Fish larvae from a Caribbean estuarine system

This study provides an estimation of the species richness of fish larvae, and a recognition of the main station groups on the basis of physical and biological characteristics in an estuary of the Sian Ka'an Biosphere Reserve, Mexican Caribbean Sea, during two seasons, October 1997 and March 1998. Circular surface tows with a conical plankton net were carried out in 67 sampling stations. Water samples for phytoplankton cell counts were also taken. Location, temperature, salinity, depth and dissolved oxygen were recorded at each sampling station. Zooplankton biomass was estimated as wet weight, and fish larvae were identified to the lowest possible taxon. Physical and biological data were included in a Principal Component Analysis in order to detect similarities among sampling stations. Phytoplankton concentration (similar to400 cell mL(-1)), fish larvae density (similar to50 ind 100 m(-3)) and zooplankton biomass (similar to30 g 100 m(-3)) were generally low. A total of 26 species were recognized. The dominant species belong to the Gobiidae (40%), Engraulidae (26.9%), Clupeidae (7.7%), Tetraodontidae (5.8%) and Atherinidae (5.2%) families. Multivariate analysis identified three groups of stations along a north-south axis, with salinity being the main factor in the formation of these groups. Species composition of each group revealed an oceanic affinity in the southern group and an estuarine origin for the other two groups. It is postulated that the low species richness observed in this tropical system is due to a high environmental variability and low primary and secondary productions.