Diel Vertical Dynamics of Gelatinous Zooplankton (Cnidaria, Ctenophora and Thaliacea) in a Subtropical Stratified Ecosystem (South Brazilian Bight)

Abstract

The diel vertical dynamics of gelatinous zooplankton in physically stratified conditions over the 100-m isobath (~110 km offshore) in the South Brazilian Bight (26°45’S; 47°33’W) and the relationship to hydrography and food availability were analyzed by sampling every six hours over two consecutive days. Zooplankton samples were taken in three depth strata, following the vertical structure of the water column, with cold waters between 17 and 13.1°C, influenced by the South Atlantic Central Water (SACW) in the lower layer (>70 m); warm (>20°C) Tropical Water in the upper 40 m; and an intermediate thermocline with a deep chlorophyll-a maximum layer (0.3–0.6 mg m-3). Two distinct general patterns were observed, emphasizing the role of (i) physical and (ii) biological processes: (i) a strong influence of the vertical stratification, with most zooplankton absent or little abundant in the lower layer. The influence of the cold SACW on the bottom layer apparently restricted the vertical occupation of most species, which typically inhabit epipelagic warm waters. Even among migratory species, only a few (Aglaura hemistoma, Abylopsis tetragona eudoxids, Beroe sp., Thalia democratica, Salpa fusiformis) crossed the thermocline and reached the bottom layer. (ii) A general tendency of partial migrations, with variable intensity depending on the different species and developmental stages; populations tended to be more widely distributed through the water column during daylight, and to become more aggregated in the upper layer during the night, which can be explained based on the idea of the “hunger-satiation hypothesis”, maximizing feeding and minimizing the chances of being predated.

Vertical distribution and structure of copepod (Arthropoda: Copepoda) assemblages in two different seasons down to 1,200 m in the tropical Southwestern Atlantic

“…McManus and Woodson (2012) proposed that plankton interacts with their environment across a range of scales and theorized that the spatial distributions of oceanic organisms (from the smallest plankton to the largest predators) are determined by the interactions between organism behavior and physical oceanographic structure and processes. It has been reported that in marine ecosystems, vertical stratification along the water column influences the distribution of fish larvae and zooplankton groups (Pilar Olivar et al 2010, Nogueira-Júnior et al 2015, Doxa et al 2016. In this study, the model generated for the sampling period influenced the compositions of the copepod assemblages at each sampling depth.…”

“…The vertical distribution of C. carinatus is limited to the deeper waters below the thermocline and the oxygen minimum layer (Verheye et al 2005, Gaard et al 2008, Teuber et al 2013. The vertical distribution of plankton assemblages helps explain the organization and dynamics of pelagic communities and the vertical flux of organic matter throughout the water column (Nogueira-Júnior et al 2015). Large-scale spatial patterns of certain zooplankton groups coincide with surface water masses, circulation, and upwelling regions.…”

Combined eDNA and Acoustic Analysis Reflects Diel Vertical Migration of Mixed Consortia in the Gulf of Mexico

“…Ctenophores in four orders were present in our dataset along with three taxa that could not be classified past phylum. Some species of ctenophores and siphonophores have been observed to vertically migrate when strong physical stratification of the water column is absent, thus some taxa present in our dataset may represent active migrators over the course of our experimental timeframe (Júnior et al, 2015). Copepods (Class Maxillopoda) appear as the most dominant potential migrator in our eDNA dataset, comprising nearly 20% of eDNA sequences at some time points.…”

In situ observations show vertical community structure of pelagic fauna in the eastern tropical North Atlantic off Cape Verde

“…However, the mesopelagic zone also contains a specific set of resident organisms that do not migrate to the surface, and instead feed on sinking particles and the migrant organisms 22 , 23 . Besides the comparatively well-known migration behavior of crustaceans and fishes, some gelatinous organisms such as pyrosomes and salps also migrate on a daily basis 24 , but more observations are needed to quantify taxon-specific distribution and migration patterns.…”