Are invasive species (‘neobiota’) a biostratigraphical and biological marker of the Anthropocene?

Humans modify the biosphere at an accelerating rate, directing evolution of species and ecosystems, trans-locating organisms across the globe, appropriating huge energy resources, and increasing biological interaction with technology. It can be argued that these changes are comparable in scale to those of deep time evolutionary transitions, with possible near-future trajectories that include mass extinction. These changes are part of a greater pattern of human modification to the atmosphere, hydrosphere and landscape that has left a distinctive geological signal of the Anthropocene.

In some places recent changes to biota are profound. The San Francisco Bay area is a clear example, being possibly the most biologically invaded aquatic ecosystem in the world. It is thus a prime setting to evaluate the degree of human impact on the biosphere and its potential biostratigraphical signal. In a seminal study by Cohen et al. (1998), some 234 neobiotic ‘invasive’ species were recognised in the Bay. They noted an accelerating trend of invasion over ca. 150 years, with about half the invasions occurring since 1960. More recently, studies of shallow sub-tidal sediments in the Bay have identified communities that are numerically dominated by invasive species. The presence of so many neobiota in San Francisco Bay, together with an established chronology of invasion, provides a means to assess the potential biostratigraphical expression of these changes over a timescale of 2 centuries.

Changes in San Francisco Bay are mirrored in Old World (e.g. Britain), and remote island (Hawaii) biological signatures. All these areas have a complex mosaic of human-influenced stratigraphic successions. But importantly, they share species that suggest inter-continental biostratigraphical ties can be established. Collectively these regions can be used to examine the global pattern of Anthropocene biotic change, and to assess the biostratigraphical pattern of the neobiota in the rock record across the world. They also comprise successions across a range of climate zones including tropical, warm temperate and cold temperate.

Methodology

Examine the biostratigraphical signature of the Anthropocene in 3 key areas, initially based on an extensive literature review: San Francisco Bay, Hawaii, and the UK.
Identify the pre-human influenced signature of the biota.
Identify the impact of the neobiota on the restructuring of ecosystems
Identify the ‘theoretical’ order of succession of neobiotic colonisation.
Assess those species with high biostratigraphical potential (those with recalcitrant skeletons, a wide distribution, a good chronology of invasion, and a known biostratigraphical record in their origin areas).
Formulate strategies to ground-truth biostratigraphies via direct collecting in the field. In particular, this component will seek to reconcile the order of appearance of taxa in sedimentary profiles with their recorded [‘theoretical’] chronologies of invasion.
Integrate biostratigraphical markers with published records of human-made sedimentary deposits, chemical markers, and plastics in the study areas to develop an overall chronology of invasive species.
Integrate the signal from all areas to examine whether a globally correlatable signature of the Anthropocene can be identified using biostratigraphy, even in remote island settings.
Examine the temporal framework of reorganisation of biosphere structure
Yr 1

a. Literature-based analysis.
b. Establish biostratigraphical signature of neobiota.
c. Characterise ecological roles of neobiota in native and ‘invasive’ locations.

Yr 2

a. Targeted collecting of key sites, integrating techniques to date biotic samples.

b. Identification of taxa that have potential for inter-regional correlation.

Yr 3

a. Develop an integrated biostratigraphy for correlation between remote successions.

b. Assess how the biostratigraphical signal may preserve.

Further Reading

Cohen, A.N. & Carlton, J.T. 1998. Accelerating invasion rate in a highly invaded estuary. Science, 279, 555-557.
Waters, C.N., et al. 2016. The Anthropocene is functionally and stratigraphically distinct from the Holocene, Science, 351, 137.
Williams et al. 2016. The Anthropocene: a conspicuous stratigraphical signal of anthropogenic changes in production and consumption across the biosphere. Earth Future, 4, doi:10.1002/2015EF000339.
Zalasiewicz et al. 2008. Are we now living in the Anthropocene. GSA Today, 18, 4-8.