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

For the first time, this study monitored six sites in a wide transect with approximately 240 km radius on the Amazon Continental Shelf (ACS) every three months. The objective was to analyze the larval composition of Brachyura, its abundance in shallow/subsurface and oblique hauls, the extent of larval dispersion related to the estuary/plume, and to predict the probability of occurrence and abundance for the temperature, salinity, and chlorophyll-a profiles of the water column. A total of 17,759 identified larvae are distributed in 8 families and 25 taxa. The water salinity was the best predictor of larval distribution. The statistical models used indicated that Panopeidae and Portunidae larvae are more frequent and more likely to occur in shallow water layers, while Calappidae occur in deeper layers, and Grapsidae, Ocypodidae, Sesarmidae, Pinnotheridae and Leucosiidae occur similarly in both strata. The larval dispersion extent varies among families and throughout the year while the groups are distributed in different salinities along the platform. The probability of occurrence of Portunidae is higher in ocean water (> = 33.5); Grapsidae, Panopeidae, and Pinnotheridae is higher in intermediate and ocean salinity waters (25.5 to 33.5); Ocypodidae, Sesarmidae and Calappidae is higher in estuarine and intermediate salinity waters (5 to 25.5), whereas Leucosiidae, euryhaline, occur in all salinities (5 to 33.5). Furthermore, the Amazon River seasonal flow and plume movement throughout the year not only regulate the larval distribution and dispersion of estuarine species but are fundamental for the ACS species, providing the necessary nutrient input for larval development in the region plankton.