Data from: Nineteenth-century collapse of a benthic marine ecosystem on the open continental shelf
Tomašových, Adam, Slovak Academy of Sciences
Kidwell, Susan M., University of Chicago
Published Jun 02, 2017 on Dryad.
Cite this dataset
Tomašových, Adam; Kidwell, Susan M. (2017). Data from: Nineteenth-century collapse of a benthic marine ecosystem on the open continental shelf [Dataset]. Dryad. https://doi.org/10.5061/dryad.0r76j
The soft-sediment seafloor of the open continental shelf is among the least-known biomes on Earth, despite its high diversity and importance to fisheries and biogeochemical cycling. Abundant dead shells of epifaunal suspension-feeding terebratulid brachiopods (Laqueus) and scallops on the now-muddy mainland continental shelf of southern California reveal the recent, previously unsuspected extirpation of an extensive offshore shell-gravel ecosystem, evidently driven by anthropogenic siltation. Living populations of attached epifauna, which formerly existed in a middle- and outer-shelf mosaic with patches of trophically diverse muds, are restricted today to rocky seafloor along the shelf edge and to the sandier shelves of offshore islands. Geological age-dating of 190 dead brachiopod shells shows that (i) no shells have been produced on the mainland shelf within the last 100 years, (ii) their shell production declined steeply during the nineteenth century, and (iii) they had formerly been present continuously for at least 4 kyr. This loss, sufficiently rapid (less than or equal to 100 years) and thorough to represent an ecosystem collapse, coincides with intensification of alluvial-plain land use in the nineteenth century, particularly livestock grazing. Extirpation was complete by the start of twentieth-century urbanization, warming, bottom fishing and scientific surveys. The loss of this filter-feeding fauna and the new spatial homogeneity and dominance of deposit- and detritus-feeders would have altered ecosystem functioning by reducing habitat heterogeneity and seawater filtering. This discovery, attesting to the power of this geological approach to recent ecological transitions, also strongly increases the spatial scope attributable to the negative effects of siltation, and suggests that it has been under-recognized on continental shelves elsewhere as a legacy of coastal land use.
Table-spatial distribution of Laques erythraeus, Leopecten diegensis and Chlamys hastata
Occurrences of Laques erythraeus, Leopecten diegensis and Chlamys hastata in living (Live) and death (Dead) assemblages, with latitude, longitude, water depth (m), year of sampling (NA if unknown) and sampling gear. Some data refer to presence-absence data (0-absent, 1-present) and some to abundance data (column Data). Occurrences are partitioned into mainland-shelf and island-shelf occurrences (column Shelf.island). Some occurrences are based on photographic surveys. The column "Survey" refers to monitoring of wastewater agencies (LA City, LA County, Orange County, Point Loma, and South Bay), to Bight-wide surveys, to photographic USGS surveys, or Melville 2012 survey (performed by authors of this study).
Summary of radiocarbon-calibrated shell ages of Laqueus erythraeus estimated by amino-acid racemization (with 95% confidence intervals on the mean age), with water depth (m), sampling year, and D/L of Aspartic and Glutamic acids.
Tomasovych and Kidwell supplement R code
Source code for evaluating the postmortem age-fequency distribution of the brachiopod Laqueus erythraeus from the Southern California Bight written in R language. Postmortem age estimates based on the Bayesian fitting of Allen et al. (2013) are assigned to a vector directly in this code. The code recreates the figures where the estimates of shell loss from the mixed layer are based on the fitting of the age-frequency distribution to two-phase exponential models, and these estimates are used to reconstruct the trajectory of production.