Journal of Fish Biology (2014) 84, 996–1013 doi:10.1111/jfb.12340, available online at wileyonlinelibrary.com Occurrence of Gobiidae larvae in a tropical Brazilian estuary, with particular emphasis on the use of size classes to categorize species guilds E. A. P. Gomes*, P. N. Campos and A. C. T. Bonecker Departamento de Zoologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro, CCS Bloco A, Ilha do Fundão, 21941-590, Rio de Janeiro, RJ, Brazil (Received 28 May 2013, Accepted 9 January 2014) 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 fsh larvae, 54⋅7 ± 79⋅8 lar- vae 100 m -3 , was recorded during the food tide and night sampling. Ctenogobius boleosoma was the most abundant species (68%), being dominant in the rainy and dry seasons and had a long reproduc- tive 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 ). Gob- ionellus 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 classifed in any guild. © 2014 The Fisheries Society of the British Isles Key words: fsh larvae; Mucuri River; tropical estuarine guilds; tropical gobies. INTRODUCTION Several marine teleosts play an important role in estuaries as they constitute permanent and temporary community components, with marine species using these habitats for feeding, reproduction, growth and protection (Raz-Guzman & Huidobro, 2002; Bar- letta et al., 2005; Bonecker et al., 2009). Characteristics of estuaries vary greatly and are determined by the shape of the estu- ary, the volume of river fow and the range of tides at the estuary mouth. Estuaries exhibit high turbidity and abrupt changes in temperature and salinity, as well as sea- sonal changes (Able & Fahay, 1998). Furthermore, the mixing of waters of different densities, the rise and fall of tides and the fow of the incoming river combine with the local characteristics of wind, temperature, precipitation and currents to result in a complex pattern of water circulation (Miranda et al., 2002). This movement of fresh or brackish water provides a wedge of saline water (Barletta & Barletta-Bergan, 2009). *Author to whom correspondence should be addressed. Tel.: +55 21 25626365; email: eduapg@hotmail.com 996 © 2014 The Fisheries Society of the British Isles