Spatial and temporal variation of planktonic cnidarian density in subtropical waters of the Southern Brazilian Bight

Abstract

The spatial and temporal variations of planktonic cnidarians were studied across the inner continental shelf (≤40 m) off the State of Paraná in southern Brazil. Monthly zooplankton samples were taken between November 1997 and March 1999 at five stations. The holoplanktonic Liriope tetraphylla and Muggiaea kochi dominated during the entire period, comprising .80% of the specimens. The coast-ocean gradient became evident due to a near-coastal (≤20 m) assemblage formed by L. tetraphylla, Solmaris corona and meroplanktonic medusae, and a distinct outer (25-40 m) assemblage formed by the medusae Corymorpha gracilis and Aglaura hemistoma and siphonophores. The estuarine runoff during warm rainy periods lowered the salinity (~30) at the inner stations (1, 2 and 3), providing appropriate conditions for the estuarine/ coastal species. Wind-driven onshore advection of outer-shelf species to the inner isobaths occurred from late autumn to winter, when the rainfall decreased and salinity increased (.35). Population peaks occurred in both summer and winter at the inner stations. For most species, the seasonal patterns were inconsistent with other studies conducted in the Southern Brazilian Bight, suggesting irregular and unpredictable seasonal distributions of abundance. Whereas in highlatitude ecosystems the dynamics of cnidarian populations follows the seasonal productivity cycle, here, complex hydrographic processes seem to be more important in determining the structure and seasonal dynamics of this community.

Macroscale abundance patterns of hydromedusae in the temperate Southwestern Atlantic (27°–56° S)

“…tetraphylla , although other hydromedusan species were also detected and are discussed below. Liriope tetraphylla is widely distributed in warm waters of all oceans [38] and frequently observed in coastal ecosystems worldwide displaying, at times, higher abundances than in the open sea [39–43]. In southern Brazil and the Río de la Plata estuarine area, L .…”

“…tetraphylla was the main contributor to both groups, highlights its plasticity and points out its distributional range, which reaches up the ~40° S in the SWA. Aglaura hemistoma , mainly associated to warm waters in the SWA, particularly to the tropical water mass of the Brazil Current [43,45], was absent in the G 4 group and those found southward in colder waters, in accordance with Rodriguez et al [75]. Continuing south, the finding of the assemblages composed by the contributions of many meroplanktonic hydromedusae (G 5, G 6, and G 7 groups) was in accordance with the environmental and faunistic features of the transitional neritic zone such as the Argentine Province [27].…”

High spatial heterogeneity of two planktonic cnidarian species related to the variability of a shelf-slope front at short time scales

“…However, as this species has been observed inhabiting areas of similar and lower salinity (e.g. : Gili et al 1988, Nagata et al 2014, factors other than salinity per se probably affected its abundance. Muggiaea atlantica and A. hemistoma displayed high spatio-temporal variability in the brief study period, apparently driven by the rapid onshore-offshore displacements of the shelf-slope front.…”

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

“…For calycophore siphonophores, the number of polygastrics (as anterior nectophores) and eudoxids (as bracts) was counted. For physonects, the number of colonies was estimated by the number of pneumatophores, and when these were absent, nectophores were counted, and the total was divided by ten to roughly approximate the actual number of colonies sampled [ 27 – 28 ]. The abundances were standardized as the number of individuals (or colonies in the case of siphonophores and pyrosomes) per 10 m -3 of filtered sea water.…”