Invertebrates in ornithogenic soils on Ross Island, Antarctica

Article (PDF Available)inPolar Biology 25(8):569-574 · August 2002with55 Reads
DOI: 10.1007/s00300-002-0386-7
Abstract
A habitat suitability model developed for soil biotic communities in the McMurdo Sound region, Antarctica predicts that soil moisture, organic carbon, and salinity exert control on the abundance and complexity of soil food chains. The model has been intensively tested in dry and carbon-poor soils of the Dry Valleys. To determine the influence of moisture and soil organic mater in wetter soils with high C content, invertebrates (nematodes, rotifers, and tardigrades) from soil samples collected in and near penguin rookeries on Ross Island (Cape Bird, Cape Crozier, and Cape Royds) were examined. Invertebrates were present in less than 50% of all collected soil samples. Although four nematode species were identified (Eudorylaimus antarcticus, Panagrolaimus davidi, Plectus antarcticus, Scottnema lindsayae), only populations of Panagrolaimus davidi were observed in soils collected from within penguin rookeries. Abundances of Panagrolaimus davidi and rotifers differed among rookeries, and year of sampling had a significant effect only on the populations of Panagrolaimus davidi. There were no temporal differences in soil moisture and soil chlorophyll a concentrations within each rookery or across rookeries. No invertebrates were correlated with soil moisture or chlorophyll a at the time of collection. Counter to our expectations, higher nutrient, organic matter, and moisture levels did not result in more abundant and diverse invertebrate communities in the rookery soils. It appears that excessive accumulations of nutrients, creating high soil salinity, may limit soil invertebrate presence within active rookeries.

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ORIGINAL PAPER
Dorota L. Porazinska Æ Diana H. Wall
Ross A. Virginia
Invertebrates in ornithogenic soils on Ross Island, Antarctica
Accepted: 8 April 2002 / Published online: 15 May 2002
Springer-Verlag 2002
Abstract A habitat suitability model developed for soil
biotic communities in the McMurdo Sound region,
Antarctica predicts that soil moisture, organic carbon,
and salinity exert control on the abundance and com-
plexity of soil food chains. The model has been inten-
sively tested in dry and carbon-poor soils of the Dry
Valleys. To determine the influence of moisture and soil
organic mater in wetter soils with high C content,
invertebrates (nematodes, rotifers, and tardigrades) from
soil samples collected in and near penguin rookeries on
Ross Island (Cape Bird, Cape Crozier, and Cape Royds)
were examined. Invertebrates were present in less than
50% of all collected soil samples. Although four nema-
tode species were identified (Eudorylaimus antarcticus,
Panagrolaimus davidi, Plectus antarcticus, Scottnema
lindsayae), only populations of Panagrolaimus davidi
were observed in soils collected from within penguin
rookeries. Abundances of Panagrolaimus davidi and
rotifers differed among rookeries, and year of sampling
had a significant effect only on the populations of Pan-
agrolaimus davidi. There were no temporal differences in
soil moisture and soil chlorophyll a concentrations within
each rookery or across rookeries. No invertebrates were
correlated with soil moisture or chlorophyll a at the time
of collection. Counter to our expectations, higher nutri-
ent, organic matter, and moisture levels did not result in
more abundant and diverse invertebrate communities in
the rookery soils. It appears that excessive accumulations
of nutrients, creating high soil salinity, may limit soil
invertebrate presence within active rookeries.
Introduction
Ice-free terrestrial environments constitute less than 2%
of continental Antarctica and the largest expanse is lo-
cated within the McMurdo Sound region (Fountain
et al. 1999). This region includes two differing ecosys-
tems: the McMurdo Dry Valleys (76.5–78.5S latitude,
160.0–164.0E longitude), which are considered the
coldest and driest deserts on Earth, with no vertebrates
and sandy soils that are low in carbon and nitrogen
(Burkins et al. 2000), and the coastal land areas of Ross
Island bordering the Ross Sea (77.2 –77.8S latitude,
166.2–169.4E longitude), a habitat for birds and marine
mammals (e.g., skua gulls, penguins, and seals). In
comparison to the Dry Valleys, these coastal soils in-
fluenced by vertebrates are higher in carbon and nitro-
gen (Mitzutani and Wada 1988). Vascular plants in both
ecosystems are absent and soil faunal representation is
limited to several invertebrates (protozoans, nematodes,
rotifers, tardigrades, springtails, and mites) (Virginia
and Wall 1999; Sinclair 2001).
Over the last decade, the diversity, ecology, and dis-
tribution patterns of soil invertebrates of the McMurdo
Dry Valleys have been documented (Powers et al. 1998;
Treonis et al. 1999, 2000; Virginia and Wall 1999;
Courtright et al. 2001; Porazinska et al. 2002), while the
soil invertebrates in the coastal zones are less studied
(Sinclair 2001). Soil invertebrates are abundant and di-
verse in temperate and tropical terrestrial habitats and
play important roles in ecosystem processes. For in-
stance, nematodes grazing on bacteria alter bacterial
abundance and activity and thus significantly affect the
rate of organic matter decomposition (Ingham et al.
1985; Freckman 1988). Soil organic material provides a
food base for soil foodwebs. In the Dry Valleys, quan-
tities of organic matter and carbon are extremely low.
The combination of low organic matter and low soil
moisture in the Dry Valleys results in a simple soil food
chain with low-diversity soil communities (Freckman
and Virginia 1997). A high percentage of Dry Valley soils
Polar Biol (2002) 25: 569–574
DOI 10.1007/s00300-002-0386-7
D.L. Porazinska (&) Æ D.H. Wall
Natural Resource Ecology Laboratory,
Colorado State University,
Fort Collins, CO 80523-1499, USA
E-mail: dorota@nrel.colostate.edu
Tel.: +1-970-4911609
Fax: +1-970-4911965
R.A. Virginia
Environmental Studies Program,
Dartmouth College, Hanover, NH 03755-3560, USA
are free of any invertebrates. A conceptual model of
habitat suitability for invertebrates in Dry Valley soil
(Freckman and Virginia 1998) indicates that carbon,
moisture, and salinity are important determinants of
habitat suitability. The model has been extensively tested
in the dry and low carbon content soils of Taylor Valley
(extremely low carbon and moisture) but has not been
applied under conditions of high soil carbon and mois-
ture. In the penguin rookeries of the McMurdo region,
the abundance of penguins causes significant inputs of
carbon and nitrogen from the marine environment to the
soil. These soils, termed ornithogenic soils, are the only
soils south of the Antarctic Circle containing high con-
centrations (14–21%) of organic matter (Campbell and
Claridge 1966; Speir and Cowling 1984; Heine and Speir
1989). Ornithogenic soils contain larger bacterial popu-
lations than the soils outside the rookeries (Ramsey 1983;
Roser et al. 1993; Beyer and Bolter 2000). The combi-
nation of high carbon and nitrogen, greater coastal
moisture, and abundant bacteria suggest a greater
availability of food supplies for microbial grazers and, in
turn, a higher invertebrate abundance and diversity than
that found in the soil food chain in the Dry Valleys. We
report a survey of abundance and diversity of soil in-
vertebrates (nematodes, rotifers, and tardigrades) from
penguin rookeries on Ross Island in order to make an
initial description of suitable habitats for invertebrates in
ornithogenic soils of Ross Island, and to draw general
comparisons with suitable habitats from the Dry Valleys.
Materials and methods
The research was conducted at penguin rookeries located at Cape
Bird (7713¢S, 16626¢E, the northern tip of Ross Island), Cape
Crozier (7727¢S, 16911¢E, the eastern tip of Ross Island), and
Cape Royds (7733¢S 16610¢E, the western tip of Ross Island). The
penguin colony at Cape Crozier has the largest bird population
(177,000 penguin pairs), followed by colonies at Cape Bird (25,000
penguin pairs) and Cape Royds (1,405 penguin pairs) (Young and
Millar 1999).
Soil samples were taken from sites within the rookeries, as well
as sites immediately surrounding the rookeries. These samples
represented a variety of habitats with a diversity of soil physical
characteristics, and included soils from crusty to soft, moist to dry,
dark to light, rocky to fine, and barren to near moss. As collected
soil samples were never solid or waterlogged, we assume soils were
not oxygen limited. Samples were collected near mosses but mosses
were not removed from the sampling sites. Soil samples were col-
lected at different time intervals during austral summer seasons.
Cape Bird was sampled twice: 29 January 1991 and 22 December
1994; Cape Crozier three times: 9 January 1995, 10 December 1995,
and 5 December 1997; and Cape Royds four times: 20 January
1990, 13 January 1994, 12 December 1994, and 10 November 1995
(Table 1). Each soil sample (0–10 cm deep) of approximately 1 kg
was collected using a sterile plastic scoop and placed into a sterile
plastic bag (Whirl-Pak). Prior to sampling for invertebrates, 5–10 g
of soil from the top 2 mm was collected to determine soil chloro-
phyll a concentrations. Soil samples for chlorophyll a were taken
from Cape Bird on 22 December 1994, Cape Crozier on 9 January
1995 and 10 December 1995, and Cape Royds on 12 December
1994 and 10 November 1995 with a sterile plastic spoon and placed
in a dark polyvinyl bottle. All samples were transported to the
McMurdo Station laboratory in insulated coolers and stored at 1C
until processed within 48 h.
Nematodes, tardigrades and rotifers were extracted within 48h
of sampling from approximately 100-g soil subsamples by wet-
sieving followed by centrifugation (Freckman and Virginia 1993,
1997; Powers et al. 1998). Nematodes were counted, identified to
species, and placed in categories of living or dead males, females,
and juveniles. After counting, all invertebrates were killed, pre-
served in 5% formalin and stored. Soil moisture (%) was deter-
mined gravimetrically from an approximately 50-g soil subsample
(soil dried at 105C for 24 h) (Jackson et al. 2000). Chlorophyll a
concentrations were determined using a method described by Holm-
Hansen et al. (1965). Briefly, 5 g soil was treated with acetone, and
concentrations of chlorophyll a were determined fluorometrically.
Chemical analyses were made on soil samples collected at Cape
Royds in January 1990. Soil pH was measured in 1:2 (w/v)
soil:water suspension (McLean 1982). Percent of organic carbon
was determined by combustion method (Nelson and Sommers
1982). Ammonium-N (NH
+
4
-N) and nitrate-N (NO
3
-N) were
determined in 2
M KCl extract using an automated ion analyzer
(Lachat Instruments, Milwaukee, Wis.) (Keeney and Nelson 1982).
ANOVA was used to determine year-to-year differences within
rookeries, and overall differences among rookeries. Wherever ap-
propriate, Scheffe’s test followed ANOVA. Whenever possible,
correlation analysis was used to establish relationships between
invertebrates, soil moisture, and soil chemical characteristics. To
conform to statistical assumptions, invertebrate data were
log(x+1) transformed prior to analysis, but non-transformed data
are presented in tables and graphs.
Results
Our objective was to sample a wide range of soil habitats
within and adjacent to the rookery sites to examine
Table 1. Number ± SD of nematodes, tardigrades, rotifers, and
chlorophyll a (chla) in soil samples from penguin rookeries at Ross
Island (N indicates number of collected soil samples). Identified
nematode species: Scottnema lindsayae, Eudorylaimus antarcticus,
Panagrolaimus davidi, Plectus antarcticus
Cape Sampling
date
N S. lindsayae E. antarcticus P. davidi P. antarcticus Tardigrades Rotifers chla
g/g dry soil
Numbers per kg dry soil
Bird Jan 1991 10 0±0 0±0 171±514 0±0 0±0 0±0 n/a
Dec 1994 19 0±0 0±0 890±1434 0±0 0±0 1476±3820 0.33±0.20
Crozier Jan 1995 14 0±0 0±0 0±0 0±0 0±0 121±286 0.89±1.74
Dec 1995 12 1±4 0±0 0±0 0±0 0±0 990±3431 0.08±0.07
Dec 1997 11 502±1009 36±49 550±999 11±36 42±140 279±636 n/a
Royds Jan 1990 11 0±0 0±0 918±1637 0±0 498±1650 0±0 n/a
Jan 1994 9 35±104 0±0 1±4 0±0 0±0 8±24 n/a
Dec 1994 22 0±0 0±0 1±3 0±0 0±0 581±1572 2.75±8.0
Nov 1995 24 0±0 0±0 0±0 0±0 0±0 0±0 0.02±0.05
570
general relationships between moisture, soil C, and in-
vertebrates. This approach was required to accommo-
date logistic problems and in turn limited sample
replication, and our ability to draw conclusions about
temporal and spatial variation in the abundance and
diversity of invertebrates. Invertebrates were found in
less than 50% of all soil samples. Over all years, a lower
proportion of soil samples with invertebrates was ob-
served at the smallest rookery (Cape Royds) than the
other two rookeries (Fig. 1). However, from year to
year, the percentage of samples with invertebrates varied
considerably (e.g., from 16.6% in December 1995 to
90.9% in December 1997 at Cape Crozier). Generally,
nematodes and rotifers occurred together in samples,
but tardigrades were detected with nematodes and roti-
fers only on two occasions (Cape Crozier December
1997 and Cape Royds January 1990) (Table 1).
Across the three penguin rookeries, four species of
nematodes were identified: Eudorylaimus antarcticus,
Panagrolaimus davidi, Plectus antarcticus,andScott-
nema lindsayae. Panagrolaimus davidi was found in all
rookeries, with significantly (P=0.05) higher densities of
Panagrolaimus davidi at Cape Bird than the two other
rookeries (Fig. 2). High relative abundance and diverse
nematode communities characteristic of the Dry Valleys,
comprising S. lindsayae, E. antarcticus, and P. antarcti-
cus, were observed at Cape Crozier in one sample (De-
cember 1997). S. lindsayae and E. antarcticus together
were observed in 6 out of 37 samples collected at Cape
Crozier. These three nematode species were never ob-
served in the rookery at Cape Bird, and from all the
samples collected at Cape Royds (66) S. lindsayae was
present in only 1 sample (January 1994).
Because of the low frequencies of samples with in-
vertebrates, temporal comparisons within each rookery
were possible only for Panagrolaimus davidi and rotifers.
Densities of Panagrolaimus davidi varied significantly
(P=0.05) with year of sampling. At Cape Bird and Cape
Crozier, higher densities of Panagrolaimus davidi were
found during the later sampling years (Cape Bird,
December 1994 and Cape Crozier, December 1997), but
at Cape Royds the pattern was reversed, with higher
densities found in the earliest sampling years (January
1990) (Table 1). In soil samples with nematodes, all
nematode life stages (males, females, juveniles, living
and dead) were found.
Rotifers were found at all rookeries, but tardigrades
were observed in only two samples (Fig. 1) (one sample
at Cape Crozier, December 1997 and one sample at
Cape Royds, January 1990). The rookery at Cape Royds
had significantly (P=0.05) less rotifers than the other
rookeries. High variance associated with the densities of
rotifers within each rookery prevented detection of any
differences among years of sampling.
Soil moisture ranged between 4 and 14%. An asso-
ciated large variation of soil moisture confirmed our
intended sampling across different habitats and ex-
plained the lack of significant temporal differences
within each rookery and among rookeries. Similarly, no
significant differences within and among rookeries were
observed for chlorophyll a. No invertebrates were cor-
related with soil moisture or chlorophyll a (all coeffi-
cients of correlation were close to zero). Chemical
analyses of soil samples from Cape Royds (January
1990) revealed a nearly neutral pH (6.7), extremely high
concentrations of extractable phosphorus (PO
3
4
P:
988.2±1975.4 mg kg
–1
dry soil) and nitrogen
(NH
þ
4
N: 1452.3±1626.9 lgkg
–1
dry soil; NO
3
N
101.1±176.2 lgkg
–1
dry soil), and lower soil carbon
than previously reported for ornithogenic soils
(2.8%±2.6) (Speir and Cowling 1984). Densities of
Panagrolaimus davidi at Cape Royds (January 1990)
were significantly correlated with soil organic carbon
(r=0.75, P=0.0103) and ammonium (r=0.79,
P=0.0047) but not with pH, phosphorus, or nitrate.
Discussion
The soils of the McMurdo Dry Valleys are character-
ized by the presence of up to three nematode species, of
Fig. 1. Proportion of soil samples with invertebrates in penguin
rookeries on Ross Island, Antarctica (black bar Cape Bird, gray bar
Cape Crozier, striped bar Cape Royds). Letters above the bars
indicate type of invertebrates present in the soil sample (N
nematodes, R rotifers, T tardigrades)
Fig. 2. Density ± SE of Panagrolaimus davidi and rotifers in soil
samples collected from penguin rookeries on Ross Island,
Antarctica (black bars P. davidi, striped bars rotifers)
571
which Scottnema lindsayae is the most abundant
(Freckman and Virginia 1997; Virginia and Wall 1999).
They contain relatively low to no densities of tardi-
grades and rotifers, and lack populations of Panagro-
laimus davidi (Wharton and Brown 1989). We observed
a contrasting pattern in penguin rookeries. Generally,
samples were abundant in Panagrolaimus davidi and
rotifers, but lacked the three other nematode species
common in the Dry Valleys. The presence of S. lind-
sayae, E. antarcticus, and P. antarcticus in the Cape
Crozier samples occurred only at sampling sites at the
margins of the rookery. These soils are probably much
more similar in their properties (carbon and nitrogen)
to those of the Dry Valleys than the soils in the pen-
guin-impacted areas of the rookery. In the soils at the
margins of the rookeries, invertebrate densities were
comparable to those found in the Taylor Valley (the
most studied Dry Valley). Panagrolaimus davidi was
the only nematode species found both within and at the
margins of the rookeries, indicating that this species is
somewhat better suited than other nematode species to
living in both ornithogenic soils and in other Ross
Island soil habitats that are more similar to Dry Valley
habitats.
Many ornithogenic soils support growth of algae and
mosses at Ross Island. Panagrolaimus davidi has previ-
ously been observed in coastal areas and when first de-
scribed was originally associated with algae and mosses
(Timm 1971). In a survey of terrestrial nematodes from
the McMurdo Sound region, many sites with algae and
mosses were free of Panagrolaimus davidi (Wharton and
Brown 1989), while in our study many sites free of algae
and mosses supported populations of Panagrolaimus
davidi. These findings indicate that presence of lower
plants is not an absolute indicator of Panagrolaimus
davidi abundance. In a study by Sinclair (2001), the
reported distribution (presence/absence) of terrestrial
invertebrates at Cape Bird is similar to our findings.
S. lindsayae populations at Cape Bird (6 out of 103
sampling sites) were never associated with penguin
rookeries, while the opposite was true for populations of
Panagrolaimus davidi (Sinclair 2001). In another study
(Sinclair and Sjursen 2001), Panagrolaimus davidi was
associated with high contents of soil chlorophyll a and
organic matter. This might imply that the distribution of
Panagrolaimus davidi is limited to soils with high organic
matter content, regardless of its origin (penguin guano
or algae and mosses).
The distribution patterns of invertebrates are gener-
ally influenced by physical and chemical characteristics
of soil. In the McMurdo Dry Valleys, where Scottnema,
Eudorylaimus,andPlectus occur, soils are described as
alkaline, and nitrogen and carbon contents are very low
compared to temperate ecosystems (Powers et al. 1998;
Courtright et al. 2001). In contrast to the Dry Valleys,
rookery soils at Cape Royds contained substantially
higher amounts of nitrogen, carbon, and phosphorus.
Counter to our expectations, higher nutrient, organic
matter, and moisture levels did not result in more
abundant and diverse invertebrate communities in the
rookery soils. Courtright et al. (2001) identified specific
habitats for each of the three Dry Valley nematode
species, based on soil properties including moisture,
organic matter, pH, salinity, and nitrogen. Generally,
however, excessive concentrations of nitrogen can neg-
atively affect both microbial and microfaunal popula-
tions. High concentrations of ammonium can be toxic to
many microbial and nematode pathogens. Thus, life in
nutrient-rich and saline soils of the rookeries might re-
quire special adaptations that only a few invertebrate
species have developed. From our data, it appears that
only Panagrolaimus davidi prefers soil habitats where
mosses may be abundant and where penguins have en-
riched soils in organic matter and ammonium. Lack of
mosses, extremely limited growth of algae, and nutrient-
poor soils possibly explain the absence of Panagrolaimus
davidi in the Dry Valleys. Similarly, high densities of
tardigrades and rotifers found in our study could imply
their preference for soil habitats rich in nutrients.
However, Sinclair (2001) reported the presence of these
invertebrates both in ornithogenic and non-ornithogenic
soils, indicating that soil nutrients are not the only fac-
tors involved in patterns of invertebrate distribution.
The general absence of S. lindsayae, E. antarcticus,and
P. antarcticus in the rookeries indicates that the habitat
conditions associated with the distribution of viable
populations of these species (as outlined in the concep-
tual model of habitat suitability by Freckman and Vir-
ginia 1998), are not met in ornithogenic soils. In the Dry
Valleys, S. lindsayae is more tolerant of dry and more
saline soils than either E. antarcticus or P. antarcticus
(Courtright et al. 2001), whereas the rookery-inhabiting
Panagrolaimus davidi seems to require soils with much
higher organic matter content than the soils typical of
dry-valley habitats. Panagrolaimus davidi, like the dry-
valley nematode species, segregates into a fairly well-
defined soil habitat by the properties proposed in the
habitat suitability model (e.g., moisture, salinity, organic
matter) of Freckman and Virginia (1998) and refined by
Courtright et al. (2001). More research on carbon- and
nutrient-rich soils is required to determine how high
levels of these resources influence soil invertebrate dis-
tribution and function in Antarctic soils.
In our study, differences in the abundance of
Panagrolaimus davidi and rotifers across the rookeries
could be associated with soil chemical differences of
these sites. Speir and Cowling (1984) reported that
ornithogenic soils at Cape Bird were characterized as
alkaline, with much higher (3–4 times) levels of am-
monium and organic carbon (up to 8 times) and lower
(4–6 times) levels of phosphorus than our soils at
Cape Royds. At both sites, ammonium was the pre-
dominant form of nitrogen, whereas nitrate is more
commonly the dominant form of inorganic-N in the
dry valleys (Campbell et al. 1998). In addition to
chemical differences, climatic differences among the
rookeries may play an important role in habitat suit-
ability. Lower temperatures with stronger winds can
572
slow down life-cycles of nematodes and affect their
reproductive rates.
Implications
Very little is known about soil ecosystem processes in the
McMurdo Sound region. Treonis et al. (2002) showed
that cotton strip decomposition under field conditions in
the Taylor Valley (soils poor in nutrients, organic mat-
ter, and moisture) was largely undetectable after 2 years.
At Cape Bird, however, bacterial biomass, microbial
activity, and decomposition rates were significantly
higher in ornithogenic soils than soils free of penguin
guano (Orchard and Corderoy 1983; Ramsey 1983).
Despite high organic matter inputs in ornithogenic soils,
moisture (up to 15%) and temperature (at 4C) limited
the activity of microbes (Orchard and Corderoy 1983).
Since high organic matter inputs did not result in higher
diversity of soil invertebrates, a combination of soil
moisture (below 5%) (Campbell et al. 1998), soil salinity,
and carbon content may be the major factors limiting
the distribution of microbiota and their influence on
decomposition processes in the Dry Valleys.
In our study of rookeries, 50% of the sampled soils
did not contain any invertebrates despite having organic
matter contents, nutrient levels, and soil moisture that
are assumed to be more favorable for invertebrates. This
absence of invertebrates at many soil sites at Ross Island
supports the hypothesis of a patchy distribution of
suitable soil habitats for invertebrates and that a com-
bination of soil factors, as well as poor dispersal, may
limit invertebrate abundance (Virginia and Wall 1999).
Studies at a regional and latitudinal scale will be needed
to further explore the range and complexity of habitats
suitable for life.
Acknowledgements We thank D. Bumbarger, E.M. Courtright,
E. Kuhn, L.E. Powers, and A.M. Treonis for their assistance in
sampling and laboratory analyses. We thank the staff of the
McMurdo Station for the laboratory support and the logistic
support of Petroleum Helicopters and the US Navy VXE-6 in the
field. This research was supported by National Science Foundation
Grants OPP 9211773, OPP 9813061, OPP 9120123, OPP 0096250,
OPP 9810219, and OPP 9624743.
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    • "Water availability is considered the main constraint on Antarctic soil invertebrates (Howard-Williams et al. 2010; Nielsen et al. 2012; Electronic supplementary material The online version of this article (doi:10.1007/s00300-015-1703-2) contains supplementary material, which is available to authorized users. Convey et al. 2014 ), but other factors such as soil chemistry (Porazinska et al. 2002; Poage et al. 2008) and structure (Wall and Virginia 1998) are also considered important drivers of community assemblage structure in Antarctic terrestrial ecosystems. Antarctic soils are highly heterogeneous in terms of edaphic characteristics, and accordingly , soil fauna show patchy distributions (e.g., Convey et al. 2014). "
    [Show abstract] [Hide abstract] ABSTRACT: The harsh climate and patchy distribution of habitable terrestrial ecosystems constrain soil invertebrate communities in continental Antarctica. The Windmill Islands in East Antarctica have a relatively gentle climate by Antarctic standards, and the region supports some of the most well-developed moss beds on the continent. These moss beds and soils are known to sustain invertebrate communities dominated by nematodes, rotifers and tardigrades, but our knowledge of the diversity and composition of these communities remains limited. We extracted soil fauna from 74 soil samples representing a wide range of microhabitats, and 24 moss samples, collected at Clark Peninsula, Bailey Peninsula and Robinson Ridge in the Windmill Islands during the 2012-2013 austral summer. Invertebrates were present in all samples, but densities varied considerably both within and between sites with limited correlation with edaphic variables or cover type. Taxa found included two species of nematodes (Plectus murrayi; Plectus frigophilus), one mite (Nanorchestes antarcticus) as well as tardigrades and rotifers (enumerated only). No springtails were found in this study, but individuals of the genus Cryptopygus were later recovered from moss collected near Casey Station. The Windmill Islands soils and moss beds support dense populations of soil fauna. However, despite the relatively mild climate conditions and favorable soil properties, species diversity is low. The diversity is possibly limited by recent deglaciation and limited dispersal opportunities to the region. Given favorable local conditions, it is likely that colonizing species will perform well, whether these arrive by natural means or are accidentally introduced by humans.
    Full-text · Article · Sep 2015
    • "Compared to the dominance of Scottnema, Plectus and Eudorylaimus in the Dry Valleys, Geomonhystera antarcticola occurs rarely and with a patchy distribution and low population densities across the Dry Valleys (Adams et al. 2006; Nielsen et al. 2011). Nearby, in coastal penguin rookeries, Panagrolaimus davidi is usually the sole species in the ornithogenic soils (Wharton and Brown 1989; Porazinska et al 2002) and has also been observed across the continent in coastal areas. Tardigrades and rotifers continue to be described with several new species named since the 1970s (Sohlenius et al. 1995; Convey and McInnes 2005; McInnes 2010). "
    [Show abstract] [Hide abstract] ABSTRACT: Terrestrial invertebrates are the largest permanent residents for much of the Antarctic continent with body lengths < 2 mm for most. The fauna consists of the arthropod taxa Collembola (springtails) and Acari (mites) as well as the microinvertebrates Nematoda, Tardigrada and Rotifera. Diversity in continental Antarctica is lower compared with warmer regions such as the Antarctic Peninsula and the subantarctic islands and several taxa such as the arthropods have considerably restricted distributions. The highest diversity of invertebrates is found along the Transantarctic Mountains of the Ross Sea Region and taxa are likely to be relicts from a warmer past that have survived in glacial refugia. Dispersal among the extremely fragmented Antarctic landscape is likely to be limited to transport via fresh- or salt-waters, particularly for the arthropod taxa, although long-distance wind dispersal is also possible for the microinvertebrates. Invertebrates possess several adaptations to low moisture levels and extreme cold temperatures in Antarctica. For example, nematodes and tardigrades avoid extreme dry and cold temperatures by entering a desiccation-resistant anhydrobiotic state. In contrast, arthropods do not have such a resistant state and freezing is lethal. Adaptations for the arthropod taxa include freeze avoidance and the production of intracellular, antifreeze proteins. Climate changes in Antarctica are likely to pose significant challenges for the invertebrate fauna. Changes in temperature, soil moisture and associated shifts in taxon distributions as well as the potential for non-indigenous species introductions are all likely to have considerable impacts on the Antarctic fauna. From a conservation perspective, there is a pressing need for terrestrial observation networks to record the present state of Antarctic terrestrial ecosystems as well as to monitor impending changes. Biosecurity measures which minimize species introductions or transfers of organisms within Antarctica will be essential.
    Full-text · Chapter · Dec 2014 · PLoS ONE
    • "The lowest nematode density was seen for cf. Panagrolaimidae which has been reported for habitats rich in nitrogen, mostly linked to ornithogenic soils in the vicinity of bird colonies [23,24,78]. Of the five genera recorded for this study, Plectus was observed for the broadest geochemical ranges (N, C, P, EC and pH) indicating higher tolerance levels to environmental stresses. "
    [Show abstract] [Hide abstract] ABSTRACT: Terrestrial life in Antarctica has been described as some of the simplest on the planet, and mainly confined to soil microfaunal communities. Studies have suggested that the lack of diversity is due to extreme environmental conditions and thought to be driven by abiotic factors. In this study we investigated soil microfauna composition, abundance, and distribution in East Antarctica, and assessed correlations with soil geochemistry and environmental variables. We examined 109 soil samples from a wide range of ice-free habitats, spanning 2000 km from Framnes Mountains to Bailey Peninsula. Microfauna across all samples were patchily distributed, from complete absence of invertebrates to over 1600 specimens/gram of dry weight of soil (gdw), with highest microfauna abundance observed in samples with visible vegetation. Bdelloid rotifers were on average the most widespread found in 87% of sampled sites and the most abundant (44 specimens/gdw). Tardigrades occurred in 57% of the sampled sites with an abundance of 12 specimens/gdw. Nematodes occurred in 71% of samples with a total abundance of 3 specimens/gdw. Ciliates and mites were rarely found in soil samples, with an average abundance of 1.3 and 0.04 specimens/gdw, respectively. We found that microfaunal composition and abundance were mostly correlated with the soil geochemical parameters; phosphorus, NO3 (-) and salinity, and likely to be the result of soil properties and historic landscape formation and alteration, rather than the geographic region they were sampled from. Studies focusing on Antarctic biodiversity must take into account soil geochemical and environmental factors that influence population and species heterogeneity.
    Full-text · Article · Jan 2014
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