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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 63 (1979)

Issue: 9. (September)

First Page: 1605

Last Page: 1606

Title: Equilibrium in Modern Coral Reefs, Western Gulf of Mexico--Role of Ecology and Ostracod Microfauna: ABSTRACT

Author(s): Paul R. Krutak, Sue E. Rickles

Article Type: Meeting abstract


Two groups of modern patch reefs are present 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, although 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 of the six sample populations, only depth, pH, and dissolved oxygen were normally distributed. Depth, pH, and dissolved oxygen data were assembled into two populations representing the Veracruz and Anton Lizardo groups, to test the null hypothesis that the variances of the respective populations were equal (F = 0.0005 level). The variances were found to be equal. T tests (0.01 level) on the population means of depth, pH, and dissolved oxygen of both Veracruz and Anton Lizardo groups disclosed that 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. 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 are present at all 33 sampling stations. Rare species living on the two reef complexes are generally restricted to the Veracruz complex. Simple diversity analysis (number of species/station) demonstrates that the Veracruz reefs are more diverse than those of Anton Lizardo. However, this difference is statistically insignificant. Comparisons f Shannon-Weiner information function and equitability values between the two complexes show that these diversity measures are also insignificant and do not reflect observed environmental differences. Ostracod species abundance and dominance on the scleractinian bioherms at Veracruz and Anton Lizardo

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are more sensitive indicators of reefal equilibrium than the measured environmental characteristics in overlying bottom waters.

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Copyright 1997 American Association of Petroleum Geologists