Search Results (5)

The northern Andaman Sea (AS) continental shelf is unique due to the diverse marine ecosystem and existences of both hypoxia and internal tides, but limited in situ observations restrict our understanding of the hydrographic dynamic process. Based on the turbidity, mean volumes of backscattering strength (MVBS), we qualitatively studied the mean distribution characteristics and temporal variation in suspended matters on the northern AS continental shelf and their relation to hypoxia and internal tides. The results of both MVBS and turbidity revealed that the suspended matters exhibited a three-layer vertical structure. The upper and lower layers exhibited high values, while the middle layer had low values. The upper boundary of the high-value region in the upper layer descended below the surface to a depth of 30 m after sunrise and returned to the surface after sunset, indicating a diel vertical migration of zooplankton and micronekton. Daytime migration depth was likely constrained by hypoxia’s upper boundary. In the lower layer, three MVBS enhancements and attenuations correlated with vertical upward and downward velocities, respectively, primarily driven by uplift or suppression. We proposed vertical velocity patterns resulted from internal bores, possibly triggered by shoaling semidiurnal internal tides. Full article

Acoustic technology is an essential tool for detecting marine biological resources and has been widely used in sound-scattering layer (SSL) research. The North Equatorial Current (NEC) warm pool region of the Central and Western Pacific Ocean has a vast distribution of micronekton and zooplankton; analyzing the SSL characteristics in this region is vital for monitoring the marine environment and studying the marine ecosystem. In this study, we statistically analyzed the spatiotemporal factors of 10–200 m SSL in the NEC of the Central and Western Pacific Ocean using acoustic survey data collected by the “Songhang” research vessel (RV) in 2022, and the influence of environmental factors on the scattering layer distribution was analyzed using the Generalized Additive Model (GAM). The results showed that the SSL in the warm pool area of the NEC is distributed in shallow waters above 100 m. The primary scatterers are micronekton and zooplankton, and this SSL had diel vertical migration behavior. By comparing Akaike’s Information Criterion of different GAMs, the model consisting of six factors, namely, temperature, current velocity, turbidity, solar altitude angle, longitude, and latitude, was remarkable. Each model’s factor effects primarily influence the contribution of the volume-backscatter strength (Sv). The cumulative deviation explanation rate of the Sv was 67.2%, among which the highest explanation rate of solar altitude angle variance was 35.4%, the most critical environmental factor. The results of this study can provide a reference for long-term studies on ecological changes and their effects on micronekton and zooplankton distribution. Full article

Myctophids, commonly vertical migrators, and partial and non-migrant stomiiforms constitute most of the mesopelagic biomass, and transport organic matter throughout the food web from the surface to the ocean’s depths. Both the diet and trophic structure of twenty-nine species of mesopelagic fish collected around the Iberian Peninsula were studied through the analysis of stomach contents, quantifying food items with a high taxonomic resolution. The investigation covered oligotrophic to productive habitats, with sampling stations distributed in five discrete zones of the western Mediterranean Sea and the northeastern Atlantic Ocean. The geographic environmental conditions, migratory behavior, and species-specific body sizes allowed for the identification of some major feeding patterns for these fish communities. The trophic niche of migrant myctophids showed a high overlap, with copepods as the primary prey category. The diet composition of generalist myctophids (e.g., Ceratoscopelus maderensis and Hygophum benoiti) reflected the distinct zooplanktonic communities between zones. Large stomiiforms (Chauliodus spp., Sigmops elongatus) preferred feeding on micronekton, while the smallest stomiiforms (e.g., Argyropelecus spp., Cyclothone spp., Vinciguerria spp.) preyed on copepods and ostracods. Given the relevance of the mesopelagic fish communities for commercially exploited species and, therefore, for maintaining the sustainability of the fisheries’ activity in the zones analyzed, the information provided in the present study is essential for a better understanding of the biology and ecology of these species. Full article

Different types and systems to discriminate plankton samples at different strata in the water column have been developed in recent decades. For sampling at sufficient depth, opening and closing zooplankton multinets are ideal because there is no contamination of one sample with organisms of the previous one. However, for bigger nets, such as those used to collect micronektonic organism, it is difficult to use multiple net units, and multiple cod ends are preferred because of their simplicity, but with the problem of sample contamination from having a common net passageway. We present here a cod-end Multisampler design, VERDA, that uses a carrousel-like system. Similar to some sediment traps, the system works like a revolver with six or eight compartments whose turning mechanism is triggered when the net arrives to a programmed depth level. This prototype was built with inexpensive and recycled components and electronics similar to Arduino^® and Teensy PCB to carry out electronic control. The net we used for testing the equipment was a mid-size midwater trawl of ca. 30 m² and total length of 58 m that works with a single towing cable and no doors. The overall system is useful for all type of ships, due to the relatively easy deployment operations and because the Multisampler does not need electrical cable or acoustics. In our case, we used a Marport^® (Reykjavik Iceland) and Scanmar (Åsgårdstrand, Norway) sensors for real-time depth monitoring and opening distance. Full article

A new species of the genus Cyphocaris Boeck, 1871, is described. The material examined was collected during the “Acoustics along the Brazilian Coast” (Abraços 1) project, by micronektonic trawls at a targeted depth of 525 m, off the Rocas Atoll, Rio Grande do Norte state, Brazil. Cyphocaris boecki sp. nov. can be grouped with the eyed species in the genus but differs from them—except for C. faurei K. H. Barnard, 1916 and C. latirama, Hendrycks & Conlan, 2003—in presenting a dorsally smooth pereonite 1. However, the new species can be distinguished from both by its maxilliped inner plate with two robust apical setae, pereopod 7 basis with weakly produced posterodistal lobe, telson lobes without setae, spines or apical nails, and other characters that are individually discussed among them. The new species can be readily differentiated from C. pedroi Sorrentino, Alves, Johnsson & Senna, 2016, also described from Brazil, by presenting eyes, a rounded lateral cephalic lobe, very elongated antenna 2 almost reaching body length, and pereopod 5 basis, with apically acute spur reaching about two-thirds of the propodus. This is the second record of the genus for Brazilian waters. Full article