Journal of Foraminiferal Research, v. 29, no. 3, p. 186–195, July 1999
BENTHIC FORAMINIFERAL COLONIZATION IN EXPERIMENTS WITH
COPPER-CONTAMINATED SEDIMENTS
ELISABETH ALVE1
AND
FRODE OLSGARD2
diversity when sediment concentrations exceed about 200
ppm (Rygg, 1985). The National Oceanic and Atmospheric
Administration (NOAA) in the United States has set an
‘‘Apparent Effects Threshold’’ (AET) of 390 ppm Cu (Long
and Morgan, 1990). The AET is the sediment concentration
of a selected chemical above which statistically significant
biological effects always occur (e.g., depression of abundance of benthic infauna). Laboratory experiments with
meiofauna have shown significant effects on faunal composition of Cu concentrations between 500 and 800 ppm
(Austen and others, 1994; Austen and McEvoy, 1997). At
present, the effects that various heavy metal concentrations
have on benthic foraminifera are only poorly understood
(see review in Alve, 1995a). The primary aim of the present
paper is to focus on benthic foraminiferal colonization patterns in defaunated sediments having different levels of Cucontamination. These data represent part of a larger data set
including macrofauna analyses from the same experiment
(Olsgard, 1999). A colonization approach was chosen for
this field experiment since settling and metamorphosis of
pelagic larvae are generally considered the most critical
phases in the development of marine benthic invertebrates
(e.g., Thorson, 1966; Woodin, 1976; Obreski, 1979; Watzin
and Roscigno, 1997).
ABSTRACT
Colonization experiments, carried out over a 32-week
period at 63 m water depth in the Oslofjord, Norway,
have shown that sediment Cu-concentrations of .900
ppm cause a change in the living (stained) foraminiferal
community structure as compared to control values of
70 ppm. The changes, which are revealed through multivariate statistical analyses (MDS-ordination and ANOSIM tests) of the different treatment assemblages, are
reflected by increased equitability and reduced abundances in treatments with high (967–977 ppm) and very
high (1761–2424 ppm) Cu-concentrations. At the species
level, a significant negative effect of the Cu-enrichment
could be observed only for Stainforthia fusiformis and
Bolivinellina pseudopunctata. There was no significant
decrease in the number of species with increasing sediment Cu-enrichment. This indicates that not even sediment [Cu] . 2000 ppm had a severe negative impact on
the foraminiferal species ability to colonize. One prominent effect of the Cu-contamination is that, at concentrations higher than about 900 ppm, the opportunistic
and dominant S. fusiformis developed an increasingly
patchy distribution pattern. Cu-contaminated sediments
alone do not seem to promote development of deformed
hard-shelled foraminiferal tests beyond the normal
range.
MATERIALS AND METHODS
EXPERIMENTAL DESIGN
INTRODUCTION
AND
FIELD WORK
An aluminium frame containing 16 propene plastic boxes
(Fig. 1), each filled (to 2 cm below the brim) with a 10-cm
thick sediment layer, was carefully placed at the sea bottom
(63 m water depth) in the middle part of the Oslofjord (N
598 40.279, E 108 36.189), Norway, on the 30th of January
1996. Three bottom-water samples (2 m above the sea floor)
were collected at the deployment site on the following day
for dissolved oxygen determination by Winkler titration.
Each plastic box had an area of 928 cm2 (29 cm 3 32 cm).
The sediment used in the boxes had been collected from the
same area in December 1995 and mixed with different
amounts of CuCl2 (a salt which is easily dissolved in seawater) in a cement mixer for about 1 hour. Four boxes (without CuCl2) served as controls whereas the 12 remaining
boxes constituted 4 different CuCl2 treatments (;150 ppm
Cu, ;300 ppm Cu, ;950 ppm Cu, and ;2000 ppm Cu,
representing very low (VL), low (L), high (H), and very
high (VH) doses, respectively) with 3 replicates of each. The
sediment samples were dosed according to a logarithmic
scale since the faunal response to Cu contamination was
expected to be logarithmic rather than linear. All boxes were
randomly placed within the Al-frame. The sediment, which
was made sterile of living fauna by freezing at 220 8C for
a minimum of 72 hours, was kept frozen while carefully
lowered to the sea bottom to avoid any loss. Defaunation
through freezing is a commonly used method in colonization experiments (e.g., Smith and others, 1989; Snelgrove
Coastal marine to brackish water environments, particularly estuaries, have traditionally served as recipients for
various kinds of anthropogenic wastes. This activity has, in
many cases, had a severe impact on the local biota. Foraminifera are among the most common and abundant naturally-occurring meiofaunal benthic components in these areas. Their abundance, and the fact that their tests have much
better preservation potential after the death of the organism
than most other meiofauna, implies that their subrecent fossil record is particularly well suited for reconstructions of
human-induced environmental impacts through time (Alve,
1995a). In other words, benthic foraminifera have a unique
potential as environmental biostratigraphic tracers to evaluate pollution impact time series, compared to other benthic
organisms. Despite this, copepods and nematodes are by far
the most commonly investigated meiobenthic taxa to assess
pollution (Coull and Chandler, 1992).
Copper (Cu) is a heavy metal typically associated with,
and enriched in, contaminated and polluted sediments (e.g.,
Sadiq, 1992); and correlations based on field data indicate
that Cu had a clear negative impact on marine macrobiota
1 Dept. of Geology, University of Oslo, P.O. Box 1047 Blindern,
N-0316 Oslo, Norway.
2 Dept. of Biology, University of Oslo, P.O. Box 1064, Blindern,
N-0316 Oslo, Norway.
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COLONIZATION OF CU-CONTAMINATED SEDIMENTS
187
the plate with the graduated core tube was carefully slid off
and the sediment transferred to the sample container. The
process was repeated down core so that the upper 0–1 cm
of sediment was sectioned into two 0.5 cm slices, and the
1–5 cm core depth was sectioned into two 2.0 cm slices.
All the foraminiferal samples were preserved in 70% ethanol within a few minutes of sample recovery.
LABORATORY PROCEDURES
Sediment Chemistry
FIGURE 1.
Schematic illustration of experimental setup.
and others, 1992; 1994). The carcasses of the organisms
which lived in the sediments and were killed during the
freezing process might have served as an extra food source
for the settling organisms during the initial phase of the
experiment. However, this must have affected all boxes in
the same way, and should therefore be of little importance
for the results.
The boxes were held in position in the frames by aluminium bars screwed through the handles of each box. An
underwater buoy fixed to each frame held the wires away
from the sediment surface of the boxes during the experiment. When the frame was lowered to the bottom, the wire
from the boat was attached to a hook on top of the buoy,
which was automatically released when the frame reached
the seabed. For further details about the experimental area
and the experimental design, see Olsgard (1999).
Just prior to collection of the frame on the 9th of September 1996, 3 replicate gravity cores (69 mm diameter)
were collected from the adjacent seabed (within a few tens
of meters from the frame) to assess the ambient benthic
foraminiferal fauna at the site. The frame was then carefully
raised to the sea surface. Polychaete tubes (predominantly
living Pseudopolydora paucibranchiata and Prionospio
cirrifera) carpeted the sediment surface in each box, thereby
reducing the possibility of loosing any of the sediment (or
animals) while the frame was being raised to the surface.
After retrieval of the frame, two different sets of subsamples
were collected from each of the 16 plastic boxes for the
following analyses: benthic foraminifera (one sediment core,
57 mm diameter) and sediment chemistry and grain size
analyses (one core, 59 mm diameter). The sediment cores
used for chemical and grain size analyses were frozen at
220 8C, and the remaining sediment in each box was
washed through 5 mm and 0.5 mm sieves for macrofaunal
analyses.
All foraminiferal sediment cores were sectioned in the
following way immediately after collection. The sediment
was gently pushed up through the core liner and the last
few millimeters of water was carefully removed with a pipette and transferred to a labeled sample container. A short
section of core tube, marked with gradations of 0.5 and 2.0
cm, was placed on top of the core tube and the sediment
core was extruded into it to the desired thickness. A metal
plate was inserted between the core tube and graduated tube,
The sediment cores for chemical analyses were sectioned
while frozen, freeze dried and homogenized in an agate
mortar. Metal concentrations in sediments were quantified
by digesting 0.3 g sediment at 95 8C in 10 ml HNO3 until
dry. The metals were then dissolved in 3 M HCl and measured by flame atomic absorption spectrometer (AAS). Organic carbon (OC) was determined using the potassium dichromate sulfuric acid oxidation method (Gaudette and others, 1974). Grain size analysis was carried out by wet sieving using a 63 mm sieve to determine the sediment silt-clay
content.
Foraminifera
The foraminiferal sediment samples were washed on a 63
mm sieve, stained with rose Bengal (1 g/l water) for 1 hour,
washed again to remove the surplus stain, and dried at 50
8C. All live (stained) benthic foraminifera were picked, identified and counted. Since dead foraminiferal cytoplasm
might react with rose Bengal weeks to months after an individual’s death (Bernhard, 1988; Hannah and Rogerson,
1997), it might be argued that some of the stained individuals recorded here represent the ones that were frozen and
killed during defaunation of the sediments. However, since
the sediments used in this experiment had been thoroughly
mixed prior to freezing, the living individuals which might
have caused an error in distinguishing between living and
dead individuals at the end of the experiment were equally
distributed throughout the experimental boxes. Consequently, the fact that there were very few stained individuals in
the lower parts of the analyzed cores (as opposed to the
surface samples, see below) shows that the possible staining
of freeze killed individuals does not represent an error in
the present data set. On the contrary, it shows that the methodologies used here were effective.
STATISTICAL ANALYSES
The faunal data for each 0–5 cm core section were normalized to the number of individuals per 10 cm2 and run
through a non-metric multidimensional scaling ordination
analysis (MDS ordination; Shepard, 1962; Kruskal, 1964)
by use of the PRIMER (Plymouth Routines In Multivariate
Ecological Research) package (Clarke and Warwick, 1994).
This statistical method determines the similarities between
samples and results are visualized by plotting the results in
a 2-dimensional ordination plot. Our calculations are based
on a similarity matrix calculated using the Bray-Curtis similarity coefficient (Bray and Curtis, 1957), with a single
square root transformation of the data to reduce the impact
of dominant species. The reliability of the results is shown
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ALVE AND OLSGARD
by a Stress value (Kruskal and Wish, 1978) which ideally
should be ,0.1, but values of ,0.2 still give a potentially
useful 2-dimensional picture. Formal significance tests for
differences between treatments were performed using the
ANOSIM permutation test (Clarke, 1993). The natural logarithm was used for the Shannon-Wiener (H(S)) and equitability (E) calculations.
RESULTS
SEDIMENT CHEMISTRY
The Cu-concentrations (upper 0–5 cm of the sediment at
the end of the experimental period) in the four control boxes
ranged between 66 and 71 ppm (Table 1, Fig. 2). The 12
remaining boxes which constituted 3 replicates of each of 4
different treatments had the following Cu-concentrations in
the upper 0–5 cm of sediment: very low (VL: 142–148
ppm); low (L: 291–314 ppm); high (H: 967–977 ppm), and
very high (VH: 1761–2424 ppm). The ambient Cu-concentration in the surface 0–5 cm sediment a few tens of meters
from the frame was 86 ppm in the single analyzed core. Cu
profiles (1 cm slices) through the surface 0–5 cm of sediment within each box indicate that the Cu was tightly bound
to the sediment. Only a minor fraction (,10%) from the
surface 1 cm in any of the boxes had leaked to the overlying
water (Olsgard, 1999). The sediments were sandy silt (30–
44% ,63 mm) with a mean organic carbon content of 3.2%.
Most of the sand sized particles were sediment aggregates
(including faecal pellets) made up of finer detrital grains.
The Winkler titration of bottom water (2 m above sea floor)
at the experimental site gave values of 4.35, 4.37, and 4.41
ml O2/l.
FORAMINIFERA
All boxes were colonized by both macro- and meiofauna,
but only the foraminifera will be discussed in detail here.
The macrofaunal data are reported in Olsgard (1999). In the
following, the word ‘‘core’’ is used in connection with data
representing the whole analyzed sediment section (i.e., 0–5
cm). The data presented in the following represent the mean
of 3 replicates for each of the different treatments and the
seabed, and 4 replicates for the control.
Species Diversity
A total of 61 living (stained) benthic foraminiferal species
were recorded, 45 of which were present in the cores from
the ambient sediments outside the frame (Table 1). Only one
of the ambient seabed species was not found in any of the
colonization boxes. The mean number of species in the ambient seabed cores (0–5 cm) was 33 (SD 5 3.8). In the
control and 4 treatments, the mean values decreased with
increasing Cu-enrichment (Fig. 3) from 22 in the control to
19 in the VH treatment (SD 5 2.5–8.3) but there was no
significant correlation between the number of species and
the copper concentration in the boxes ([Cu]), r 5 20.20, p
5 0.45. All cores had the highest number of living species
in the surface 0–0.5 cm (ambient seabed 25; control and
treatments 12–18) but for the 3–5 cm depth interval, there
were significantly more species in the seabed cores (16) than
in any of the colonization boxes (control and treatments 2–
4).
As opposed to the number of species, the Shannon-Wiener diversity index and the equitability showed minimum
values in the control, VL, and L boxes (replicate means:
H(S) 5 0.63–0.71; E 5 0.20–0.23), whereas the values in
the H and VH boxes were clearly higher (H(S) 5 1.39 &
1.64; E 5 0.48 & 0.57) and approached those of the ambient
seabed assemblages (H(S) 5 1.92; E 5 0.55) (Fig. 4).
Abundance Patterns
The numerical densities of living foraminifera are presented in two different ways; as the number of individuals
per 10 cm2 for the whole 0–5 cm core sections, and as the
number of individuals per 10 cm3 for the core slices. The
latter is the most common way to present living benthic
foraminiferal abundances, but the former method has also
been used here to avoid confusion between densities representing a whole core and those representing core sections.
There was no significant difference in the foraminiferal
density between the seabed, control, and VL cores (mean
values 334, 298, and 277 individuals/10 cm2 respectively).
Reduced abundances were found in the L cores while minimum mean values of 86 and 81 individuals/10 cm2 occurred in the H and VH cores respectively (Fig. 5). A characteristic feature was the particularly high standard deviation (SD 5 101) for the VH cores which exceeds the mean
value. There was a significant negative correlation (r 5
20.57, p 5 0.022, n 5 16) between the numerical density
of foraminifera and increasing concentration of Cu in the
sediments.
All sediment cores had the highest foraminiferal numerical density in the surface 1 cm (Fig. 6). In the seabed cores,
62–69% (mean 65%) of the living individuals occurred in
the surface 1 cm. Only one of the VH replicate cores had a
comparably low figure (56%) for the surface 1 cm. For the
control and treatments the mean values for the surface 0–1
cm were 92% (control), 86% (VL), 93% (L), 89 (H), and
80% (VH).
Faunal Compositions
Stainforthia fusiformis (Williamson) was the most abundant species in all cores except one of the VH replicates
(Table 1). Detailed size measurements were not performed
but it was evident that ‘‘juveniles’’ (length , 125 mm) of
this species were by far outnumbered by adult individuals
(length . 150 mm). Stainforthia fusiformis had a significantly higher numerical density than the sum of all other
species in the control, VL, and L cores where its relative
abundance was about 88%. The 4 lowest densities of S.
fusiformis occurred in the H and VH cores and the density
showed a significant negative correlation with the sediment
[Cu] (r 5 20.57, p 5 0.017, n 5 16). By contrast, the
numerical density of the other species did not show any
significant difference between the control and any of the
treatments (Fig. 7).
In addition to S. fusiformis, the following 5 species were
most abundant (.10 individuals/10 cm2) in the ambient seabed cores (listed in decreasing order): Elphidium excavatum
(Terquem), Nonionella turgida (Williamson), Bolivinellina
COLONIZATION OF CU-CONTAMINATED SEDIMENTS
189
TABLE 1. Numerical density of all recorded foraminiferal species, faunal parameters, relative abundance of Stainforthia fusiformis, absolute
abundance of all species minus S. fusiformis, and mean sediment Cu-concentrations for all analyzed cores (0–5 cm sediment depth). A 5 ambient
seabed; C 5 control; VL, L, H, and VH 5 treatments with very low, low, high and very high sediment [Cu] respectively, * 5 data from one single
core; ** 5 values at the end of the experiment.
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ALVE AND OLSGARD
FIGURE 4. Mean values and SD for Shannon-Wiener diversity index (H(S)) and equitability (E) in ambient seabed, control, and treatment cores (bulk 0–5 cm sediment depth). VL 5 very low; L 5 low;
H 5 high; VH 5 very high [Cu].
FIGURE 2. Sediment Cu-concentrations in different treatments at
the end of the experimental period (error bars: 95% confidence intervals). C 5 control; VL 5 very low; L 5 low; H 5 high; VH 5 very
high [Cu].
pseudopunctata (Höglund), Nonionellina labradorica
(Dawson), and Bulimina marginata d’Orbigny. In the control and treatment cores, only S. fusiformis had mean densities (for each set of replicates) of .10 individuals/10 cm2.
Elphidium excavatum was the second most abundant species, irrespective of sediment [Cu]. The abundance of the
third most common species, B. pseudopunctata, showed a
weak but significant negative correlation (r 5 20.61, p 5
0.013, n 5 16) with increasing sediment Cu-concentration
(Fig. 8). Both juveniles and adults were recorded for all
common species.
The 2-dimensional MDS ordination of the faunal data for
all replicate cores showed the following distinct pattern: the
ambient seabed cores and a mixture of control and various
treatment cores ploted as two separate groups, whereas two
of the H and two of the VH cores ploted progressively further away (Fig. 9). The two VH cores showed the greatest
distance to the field represented by the majority of cores.
FIGURE 3. Number of species (mean values and SD for replicates)
in ambient seabed, control, and treatment cores (bulk 0–5 cm sediment
depth). VL 5 very low; L 5 low; H 5 high; VH 5 very high [Cu].
This relationship indicates that the H cores, and even more
so the VH cores, have faunal characteristics different from
those of the other cores. The obtained Stress value was 0.09,
which means that the plot gives a representative picture of
the individual distances (dissimilarities) between the various
replicates. A pairwise, one-way ANOSIM test (35 permutations) showed an almost significant difference between the
control and H assemblages (p 5 0.086) and a significant
difference between the control and VH assemblages (p 5
0.029), but not a significant difference between the control
and the less Cu-enriched assemblages (p 5 0.1).
Test Deformation
Observation with a dissection microscope during specimen removal from the sediments revealed that a few (1–2)
individuals with deformed tests were present in some samples irrespective of sediment Cu-concentration.
DISCUSSION
The fact that both the overall number of species and the
abundance of species other than Stainforthia fusiformis
were similar in the colonization boxes (Figs. 3 and 7), suggests that the dispersal and colonization mainly happened
through passive suspension and transport of individuals
FIGURE 5. Numerical density of individuals (mean values and SD
for replicates) in ambient seabed, control, and treatment cores (bulk
0–5 cm sediment depth). VL 5 very low; L 5 low; H 5 high; VH 5
very high [Cu].
COLONIZATION OF CU-CONTAMINATED SEDIMENTS
FIGURE 6. Numerical density of individuals (mean values and SD
for replicates) in ambient seabed, control, and treatment sediment core
sections. VL 5 very low; L 5 low; H 5 high; VH 5 very high [Cu].
from the surrounding seabed into the boxes. Furthermore,
the low abundance of other species and the strong predominance of the opportunistic Stainforthia fusiformis in the
boxes compared to the ambient seabed indicates that the
colonization was slow, allowing biological and possible toxic effects to dominate the faunal development, rather than
physical processes (for discussion of colonization patterns,
see Alve, 1999). Even though the abundance of macrofauna
was 2–3 times higher in the colonization boxes compared
to the ambient seabed, the abundance of foraminifera in the
control, VL, and L cores was comparable to that of the
ambient seabed cores (Fig. 5). Consequently, there is no
evidence that the macrofauna had a negative impact (e.g.,
through predation; Buzas, 1978; Buzas and others 1989) on
the foraminiferal colonization pattern.
Not even [Cu] of about 2000 ppm had a severe negative
effect on their ability to colonize. This is clear from the fact
that all common foraminiferal species at the experiment site
were recorded in the boxes after 32 weeks irrespective of
sediment Cu-concentration, and the lack of a significant correlation between the number of species and [Cu] in the colonization boxes. To the extent that it is possible to compare
colonization experiments with field observations, these results indicate that foraminifera do not follow the pattern
seen for macrofauna where the number of species is roughly
halved for each 10-fold increase in sediment Cu-concentration (Rygg and Skei, 1984; Rygg, 1985). This response was
based on correlation of field data (copper was not the only
contaminant present in high concentration) and is therefore
not necessarily of a cause-effect type. On the other hand,
the macrofaunal responses in the present study did not show
any significant differences in the number of species between
control and treatments (Olsgard, 1999). So far, there are too
few data available on how the number of benthic foraminiferal species vary with different sediment heavy metal
concentrations to draw any firm conclusions. However, field
studies in areas primarily contaminated by heavy metals
have shown varying degrees of reduced foraminiferal species diversity with increasing metal concentrations (Ellison
and others, 1986; Alve, 1991). The possibility that these
more or less pronounced reductions might be due to one or
more of the other metals separately, to synergistic effects or
even other unrecorded stress factors, can not be excluded.
191
FIGURE 7. Numerical density of Stainforthia fusiformis and all other species (mean values and SD for replicates) in ambient seabed,
control, and treatment cores (bulk 0–5 cm sediment depth). VL 5 very
low; L 5 low; H 5 high; VH 5 very high [Cu].
Despite the fact that the number of species was not significantly affected (no difference between the control and
Cu treatments, Fig. 3), the variations in H(S) and E (Fig. 4)
reflect that the foraminiferal assemblage compositions in the
H and VH cores are different from those of the control, VL,
and L cores. This illustrates how additional faunal information can be gained by using species diversity indices
which take into account the distribution of specimens among
the species as opposed to only the number of species. The
higher values of H(S) and E in the H and VH cores approached those of the ambient seabed but the community
structures were different (Fig. 9). The higher values merely
reflect the lower abundance of Stainforthia fusiformis (i.e.,
reduced dominance) in the H and VH cores relative to the
other boxes. Additionally, the MDS ordination (Fig. 9), the
ANOSIM tests, and the abundance data (Fig. 5) strongly
show that the H and VH assemblages have faunal characteristics different from those of the controls. In summary,
the faunal data indicate that sediment [Cu] of 900 ppm cause
a significant change in the foraminiferal community structure.
A closer look at the species response reveals that Stain-
FIGURE 8. Linear correlation between numerical density of Bolivinellina pseudopunctata and sediment Cu-concentrations. Solid line
is regression line; dashed lines are 95% confidence limits.
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ALVE AND OLSGARD
FIGURE 9. (A) MDS-ordination of all replicate cores (0–5 cm sediment depth) in relation to faunal composition. (B) Superimposed circles
reflecting relative [Cu] in the surface sediment (0–5 cm) for each core.
forthia fusiformis was the most successful colonizer of these
initially defaunated oxic sediments in the same way as it
was in dysoxic sediments in Drammensfjord (Norway) after
reoxygenation of sediments which had been anoxic for .5
years (Alve, 1995b). This strongly supports the assumption
that it is an opportunist with a high turnover rate (Alve,
1994; Alve and Murray, 1997). The fact that it is the most
abundant species in all treatments, except one VH replicate,
indicates that it can survive and probably reproduce in sediments with extremely high Cu-concentrations (.2000
ppm). However, the abundance, even of this tolerant species,
shows a significant negative correlation with sediment [Cu]
and an extremely patchy distribution when exposed to the
maximum values. Even though a slightly reduced abundance
occurred in the L treatment, a significant reduction (compared to the control) is seen only in the H and VH treatments (Fig. 7), indicating that sediment Cu-concentration of
more than 900 ppm has a negative effect on its reproduction.
The only other species whose abundance was significantly
negatively affected by the increased [Cu] was Bolivinellina
pseudopunctata (Fig. 8). It seems that for most of the meiofaunal taxa and metals studied, the more toxicant the greater the effect for most of the life-history parameters measured (Coull and Chandler, 1992; Austen and others, 1994).
The pronounced patchiness of S. fusiformis in the H and
even more so in the VH treatments compared to the ambient
seabed and control, is also consistent with the increasing
standard deviation (for a given mean abundance) with increased perturbation as seen in other meiofaunal and macrofaunal species (Warwick and Clarke, 1993). The macrofauna in the present study showed a significantly lower
abundance in the H and VH cores compared to the control
(Olsgard, 1999) indicating that the reduced abundance of
foraminifera in these cores was not due to predation or other
effects related to physical disturbance like bioturbation.
The overall abundance of the remaining foraminifera (i.e.,
all minus S. fusiformis) showed drastically reduced values
in the control compared to the ambient seabed, whereas
there was no significant difference between the control and
any of the treatments (Fig. 7). This may be explained in
different ways. First, the colonization might have happened
just prior to collection of the frame through suspension,
transport and subsequent settlement of nearby surface sediments carrying ambient seabed assemblages. However, this
is not likely because the extremely high relative abundance
of S. fusiformis (mostly adults) in the boxes compared to
the ambient seabed (Table 1) strongly suggests that it had
lived in the boxes long enough to reproduce one or more
times. Furthermore, most of the macrofauna had grown to
maturation by the time of collection, reflecting that they had
colonized several months earlier and there is no reason why
the foraminifera should take longer to settle on the new
substrates. Previous foraminiferal colonization experiments
have shown that shallow water and shelf assemblages may
colonize new habitats within days to weeks (e.g., Schafer,
1976; Ellison and Peck, 1983; Buzas, 1993; Alve, 1999).
Second, the foraminifera may have been successively introduced to the boxes throughout the colonization period
and just continued to live there without reproducing. Even
though the life cycle is known for about 50 foraminiferal
species (see review in Lee and others, 1991), our present
knowledge concerning foraminiferal reproduction rates under different environmental conditions is very limited. Most
information so far is based on seasonal studies which typically have been carried out in shallow (,30 m) water settings. Based on samples collected every 2 to 4 weeks from
July 1973 to May 1975, Wefer (1976) suggested that Elphidium excavatum had a growth period of about 3 months
between each reproductive cycle and that it was about 3–5
months for the other investigated species. However, irrespective of whether foraminifera reproduce once or several
times a year or not, most investigations show that reproduction occurs at least during the spring months (e.g., Lutze
and Wefer, 1980; Erskian and Lipps, 1987; Cearreta, 1988;
Kitazato and Matsushita, 1996) which is the time period
when the present colonization experiment was conducted.
Additionally, some species are thought to reproduce
throughout the year (e.g. Nonion depressulus, Murray,
1983; Ammonia beccarii, Basson and Murray, 1995; Stainforthia fusiformis, as Fursenkoina fusiformis, Murray,
1992), and Boltovskoy and Lena (1969) suggested that the
life cycle of small species probably is as short as one month.
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COLONIZATION OF CU-CONTAMINATED SEDIMENTS
Consequently, if they actually have not reproduced in the
colonization boxes, it must be due to some unknown factors,
probably related to attributes of the environment within the
experimental boxes. For example, the fact that .80% of the
foraminifera in the colonization boxes occurred in the surface 0–1 cm of sediment, as opposed to 65% in the ambient
seabed, indicates that the overall biological and geochemical
conditions had not yet stabilized and that the foraminiferal
communities within the boxes were in an early stage of
succession. The possible lack of reproduction can not be
due to the Cu-enrichment, as the pattern was the same both
in the control and in the various treatments, indicating that
not even the highest [Cu] had a significant effect on their
ability to survive.
Third, the foraminifera may have reproduced one or several times in all treatments irrespective of sediment [Cu]. If
this is the case, it is a remarkable observation implying that,
for all the common species in this area, only the reproduction pattern of S. fusiformis and Bolivinellina pseudopunctata were negatively affected.
Overall, the benthic foraminifera seem to be able to survive extremely high sediment Cu-concentrations implying
that they have some sort of self-protecting defense mechanism. One possible explanation involves attributes of their
proteins. Bresler and Yanko (1995) have shown that the
ubiquitous tryptophan-containing proteins are present in at
least some foraminiferal species. These proteins are known
to bind copper, thereby rendering it non-toxic (Engel and
Brouwer, 1987). However, as Bresler and Yanko showed,
not all tryptophan-containing proteins in their foraminifera
had a high-binding affinity for this metal. Thus, the effects
of the copper-binding proteins may differ between species.
Another possibility involves the bioavailability of the metal.
The most bioavailable and toxic form of Cu is the free cupric ion (Cu21) in seawater or interstitial water (Bryan and
Langston, 1992; Austen and others, 1994; Phillips, 1995).
In fine-grained organically rich sediments, Cu is likely to
be adsorbed to the sediment and thereby less biologically
available (e.g., Tietjen, 1980; Austen and others, 1994). It
is possible that the fine-grained nature and the relatively
high organic carbon content of the sediments used in the
present experiment caused Cu to be less bioavailable than
what would have been the case if it had been performed
with more coarse grained sediments. It is important to note
that this experiment was performed in one particular environmental setting. Consequently, the results are not necessarily valid for other habitats (i.e, shallow estuaries, open
bays, and the continental shelf).
Abnormal test shapes in benthic foraminifera (generally
,1% of the living or dead assemblage) are known to occur
under natural conditions in all environments whereas high
abundances have so far been recorded in polluted areas only
(Alve, 1995a), some of which are primarily contaminated
by heavy metals. The latter includes Cu (Alve, 1991; Sharifi
and others, 1991; Yanko and Kronfeld, 1992). Culture experiments, carried out over a 12 week period, have also
indicated that the presence of Cu (culture medium with 10
and 20 ppb of Cu in filtered sea water, I. Croudace, personal
communication) caused Ammonia beccarii to develop abnormal chambers (Sharifi and others, 1991). In the present
study, elevated concentrations of Cu in the sediment, even
to levels higher than those present in most polluted areas,
did not cause the colonizing foraminifera to develop deformed tests beyond the normal range of abundance. These
results suggest that Cu is not solely responsible for the higher than normal abundances of deformed foraminiferal tests
recorded in many polluted areas.
CONCLUSIONS
Boxes containing ambient seabed sediments blended with
various amounts of CuCl2 were left to colonize for 32 weeks
(30th January to 9th September, 1996) at 63 m water depth
in the Oslofjord, Norway. By the end of the experimental
period, all species that were common in the ambient seabed
sediments had colonized the initially defaunated sediments
irrespective of sediment Cu-concentration. There was no
statistically significant correlation between the number of
species and the sediment [Cu] in the colonization boxes. On
the other hand, sediment [Cu] of .900 ppm caused a change
in the benthic foraminiferal community structure compared
to the control which had [Cu] of 70 ppm. Stainforthia fusiformis was by far the most successful colonizer. It was the
predominant species, not only in the control, but also in all
the treatment boxes except one of the most contaminated
ones, and had probably reproduced several times during the
32 week period. In addition to S. fusiformis, Bolivinellina
pseudopunctata was the only other species which showed
a significant negative correlation with sediment [Cu]. Stainforthia fusiformis was the only species which occurred in
abundances similar to that of the ambient seabed populations even at maximum sediment Cu-concentrations (.2000
ppm). However, the absolute abundance data indicate that
sediment [Cu] starts to negatively effect its reproduction
when concentrations reach 900 ppm. This is suggested by
the facts that the lowest numerical densities and most pronounced patchiness of Stainforthia fusiformis occurred in
the most and second most contaminated boxes. It is not clear
whether the other species actually reproduced in the colonization boxes. Copper contamination alone does not seem
to cause development of foraminiferal test deformities beyond what is normally found in uncontaminated areas.
ACKNOWLEDGMENTS
We are grateful to Jane Indrehus and Geir A. Thorstensen
for technical assistance in the field and laboratory, Mohammed I. Abdullah and Arne Pettersen for metal analyses and
assistance and advice with metal spiking of sediments, and
Joan M. Bernhard and the reviewers Charles Schafer and
Jean-Pierre Debenay for constructive comments on the manuscript. We thank the technical staff of the Biological department’s workshop (Oslo University) for making the aluminium frame. The efforts of the crew onboard RV ‘‘Trygve
Braarud’’ and ‘‘Bjørn Føyn’’ are greatly appreciated. This
work was funded by the Norwegian Research Council,
NATO and the Norwegian State Pollution Control Authority, which are gratefully acknowledged.
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Received 12 October 1998
Accepted 18 March 1999