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Coastal Ecosystem
Biological Contaminants

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Estimating Impacts Of Past Natural And Anthropogenic Disturbances On Shelf Macrobenthic Communities: A Field Test Using Dead-Shell Assemblages Website

Principal Investigator(s):
Susan M. Kidwell - University of Chicago
Adam Tomasovych - University of Chicago

Associate Investigator(s):

Period: 2/1/2008 - 1/1/2010

Current Status: Completed Last Updated: 9/30/2010
Federal Funds: State Funds:

(1) To refine and field-test a new method of assessing human impact on seafloor communities and of generating historical ecological information for the southern California continental shelf, using the dead-shell material present in sediment that is produced by bivalves (clams, cockles, scallops), which are a significant component of diversity and biomass in the living community. Excellent existing data for the compostion of living communities in the southern California Bight for the last 30 years will be used to quantify the fidelity of death assemblages to ecological conditions and their ability to capture a memory of preceding decades, and (2) to determine whether the composition and structure of the bivalve community has shifted signficantly during this period of improving wastewater treatment. A series of increasingly old death assemblages, archived from 1975 and to be extracted from sedimentary cores, will then be used (3) to help fill the data gap that exists for bivalve communities before the mid-1970s initiation of Bight-wide surveys and biomonitoring of ocean outfalls. In particular we hope (4) to determine the natural baseline condition of these communities during earlier phases of human impact and before urban settlements, for use as remediation targets. By generating a history of bivalve communities that extends back beyond the onset of urban stresses, the project would (5) bring useful new information to the challenge of distinguishing and ranking the impacts of natural (decadal and longer climate changes) versus human cultural forces (nutrients, suspended solids, and toxins associated with wastewater outfalls and runoff from diffuse sources).

This project will use (a) existing data from live-surveys and newly generated data from dead-shell assemblages from the (b) 1975 AHF-BLM survey and(c) Bight 2003 survey to test for trends in living community and death assemblage composition over time, and to quantify the degree to which local death assemblages track changes in the living community. (d) Death assemblages from older intervals of the geological record will be acquired from coring programs being planned as part of the Bight 2008 survey to insure access to early-impact and pre-impact periods. (e) Amino acid racemization dating will be used to a decadal-resolution chronology for species that are anomalously abundant in the death assemblage. (f) Multivariate techniques will be used to integrate information on changes in living and death assemblages, the ecological tolerances of anomalously abundant species in past death assemblages, the spatial distribution of sample-stations relative to major wastewater outfalls, and already existing environmental and cultural information in order to estimate the relative importance of natural and anthropogenic forcing factors on community change.

The continental shelf of the Southern California Bight has experienced marked variation in climate and in human inputs of nutrients, toxins, and solid sediment during the last 100 years. However, it is poorly known whether seafloor communities bight-wide and at a distance from wastewater outfalls have shifted in composition, affecting our sense of what the natural, remediated state of these communities would be, and the relative importance of natural and human forces on community change are difficult to establish. Proof-of-concept work funded by NSF has found via a global meta-analysis a high fidelity of molluscan death assemblages to local living communities under stable conditions, with “live-dead” mismatches indicating strong human modification of the local living community; studies elsewhere have established the decadal time resolution of amino-acid racemization dating. Pilot work on death assemblages from the Bight 2003 survey show that bivalve shells are sufficiently abundant and intact to support a quantitative analysis of this type, and preliminary analysis of live-survey data and archived death assemblages from 1975 both indicate that community composition has shifted bight-wide. This project will leverage the millions of dollars of investment already made by state and federal agencies to characterize and monitor the physical environment and biological communities of the southern California Bight over the last 30 years.



Publications & other print media:
Predicting the effects of increasing temporal scale on species composition, diversity, and rank-abundance distributions
Author(s): Adam Tomasovych and Susan M. Kidwell

The Effects of Temporal Resolution on Species Turnover and on Testing Metacommunity Models
Author(s): Tomasovych, Adam; Kidwell, Susan M.

Preservation of Spatial and Environmental Gradients by Death Assemblages
Author(s): Tomasovych, Adam; Kidwell, Susan M.

Fidelity of variation in species composition and diversity partitioning by death assemblages: time-averaging transfers diversity from beta to alpha levels
Author(s): Tomasovych, Adam; Kidwell, Susan M.

Mixed carbonate-siliciclastic sedimentation on a tectonically active margin: example from the Pliocene of Baja California Sur, Mexico / (2009)
Dorsey, Rebecca J., Kidwell, Susan M.

Sensitivity of taphonomic signatures to sample size, sieve size, damage scoring system, and target taxa (2009)
Kidwell, Susan M., Rothfus, Thomas A.

Tomasovych, A. and S.M. Kidwell, 2009. Fidelity of variation in species composition and diversity partitioning by death assemblages: time- averaging transfers diversity from beta to alpha levels . Paleobiology 35: 97- 121.

Tomasovych, A. and S.M. Kidwell, 2009. Preservation of spatial and environmental gradients by death assemblages. Paleobiology 35: 122-148

Kidwell, S.M., 2008. Ecological fidelity of open marine molluscan death
assemblages: effects of post-mortem transportation, shelf health, and taphonomic inertia. Lethaia 41: 199-217.

Kidwell, S.M., 2007. Discordance between living and death assemblages as evidence for anthropogenic ecological change. Proc Nat Acad Science USA 104(45): 17701-17706. [Commentary by J.P. Smol, 2007. Marine sediments tell it like it was. PNAS 104: 17563-64]

Rogers, RR, and SM Kidwell, 2007. The origin and interpretation of bonebeds, p. 1-63. In Rogers, RR, D Eberth and A Fiorillo, eds, Bonebeds: Genesis, Analysis, and Paleobiological Significance. Univ Chicago Press.

Best, M.M.R, T. C.W. Ku, S. M. Kidwell, and L. M. Walter, 2007 Carbonate preservation in shallow marine environments: Unexpected role of tropical siliciclastics. J. Geology 115, p. 437-456

Olszewski, T.A. and S.M. Kidwell, 2007. The preservational fidelity of evenness in molluscan death assemblages. Paleobiology 33: 1-23.

Lötze, H.K., H.S. Lenihan, B.J. Bourque, R. Bradbury, R.G. Cooke, M. Kay, S.M. Kidwell, M.X. Kirby, C.H. Peterson, J.B.C. Jackson, 2006. Depletion, degradation, and recovery potential of estuaries and coastal seas worldwide. Science 312: 1806-1809.

Valentine, J.W., D. Jablonski, S.M. Kidwell, and K. Roy, 2006. Assessing the fidelity of the fossil record by using marine bivalves. Proc Nat Acad Science USA 103: 6599-6604.



Video, electronic, and computer products:

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