The invasive foraminifera Trochammina hadai as a biostratigraphic marker of the Anthropocene in San Francisco Bay
Abstract
Modification of the biosphere through the introduction of neobiota is a part of the major human impact to the Earth System. Neobiota are now present worldwide and often significantly outnumber native faunas and floras. Few ecosystems have been as severely affected by the arrival of neobiota as San Francisco Bay. Some 234 invasive species comprising up to 97% of individuals and 99% of the biomass are known to be present in the bay (Cohen and Carlton, 1998). One of the most abundant neobiotic species is Trochammina hadai, a benthic foraminifera native to Japan that was introduced to San Francisco Bay in 1983 (McGann, 2000). Here we present sediment core data showing T. hadai distributed widely in San Francisco Bay with an average peak abundance of 77.7% of the total foraminiferal assemblage. Prior to its introduction, the foraminiferal record of the bay shows a stable benthic assemblage exhibiting little change across the last 125,000 years. During this ~125,000 year interval, Elphidium excavatum, a benthic foraminifera native to the bay was most abundant, comprising 63% of the foraminiferal assemblage in the upper Pleistocene and 75% of the assemblage in the Holocene. Following the introduction of T. hadai, E. excavatum has an average recorded abundance of 19% (Lesen and Lipps, 2011). Given that the cores were taken in 1990, this species demonstrates an explosive introduction and represents an abrupt shift in the foraminiferal record. Fly ash particles emitted from coal-fired power plants are used both as a proxy for identifying sedimentary deposits of Anthropocene age and as a chronometer for correlating time horizons between the cores. This multi-proxy approach, combining biological components with fly ash, can be used to establish a wide-spread San Francisco Bay marker of the Anthropocene.
Cohen, A.N. & Carlton, J.T. 1998. Accelerating invasion rate in a highly invaded estuary. Science 279, 555-558. Lesen, A.E. & Lipps, J.H. 2011. What have natural and human changes wrought on the foraminifera of San Francisco Bay late Quaternary estuaries? Quaternary Research 76, 211-219. McGann, M., Sloan, D. & Cohen, A.N. 2000. Invasion by a Japanese marine microorganism in western North America. Hydrobiologia 421, 25-30.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGC53H1232H
- Keywords:
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- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 1990 Uncertainty;
- INFORMATICS;
- 3275 Uncertainty quantification;
- MATHEMATICAL GEOPHYSICS