The structure and seasonal dynamics of larvae of the Gobiidae family in the Mucuri Estuary (Bahia, Brazil) were studied for nine consecutive years. Sampling was conducted at three stations in the lower estuary channel, between 2002 and 2010, in relation to season, day and night and tidal variations. A total of 5802 Gobiidae larvae, representing 15 taxa (12 species and three morphotypes), were collected in the Mucuri Estuary during this time. The highest mean ± s.d. density of fish larvae, 54·7 ± 79·8 larvae 100 m(-3), was recorded during the flood tide and night sampling. Ctenogobius boleosoma was the most abundant species (68%), being dominant in the rainy and dry seasons and had a long reproductive period. This species was classed as a marine estuarine-opportunist because it was observed at high frequencies and active larvae entering the estuary between 6·1 and 12·0 mm standard length (L(S)). Gobionellus oceanicus, second in abundance (12%), occurred only in later larval stages but did not use the estuary as a preferred location for spawning, being classed a marine estuarine dependent. Microgobius carri (11%) was represented in all L(S) classes and was resident in the estuary for spawning, remaining there throughout their life cycle. The other species were considered rare due to their low densities and could not be classified in any guild.

This study aims to describe the spatial and temporal distribution patterns of Gobiidae larvae at a tropical estuarine system in south-east Brazil (Macaé). The samples were collected in six stations, through oblique hauls using a bongo net (330 mm mesh size), coupled to a flowmeter, during the night in the ebb and flood tides in March, July and October 2006 and in February 2007. In the Macaé River estuary was collected a total of 1,234 Gobiidae larvae, representing nine taxa. The highest densities occurred in the river mouth during the flood tide in the rainy season. The most abundant groups were: Gobiosoma parri, Gobionellus oceanicus and Ctenogobius boleosoma. Gobiosoma parri was also dominant at the Macaé estuary, which also presented higher densities in the coastal stations during the rainy season (March), both the flood as the ebb tide. Gobionellus oceanicus and Ctenogobius boleosoma were characteristic of the dry season in the mouth and river stations during the flood tide. The abiotic factors chlorophyll-a and temperature were considered biologically significant for Gobiidae larvae distribution. The spatial and seasonal variations together with the tide influence the distribution of the fish larvae Gobiidae family in the Macaé River estuary and its coastal zone.