Meroplankton community structure across oceanographic fronts along the South Brazil Shelf

Abstract

The influence of oceanographic fronts on the abundance and community composition of invertebrate larvae, mostly of benthic species, along nearly 2000 km of the southwestern Atlantic shelf (21-34°S) was investigated. Meroplankton was sampled through vertical hauls at 89 stations, distributed along 14 crossshelf transects, during late spring 2010 and early summer 2011. Salinity and temperature were registered with a CTD/rosette system, which provided seawater for chlorophyll-a and nutrient concentrations estimations. Vertical profiles of temperature, salinity, chlorophyll-a and nutrients were used as proxies of the fronts. In addition, high-resolution thermosalinograph data were used to detect surface frontal features. Meroplankton abundance peaks were found at several fronts intersected by the ship, including upwelling zones, estuarine and plume fronts, a shelf-break front, and two cyclonic eddies. Furthermore, meroplankton abundance was also relatively higher at small-scale thermal and/or saline surface fronts observed along the shelf. Such increases in meroplankton abundance are likely to be ascribed to high nutrient input and primary production. Distinct taxa of invertebrate larvae occurred at different types of fronts, besides the coastal realm, which was virtually dominated by decapod, cirripede and bivalve larvae. Small-scale shelf fronts presented high abundances of decapod and gastropod larvae, for instance, while larvae of polychaetes were the most frequent in the estuarine front of Patos Lagoon section. Highlights► The sampling area covers 13° of latitudinal gradient and up to 400 km offshore. ► Large-scale maps of abundance of the main meroplanktonic groups are presented. ► Physical, chemical and biological variables are analyzed together. ► Influence of distinct types of fronts on meroplankton abundance is discussed.

Oceanographic structure and seasonal variation contribute to high heterogeneity in mesozooplankton over small spatial scales

“…In particular, the fronts formed in the transition between coastal bays and their oceanic adjacent regions affect the distribution of meroplankton (i.e. mainly composed of pelagic larvae of invertebrates) (Shanks et al, 2003;Ayata et al, 2011;Brandão et al, 2020).…”

Larval dispersal of Brachyura in one of the largest estuarine/marine systems in the world

“…Increases in meroplankton abundance are likely to be ascribed to high nutrient input and primary production, e.g. chlorophyll- a between 4 and 5 (mg/m 3 ) [ 15 ] and the fact that chlorophyll- a is widely available in PCA, this factor does not explain the variation in larval abundance. Although plume flow was not closely followed in this study, its influence on the salinity is notorious and, consequently, on the larval community of brachyurans on the continental shelf, diverging from other coastal regions due to the peculiar characteristic and strength of this hydrological system.…”

Larval dispersal of Brachyura in the largest estuarine / marine system in the world

“…Increases in meroplankton abundance are likely to be ascribed to high nutrient input and primary production, e.g. chlorophyll-a between 4 and 5 (mg/m³) [15] and the fact that chlorophyll-a is widely available in PCA, this factor does not explain the variation in larval abundance. Although plume flow was not closely followed in this study, its influence on the salinity is notorious and, consequently, on the larval community of brachyurans on the continental shelf, diverging from other coastal regions due to the peculiar characteristic and strength of this hydrological system.…”

“…However, obtaining a successful experiment simulating environmental conditions and guaranteeing complete larval development, especially counting on obtaining ovigerous females whose eggs are in hatching conditions is not an easy task, which certainly contributes to the lack of data for most species. On the other hand, investigating larval distribution in a natural environment (estuary and continental shelf) and providing valuable information on the species life cycle and migratory behavior, also presents several difficulties especially in countries where research investment is low, justifying the low number of publications on this topic compared to studies developed with the adult population in the same environments [14][15][16][17][18][19][20]. This scenario is aggravated in the vast and complex Amazon region, which harbirs one of the largest aquatic diversities on the planet so that a significant portion of species is still unidentified and has unknown distribution limits [21][22][23], except for some relatively well documented commercial fish groups [24][25][26] and, recently, zooplankton [18], shrimps [27] and thalassinoids [28].…”