The Impact of a Southern Ocean Cyclonic Eddy on Mesopelagic Micronekton

Abstract

Mesoscale eddies shape the foraging ecology of predators such as marine mammals and seabirds. A growing number of animal tracking studies show that predators alter their swimming, diving, and foraging behavior within mesoscale eddies. However, little is known about how Southern Ocean eddies influence the distribution of mesopelagic micronekton (fish, squid, and crustaceans), which are major prey items of megafauna. Studies in other oceanic regions have found that eddies can influence the abundance and community composition of micronekton. Here, we analyze acoustic observations from a 14‐day survey of a cyclonic mesoscale eddy, its surrounding waters, and the Polar Frontal Zone (PFZ) waters where the eddy formed. We report and interpret spatial patterns of acoustic backscatter at 18 and 75 kHz, proxies indicating combined changes in species, size, and abundance of micronekton. We find that the vertical distribution of acoustic backscatter matched the underwater light conditions characteristic of the eddy core, periphery, and surrounding waters, at scales smaller than 10 km. The median water‐column integrated acoustic backscatter values in the eddy core were only half of those measured in the Sub‐Antarctic Zone waters surrounding the eddy, but similar to those measured in the PFZ, where the eddy originated 27 days prior. These results suggest that, as for physical and chemical tracers, the eddy maintained its biological characteristics from its source waters creating a unique habitat compared to its surroundings.

Hydroacoustic method and GIS-Dashboard visualization for fish size in Banggai Sea Waters

“…ESP3 is an acoustic data processing application developed by the National Institute of Water and Atmospheric Research (NIWA), New Zealand [16]. This application can be used freely for various acoustic data processing such as studies of gas leaks from underwater faults [17,18], abundance of marine organisms [19][20][21], and other studies within the scope of hydroacoustic [22][23][24]. Fish density calculations were conducted using the Microsoft Excel application based on the results of processing in ESP3.…”

Intraseasonal variability of the Deep Scattering Layer observed by subsurface mooring deployed east of Taiwan Island

“…The CEs, related to cold core region, is actually a local aggregation zone of zooplankton and micronekton (Zimmerman and Biggs, 1999), typically characterized by high levels of primary productivity and plankton biomass due to nutrients upwelling in the core (Vaillancourt et al, 2003). The integrated and vertical distribution of the acoustic scattering inside the CEs was similar to its origin waters (Della et al, 2022). At the same time, there are cases where biomass in AEs has increased or decreased.…”

A Global Assessment of Eddy‐Induced Salinity Anomalies and Salt Transport by Eddy Movement

“…Studies have demonstrated that mesoscale eddies exhibit water properties that differ from those of the surrounding water (Della Penna et al., 2022; Frenger et al., 2015; Gaube et al., 2014; Sun et al., 2017, 2022; Sun, Dong, Tan, & He, 2019; Wang et al., 2021). Salinity anomalies exist within individual eddies as a result of the geostrophic depression and uplift of the background isopycnal surfaces associated with anticyclonic and cyclonic eddies, respectively (Della Penna et al., 2022; Dong et al., 2014; Frenger et al., 2015).…”

“…Studies have demonstrated that mesoscale eddies exhibit water properties that differ from those of the surrounding water (Della Penna et al., 2022; Frenger et al., 2015; Gaube et al., 2014; Sun et al., 2017, 2022; Sun, Dong, Tan, & He, 2019; Wang et al., 2021). Salinity anomalies exist within individual eddies as a result of the geostrophic depression and uplift of the background isopycnal surfaces associated with anticyclonic and cyclonic eddies, respectively (Della Penna et al., 2022; Dong et al., 2014; Frenger et al., 2015). The salinity anomalies within eddies tend to move with mesoscale eddies, which usually feature nonlinearity and amplified velocities, due to the advective trapping of fluid contained in their interiors (Chelton et al., 2007; Dong et al., 2014; McGillicuddy, 2016).…”