Distribution and abundance of turritelline gastropods (Cerithioidea: Turritellidae) in Hong Kong and the English Channel: implications for a characteristic fossil assemblage

Abstract

Abundant species are typically also viewed as ecologically dominant, and are frequently used to characterize the communities in which they live. Such characteristic assemblages may also be used as indicators of environmental conditions, such as relative stability. Fossil and modern turritelline gastropods are often the most abundant species in the marine assemblages and communities in which they occur, forming ‘turritelline-dominated assemblages’ (TDAs). We use data on modern Turritella bacillum from waters around Hong Kong as a case study to analyse fluctuations in abundance over 25 years. While turritellines were not always dominant in the area surveyed (~1650 km2), populations were notably persistent, and rebound after decline of abundances occurred within ~5 years at some sites. δ18O sclerochronology suggests that individuals were ~1–2 years old. It is also notable that T. bacillum was found to be abundant at salinities as low as 10–15 psu, despite the general characterization of turritellines as fully marine. Comparison with data on modern T. communis in the western English Channel corroborates this pattern, as localized sites of high abundance also appear transient. These results have implications for the interpretation of TDAs in the fossil record: they may signify the cumulative result of short-lived, spatially restricted populations, possibly resulting from essentially stochastic larval settlement. This suggests that the palaeoenvironmental setting of fossil TDAs does not always control their occurrence on short temporal scales.

Patterns and processes in the history of body size in turritelline gastropods, Jurassic to Recent

“…The evolutionary benefits of small size most relevant to turritellines are the potential for increased reproductive output and lower energy requirements to attain sexually mature size. Early reproduction is most advantageous during phases of population growth (Lande 1982; Charlesworth 1994; Blanckenhorn 2000), and turritelline gastropods are well known for their population booms recorded in a fossil record of numerous “turritelline-dominated assemblages” throughout the history of the group (Allmon 2007; Anderson et al 2017; Shin et al 2020). Extinction risk across stage boundaries is more often higher for small-bodied genera (Payne and Heim 2020; Monarrez et al 2021), but in this analysis, smaller turritelline species tend to have longer geologic durations (Supplementary Fig.…”

“…The heavily r-selected reproductive strategy of turritellines is an intrinsic limitation that may be responsible for preventing other life-history strategies (that may be associated with larger size) from being explored. Turritellines’ life-history traits of short life span, rapid development, and high reproductive output allow for population booms that characterize their abundant fossil record (Allmon 2007; Plotnick 2018; Shin et al 2020).…”

“…Turritellines’ moderate size and short life span persist across global climate regime changes, indicating physiological size limitations due to growth rate and longevity (Anderson and Allmon 2020). A lack of correlation with environmental proxies suggests that local and regional ecological heterogeneity may be more important in shaping turritelline body-size distributions than conditions expected to vary with latitude (Anderson and Allmon 2020; Shin et al 2020). Turritelline gastropods’ morphological, reproductive, and life-history strategies remain almost unchanged over their 160 Myr history, suggesting their adaptive resilience (Allmon 2011; Anderson and Allmon 2020).…”

“…We also tested this dataset for patterns of size and latitudinal distribution, size and temporal distribution, and size compared with proxies for climate change, productivity, and pH in order to evaluate possible environmental drivers of body-size trends in turritelline history. We expect high productivity to release suspension feeders from metabolic trade-offs (Teusch et al 2002; Anderson and Allmon 2020; Shin et al 2020) and normal to high levels of carbonate saturation for shell construction (Allmon 2007; Anderson and Allmon 2020) to favor increased growth and therefore larger size in turritelline gastropods.…”