ECOLOGY
Researcher collecting bulk surface sediment samples from a modern coral reef in Bocas del Toro, Panama. Image credit: Sean Mattson (International Center for Tropical Agriculture, Cali, Colombia).
Human exploitation of Caribbean shark communities
The size and diversity of Caribbean shark populations prior to human exploitation have been difficult to quantify due to a lack of long-term, empirical data. Erin Dillon et al. collected fossil shark dermal denticles, which are microscopic tooth-like scales, from the marine sediments of an approximately 7,000-year-old coral reef in the western Caribbean along the coast of Panama and denticles from three nearby modern reefs to serve as a proxy to estimate the abundance and composition of shark communities before and after human settlement. The authors also compiled and analyzed published records of human habitation and fishing practices to contextualize the data. The dermal denticle assemblages showed a 71% decrease in mean accumulation rates between the two time periods, suggesting that Caribbean sharks may have been up to three times more abundant before humans began using marine resources in the region. The results also showed a shift in the composition of the shark communities, with fast-swimming, pelagic sharks experiencing the largest declines. According to the authors, further research into historical dermal denticle assemblages can improve understanding of the impacts of human exploitation on shark communities over time and help guide conservation efforts in the Caribbean and elsewhere. — M.H.
ENVIRONMENTAL SCIENCES
Protective infrastructure along the San Francisco Bay shoreline.
Economic impacts of sea-level rise protection
As sea levels rise, coastal cities are increasingly investing in levees and seawalls to mitigate flooding. While protective structures can reduce flood damage locally, they can exacerbate flooding along other parts of the shoreline to an extent that has not been sufficiently quantified. Michelle Hummel et al. used a 2D, depth-averaged hydrodynamic model of San Francisco Bay to simulate tidal circulations and shoreline interactions under four possible sea-level rise scenarios for 30 different shoreline modification scenarios in which only one stretch of shoreline is protected by construction of a new seawall. The authors integrated maximum water depths extracted from the models with topographical and building stock data to estimate the local reductions and regional increases in economic damage and flooding associated with each scenario. The results varied with local geography and development density, but, under one scenario, the net increase in flooding across the bay was 36 million cubic meters, and another scenario resulted in external damages totaling $723 million. The authors suggest that protective coastal structures may need to be planned at regional levels, spanning multiple jurisdictions to account for such hydrodynamic interactions. According to the authors, the analysis could be extended to other densely populated estuaries. — M.H.
IMMUNOLOGY AND INFLAMMATION
Dysfunctional telomeres and intestinal inflammation
Inflammatory bowel disease (IBD) is a chronic and disabling condition with limited therapeutic options. Past research has found that the intestinal cells of people with IBD have short telomeres, which are repetitive DNA sequences situated at the ends of chromosomes that offer protection from damage. Deepavali Chakravarti, Rumi Lee, et al. report that telomere erosion is not only a consequence of the inflammatory process but also a driver of intestinal inflammation. Analysis of intestinal biopsies from people with IBD revealed that telomere shortening is positively associated with disease severity and may underlie disease recurrence. In molecular studies, IBD intestinal organoids showed telomere-associated DNA damage and activation of the ATM/YAP1/pro-IL-18 signaling pathway, which promotes inflammation. The production of pro-IL-18, a cytokine that acts as a major driver of IBD, was reduced by pharmacological interventions that suppressed DNA damage, inhibited YAP1, or activated the telomerase enzyme, which catalyzes the addition of nucleotides to telomeres. In intestinal organoids from healthy individuals, the induction of telomere dysfunction led to DNA damage and activation of the ATM/YAP1/pro-IL-18 signaling pathway. Together, the findings suggest that telomere dysfunction instigates intestinal inflammation via DNA damage–mediated activation of the ATM/YAP1/pro-IL-18 pathway. According to the authors, the findings suggest potential therapeutic strategies for IBD. — J.W.
EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES
Exposure of explosive ash deposits, 30–40 kilometers north of the Toba caldera. Image credit: Stephen Self (University of California, Berkeley, CA).
Toba supereruption and global climate
The eruption of the Toba volcano in Indonesia around 74,000 years ago was the largest volcanic eruption in the past 2 million years, but its impacts on climate and human evolution remain unclear. Benjamin Black et al. ran an ensemble of 42 global climate model simulations with various parameters for the magnitude of sulfur emissions, time of year of the eruption, background climate state, and sulfur injection altitude to make a probabilistic assessment of the range of climate disruptions the Toba eruption may have caused. The results suggest there was significant regional variation in climate impacts. The simulations predicted cooling in the Northern Hemisphere of at least 4 °C, with regional cooling as high as 10 °C, depending on the model parameters. In contrast, even under the most severe eruption conditions, cooling in the Southern Hemisphere was unlikely to exceed 4 °C, although regions in southern Africa and India may have experienced changes in precipitation at the highest sulfur emission level. The results corroborate independent archaeological evidence suggesting that early humans in these regions thrived through the Toba eruption interval. According to the authors, the ensemble simulation approach could be used to better understand other past and future explosive eruptions. — M.H.
CHEMISTRY
Most plastic persists in the environment. A recently developed polymer degrades in a week and doesn’t leave microplastics behind. Image credit: Shutterstock/Larina Marina.
Degradable plastic polymer breaks down in sunlight and air
Posted on July 9, 2021
Amy McDermott
Plastic trash chokes shorelines and oceans, in part because plastic polymers do not easily decompose. But a new kind of environmentally degradable plastic could help change that: It breaks down in about a week in sunlight and air, according to a recent study in the Journal of the American Chemical Society (JACS). Chemical characterization using nuclear magnetic resonance (NMR) and mass spectroscopy, among other techniques, revealed that the plastic decomposed rapidly in sunlight from a petroleum-based polymer into succinic acid, a naturally occurring nontoxic small molecule that doesn’t leave microplastic fragments in the environment.