ALL OR NOTHING? MODERN POPULATION DYNAMICS FOR A CHARACTERISTIC FOSSIL ASSEMBLAGE

Abundant species are typically viewed as also ecologically dominant, and are frequently used to categorize the community in which they live. Such characteristic assemblages may be used to indicate relative environmental stability or change, for example in the case of fossil and Recent turritelline-dominated assemblages (Gastropoda: Turritellidae, TDAs). We use modern Turritella bacillum Kiener, 1843 data from waters around Hong Kong, a sub-tropical coastal city, as a case study to analyse fluctuations in abundance over 25 years. While the area surveyed (ca. 1650 km²) was not always noted to be turritelline-dominant, there was notable persistence, and rebound of abundances within 2-3 years at some sites. Comparison with literature data on T. communis Risso, 1826 in the Northeastern Atlantic covering ~ 85 years somewhat corroborates this pattern, as sites of high abundance were localized over geographic scales of ca. 300 & 500 km² respectively, and also appeared transient during this duration. Further work will include investigating potential environmental stressors, and to compare our results with other available well-documented turritelline populations. These results have implications for the interpretation of TDAs in the fossil record, as they may signify short-lived, spatially restricted population and environmental change. By juxtaposing this modern comparison with fossil TDAs, further insight may be gained into the formation and temporal resolution captured by these phenomenon.