Larval fish assemblages and the factors affecting their spatial and seasonal dynamics in the southern Gulf of Mexico were studied. The ichthyoplankton material came from three oceanographic cruises during spring (1983), winter (1984) and summer (1987). To determine ichthyoplankton assemblages,
a c1ustering method based on the Bray-Curtis dissimilarity index was applied. Three distinct fish larvae assemblages were identified, corresponding to the physiography of the area. Occurrence of the main fish larvae species in each one reflects principally the spawning strategies of adult
fish. The "coastal assemblage" occupied the east shallow coastal area; its characteristic species being closely related to the estuarine and lagoonal systems, comprising mainly Sciaenidae, Carangidae and Triglidae. The "neritic assemblage" occupied the continental shelf and its characteristic
species consisted of larvae whose adults inhabit the neritic province and spawn in the same zone, like some species of Bothidae, Cynoglossidae and Bregmacerotidae. The "oceanic assemblage" occupied deep water areas and its main components were species whose adults inhabit the mesopelagic province,
most were myctophid and gonostomatid fishes. Major factors affecting spatial and seasonal variations of ichthyoplankton assemblages are proposed to be the main circulation pattern in the southern gulf, continental water discharges, mixing processes, and fish spawning areas and periods.
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