Spatial variation of the average environmental parameters in the mixed layer. (A) temperature, (B) salinity, (C) zooplankton volume, (D) nitrates, (E) nitrites, (F) turbidity, (G) phosphates, (H) silicates and (I) planktonic cnidarians volume. Sampling stations (▲). Range of variation on the colour scales (darker tones represent high values): 26.66°C to 27.30°C in A, 33.56 to 36.38 in B, 32.32 to 1,135.47 ml/1,000 m3 in C, 0.70 to 2.83 μmol L−1 in D, 0.03 to 0.51 μmol L−1 in E, 0.21 to 1.20 nephelometric units in F, 0.94 to 5.22 μmol L−1 in G, 3.79 to 57.76 μmol L−1 in H and 4.71 to 1,000 ml/1,000 m3 in I. Southern Gulf of Mexico. Autumn 1998.