DOI: 10.5061/dryad.0r76j
title: Data from: Nineteenth-century collapse of a benthic marine ecosystem on the open continental shelf

description: 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.
description: Table-spatial
 distribution of Laques erythraeus, Leopecten diegensis and Chlamys
 hastataOccurrences 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).Table-spatial
 distribution.xlsTable-agesSummary 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 codeSource 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.Laqueus postmortem age analyses.txt