Factors affecting the seasonal variability of planktonic shrimps (Dendrobranchiata) along an estuary–ocean gradient on the Amazon continental shelf

Abstract

Dendrobranchiata shrimp taxonomic composition and spatial and temporal distribution on the Amazon continental shelf (ACS) were investigated along a transect between the sources of the Amazon and Pará Rivers, encompassing an extension of ~250 km towards the continental slope. Plankton was collected with oblique trawls (200 μm mesh size), and nine taxa were found; 59.4% were larvae (mysis or decapodid stages) and 40.6% were juveniles or adults. Acetes was negatively related to chlorophyll-a and temperature, and Luciferidae were positively correlated with months. This study provides novel information on the density distribution of dendrobranchiate shrimps, thus helping to pave the way to characterize a large-scale, hugely relevant area that is poorly studied. As in other tropical coastal areas, there is here an increase in number of taxa with increased distance from the coast. Luciferidae, Solenoceridae and Penaeidae were the most frequent families whereas Sicyoniidae and Sergestidae had the lowest frequency of occurrence nearer the slope. Despite the low larval density of penaeid shrimps, their presence in all months and at all sampling sites along the ACS proves the importance of this area for shrimps with socioeconomic relevance, as well as its importance as a nursery and growth habitat for dendrobranchiate shrimps.

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

“…The water salinity varied widely (range of 36), with a minimum of 2 (May, rainy season) and a maximum of 38 (January), while increasing gradually away from the coast. The chlorophyll- a content ranged from 0.3 to 85.1 μg/L -1 , in January, decreasing as the coast-ocean distance increased (for detailed environmental variables in this region, see [ 27 ]). The Amazon River outflow was higher (291,900 m 3 .s -1 ) in May and lower (≈110,000 m 3 .s -1 ) in October 2013–2014, with a water volume variation similar to the historical average from 1985 to 2015 ( Fig 2 , S1 Table ).…”

“…This scenario is aggravated in the vast and complex Amazon region, which harbours 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]. In estuarine and coastal Amazonian regions, data on the distribution of Brachyura larvae and their regulatory factors are extremely limited [29] and practically nonexistent for the extended continental shelf (� 240 km from the coast) [30], one of the widest in the world.…”