Community structure of benthic foraminifera in the Gulf of Mexico

Abstract

The classic papers of Phleger [Phleger, F.B, 1951. Foraminifera Distribution, Part I. Geological Society of America Memoir 46, 1–88.] and Parker [Parker, F.L., 1954. Distribtuion of the foraminifera in the Northeastern Gulf of Mexico. Bulletin of the Museum of Comparative Zoology 111, 453–588, 13 plates.] form the benchmark foraminiferal data sets for the northwestern and northeastern Gulf of Mexico, respectively. These pioneer researchers occupied stations from shelf to abyssal depths. SHE analysis, a method examining the distribution of cumulative sample values of species richness ( S), the information function ( H) and evenness ( E) with increasing number of individuals ( N), was used to establish 18 foraminiferal communities and evaluate their community structure. Regression analyses, as well as plots of ln S, H and ln E versus ln N (Biodiversitygrams, BDGs), indicate that the majority of the communities exhibit a log series pattern. Theoretical log series values of S, H and E are similar to the regression estimates from observed values in the northeastern Gulf. In the northwestern Gulf, however, observed values of species richness are lower and evenness higher than those expected for a log series, indicating a dramatic difference in community structure between east and west. Since the sampling time of Phleger, subsequent workers have found higher values of species richness and lower values of evenness in the northwestern Gulf. Either biodiversity values have changed since Phleger's 1947 (1951) sampling suggesting a fundamental change in the environmental regime of the northwestern Gulf of Mexico or, as has been suggested, Phleger's data are incorrect due to some sampling methodology. A comprehensive study with suitable experimental design including downcore samples will be required to resolve this dichotomy.