The Environmental Significance of the Nearshore Foraminifera Around the Island of St John, United States Virgin Islands, Greater Antilles: A Preliminary Report [DRAFT]

Wilson, Brent

Looked at the occurrence of foraminifera around St. John and attempted to correlated their occurrence with pollution susceptibility, physical and chemical factors (found none). Identified 93 species of benthonic Foraminifera. Includes a table with a list of species and their occurrence in the 12 study sites. Discussion covers general character of the species found and environmental significance of species. Benthonic foraminiferal faunas were examined in twelve sediment samples taken in small embayments around the island of St. John. An attempt was made to relate the foraminiferal assemblages to previously calculated enclosure and pollution susceptibility indices, and to known physical and chemical factors. The samples yielded 95 species of benthonic Foraminifera, the majority of which were rare. One sample, from a creek at the head of Coral Harbor, did not yield foraminifera. The values of the species number, Information Function, and Equitability Index showed no geographic trends, although the values of all these indices were lowest at the same locality, Princess Bay. Nor did values of these indices show any significant correlation with enclosure and pollution susceptibility indices for the bays, although Princess Bay, which had the greatest pollution susceptibility index, yielded the least diverse assemblage encountered. This suggests that, although foraminiferal assemblages have previously been shown to be good indicators of pollution, they cannot be used to predict the pollution susceptibility of small embayments. Cluster analysis grouped samples into four clusters, the largest of which contained most samples from the north coast, and that from Hansen Bay on the south coast. All were dominated by Archaias angulatus, Affiphlsteglna gibbosa, Discorbis rosea and Peneroplis carinatus. However, the north coast samples from Trunk and Maho Bays formed a separate cluster that was dominated by Peneroplis proteus. A third cluster contained samples from Princess Bay and Coral Harbor, while the fourth cluster contained a single sample from Fish Bay. The samples from Princess Bay and Coral Harbor were dominated by Ammonia sobrina. It is possible that frequencies of this infaunal species might be useful as an index of low sediment oxygen levels. Low frequencies of this species in Hansen, Haulover, Fish and Maho Bays therefore suggest that mildly dysaerobic sediment conditions may occur here also. The proportions of chemically altered Archaias anguiatus did not show any geographic trend. High proportions were found at cruz, Francis, Haulover and Fish Bays, but these bays were separated by others yielding only low proportions of altered tests. The alteration, which is caused by bacterial action and occurs at the sediment/water interface, may indicate mildly dysaerobic waters at the interface in those bays that yield high proportions of altered tests. Many specimens of Asterigerina carinata and Amphistegina gibbosa in Fish Bay show iron staining. These may be related to a nearby geochemical anomaly. The species Ouinqueloculina compressiostoma Zheng is recorded from the Caribbean region for the first time.