Relationship between zooplankton biomass and continental water discharges in the southern Gulf of Mexico (1984-2001)

Zooplankton biomass is recognized as an important indicator of secondary production, its spatial and temporal variation in neritic zones is particularly affected by discharges of the rivers, and the spatial-temporal effect of continental water discharges on the distribution of zooplankton biomass in the southern Gulf of Mexico was analyzed for 5 areas off the coasts of Veracruz, Tabasco and Campeche. The analyzed material was obtained from 534 samples collected during different climatic seasons from 1984 to 2001. The discharge volumes of 5 hydrological regions were obtained from the government's data base. The results obtained indicated that biomass variation throughout the seasons in the different areas was very similar to the pattern of discharges. The greater biomass values were recorded off Tabasco and the lower values off Veracruz, where the greater and lower continental water discharges were recorded respectively. Biomass variation depended on the discharges, not only in terms of an annual cycle, but was also directly related to the volumes discharged into the ocean. A Tree analysis made it possible to conclude that biomass is always low on the outer shelf and oceanic region of the southern Gulf of Mexico, independently of the season of the year or of a particular area. A greater biomass was recorded on the shallow shelf, with a magnitude that varied in relation to the area and season. The biomass off Campeche did not depend on the continental water discharges, but was generated on the Yucatan shelf.