Fig 1.
Geographic location of the study area in the North Brazilian continental shelf and adjacent Western Equatorial Atlantic Ocean, showing the sampled stations.
Fig 2.
(a) Surface currents vectors and indicators of the predominant current in the area (NBC = North Brazilian Current; RETRO = North Brazilian Current retroflection; NECC = North Equatorial Counter Current). (b) Sea level anomalies and indicators of cyclonic and anticyclonic eddies. (c) Sea surface salinity and estimated position of 35 isohaline delimitating the Amazon River plume (ARP) and tropical surface water (TSW). (d) Sea surface temperature. (e) Surface density (f) Surface dissolved oxygen. (g) Surface fluorescence. (h) Total zooplankton biomass found in the first 200 m of the water column (mean of samples collected with 120 and 300 μm mesh nets). All collected data are from October 2012.
Fig 3.
Vertical profiles and contours of (a) Salinity, traced line is the position of 35 isohaline delimitating the Amazon River plume. (b) Temperature. (c) Density. (d) Fluorescence. (e) Dissolved oxygen. Upper bars indicate the main mesoscale processes observed in the area. All collected data are from October 2012.
Table 1.
Basic statistics of planktonic cnidarian species from neritic and oceanic provinces in the Western Equatorial Atlantic Ocean off North Brazil.
Mean abundance (ind. 100 m-3) per station and standard deviation, range of abundance and frequency of occurrence (f; considering both provinces; n = 87 samples). Species are sorted by frequency of occurrence. In all cases, both meshes were pooled.
Fig 4.
Geographic distribution of species richness and total abundance of hydromedusae and siphonophores found in the top 200 m of the water column (mean of samples collected with 120 and 300 μm mesh nets) in October 2012.
Fig 5.
Geographic distribution and abundance of the dominant hydromedusae found in the top 200 m of the water column (mean of samples collected with 120 and 300 μm mesh nets) in October 2012.
Species are sorted according to total abundance.
Table 2.
Results of the analysis of variance testing differences in the abundance of representative planktonic cnidarian species among neritic and oceanic provinces inside (ARP) and outside (Out ARP) the influence of the Amazon River Plume and Tukey post-hoc test.
Significant p-values (< 0.05) are in bold. Different Letters indicate significant pair-wise difference among areas in the Tukey test. Species are sorted according to total abundance.
Fig 6.
Geographic distribution and abundance of the dominant siphonophores found in the top 200 m of the water column (mean of 120 and 300 μm meshes) in October 2012.
*Except for Nanomia bijuga. Species are sorted according to total abundance.
Fig 7.
Cluster analysis dendogram indicating five groups of stations with similar planktonic cnidarian communities in the Western Equatorial Atlantic Ocean.
Table 3.
Results of Similarity Percentage analysis (SIMPER), showing the relative contribution of planktonic cnidarian species in the formation of the groups defined in the Cluster analysis.
Fig 8.
Redundancy analysis relating dominant planktonic cnidarian species to environmental gradients and mesoscale processes in the Western Equatorial Atlantic Ocean.
L.tet = Liriope tetraphylla, D.boj = Diphyes bojani, A.hem = Aglaura hemistoma, E.mit = Eudoxoides mitra, B.bas = Bassia bassensis, A.tet = Abylopsis tetragona, N.bij = Nanomia bijuga, C.app = Chellophyes appendiculata, A.esc = Abylopsis eschscholtzii, S.chu = Sulculeolaria chuni, D.dis = Diphyes dispar, A.oke = Agalma okeni, E.spi = Eudoxoides spiralis, S.eur = Sminthea eurygaster, C.leu = Ceratocymba leuckartii, S.tur = Sulculeolaria turgida, R.vel = Rhopalonema velatum, L.cam = Lensia campanella, A.ele = Agalma elegans, C.sp1 = Cytaeis sp. 1, S.bit = Solmundella bitentaculata, S.bil = Sulculeolaria biloba, P.inc = Persa incolorata, E.hya = Enneagonum hyalinum, M.koc = Muggiaea kochii, ARP = Presence of Amazon River Plume, NBC = North Brazilian Current, NECC = North Equatorial Countercurrent, Eddy + = Anticyclonic eddy, Eddy— = Cyclonic eddy, SST = Sea surface temperature, SSS = Sea surface salinity, DO = Dissolved oxygen, Flu = Fluorescence, Zoo = Zooplankton Biomass.
Table 4.
Summary of the Redundancy Analysis (RDA) performed between the cnidarian assemblage and environmental explanatory variables from the Western Equatorial Atlantic Ocean.
Fig 9.
Schematic representation of the Amazon River Plume (ARP) and associated oxygen minimum zone (OMZ) and effects of habitat structure on planktonic cnidarian assemblages in the Equatorial Western Atlantic Ocean.