Acoustic backscatter observations with implications for seasonal and vertical migrations of zooplankton and nekton in the Amundsen shelf (Antarctica)

La, Hyoung Sul; Ha, Ho Kyung; Kang, Cheon Yoon; Wåhlin, Anna; Shin, Hyoung Chul

doi:10.1016/j.ecss.2014.11.020

Cited by 15 publications

(18 citation statements)

References 64 publications

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“…They argued that absolute light intensity below sea ice decreases to the thresholds at which the feeding activity of fish slows down. Moreover, DVM below 2 m thick ice in the Canada Basin during the midnight sun was recently reported by La et al (2018). Following Fortier et al (2001), we speculate that the absolute light intensity through the PW layer at CA13 was below the threshold of predator perception, allowing DVM during the midnight sun 2004.…”

Section: Dvm Seasonal Cycle Sea-ice Cover and Suspended Particlessupporting

confidence: 77%

“…2). This can indicate high concentrations of phytoplankton (e.g., La et al, 2018), which zooplankton feed on. The availability of phytoplankton can be an important factor triggering seasonal variability in DVM (e.g., La et al, 2015).…”

Section: Dvm Seasonal Cycle Sea-ice Cover and Suspended Particlesmentioning

confidence: 99%

“…At this latitude no actual daylight is experienced during short winter daylight hours, with the exception of civil twilight when solar illumination is still sufficient for the human eye to distinguish terrestrial objects. This geographical position makes our DVM observational site vastly different from those at Svalbard (astronomical twilight; the Sun is between 12 and 18 • below the horizon at ∼ 80 • N; e.g., Grenvald et al, 2016;Darnis et al, 2017), Canada Basin (nautical twilight; the Sun is between 6 and 12 • below the horizon at ∼ 77.5 • N; La et al, 2018), and northeast Greenland (nautical twilight, ∼ 74.5 • N; Petrusevich et al, 2016). Civil twilight is observed at the CA13 latitude from 19 November to 21 January.…”

Section: Introductionmentioning

confidence: 99%

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Sea-ice and water dynamics and moonlight impact the acoustic backscatter diurnal signal over the eastern Beaufort Sea continental slope

et al. 2020

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Abstract. A 2-year-long time series of currents and acoustic backscatter from an acoustic Doppler current profiler, moored over the eastern Beaufort Sea continental slope from October 2003 to September 2005, were used to assess the dynamics and variability of the sound-scattering layer. It has been shown that acoustic backscatter is dominated by a synchronized diel vertical migration (DVM) of zooplankton. Our results show that DVM timings (i) were synchronous with sunlight and (ii) were modified by moonlight and sea ice, which attenuates light transmission to the water column. Moreover, DVM is modified or completely disrupted during highly energetic current events. Thicker ice observed during winter–spring 2005 lowered the backscatter values but favored extending DVM toward the midnight sun. In contrast to many previous studies, DVM occurred through the intermediate water layer during the ice-free season of the midnight sun in 2004. In 2005, the midnight-sun DVM was likely impacted by a high acoustic scattering generated by suspended particles. During full moon at low cloud cover, the nighttime moonlight illuminance led to zooplankton avoidance of the subsurface layer, disrupting DVM. Moreover, DVM was disrupted by upwelling, downwelling, and eddy passing. We suggest that these deviations are consistent with DVM adjusting to avoid enhanced water dynamics. For upwelling and downwelling, zooplankton likely respond to the along-slope water dynamics dominated by surface- and depth-intensified flow, respectively. This drives zooplankton to adjust DVM by aggregating in the low or upper intermediate water layer for upwelling and downwelling, respectively. The baroclinic eddy reversed DVM below the eddy core.

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Section: Dvm Seasonal Cycle Sea-ice Cover and Suspended Particlessupporting

confidence: 77%

Section: Dvm Seasonal Cycle Sea-ice Cover and Suspended Particlesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sea-ice and water dynamics and moonlight impact the acoustic backscatter diurnal signal over the eastern Beaufort Sea continental slope

et al. 2020

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“…This assumption works well in the case of horizontal velocities measured with suspended particles that include zooplankton because horizontal movements between individual zooplankton are mostly uncorrelated (Heywood ; Ott ). However, vertical ocean current velocities are generally small (often order mm s −1 ); therefore, the swimming velocities of zooplankton (often order mm s −1 and larger) can make up a larger fraction of the total vertical movement than of the total horizontal movement of suspended particles (Heywood ; Jiang et al ; La et al ). Measured ADCP vertical velocities tend to be lower than vertical swimming speeds of zooplankton because ADCPs average the speeds of all particles, including sediments and nonmigrating biological organisms (Plueddemann and Pinkel ; Heywood ).…”

Section: Methodsmentioning

confidence: 99%

Acoustic detection of zooplankton diel vertical migration behaviors on the northern Gulf of Mexico shelf

Parra

Greer

Book

et al. 2019

Limnology & Oceanography

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Zooplankton respond to light levels, oceanographic conditions, and other cues through diel vertical migrations (DVMs), which can occur at dawn and dusk. However, unraveling the influence of these drivers is difficult without high‐resolution time series data encompassing multiple events that can alter zooplankton DVM. We address this knowledge gap with an interseasonal study using high‐resolution measurements of zooplankton DVMs on the freshwater‐influenced northern Gulf of Mexico shelf. Sampling encompassed 6 months of acoustic backscatter and vertical velocity profiles at five locations, supplemented with zooplankton taxonomic composition and abundance from in situ imaging, net samples, glider profiles, and remote sensing. Relative backscatter anomalies (RBAs) displayed a daily pattern that changed abruptly at dawn and dusk, with lower daytime (2–15 dB lower) values relative to nighttime. Daily variability intensified from autumn to spring. The DVM pattern changed in structure on shorter temporal scales (days to weeks), associated with factors including onshore and off‐shelf currents, lunar variability, cloud cover, and harmful algal bloom passage. In situ imaging and net observations showed that the most likely acoustically observed migrating zooplankton were chaetognaths, shrimp (performing reverse DVMs), copepods, and ostracods. Shrimp and chaetognath orientations also showed diel variability, with individuals more frequently oriented vertically during the daytime. Daily RBA and vertical velocity anomaly patterns could be caused by reverse DVM to the near‐surface or nocturnal DVM to the near‐bottom (outside the acoustic detection range) or diel changes in organism orientation. Pattern complexities suggest that multiple behaviors are happening and being observed simultaneously.

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“…Many polar zooplankton, including the large biomass-dominant copepods, chaetognaths, salps, key euphausiid species and possibly pteropods, undertake seasonal vertical migration 5–8 . They actively feed and reproduce in spring and summer and migrate to deeper water during autumn in the preparation for overwintering, and remain in deep water during the long winter period.…”

Section: Introductionmentioning

confidence: 99%

Zooplankton and micronekton respond to climate fluctuations in the Amundsen Sea polynya, Antarctica

Park

Wåhlin

et al. 2019

Sci Rep

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The vertical migration of zooplankton and micronekton (hereafter ‘zooplankton’) has ramifications throughout the food web. Here, we present the first evidence that climate fluctuations affect the vertical migration of zooplankton in the Southern Ocean, based on multi-year acoustic backscatter data from one of the deep troughs in the Amundsen Sea, Antarctica. High net primary productivity (NPP) and the annual variation in seasonal ice cover make the Amundsen Sea coastal polynya an ideal site in which to examine how zooplankton behavior responds to climate fluctuations. Our observations show that the timing of the seasonal vertical migration and abundance of zooplankton in the seasonally varying sea ice is correlated with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). Zooplankton in this region migrate seasonally and overwinter at depth, returning to the surface in spring. During +SAM/La Niña periods, the at-depth overwintering period is shorter compared to −SAM/El Niño periods, and return to the surface layers starts earlier in the year. These differences may result from the higher sea ice cover and decreased NPP during +SAM/La Niña periods. This observation points to a new link between global climate fluctuations and the polar marine food web.

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Acoustic backscatter observations with implications for seasonal and vertical migrations of zooplankton and nekton in the Amundsen shelf (Antarctica)

Cited by 15 publications

References 64 publications

Sea-ice and water dynamics and moonlight impact the acoustic backscatter diurnal signal over the eastern Beaufort Sea continental slope

Sea-ice and water dynamics and moonlight impact the acoustic backscatter diurnal signal over the eastern Beaufort Sea continental slope

Acoustic detection of zooplankton diel vertical migration behaviors on the northern Gulf of Mexico shelf

Zooplankton and micronekton respond to climate fluctuations in the Amundsen Sea polynya, Antarctica

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