Large-Scale Ichthyoplankton and Water Mass Distribution along the South Brazil Shelf

Erik V Thuesen,Carlos Alberto Eiras Garcia,Luis Carlos Pinto De Macedo-Soares,Andrea Santarosa Freire,José Henrique Muelbert

doi:10.1371/journal.pone.0091241

Erik V Thuesen, Carlos Alberto Eiras Garcia + Show 3 more

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https://doi.org/10.1371/journal.pone.0091241

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Abstract

Ichthyoplankton is an essential component of pelagic ecosystems, and environmental factors play an important role in determining its distribution. We have investigated simultaneous latitudinal and cross-shelf gradients in ichthyoplankton abundance to test the hypothesis that the large-scale distribution of fish larvae in the South Brazil Shelf is associated with water mass composition. Vertical plankton tows were collected between 21°27′ and 34°51′S at 107 stations, in austral late spring and early summer seasons. Samples were taken with a conical-cylindrical plankton net from the depth of chlorophyll maxima to the surface in deep stations, or from 10 m from the bottom to the surface in shallow waters. Salinity and temperature were obtained with a CTD/rosette system, which provided seawater for chlorophyll-a and nutrient concentrations. The influence of water mass on larval fish species was studied using Indicator Species Analysis, whereas environmental effects on the distribution of larval fish species were analyzed by Distance-based Redundancy Analysis. Larval fish species were associated with specific water masses: in the north, Sardinella brasiliensis was found in Shelf Water; whereas in the south, Engraulis anchoita inhabited the Plata Plume Water. At the slope, Tropical Water was characterized by the bristlemouth Cyclothone acclinidens. The concurrent analysis showed the importance of both cross-shelf and latitudinal gradients on the large-scale distribution of larval fish species. Our findings reveal that ichthyoplankton composition and large-scale spatial distribution are determined by water mass composition in both latitudinal and cross-shelf gradients.

Highlights

Ichthyoplankton distribution is under the influence of environmental factors that regulate life history traits and determine its geographical range [1,2,3]
Oceanographic conditions Six water masses were identified in the study area down to the maximum zooplankton sampling depth (130 m): Subtropical Shelf Water (STSW), Shelf Water (SW), Tropical Water (TW), Plata Plume Water (PPW), Subantarctic Shelf Water (SASW) and South Atlantic Central Water (SACW) (Figure 2)
Three water masses were present in the shelf area (SW, STSW and PPW), except at stations near the coast in the Cape Frio-Cape Sao Tomeand Cape Santa Marta regions, where SACW was found closer to the surface, and at stations located in the southern part of the study area (Chuı), where SASW was present

Summary

Introduction

Ichthyoplankton distribution is under the influence of environmental factors that regulate life history traits and determine its geographical range [1,2,3]. Latitudinal influence is important in determining large-scale distribution, since fish larvae are dependent on temperature as well as long photoperiods for their development [7]. A latitudinal gradient is reported to be related to differences in larval assemblage composition in the North Pacific Ocean [10], to variability in egg size and newly hatched larval length of the anchovy Engraulis rigens in the Chilean coast [11], and to influence the growth rate and spawning season of the sea bass Dicentrarchus labrax in estuaries in Portugal [7]. In the continental shelf and slope, ichthyoplankton species composition is strongly influenced by ocean currents and water masses [8,13,14]

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