ABSTRACT

Two groups of modern patch reefs exist off Veracruz, Mexico. Terrigenous sediments of the Rio Jamapa are being deposited between the two complexes. Longshore drift of these sediments is causing declining coral growth on the southern (Anton Lizardo) group, while corals on the northern (Veracruz) group are healthy. These differences in coral diversity should be reflected in the water chemistry and microfauna. Environmental data collected (depth, salinity, pH, temperature, Eh, and dissolved oxygen) were treated as random samples from populations whose normality (or lack thereof) was established by chi-squared goodness-of-fit tests. Chi-square testing at the 0.01 level demonstrated that out of the six sample populations, only depth, pH, and dissolved oxygen (DO) were normally distributed.Depth, pH, and DO data were assembled into two populations representing the Veracruz and Anton Lizardo groups. This allowed testing the null hypothesis that the variances of the respective populations were equal (F = 0.005 level). The variances were found to be equal. T tests (0.01 level) on the population means of depth, pH, and DO of both Veracruz and Anton Lizardo groups disclosed there is no significant difference between the two groups of reefs in terms of these characteristics. Analysis of the dominant ostracod species in 33 samples collected on the reefs indicates two distinct biofacies exist. Loxocorniculum tricornatum Krutak dominates the Veracruz group; whereas, L. cf. L. postdorsoalata "group" (Teeter) characterizes the Anton Lizardo stations. Two ostracod species, L. tricornatum and Morkhovenia inconspicua (Brady), are cosmopolitan, and occur at all 33 sampling stations. Rare species living on the two reef complexes are generally restricted to the Veracruz complex. Simple diversity analysis (no. of species/station) demonstrates that the Veracruz reefs are more diverse than those of Anton Lizardo. However, this difference is statistically insignificant. Comparisons of Shannon-Weiner information function and equitability values between the two complexes show these diversity measures are also insignificant and do not reflect the observed environmental differences. Ostracod species abundance and dominance on the scleractinian bioherms at Veracruz and Anton Lizardo are more sensitive indicators of reefal equilibrium than the measured environmental characteristics in overlying bottom waters.