BULLETIN OF MARINE SCIENCE, 70(1): 19–32, 2002 19 SPATIO-TEMPORAL VARIATION OF ICHTHYOPLANKTON ASSEMBLAGES IN TWO LAGOON SYSTEMS OF THE MEXICAN CARIBBEAN Laura Sanvicente-Añorve, Xavier Chiappa-Carrara and Alberto Ocaña-Luna ABSTRACT Spatial and seasonal variation of larval fish assemblages from two lagoon systems in the Sian Ka’an Biosphere Reserve was surveyed every 3–4 mo for 1 yr (1996–1997). The two systems, which are on the east coast of Mexico’s Yucatán Peninsula connect with the Caribbean Sea and have different amount of intrusion of Caribbean water. Ichthyoplankton data from surface plankton tows (500 mm mesh net) were analyzed using Correspon- dence Analysis to identify the main larval fish assemblages in each season. Two groups were recognized: one was oceanic influenced and the other was estuarine. The dragonet Diplogrammus pauciradiatus and the clupeids Opisthonema oglinum and Jenkinsia lamprotaenia characterized the oceanic assemblage. The estuarine assemblage was char- acterized by Gobiidae and Membras martinica year around and, by Hyporhamphus unifasciatus, Lupinoblennius nicholsi, Anchoa hepsetus, Archosargus rhomboidalis, and Microgobius spp. in some seasons. We propose that seasonal variations in Caribbean water inflow and reproductive strategies of adult fish in the two lagoons determine the spatial variations of the ichthyoplankton assemblages. The coastal portion of the Sian Ka’an Biosphere Reserve, located along the coast of the Yucatán Peninsula, is a strip of marshes or muddy soils that are temporarily or perma- nently covered with water. This reserve is the largest protected region of this type in Mexico (Morales, 1992) and covers over 528,000 ha of which nearly a third is covered by marshes (Olmsted and Durán, 1990). Productivity of these systems is mainly due to de- composition of plant material resulting in detritus that is available directly or indirectly to the biota, and to a wide oceanic front that allows physical exchange with adjacent neritic waters (Trejo-Torres et al., 1993; Vega-Cendejas, 1998). After Sian Ka’an was designated as a Biosphere Reserve in 1986, a number of ichthyoplankton studies have been made in the neritic waters of the Mexican Caribbean (Ordóñez-López et al., 1992; Sánchez-Velasco and Flores-Coto, 1994; Vásquez-Yeomans et al., 1998; Vásquez-Yeomans and Richards, 1999). In the lagoon systems of the Re- serve, we gave a first attempt (Sanvicente-Añorve et al., 1999) to study the composition and spatial distribution of ichthyoplankton during 1996–97. To continue this research line, in this work we determine the larval fish assemblages in two lagoon systems of the Sian Ka’an Biosphere Reserve. The characteristic species are identified, and their rela- tionship with hydrological features is assessed using the same data set. Both lagoon sys- tems are shallow (<1.5 m) though some deeper pools (>2 m) are found both in the Laguna Campechén and the Punta Allen inlet, near Bahía Ascensión.