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Alegret, Ortiz & Kaminski (eds.), 2012. Ninth International Workshop on Agglutinated Foraminifera, Abstract Volume
Comparison of modern foraminiferal population densities from the Caroni
Swamp, Trinidad, and Cowpen Marsh, England
Ashleigh COSTELLOE 1 , Brent WILSON 1 and Benjamin HORTON 2
1 Department of Chemical Engineering, University of the West Indies, St. Augustine, Trinidad.
2 Sea-level Research Laboratory, Department of Earth and Environmental Science, University of
Pennsylvania, Philadelphia, PA 19104-6316, USA.
e-mail: ashleighcostelloe@gmail.com
A time series of foraminiferal population densities from two wetlands, the Caroni Swamp in
the tropical southern Caribbean and Cowpen Marsh in the temperate northeast England, were
compared to determine the significance of environmental differences between marsh and
swamp. The Caroni Swamp is located on the eastern side of Trinidad - the most southern
island in the Caribbean archipelago. The mangrove swamp opens to the Gulf of Paria where
the water salinity and productivity is directly affected by seasonal discharge from the Orinoco
River in Venezuela. During a rainy season (July to December) a plume of low density water,
with low salinity and high productivity, expands from the northeastern coastline of South
America through the Gulf of Paria. This seasonal change in water salinity is expected to affect
foraminifera living at the Caroni Swamp, by placing stress on the number of specimens that
can be sustained in the harsh conditions typical of tropical swamps. In contrast to the negative
effect lower water salinity may have on foraminiferal populations, the Orinoco plume
transports coastal “seed” phytoplankton and additional nutrients (eg. tannins) which should
encourage population growth. During a wet season Bidigare et al. (1993) found that the
subsurface chlorophyll maximum (SCM) averaged 77 ± 12 m, while in a dry season shallower
SCM depths were recorded (an average of 39 ± 16 m).
Three stations from highest high tide, mid-tide and lowest low tide were sampled once
a month for one year (February 2011 to 2012) at three sites in the Caroni Swamp. At Cowpen
Marsh, a transect with 31 stations from high, middle and low marsh was sampled bi-weekly
from May 1995 to 1996 by Horton et al. (2006, 2007). For the purpose of this study, only the
living foraminifera collected on the 1 st of each month were examined and compared with
those monthly samples from Caroni Swamp. Horton et al. (2006) collected 10 cm 3 (10cm 2 x
1cm) of sediment from each station in the high marsh (stations 1-5), middle marsh (stations 6-
14) and low marsh (stations 15-18). In contrast, four replicates of 75 cm 3 of sediment from
each site were collected at Caroni Swamp, giving a total of 900 cm 3 (75 cm 3 x 4 replicates x 3
sites) of sediment per high, middle and low swamp stations.
The average total abundance of foraminifera recorded from high, middle and low
swamp at Caroni Swamp was 0.05, 0.11 and 0.06 sp./cm 3 , respectively. In contrast, that
recorded from Cowpen high, middle and low marsh were consistently greater: 158, 341.7 and
330.4 sp./cm 3 , respectively. Comparison of the two time series of monthly percentage
abundances (sp./cm 3 ) shows that foraminiferal populations from Cowpen high marsh steadily
increase through the year (r =0.9221, p =0.0005) with a bloom from January to May (winter
& spring); Caroni high swamp shows stationarity (r =0.0436, p =0.8868) with a bloom from
February to August (dry season). That for Cowpen middle marsh is an almost linear increase
through the year (r =0.9899, p =0.0015) with a bloom from August to November (summer &
autumn); Caroni middle swamp displays stationarity (r =0.0245, p =0.9355) with a population
bloom from July to October (wet season). Percentage abundances of foraminiferal populations
from Cowpen low marsh steadily increase throughout the year (r =0.9878, p =0.0014) with no
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