The Environmental Stories of Microfossils:
A New Research Path for Micropaleontology
by Ron Martin
MICROFOSSIL: A fossil too small to be studied without the aid of a microscope, such as the foraminifer.
It may be the remains of an organism or part of a larger organism.
MICROPALEONTOLOGY: The study of microfossils.
In 1877, long before exploration geologists started using foraminifera to find energy resources, these microfossils were used to date strata in a water well near Vienna, Austria. In 1911, J. A. Udden of Augustana College in Illinois started using microfossils to correlate aquifers. Udden later forsook academe to head the Texas Bureau of Economic Geology, where he no longer used microfossils to study water, but to find petroleum. Pioneering efforts during the 1960s of Orville Bandy and coworkers, who examined the response of foraminiferal populations to sewage effluent in shallow marine waters, lay dormant. But in the last decade, we seem to have come full circle since Udden’s time, and micropaleontology has embarked on a new research path: environmental geology.
The fossil record typically has been viewed as incomplete—and therefore flawed—at least since the time of Lyell and Darwin. Only recently have biologists and paleontologists realized the record’s relative completeness and its potential as a tool for evaluating and monitoring environmental disturbances, both natural and anthropogenic. Such studies have important implications for industry- and government-funded environmental remediation, and for understanding the history of biodiversity and its application to conserving and managing ecosystems.
Environmental geology—using geology’s traditional disciplines to understand current changes in the environment—is an evolving field. Thus, environmental applications of micropaleontology are incredibly diverse, as are the taxa used (foraminifera, dinoflagellates, diatoms, pollen, ostracodes and thecamoebae). Some applications include:
• Basic stratigraphic and paleoecological studies of seismic hazard sites and their histories
• Correlating aquifers that are discontinuous in time and location
• Engineering, including aligning the Chunnel
connecting England and France as it was being excavated from both sides
English Channel, and siting the Thames River flood control barrier
• Using foraminiferal tracers in the Holocene record to evaluate the frequency of storms and their con-tributions to coastal sedimentation
• Evaluating indicator species, abnormal
morphologies and cellular defense mechanisms in response to pollution
Seeing the big picture
TIME-AVERAGING: The mixing of hard parts of
different generations and habitats before final burial.
| Along with erosion, the process
of time-averaging has long been viewed as an insurmountable obstacle to
using the fossil record for understanding ecological change. Time-averaging
has, however, come to be viewed in a positive light because it can actually
enhance the expression of ecological signals by damping and filtering out
Short-term (high-frequency) population phenomena are indeed often lost in the fossil record of the last few hundredto few thousand years. But this loss is advantageous for understanding long-term processes. Time-averaged assemblages are more likely to represent long-term environmental conditions and ecological dynamics. The dominance of a particular set of environmental parameters will increase with time while comparatively short-term (and perhaps unrepresentative) fluctuations are damped or completely filtered out over time. High loss rates in death assemblages normally involve the ecologically most transient parts of communities. Some death assemblages appear comparable to the results of repeated biological surveys that document changes in a community’s species composition and diversity over several decades or more—including sudden phenomena that might be missed by short-term sampling regimes. The creatures that leave behind microfossils often have short life spans (weeks to months) and thus respond quickly to environmental changes. They are frequently abundant in small time-averaged samples of only a few cubic centimeters.
Scanning electron microscope
image of the
Thus microfossils are ideal for evaluating the environmental changes
time-averaged assemblages may document. For example, understanding local,
rather than regional, climatic and geologic controls on rates of sea-level
change is of obvious ecological and economic importance for managing coastal
wetlands. Sea-level curves (used to infer seal-level changes) constructed
from seasonal assemblages of marsh foraminifera formed over the last 200
years along Delaware Bay are noisy and essentially impossible to interpret.
When seasonal assemblages collected over a span of two years are summed
through “artificial time-averaging,” however, the resulting sea-level curves
strongly resemble those constructed from assemblages in other areas. This
resemblance implies that regional changes, not just isolated local factors,
are involved in forming these fossil assemblages. In fact, we have
been able to reproduce up to about 99 percent of long-term ecological signals
using artificial time-averaged assemblages in our regression models of
New research in micropaleontology offers subtle but far-reaching clues to the states of environments before anthropogenic influences—making it easier to compare environments and measure how humans affect them. Micropaleontological studies have already detected significant anthropogenic effects in seemingly healthy environments over time spans of only decades. For example, although recent short-term (several years) studies found no evidence of elevated nutrient levels in waters off the Florida Keys, other studies of foraminiferal assemblages have documented a shift between 1961 and 1992 off Key Largo, Fla., from large, long-lived, algal-symbiont bearing taxa to smaller, fast-growing, heterotrophic taxa. This shift might have resulted from increased nutrient loading in the Keys. Similar results have come from studies of coral colonies in Biscayne Bay, Fla., and of outbreaks of the Crown-of-Thorns starfish on the Great Barrier Reef of Australia.
Research also suggests that entire regions have experienced permanent changes after human settlement. Based on diatom and pollen assemblages, it appears that the Chesapeake Bay has shifted to a new stable state as a result of human activities. Sedimentation, eutrophication and anoxia (lack of oxygen caused by eutrophication and then die-off of diatom blooms) all increased dramatically after humans settled in the Chesapeake Bay region. Increased sedimentation and eutrophication were related to land use (deforestation and agriculture), sewage input and freshwater runoff.
Using microorganisms and micro-fossils to understand environmental changes
is a hot research area, and scientists will gather this year for a second
international conference on the topic. The Avalon Institute of Applied
Science and Dalhousie University’s Centre for Marine Geology, both in Canada,
along with the Geological Laboratory of the University of Angers in France,
is hosting the second international conference on “Applications of Microorganisms
to Environmental Problems,” Aug. 27–30 in Winnipeg, Canada. The first conference
on this topic was held in 1997 in Israel and was so well attended that
the organizers saw the need for a second conference, according to Valentina
Yanko-Hombach, president of the conference. “This is a very popular subject
right now,” Yanko-Hombach says. Some highlights of the conference are how
microorganisms work as indicators of past and recent environments, what
they indicate about oxygen-depleted environments and pollution, and methods
for analyzing data to determine microorganism ecology. More information
about the Avalon conference is at <http://www.ilos.net/~hombach/
Martin is an
associate professor in the Department of Geology at the University of Delaware.
His primary research interests are the preservation and formation of fossil
assemblages and their use in paleonvironmental interpretation and environmental
assessment; and ongoing changes in biogeochemistry and the implications
for the evolution of marine biodiversity. Martin holds a doctorate in protozoology
from the University of California at Berkeley. He was an operations micropaleontologist
with Unocal in Houston from 1981 to 1985. Currently he is an associate
editor for Palaios and the Journal of Foraminiferal Research.
In 1998, he published
One Long Experiment: Scale and Process in Earth
“A Journey Through Time” by S. R. Cooper. Geotimes, vol. 44(5), 1999, p. 14-18.
“Chesapeake Bay Watershed Historical Land Use: Impacts on Water Quality and Diatom Communities” by S. R. Cooper. Ecological Applications, vol. 5, 1995, p. 703-723.
“Decadal-Scale Changes in Benthic Foraminiferal Assemblages Off Key Largo, Florida” by E. Cockey, P. Hallock and B. Lidz. Coral Reefs, vol. 15, 1996, p. 237-248.
“Environmental Applications of Foraminiferal Studies,” edited by D. B. Scott and J. H. Lipps. Journal of Foraminiferal Research, vol. 25(3), 1995, p. 189-286.
“Reflections on Community Ecology and the Community of Ecology: The View from a 1998 Penrose Conference on ‘Linking Spatial and Temporal Scales in Paleoecology and Ecology’” by A. S. Cohen. Palaios, vol. 13(6), 1998, p. 603-605.
“Taphonomy as a Tool in Paleoenvironmental Reconstruction and Environmental Assessment,” edited by R. E. Martin, R. T. Patterson, S. T. Goldstein and A. Kumer. Palaeogeography, Palaeoclimatology, Palaeoecology, vol. 149 (1-4), 1999, p. vii-434.
Taphonomy: A Process Approach by R. E. Martin. Cambridge University Press. 1999, 508 p.
“The Quality of the Fossil Record: Populations, Species, and Communities” by S. M. Kidwell and K. W. Flessa. Annual Review of Ecology and Systematics, vol. 26, 1995, p. 269-299.