Gut bacterial communities in Atlantic bottlenose dolphins (Tursiops truncatus) throughout a disease-driven (Morbillivirus) unusual mortality event.

Gut microbiomes are important determinants of animal health. In sentinel marine mammals where animal and ocean health are connected, microbiome impacts can scale to ecosystem-level importance. Mass mortality events affect cetacean populations worldwide, yet little is known about the contributory role of their gut bacterial communities to disease susceptibility and progression. Here, we characterized bacterial communities from fecal samples of common bottlenose dolphins, Tursiops truncatus, across an unusual mortality event (UME) caused by dolphin Morbillivirus (DMV). 16S rRNA gene sequence analysis revealed similar diversity and structure of bacterial communities in individuals stranding before, during, and after the 2013-2015 Mid-Atlantic Bottlenose Dolphin UME and these trends held in a subset of dolphins tested by PCR for DMV infection. Fine-scale shifts related to the UME were not common (10 of 968 bacterial taxa) though potential biomarkers for health monitoring were identified within the complex bacterial communities. Accordingly, acute DMV infection was not associated with a distinct gut bacterial community signature in T. truncatus. However, temporal stratification of DMV-positive dolphins did reveal changes in bacterial community composition between early and late outbreak periods, suggesting that gut community disruptions may be amplified by the indirect effects of accumulating health burdens associated with chronic morbidity.

Harmful cyanobacterial aerosolization dynamics in the airshed of a eutrophic estuary.

In addition to obvious negative effects on water quality in eutrophic aquatic ecosystems, recent work suggests that cyanobacterial harmful algal blooms (CHABs) also impact air quality via emissions carrying cyanobacterial cells and cyanotoxins. However, the environmental controls on CHAB-derived aerosol and its potential public health impacts remain largely unknown. Accordingly, the aims of this study were to 1) investigate the occurrence of microcystins (MC) and putatively toxic cyanobacterial communities in particulate matter ≤ 2.5 µm in diameter (PM2.5), 2) elucidate environmental conditions promoting their aerosolization, and 3) identify associations between CHABs and PM2.5 concentrations in the airshed of the Chowan River-Albemarle Sound, an oligohaline, eutrophic estuary in eastern North Carolina, USA. In summer 2020, during peak CHAB season, continuous PM2.5 samples and interval water samples were collected at two distinctive sites for targeted analyses of cyanobacterial community composition and MC concentration. Supporting air and water quality measurements were made in parallel to contextualize findings and permit statistical analyses of environmental factors driving changes in CHAB-derived aerosol. MC concentrations were low throughout the study, but a CHAB dominated by Dolichospermum occurred from late June to early August. Several aquatic CHAB genera recovered from Chowan River surface water were identified in PM2.5 during multiple time points, including Anabaena, Aphanizomenon, Dolichospermum, Microcystis, and Pseudanabaena. Cyanobacterial enrichment in PM2.5 was indistinctive between subspecies, but at one site during the early bloom, we observed the simultaneous enrichment of several cyanobacterial genera in PM2.5. In association with the CHAB, the median PM2.5 mass concentration increased to 8.97 µg m-3 (IQR = 5.15), significantly above the non-bloom background of 5.35 µg m-3 (IQR = 3.70) (W = 1835, p < 0.001). Results underscore the need for highly resolved temporal measurements to conclusively investigate the role that CHABs play in regional air quality and respiratory health risk.