The neritic zooplankton of the northwestern Gulf of Mexico

Abstract

Copepod species and major groups of zooplankton were identified from 513 samples taken at 20 stations on 5 transects in the coastal waters of the northwestern Gulf of Mexico. Monthly samples, using oblique tows and a GULF V sampler (approximately 200 um mesh size), were taken over a 3-year period from 1963 to 1965. The bottom depths of the sampling stations ranged from 8 to 73 m. Temporal and spatial distributional patterns were examined in detail for major groups of zooplankton and common species of calanoid and cyclopoid copepods. The relationships between the densities of these groups and various physical and chemical factors were also examined. Total zooplankton densities averaged over the entire sampling area peaked in April and September. The highest mean densities occurred in April (2870 organisms/m³) and the lowest densities occurred in February (1124/m³). Mean zooplankton densities decreased from 3412 organisms/m³ at the 8 m stations to 1131/m at the 73 m stations. The greatest mean densities occurred in 1964. The dominant groups of zooplankton, determined by their average densities in the sampling area, were the copepods (61% of total zooplankton), larvaceans (7.7%), bivalve larvae (5.5), ostracods (Euaonahoeaia) (4.7%), and gastropod larvae (3.6%). All groups had density peaks in the spring although peaks also occurred during other seasons. Densities of all groups except the ostracods appeared to decrease with the bottom depth of the station. In general, the densities of the major groups of zooplankton showed little relationship with surface temperature, surface salinity, or the other physical factors examined. ...