Diel and Tidal Rhythms of Emercenge Events Based on Acousitc Observations in a Shallow Estuary

Field observations of emergence events by epibenthic animals were conducted with two Tracor Acoustic Profiling Systems (TAPS) in the Damariscotta River estuary, Maine, in fall 2005 and summer 2006. Spectral analysis revealed that periodic temporal variability of the acoustic signals was concentrated at four periods. One was the solar day (24 h) and the other three were lunar tidal periods of 25.82 (diurnal or Oi), 12.42 (semidiurnal or M2) and 6.21 h (half the semidiurnal period). The mysid Neomysis americana showed strong nocturnal migration patterns of water-column activity during its peak summer emergence season, regulated by the diel cycle. Toward the end of the emergence season in fall, however, as phytoplankton standing stocks waned, the dominant rhythm regulating their behavior shifted from a diel to semidiurnal. The timing of mysid abundance peaks in the fall coincided with low slack tides near the surface, but with maximal flood tidal speed near the bottom, providing a plausible mechanism of retention and selective tidal stream transport within the estuary, respectively. Behaviors of smaller organisms, most likely dominated by copepods, were regulated by both M2 and half of M2 components. The phase difference between the acoustic backscatter and the tidal currents suggests that the signal results from smaller organisms emerging into the water column, instead of resuspension of sediment by tidal currents. The timing of their emergence varies depending on TAPS frequency, suggesting emergence by several species. Changes in the magnitudes of each frequency component in the power spectrum can be related to ontogenetic changes in behavior of mysids, intensity of tides, and seasonal food availability. This study suggests the multiple emergence events may affect the degree of benthic-pelagic coupling and reveals the mechanism of previously observed phenomenon (midnight sinking and dawn ascent) by increased sampling resolution

Southern resident killer whales encounter higher prey densities than northern resident killer whales during summer

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sato, M., Trites, A. W., & Gauthier, S. Southern resident killer whales encounter higher prey densities than northern resident killer whales during summer. Canadian Journal of Fisheries and Aquatic Sciences, 78(11), (2021): 1732–1743, https://doi.org/10.1139/cjfas-2020-0445.The decline of southern resident killer whales (Orcinus orca) may be due to a shortage of prey, but there is little data to test this hypothesis. We compared the availability of prey (Chinook salmon, Oncorhynchus tshawytscha) sought by southern residents in Juan de Fuca Strait during summer with the abundance and distribution of Chinook available to the much larger and growing population of northern resident killer whales feeding in Johnstone Strait. We used ship-based multifrequency echosounders to identify differences in prey fields that may explain the dynamics of these two killer whale populations. Contrary to expectations, we found that both killer whale habitats had patchy distributions of prey that did not differ in their frequencies of occurrence, nor in the size compositions of individual fish. However, the density of fish within each patch was 4–6 times higher in the southern resident killer whale habitat. These findings do not support the hypothesis that southern resident killer whales are experiencing a prey shortage in the Salish Sea during summer and suggest a combination of other factors is affecting overall foraging success.This study was funded by Fisheries and Oceans Canada

Fish and Zooplankton Distributions in a Seasonally Hypoxic Fjord

Hypoxia has been identified as a major threat to marine ecosystem health in the world’s coastal waters including Puget Sound. This study is evaluating the potential effects of hypoxia on fish and zooplankton distributions in Hood Canal, WA, using multifrequency acoustics and net sampling. Field surveys were conducted monthly from June to October in 2012 and 2013 to characterize pre-, during, and post-hypoxia nekton distributions at four sites along the Canal. Using the repeated samplings and high-resolution survey data, we are examining how seasonal and inter-annual difference in the timing and intensity of hypoxia affects distributions of predators (primarily Pacific herring and Pacific hake) and prey (primarily copepods and euphausiids). Depth of the zooplankton backscatter layer changed seasonally with hypoxia intensity. Toward late-summer, the daytime zooplankton layer was closer to the surface, increasing the vertical separation between zooplankton and fish. In spite of low oxygen levels in late-summer, fish remained in low-oxygen regions of Hood Canal. This suggests a decrease in energy flow toward higher trophic level during hypoxia

High frequency diffraction of an electromagnetic plane wave by an imperfectly conducting rectangular cylinder

Copyright @ 2011 IEEEWe shall consider the the problem of determining the scattered far wave field produced when a plane E-polarized wave is incident on an imperfectly conducting rectangular cylinder. By using the the uniform asymptotic solution for the problem of the diffraction of a plane wave by a right-angled impedance wedge, in conjunction with Keller's method, the a high frequency far field solution to the problem is given

Simultaneous observations of the cusp with IMAGE Low Energy Neutral Atom Imager and SuperDARN radar

The Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft observed significant emission in the high-latitude magnetosheath direction during an extreme solar wind condition on April 11, 2001. The emission was modulated in such a manner that the sources shifted equatorward in the high-latitude sheath while sometimes undergoing brief poleward returns. This modulation and the IMF BZ tend to have correlative variations. During this interval of interest, SuperDARN was receiving strong backscattered signals from large potions of the dayside ionosphere. This observation indicates that the equatorward motion of the cusp latitude consists of rapid and slow phases. This kind of equatorward shift appears to correlate with the motion of the emission observed by LENA in the direction of the high-latitude sheath, which gives evidence for a means for monitoring the high-altitude cusp using IMAGE/LENA. It thus appears that the two remote sensing observations, i.e., IMAGE/LENA and SuperDARN radar would provide promising opportunities to understand the detailed dynamics of the polar cusp extending from the low-altitudes to the high-altitudes

Inhibition of EP4 Signaling Attenuates Aortic Aneurysm Formation

BACKGROUND: Aortic aneurysm is a common but life-threatening disease among the elderly, for which no effective medical therapy is currently available. Activation of prostaglandin E(2) (PGE(2)) is known to increase the expression of matrix metalloproteinase (MMP) and the release of inflammatory cytokines, and may thus exacerbate abdominal aortic aneurysm (AAA) formation. We hypothesized that selective blocking of PGE(2), in particular, EP4 prostanoid receptor signaling, would attenuate the development of AAA. METHODS AND FINDINGS: Immunohistochemical analysis of human AAA tissues demonstrated that EP4 expression was greater in AAA areas than that in non-diseased areas. Interestingly, EP4 expression was proportional to the degree of elastic fiber degradation. In cultured human aortic smooth muscle cells (ASMCs), PGE(2) stimulation increased EP4 protein expression (1.4 ± 0.08-fold), and EP4 stimulation with ONO-AE1-329 increased MMP-2 activity and interleukin-6 (IL-6) production (1.4 ± 0.03- and 1.7 ± 0.14-fold, respectively, P<0.05). Accordingly, we examined the effect of EP4 inhibition in an ApoE(-/-) mouse model of AAA infused with angiotensin II. Oral administration of ONO-AE3-208 (0.01-0.5 mg/kg/day), an EP4 antagonist, for 4 weeks significantly decreased the formation of AAA (45-87% reduction, P<0.05). Similarly, EP4(+/-)/ApoE(-/-) mice exhibited significantly less AAA formation than EP4(+/+)/ApoE(-/-) mice (76% reduction, P<0.01). AAA formation induced by periaortic CaCl(2) application was also reduced in EP4(+/-) mice compared with wild-type mice (73% reduction, P<0.001). Furthermore, in human AAA tissue organ cultures containing SMCs and macrophages, doses of the EP4 antagonist at 10-100 nM decreased MMP-2 activation and IL-6 production (0.6 ± 0.06- and 0.7 ± 0.06-fold, respectively, P<0.05) without increasing MMP-9 activity or MCP-1 secretion. Thus, either pharmacological or genetic EP4 inhibition attenuated AAA formation in multiple mouse and human models by lowering MMP activity and cytokine release. CONCLUSION: An EP4 antagonist that prevents the activation of MMP and thereby inhibits the degradation of aortic elastic fiber may serve as a new strategy for medical treatment of AAA

Serotonin and cholecystokinin synergistically stimulate rat vagal primary afferent neurones

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65669/1/jphysiol.2004.064816.pd

Ventrolateral Origin of Each Cycle of Rhythmic Activity Generated by the Spinal Cord of the Chick Embryo

BACKGROUND: The mechanisms responsible for generating rhythmic motor activity in the developing spinal cord of the chick embryo are poorly understood. Here we investigate whether the activity of motoneurons occurs before other neuronal populations at the beginning of each cycle of rhythmic discharge. METHODOLOGY/PRINCIPAL FINDINGS: The spatiotemporal organization of neural activity in transverse slices of the lumbosacral cord of the chick embryo (E8-E11) was investigated using intrinsic and voltage-sensitive dye (VSD) imaging. VSD signals accompanying episodes of activity comprised a rhythmic decrease in light transmission that corresponded to each cycle of electrical activity recorded from the ipsilateral ventral root. The rhythmic signals were widely synchronized across the cord face, and the largest signal amplitude was in the ventrolateral region where motoneurons are located. In unstained slices we recorded two classes of intrinsic signal. In the first, an episode of rhythmic activity was accompanied by a slow decrease in light transmission that peaked in the dorsal horn and decayed dorsoventrally. Superimposed on this signal was a much smaller rhythmic increase in transmission that was coincident with each cycle of discharge and whose amplitude and spatial distribution was similar to that of the VSD signals. At the onset of a spontaneously occurring episode and each subsequent cycle, both the intrinsic and VSD signals originated within the lateral motor column and spread medially and then dorsally. By contrast, following a dorsal root stimulus, the optical signals originated within the dorsal horn and traveled ventrally to reach the lateral motor column. CONCLUSIONS/SIGNIFICANCE: These findings suggest that motoneuron activity contributes to the initiation of each cycle of rhythmic activity, and that motoneuron and/or R-interneuron synapses are a plausible site for the activity-dependent synaptic depression that modeling studies have identified as a critical mechanism for cycling within an episode