including A4b bacteria and members of the family Saprospiraceae in the phyla Chloroflexi (syn. Chloroflexota) and Bacteroidetes (syn. Bacteroidota), respectively, as well as protists in the genera Labyrinthula and Aplanochytrium in the class Labyrinthulomycetes, and Pseudoperkinsus tapetis in the class Ichthyosporea were core constituents across temperatures, pCO2 levels, and time, suggesting that they play an important, albeit unknown, role in maintaining the structural and functional stability of the Pacific oyster spat microbiome in response to ocean warming and acidification. These findings highlight the flexibility of the spat microbiome to environmental changes.IMPORTANCEPacific oysters are the most economically important and widely farmed species of oyster, and their production depends on healthy oyster spat. In turn, spat health and productivity are affected by the associated microbiota; yet, studies have not scrutinized the effects of temperature and pCO2 on the prokaryotic and eukaryotic microbiomes of spat. Here, we show that both the prokaryotic and, for the first time, eukaryotic microbiome of Pacific oyster spat are surprisingly resilient to changes in acidification, but sensitive to ocean warming. The findings have potential implications for oyster survival amid climate change and underscore the need to understand temperature and pCO2 effects on the microbiome and the cascading effects on oyster health and productivity.

Lethal and sublethal implications of low temperature exposure for three intertidal predators

Benthic invertebrate predators play a key role in top-down trophic regulation in intertidal ecosystems. While the physiological and ecological consequences of predator exposure to high temperatures during summer low tides are increasingly well-studied, the effects of cold exposure during winter low tides remain poorly understood. To address this knowledge gap, we measured the supercooling points, survival, and feeding rates of three intertidal predator species in British Columbia, Canada - the sea stars Pisaster ochraceus and Evasterias troschelii and the dogwhelk Nucella lamellosa - in response to exposure to sub-zero air temperatures. Overall, we found that all three predators exhibited evidence of internal freezing at relatively mild sub-zero temperatures, with sea stars exhibiting an average supercooling point of -2.50 °C, and the dogwhelk averaging approximately -3.99 °C. None of the tested species are strongly freeze tolerant, as evidenced by moderate-to-low survival rates after exposure to -8 °C air. All three predators exhibited significantly reduced feeding rates over a two-week period following a single 3-h sublethal (-0.5 °C) exposure event. We also quantified variation in predator body temperature among thermal microhabitats during winter low tides. Predators that were found at the base of large boulders, on the sediment, and within crevices had higher body temperatures during winter low tides, as compared to those situated in other microhabitats. However, we did not find evidence of behavioural thermoregulation via selective microhabitat use during cold weather. Since these intertidal predators are less freeze tolerant than their preferred prey, winter low temperature exposures can have important implications for organism survival and predator-prey dynamics across thermal gradients at both local (habitat-driven) and geographic (climate-driven) scales.

Extreme heatwave drives topography-dependent patterns of mortality in a bed-forming intertidal barnacle, with implications for associated community structure

Heatwave frequency and intensity will increase as climate change progresses. Intertidal sessile invertebrates, which often form thermally benign microhabitats for associated species, are vulnerable to thermal stress because they have minimal ability to behaviourally thermoregulate. Understanding what factors influence the mortality of biogenic species and how heatwaves might impact their ability to provide habitat is critical. Here, we characterize the community associated with the thatched barnacle, Semibalanus cariosus (Pallass, 1788), in British Columbia (BC), Canada. Then, we investigate what site-level and plot-level environmental factors explained variations in barnacle mortality resulting from an unprecedented regional heatwave in BC, Canada. Furthermore, we used a manipulative shading experiment deployed prior to the heatwave to examine the effect of thermal stress on barnacle survival and recruitment and the barnacle-associated community. We identified 50 taxa inhabiting S. cariosus beds, with variations in community composition between sites. Site-scale variables and algal canopy cover did not predict S. cariosus mortality, but patch-scale variation in substratum orientation did, with more direct solar irradiance corresponding with higher barnacle mortality. The shading experiment demonstrated that S. cariosus survival, barnacle recruitment, and invertebrate community diversity were higher under shades where substratum temperatures were lower. Associated community composition also differed between shaded and non-shaded plots, suggesting S. cariosus was not able to fully buffer acute thermal stress for its associated community. While habitat provisioning by intertidal foundation species is an important source of biodiversity, these species alone may not be enough to prevent substantial community shifts following extreme heatwaves. As heatwaves become more frequent and severe, they may further reduce diversity via the loss of biogenic habitat, and spatial variation in these impacts may be substantial.

Seasonal and annual dynamics of western Canadian boreal forest plant communities: A legacy data set spanning four decades

As boreal forests rapidly warm due to anthropogenic climate change, long-term baseline community data are needed to effectively characterize the corresponding ecological changes that are occurring in these forests. The combined seasonal dynamics (SEADYN) and annual dynamics (ANNDYN) data set, which documents the vegetative changes in boreal forests during the snow-free period, is one such source of baseline community data. These data were collected by George H. La Roi and colleagues in Alberta, Canada from 1980 to 2015 within permanent sampling plots established in the Hondo-Slave Lake area (eight stands; 1980-2015) in central Alberta and the Athabasca Oil Sands (AOS) region (17 stands; 1981-1984) near Fort McMurray in northeastern Alberta. Various data were collected, with temporal and spatial coverage differing by data set. These data sets include, but are not limited to, cover of each identified vascular plant and bryoid (moss, liverwort, and lichen) species; forest mensuration; forest litter production; and soil temperature and moisture. Notably, permanent sampling plots were set up as a grid, which will facilitate analyses of spatial relations. These data can be used to analyze long-term changes in seasonal dynamics and succession within boreal forest communities and serve as a baseline for comparison with future forest conditions in unmanaged, managed, and reclaimed forests. Data are released under a CC-BY license; please cite this data paper when using the data for analyses.

The journey of hull-fouling mobile invaders: basibionts and boldness mediate dislodgement risk during transit

Vessel hull-fouling is responsible for most bioinvasion events in the marine environment, yet it lacks regulation in most countries. Although experts advocate a preventative approach, research efforts on pre-arrival processes are limited. The performance of mobile epifauna during vessel transport was evaluated via laboratory simulations, using the well-known invasive Japanese skeleton shrimp (Caprella mutica), and its native congener C. laeviuscula as case study. The invader did not possess any advantage in terms of inherent resistance to drag. Instead, its performance was conditioned by the complexity of secondary substrate. Dislodgement risk was significantly reduced when sessile fouling basibionts were added, which provided refugia and boosted the probability of C. mutica remaining attached from 7 to 65% in flow exposure trials. Interestingly, the invader exhibited significantly higher exploratory tendency and motility than its native congener at zero-flow conditions. Implications in terms of en-route survivorship, invasion success and macrofouling management are discussed.

Ecological and environmental context shape the differential effects of a facilitator in its native and invaded ranges

Invasive species often exhibit disproportionately strong negative effects in their introduced range compared to their native range, and much research has been devoted to understanding the role of shared evolutionary history, or lack thereof, in driving these differences. Less studied is whether introduced species, particularly those that are important as facilitators in their native range, have persistent positive effects in their invaded range despite a lack of a shared evolutionary history with the invaded community. Here, we manipulated the density of a habitat-forming facilitator, the high intertidal acorn barnacle Balanus glandula, factorially with herbivore density in its native range (Bluestone Point, British Columbia, Canada) and invaded range (Punta Ameghino, Chubut Province, Argentina) to determine how this facilitator differentially affects associated species at these two locations. Given that high intertidal species at Punta Ameghino (PA) are evolutionarily naïve to barnacles, we predicted that the positive effects of B. glandula at PA would be absent or weak compared to those at Bluestone Point (BP). However, we found that B. glandula had an equally positive effect on herbivore biomass at PA compared to BP, possibly because the moisture-retaining properties of barnacle bed habitats are particularly important in seasonally dry Patagonia. Barnacle presence indirectly decreased ephemeral algal cover at BP by increasing grazer pressure, but barnacles instead facilitated ephemeral algae at PA. In contrast, B. glandula increased perennial algal cover at BP, but generally decreased perennial algal cover at PA, likely due to differences in dominant algal morphology. Though our experiment was limited to one location on each continent, our results suggest that shared evolutionary history may not be a prerequisite for strong facilitation to occur, but rather that the nature and strength of novel species interactions are determined by the traits of associated species and the environment in which they occur.

Foregut Development and Metamorphosis in a Pyramidellid Gastropod: Modularity and Constraint within a Complex Life Cycle

Pyramidellids are tiny ectoparasitic gastropods with highly derived feeding structures for piercing and sucking. We attempted to resolve homology controversies about unique pyramidellid feeding structures by examining foregut development through larval and metamorphic stages, using sections for light and electron microscopy. We anticipated that, like many marine invertebrate larvae, post-metamorphic structures would differentiate extensively in late larvae to speed metamorphic transition. Previous studies of gastropods suggested that development of juvenile feeding structures in larvae was facilitated by foregut subdivision into dorsal and ventral developmental modules, and spatial uncoupling of these modules may have facilitated adaptive radiation in neogastropods. Observations of Odostomia tenuisculpta suggested that the stylet may be derived from cuticle-secreting buccal epithelium surrounding the proximal end of the salivary duct, whereas the stylet sheath could be either a derived jaw or a radular tooth. The anterior half of the remarkable buccal pump of these euthyneuran gastropods develops from the larval esophagus, which is unorthodox compared to caenogastropods, where extensive post-metamorphic specialization of a dorsal module component has not been previously described. The introvert tube develops from pouches of the distal larval esophagus and may actually be an eversible oral tube rather than an acrembolic proboscis. Minimal differentiation of presumptive juvenile foregut structures occurred during the larval stage of O. tenuisculpta, when compared to other gastropods. The stylet, stylet sheath, and buccal pump may be incompatible with functioning of the larval esophagus; thus, an explosive period of morphogenesis is necessary at metamorphosis. Although dorsal and ventral modules were recognizable during the development of O. tenuisculpta, we failed to find evidence that this modularity facilitated the extreme evolutionary remodeling of post-metamorphic feeding structures.

Electron ionization mass spectrometric analysis of air- and moisture-sensitive organometallic compounds

Electron ionization (EI) is a reliable mass spectrometric method for the analysis of the vast majority of thermally stable and volatile compounds.

Chemical stability and degradation mechanisms of triangular Ag, Ag@Au, and Au nanoprisms

Anisotropic metal nanoparticles have found use in a variety of plasmonic applications because of the large near-field enhancements associated with them; however, the very features that give rise to these enhancements (e.g., sharply curved edges and tips) often have high surface energies and are easily degraded. This paper describes the stability and degradation mechanisms of triangular silver, gold-coated silver, and gold nanoprisms upon exposure to a wide variety of adverse conditions, including halide ions, thiols, amines and elevated temperatures. The silver nanoprisms were immediately and irreversibly degraded under all of the conditions studied. In contrast, the core-shell Ag@Au nanoprisms were less susceptible to etching by chlorides and bromides, but were rapidly degraded by iodides, amines and thiols by a different degradation pathway. Only the pure gold nanoprisms were stable to all of the conditions tested. These results have important implications for the suitability of triangular nanoprisms in many applications; this is particularly true in biological or environmental fields, where the nanoparticles would inevitably be exposed to a wide variety of chemical stimuli.