Some species are so linked to specific environments that their habitat association almost becomes a species-defining character and is used by managers and policymakers to direct their conservation. The American lobster Homarus americanus is among the most valuable fisheries species in North America and among the best-studied benthic marine invertebrates in the world. Its populations and habitats have been studied and detailed in publications for over 35 yr. This lobster species was known to dwell in shelters, and their populations had historically been concentrated in shelter-providing boulder habitat. Our study revisited 20 long-term monitored sites at 10 m depth along more than 320 km of the Gulf of Maine. Surprisingly, we recorded fundamental changes in lobster abundance, habitat use, and distribution. Specifically, lobster population densities declined overall and occupancy in boulder habitats declined 60%, while densities on featureless ledge and sediment habitats increased 633 and 280%, respectively, from 2000 to 2019. Lobster rock shelter occupancy declined in recent years, but average body size increased, due in part to declines in smaller size classes. These demographic changes may result from both reduced recruitment and intraspecific competition resulting from the lower population densities. Habitat changes at our monitored sites included declines in kelp abundance, increases in diminutive algal turfs, and nearly 3°C warming of benthic water temperature in July (1995-2021), some of which may have contributed indirectly to those shifts. While these changes in shallow water habitat and demography have implications for the lobster fishery and stock assessments, it also illustrates previously undescribed behavioral plasticity. Keywords:Homarus americanus, Habitat selection, Population structure, Habitat complexity, Intraspecific competition, Behavior, Climate change
An article by ASCC researcher Dr. Lauren Ross with affiliate researchers from Chilean & Spanish institutions has been published in Microorganisms. This publication shares environmental analysis of and research on Harmful Algae Blooms (HABs).
Abstract
Over the recent decades, an apparent worldwide rise in Harmful Algae Blooms (HABs) has been observed due to the growing exploitation of the coastal environment, the exponential growth of monitoring programs, and growing global maritime transport. HAB species like Alexandrium catenella—responsible for paralytic shellfish poisoning (PSP)—Protoceratium reticulatum, and Lingulaulax polyedra (yessotoxin producers) are a major public concern due to their negative socioeconomic impacts. The significant northward geographical expansion of A. catenella into more oceanic-influenced waters from the fjords where it is usually observed needs to be studied. Currently, their northern boundary reaches the 36°S in the Biobio region where sparse vegetative cells were recently observed in the water column. Here, we describe the environment of the Biobio submarine canyon using sediment and water column variables and propose how toxic resting cyst abundance and excystment are coupled with deep-water turbulence (10−7 Watt/kg) and intense diapycnal eddy diffusivity (10−4 m2 s−1) processes, which could trigger a mono or multi-specific harmful event. The presence of resting cysts may not constitute an imminent risk, with these resting cysts being subject to resuspension processes, but may represent a potent indicator of the adaptation of HAB species to new environments like the anoxic Biobio canyon. Keywords: microalgae toxins, submarine canyon, sediment anoxia, dinoflagellate resting cyst, encystment, excystment process
Dielectric media are very promising for near-field radiative heat transfer (NFRHT) applications as these materials can thermally emit surface phonon polaritons (SPhPs) resulting in large and quasi-monochromatic heat fluxes. Near-field radiative heat flux between dissimilar dielectric media is much smaller than that between similar dielectric media and is also not quasi-monochromatic. This is due to the mismatch of the SPhP frequencies of the two heat-exchanging dielectric media. Here, we experimentally demonstrate that NFRHT between dissimilar dielectric media increases substantially when a graphene sheet is deposited on the medium with a smaller SPhP frequency. An enhancement of ∼2.7 to 3.2 folds is measured for the heat flux between SiC and LiF separated by a vacuum gap of size ∼100–140 nm when LiF is covered by a graphene sheet. This enhancement is due to the coupling of SPhPs and surface plasmon polaritons (SPPs). The SPPs of graphene are coupled to the SPhPs of LiF resulting in coupled SPhP-SPPs with a dispersion branch monotonically increasing with the wavevector. This monotonically increasing branch of dispersion relation intersects the dispersion branch of the SPhPs of SiC causing the coupling of the surface modes across the vacuum gap, which resonantly increases the heat flux at the SPhP frequency of SiC. This surface phonon-plasmon coupling also makes NFRHT quasi-monochromatic, which is highly desired for applications such as near-field thermophotovoltaics and thermophotonics. This study experimentally demonstrates that graphene is a very promising material for tuning the magnitude and spectrum of NFRHT between dissimilar dielectric media. Keywords: Near Field Radiative Heat Transfer, Surface Phonon And Plasmon Coupling, Dissimilar Dielectrics, Graphene, Surface Phonon Polaritons, Surface Plasmon Polaritons
Pore pressure monitoring in soil is used to understand subsurface hydrodynamics and the influence of infiltration and exfiltration processes influencing beach erosion and morphology in sandy soils. In this work, we develop a low-power, multi-sensor, long-range wireless probe applicable for short-time, frequent, real-time monitoring of pore pressure and coastal environments at various soil depths. The probe features eight pressure and temperature sensors aligned vertically on a copper pipe at different depths from the soil surface to resolve hydraulic gradients influencing sediment stability. The LoRa sensor probe features data compression and real-time data transmission for faster transmission. The sampling frequency of the developed instrument is variable to capture rapid dynamic variations in pressure according to environmental conditions. The device in this work logs the collected data onto an SD card locally in addition to wireless transmission. The fabricated waterproof probe is tested and calibrated in the laboratory using a water container at different water heights, with minor sensor-to-sensor variations. Comprehensive field tests indicate a promising wave event detection and wireless pore pressure monitoring platform suitable for various soil types, including heterogeneous soils. Keywords: Sensors, Probes, Soil, Sea measurements, Monitoring, Batteries, Temperature sensors, Real-time systems, Printed circuits, Multiplexing, Coastal environment, environment monitoring, Internet of Things, LoRaWAN, pressure sensor, soil pressure
In the design of slab-on-girder highway bridges consisting of conventional materials like concrete and steel in the United States, the vehicular live load carried by a single girder is calculated using distribution factors (DFs) defined in the American Association of State Highway and Transportation Officials (AASHTO) design specifications. However, shears for the recently developed fiber reinforced polymer composite tub (CT) girder do not exist within current design codes, and to-date in-service CT girder bridges have been designed using AASHTO shear DFs for concrete box girders. To assess shear live load distribution in CT girder bridges, diagnostic live load tests were performed on two in-service highway bridges under heavy truck loads. High-fidelity finite element (FE) models calibrated to the test results were simplified to reflect conventional design assumptions. The high-fidelity FE models indicated that AASHTO over-predicted live load shears in the most heavily loaded interior girder by as much as 35 %, but can under-predict exterior girder live load shear. Parametric studies using the simplified FE models indicated that while the most influential parameter on CT girder shear DFs is girder spacing, girder bottom flange width can also play a significant role. The simulations and diagnostic live load tests both indicate that the AASHTO shear DFs expressions for concrete box, slab-on-girder bridges that are currently used in CT girder design typically over-predict shear DFs for interior CT girders. Simulations with the simplified model indicate over-predictions of DFs for interior CT girders of up to 30 % for longer spans and large girder spacing. However, in the CT girder that experienced the greatest shear strain during field load testing, measured strains in the most heavily loaded web were 22 % higher than the average girder web shear strain, a factor not currently accounted for by existing AASHTO DFs or in CT girder design.
Advanced Structures & Composites Center