Abstract Bioseston is a heterogeneous assemblage of bacterioplankton, phytoplankton, zooplankton, and planktonic debris. A detailed knowledge of biosestons is essential for understanding the dynamics of trophic flows in marine ecosystems. The distributional features of seston biomass in plankton (micro- and mesoplankton) in the Southwest Atlantic Ocean (Rio de Janeiro State, Brazil) were analyzed using stratified samples gathered to a depth of 2,400 m during night time. The horizontal pattern of biomass distribution was analyzed vis-a-vis station depth during both wet and dry periods, with higher values recorded in the continental shelf than in the slope, confirming the terrestrial contribution of nutrient sources to the marine environment. This horizontal variation reinforces the occurrence of seasonal vortices in Cabo Frio and Cabo de São Tomé on the central coast of Brazil. Environmental variables reflect the hydrological signatures of the water masses along the Brazilian coast. The largest seston biomass was related to high temperatures, salinities, and low inorganic nutrient concentrations in tropical and South Atlantic central waters. The observed distribution patterns suggest that seston biomass in plankton in the region may be structured based on partitioned horizontal and vertical habitats and food resources. bacterioplankton phytoplankton zooplankton debris ecosystems micro (micro mesoplankton Rio State Brazil 2400 2 400 2,40 time visavis vis periods slope environment temperatures salinities waters resources 240 40 2,4 24 4 2,

This study analyzes the occurrence and distribution of lanternfish (Myctophidae) larvae along the Brazilian coast (12-22ºS) between 200 m and the surface. Three cruises were conducted during the spring/1998, winter/1999 and autumn/2000. A total of 3,394 lanternfish larvae were identified representing 27 species and Lepidophanes guentheri (Goode & Bean, 1896) was the most abundant. Most of the identified taxa were in the postflexion stage. Myctophid larvae were more numerous during the winter. Most taxa were distributed widely from 12-22ºS, including some seamounts, and occurred mainly outside the 1,000 m isobath. Although there was no difference in the myctophid community among the coastal, oceanic and seamount regions it was significantly different during the three seasons. During the spring and autumn Hygophum reinhardtii (Lütken, 1892) was the discriminating species while in the winter there were more L. guentheri.