Discordance between living and death assemblages as evidence for anthropogenic ecological change

Mismatches between the composition of a time-averaged death assemblage (dead remains sieved from the upper mixed-zone of the sedimentary column) and the local living community are typically attributed to natural postmortem processes. However, statistical analysis of 73 molluscan data sets from estua...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2007-11, Vol.104 (45), p.17701-17706
Main Author: Kidwell, Susan M
Format: Article
Language:English
Subjects:
Animals
Biological Sciences
Biological taxonomies
Conservation of Natural Resources
Datasets
Death
Ecology
Ecosystem
Environment
Eutrophication
Extinction, Biological
Geologic Sediments
Grasses
Human ecology
Humans
Inertia
Lagoons
Lakes
Life
Marine ecology
Mollusca
Mollusks
Phylogeny
Sediments
Statistical analysis
Synecology
Time
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Summary:Mismatches between the composition of a time-averaged death assemblage (dead remains sieved from the upper mixed-zone of the sedimentary column) and the local living community are typically attributed to natural postmortem processes. However, statistical analysis of 73 molluscan data sets from estuaries and lagoons reveals significantly poorer average "live-dead agreement" in settings of documented anthropogenic eutrophication (AE) than in areas where AE and other human impacts are negligible. Taxonomic similarity of paired live and dead species lists declines steadily among areas as a function of AE severity, and, for data sets comprising only adults, rank-order agreement in species abundance drops where AE is suspected. The observed live-dead differences in composition are consistent with eutrophication (anomalous abundance of seagrass-dwellers and/or scarcity of organic-loving species in the death assemblage), suggesting compositional inertia of death assemblages to recent environmental change. Molluscan data sets from open shelf settings (n = 34) also show higher average live-dead discordance in areas of AE. These results indicate that (i) live-dead discordance in surficial grab samples provides valuable evidence for strong anthropogenic modification of benthic communities, (ii) actualistic estimates of the ecological fidelity of molluscan death assemblages tend to be erroneously pessimistic when conducted in nonpristine settings, and (iii) based on their high fidelity in pristine study areas, death assemblages are a promising means of reconstructing otherwise elusive preimpact ecological baselines from sedimentary records.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0707194104