Assessing the Risks of Potential Bacterial Pathogens Attaching to Different Microplastics during the Summer–Autumn Period in a Mariculture Cage

As microplastic pollution continues to increase, an emerging threat is the potential for microplastics to act as novel substrates and/or carriers for pathogens. This is of particular concern for aquatic product safety given the growing evidence of microplastic ingestion by aquaculture species. However, the potential risks of pathogens associated with microplastics in mariculture remain poorly understood. Here, an in situ incubation experiment involving three typical microplastics including polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP) was conducted during the summer–autumn period in a mariculture cage. The identification of potential pathogens based on the 16S rRNA gene amplicon sequencing and a custom-made database for pathogenic bacteria involved in aquatic environments, was performed to assess the risks of different microplastics attaching potential pathogens. The enrichment of pathogens was not observed in microplastic-associated communities when compared with free-living and particle-attached communities in surrounding seawater. Despite the lower relative abundance, pathogens showed different preferences for three microplastic substrates, of which PET was the most favored by pathogens, especially potentially pathogenic members of Vibrio, Tenacibaculum, and Escherichia. Moreover, the colonization of these pathogens on microplastics was strongly affected by environmental factors (e.g., temperature, nitrite). Our results provide insights into the ecological risks of microplastics in mariculture industry.

Unravelling Light and Microbial Activity as Drivers of Organic Matter Transformations in Tropical Headwater Rivers

Connecting tropical rainforests to larger rivers, tropical headwaters export large quantities of carbon and nutrients as dissolved organic matter (DOM), and are thus a key component of the global carbon cycle. This DOM transport is not passive, however; sunlight and microbial activity alter DOM concentrations and compositions, affecting riverine greenhouse gas emissions and downstream ecosystems. The effects of sunlight and microbial turnover/activity on DOM concentrations and compositions in tropical headwaters are currently poorly understood, but novel Size Exclusion Chromatography (SEC) techniques coupled to suitable detectors can for the first time quantify their influences. Here, we present in-situ incubation experiments from from headwaters of the Essequibo River, in the Iwokrama Rainforest, Guyana, where sunlight oxidised up to 9% of dissolved organic carbon (DOC) over 12 hours, at higher rates than in larger tropical rivers. DOM transformations occurred in both photo-sensitive and supposedly photo-resistant pools. Microbial activity had varying, less clear influences on DOC concentrations over the same time span; compositionally, this appeared to extend beyond known bio-labile components. Biopolymers were particularly reactive to both processes. We show sunlight has the greater potential to mineralise headwater DOM and thus potentially influence degassing. Our approach provides a future template to constrain DOM transformations along river networks, identify biogeochemical activity hotspots, and improve greenhouse gas emissions estimations under changing environmental conditions.

Vibrio Colonization Is Highly Dynamic in Early Microplastic-Associated Biofilms as Well as on Field-Collected Microplastics

Microplastics are ubiquitous in aquatic ecosystems and provide a habitat for biofilm-forming bacteria. The genus Vibrio, which includes potential pathogens, was detected irregularly on microplastics. Since then, the potential of microplastics to enrich (and serve as a vector for) Vibrio has been widely discussed. We investigated Vibrio abundance and operational taxonomic unit (OTU) composition on polyethylene and polystyrene within the first 10 h of colonization during an in situ incubation experiment, along with those found on particles collected from the Baltic Sea. We used 16S rRNA gene amplicon sequencing and co-occurrence networks to elaborate the role of Vibrio within biofilms. Colonization of plastics with Vibrio was detectable after one hour of incubation; however, Vibrio numbers and composition were very dynamic, with a more stable population at the site with highest nutrients and lowest salinity. Likewise, Vibrio abundances on field-collected particles were variable but correlated with proximity to major cities. Vibrio was poorly connected within biofilm networks. Taken together, this indicates that Vibrio is an early colonizer of plastics, but that the process is undirected and independent of the specific surface. Still, higher nutrients could enhance a faster establishment of Vibrio populations. These parameters should be considered when planning studies investigating Vibrio on microplastics.

52 Effects of an energy or protein supplement on forage dry matter intake for steers grazing summer native range

The objective of this study was to determine the effects of supplementation level and type on forage intake of steers grazing a high-quality native range. This study was conducted in late May through the end of June. On d 0, steers (n=16, initial BW = 193.7 kg ± 14.3 kg) were randomly assigned to one of 5 dietary treatments, fed once daily in individual stalls for 28 d. Treatments were control (no supplement, n=4), or supplemented with either cottonseed meal or dry rolled corn, each at either 0.45 kg or 1.81 kg as-fed/d (n=3 for each combination). Beginning on d 7, steers were orally administered titanium dioxide boluses (10 g/steer) once daily for 21 d. Fecal samples were collected from the rectum once daily for 14 d, analyzed for Ti concentration via a handheld X-ray fluorescence analyzer, and total fecal output was estimated. Diet digestibility was estimated after a 288-h in situ incubation of forage and fecal samples to determine indigestible NDF. Some steers had orts, therefore actual mean supplement intake was used in analysis. Results were analyzed with regression, with animal as the experimental unit. Mean estimated forage DMI of unsupplemented animals was 1.6% BW. Contrary to expectation, corn supplemented steers exhibited greater forage DMI as a percentage of BW than cottonseed meal supplemented steers (P = 0.01; 1.5 vs. 1.1, respectively).

Comparison of in situ techniques to evaluate the recovery of indigestible components and the accuracy of digestibility estimates

Indigestible components, including indigestible dry matter (iDM) and indigestible neutral detergent fiber (iNDF), play an integral role as internal markers for determining ruminal kinetics and digestibility estimations. However, the accuracy of internal markers is dependent upon the incubation technique utilized as bag type (BT) and incubation length (IL) can be significant sources of error. Previous studies have primarily focused on iDM and iNDF as digestibility markers, but few studies have compared digestibility estimates to those of acid detergent insoluble ash (ADIA). Therefore, our objective was to investigate the effect of BT (F57, F58, and Dacron) and IL (288 and 576 h) on iDM and iNDF residues, DM and NDF digestibilities, and fecal recoveries when using in situ incubations. Additionally, we evaluated the accuracy of digestibility estimates when using iDM, iNDF, and ADIA. For iDM and iNDF, feed residues demonstrated a BT × IL interaction (P < 0.01). However, fecal residues were only influenced by the main effects of BT and IL (P < 0.01), with the F58 BT and 288-h IL having the greatest residues for both iDM and iNDF. The variation in residues was greatly reduced when using iNDF compared with iDM. Fecal recovery estimates most closely approximated 100% recovery when utilizing ADIA and iDM using the F57 × 576 h incubation method (P < 0.01), although recovery was overestimated for all incubation combinations. Fecal NDF recovery estimates better represented the excretion profiles when the F57 × 576 h combination was used with iDM as the internal marker (P < 0.01). Estimates of DM and NDF digestibility were the most accurate when utilizing ADIA (P < 0.01) relative to all other treatments. Our results indicate that the proper methodological application is specific to the purpose of the inferences. When evaluating fecal recoveries and digestibility, ADIA or iDM with F57 at 576-h in situ incubation provides the greatest accuracy.

Heat, health and hatchlings: associations of in situ nest temperatures with morphological and physiological characteristics of loggerhead sea turtle hatchlings from Florida

Incubation temperatures, in addition to an embryo’s genetic makeup, are critical in many aspects of adequate sea turtle embryonic development. The effects of high and low incubation temperatures on hatchling quality have been previously examined; however, many of these studies were conducted on relocated or laboratory-reared nests, which do not accurately reflect natural nest temperature fluctuations. To observe the impacts of varying in situ incubation temperatures on loggerhead sea turtle (Caretta caretta) hatchling morphology, various health variables and locomotor performance, temperature data loggers were deployed in 15 loggerhead nests on Juno Beach, Florida, between May and July 2018. Over the course of the study period, 10 morphological traits were measured, blood analytes and heart rate were assessed for the establishment of reference intervals and the self-righting response in seawater was evaluated. Warmer months were associated with smaller body size and higher body condition index, larger umbilical scar size, slower righting time, lower heart rates and higher packed cell volume, hemoglobin, total solids, total white blood cell count, absolute heterophils and absolute basophils. These findings provide evidence that higher in situ incubation temperatures have the potential to adversely affect hatchlings from warmer nests due to increased risk of predation from smaller body sizes, decreased physical responses and overall fitness, altered hemodynamic balance (e.g. dehydration) and potential inflammation and/or stress. With rising temperatures, we predict sea turtle hatchlings may have increasing risks of developing suboptimal physiological features affecting overall fitness and ultimately survival. These results demonstrate that rising environmental temperatures can negatively impact sea turtle hatchlings, thus representing additional stress on sea turtle populations and contributing to our understanding of potential pathophysiological effects of climate change on the delicate life-stage class of the sea turtle hatchling. This information will be useful for formulating effective future sea turtle management plans.

Major role of ammonia-oxidizing bacteria in N₂O production in the Pearl River estuary

Nitrous oxide (N2O) has significant global warming potential as a greenhouse gas. Estuarine and coastal regimes are the major zones of N2O production in the marine system. However, knowledge on biological sources of N2O in estuarine ecosystems remains controversial but is of great importance for understanding global N2O emission patterns. Here, we measured concentrations and isotopic compositions of N2O as well as distributions of ammonia-oxidizing bacterial and archaeal amoA and denitrifier nirS genes by quantitative polymerase chain reaction along a salinity gradient in the Pearl River estuary, and we performed in situ incubation experiments to estimate N2O yields. Our results indicated that nitrification predominantly occurred, with significant N2O production during ammonia oxidation. In the hypoxic waters of the upper estuary, strong nitrification resulted in the observed maximum N2O and ΔN2Oexcess concentrations, although minor denitrification might be concurrent at the site with the lowest dissolved oxygen. Ammonia-oxidizing β-proteobacteria (AOB) were significantly positively correlated with all N2O-related parameters, although their amoA gene abundances were distinctly lower than ammonia-oxidizing archaea (AOA) throughout the estuary. Furthermore, the N2O production rate and the N2O yield normalized to amoA gene copies or transcripts estimated a higher relative contribution of AOB to the N2O production in the upper estuary. Taken together, the in situ incubation experiments, N2O isotopic composition and concentrations, and gene datasets suggested that the high concentration of N2O (oversaturated) is mainly produced from strong nitrification by the relatively high abundance of AOB in the upper reaches and is the major source of N2O emitted to the atmosphere in the Pearl River estuary.

Calanoid copepod grazing affects plankton size structure and composition in a deep, large lake

Cultural oligotrophication is expected to shift lake zooplankton to become dominated by calanoid copepods. Hence, understanding the influence of calanoids on the taxonomic and size structure of the lower plankton food web is crucial for predicting the effects of oligotrophication on energy fluxes in these systems. We studied the effect of an omnivorous calanoid, Eudiaptomus gracilis, on the lower planktonic food web using an in situ incubation approach in large and deep Lake Constance. We show that E. gracilis significantly reduced ciliate, phytoplankton, rotifer, but increased bacteria biovolume. Highest clearance rates were observed for ciliates whose biovolume declines may have caused a release of predation pressure on bacteria. E. gracilis grazing shifted the size structure of the phytoplankton community by reducing mean phytoplankton cell size (directional selection) and simultaneously increasing cell size variance (disruptive selection). Ciliate cell sizes experienced a similar selective regime in one of the experiments, whereas in the other two experiments, no change of size structure was detected. Results suggest strong influences of E. gracilis grazing on the lower plankton food web and a significant shift in phytoplankton size structure. For evaluating detailed effects of omnivorous consumers on plankton size structure, cascading interactions need to be considered.