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Comparison of patterns of spatial variation of microgastropods between 2 contrasting intertidal habitats

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Small-scale spatial variation in the distribution of the macrofauna. of marine intertidal shores has long been recognized, but there have been few quantitative studies about the scales of patchy distribution of the microbenthos on rocky shores. Patchiness has important implications for comparative and descriptive studies of distribution and abundance because it confounds comparisons of abundance at the largest spatial scales unless the smaller scales are appropriately incorporated into the sampling designs. Spatial variation in the distribution of a number of species of intertidal microgastropods across 2 different habitats (sediment and coralline turf) in Botany Bay, Australia, is described using a nested, hierarchical sampling design. Significant variation was detected mainly at small scales, ranging from less than 1 to 10 m. Moreover, the species showed different patterns of variation depending on the type of habitat and the time of sampling. There was no relation between these patterns and the taxonomic relations of the species. These data illustrate the scales of variability that must be considered when planning long-term or baseline investigations of microbenthos to assure that the study adequately represents different habitats and that subsequent ecological inferences are valid.
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MARINE ECOLOGY PROGRESS SERIES
Mar Ecol Prog Ser
Vol. 220: 201211, 2001 Published September 27
INTRODUCTION
Variation in distribution and abundance is a central
theme of ecology and basic to both descriptive and
experimental approaches to environmental science.
There are, however, no simple patterns of variation,
which has many implications for the development of
ecological generalizations and predictive models of
patterns of abundance and the processes influencing
such patterns. Variation occurs at a hierarchy of differ-
ent scales, from dispersion within and across patches
of habitat (e.g. Morrisey et al. 1992a, Thompson et al.
1996, Underwood 1996a, Underwood & Chapman
1996), to variation across habitats (e.g. Archambault &
Bourget 1996, Miller & Ambrose 2000) up to distribu-
tions at a biogeographical scale (e.g. Kaustuv et al.
1998). Similarly, on a temporal scale, changes in abun-
dances and distributions can change quite markedly
over periods of days, months, decades, etc. (Menge et
al. 1985, Barry & Dayton 1991, Morrisey et al. 1992b).
The relations between temporal and spatial variation
in abiotic variables and biological patterns and pro-
cesses in aquatic assemblages are poorly understood,
particularly the importance of small-scale variations in
such measures. Patterns of reproduction, recruitment,
dispersal, predation etc., often independent by time
and space (Dayton & Tegner 1984, Chapman & Under-
wood 1998, Underwood 1999), and unpredictable indi-
rect effects of interactions, can strongly influence any
patterns observed (Menge et al. 1994, Menge 1995).
Many marine environments are considered physically
© Inter-Research 2001
*E-mail: colabarr@bio.usyd.edu.au
Comparison of patterns of spatial variation of
microgastropods between two contrasting
intertidal habitats
C. Olabarria*, M. G. Chapman
Centre for Research on Ecological Impacts of Coastal Cities, Marine Ecology Laboratories A11, University of Sydney,
New South Wales 2006, Australia
ABSTRACT: Small-scale spatial variation in the distribution of the macrofauna of marine intertidal
shores has long been recognized, but there have been few quantitative studies about the scales of
patchy distribution of the microbenthos on rocky shores. Patchiness has important implications for
comparative and descriptive studies of distribution and abundance because it confounds comparisons
of abundance at the largest spatial scales unless the smaller scales are appropriately incorporated
into the sampling designs. Spatial variation in the distribution of a number of species of intertidal
microgastropods across 2 different habitats (sediment and coralline turf) in Botany Bay, Australia, is
described using a nested, hierarchical sampling design. Significant variation was detected mainly at
small scales, ranging from less than 1 to 10 m. Moreover, the species showed different patterns of
variation depending on the type of habitat and the time of sampling. There was no relation between
these patterns and the taxonomic relations of the species. These data illustrate the scales of variabil-
ity that must be considered when planning long-term or baseline investigations of microbenthos to
assure that the study adequately represents different habitats and that subsequent ecological infer-
ences are valid.
KEY WORDS: Australia · Intertidal habitats · Microgastropods · Spatial scale · Patchiness
Resale or republication not permitted without written consent of the publisher
Mar Ecol Prog Ser 220: 201211, 2001
unstable, although the persistence (Dayton & Tegner
1984) of the biological components of these systems is
unclear. Underwood & Denley (1984) emphasized that
predictability of community structure cannot depend
exclusively on ‘typical’ areas but must include consid-
eration of natural variability of the biota and their
environment.
Numerous intrinsic ecological issues require de-
tailed quantitative understanding of the scales at
which there are predictable patterns in the abun-
dances of animals and plants and the natural scales of
variability in these patterns. Understanding the pro-
cesses that regulate structure and dynamics of interac-
tions among species requires recognition of the scales
at which they operate and, therefore, quantitative
description of spatial and temporal variation in abun-
dances and diversity (Livingston 1987, Bourget et al.
1994, Metaxas & Scheibling 1994, Underwood 1996a,
Underwood & Chapman 1998a). In addition, identifica-
tion of scale- and habitat-dependent ecological pat-
terns is central to management of fragmented habitats
(Eggleston et al. 1999), and the statistical interaction
between temporal and spatial variability is the focus of
attention for detecting the magnitude of environmental
perturbations (Underwood 1996b). Therefore, accurate
description of patterns is a prerequisite to the under-
standing of ecological processes, development of gen-
eral predictive models, assessment of environmental
impacts, restoration of habitat and many practical
managerial issues.
Although there is a long history of study of patterns
of distribution and abundance, it has, until recently,
been primarily focussed on responses of organisms to
large-scale physical variables (e.g. patterns of zona-
tion in response to emersion or alongshore changes in
response to wave exposure; Lewis 1964). Recent em-
phasis on the importance of patchiness in ecological
interactions (Pickett & White 1985) has focussed on
the large amounts of variability within and among
patches of habitat, often at small spatial scales (e.g.
Downing 1991, Lohse 1993, Chapman 1994, Chapman
et al. 1995, Farnsworth & Ellison 1996, Thompson et
al. 1996, Underwood 1996a, Underwood & Chapman
1996, 1998a). Such patterns have mostly been de-
scribed for the larger components of fauna on inter-
tidal rocky shores or of benthos in soft-sediments (e.g.
Harris 1972, Coull et al. 1979, Phillips & Fleeger 1985,
Thrush 1986, 1991, Morrisey et al. 1992a,b, Hewitt et
al. 1997, Schneider et al. 1997). These studies indicate
that such patterns are variable and complex. Despite
some studies carried out by Underwood (1996a) and
Underwood & Chapman (1996), there are few com-
parisons of the same suite of species across different
habitats to test models of the importance of species-
specific or habitat-specific characteristics in determin-
ing patterns of and variability in abundance or distrib-
ution.
Diverse assemblages of small marine organisms
occur in many natural habitats, e.g. mussel beds
(Lohse 1993), algal beds (Akioka et al. 1999), kelp
holdfasts (Moore 1973) or sediment (Morrisey et al.
1992a,b). These assemblages often contain many spe-
cies that use similar resources (e.g. grazers on diatoms)
but also different trophic levels (e.g. grazers, preda-
tors, detritivores). Such assemblages have great poten-
tial for measuring changes to biodiversity (Gee &
Warwick 1996) and assessing environmental impacts
(Smith & Simpson 1993). A diverse component of the
assemblage can be found in small patches of habitat
under a variety of different environmental conditions,
they can develop in natural and artificial habitats
placed in different areas (Costello & Thrush 1991), and
they can potentially be transplanted from site to site.
One component of intertidal fauna that forms an
ideal test assemblage for many models of ecological
processes and responses to environmental change are
microgastropods (i.e. gastropods with adult size of
<2 mm) because: (1) they are relatively quick and easy
to identify without killing them; (2) they can be han-
dled, marked (for measures of growth, etc.) and moved
among patches of habitat with little mortality; (3) they
are very diverse and abundant in small patches of
habitat; and (4) they have a wide range of phylogenetic
and trophic levels. Despite their diverse nature, little is
known about the basic ecology of most Australian
microgastropods (Beesley et al. 1998) and there have
been no quantitative descriptions of their spatial or
temporal patterns of variability. However, studies on
the basic ecology and life histories of European micro-
gastropod species are most abundant, and some have
shown the importance of substratum, mortality, re-
cruitment and migration of adults in determining the
pattern of spatio-temporal variation (Smith 1973,
Wigham 1975, Southgate 1982, Fernández et al. 1988).
This paper describes patterns of variability of a sub-
set of microgastropods at a hierarchy of spatial scales
in 2 different habitats (sediment and coralline turf)
on 1 shore. The study was done on a single shore
because many larger intertidal gastropods on these
shores show greatest variability in abundances at
small spatial scales along single shores (Underwood &
Chapman 1996). It is also necessary to determine the
scales of spatial replication needed to sample species
representatively within a shore before valid compar-
isons can be made across shores. The spatial scales in
this study varied from <1 to 300 m. The species were
chosen to represent different species in the same
genus or family and a number of different families
of primarily grazing snails. Coralline turf (i.e. algal
beds composed primarily of erect coralline algae) are
202
Olabarria & Chapman: Spatial variation of microgastropods
potentially very important habitats on intertidal rocky
shores in temperate areas (Akioka et al. 1999). These
habitats may modify the spatial distribution and abun-
dance of associated fauna due to reduction of pre-
dation and protection from wave-exposure, and by
offering different availability of trophic resources
(Grahame & Hanna 1989, Akioka et al. 1999). Inter-
tidal and shallow subtidal sandy habitats are charac-
terized by a high abundance and diversity of infaunal
assemblages.
These data were used to test the hypotheses that:
(1) as has been described for larger intertidal gas-
tropods, most of the spatial variation in abundance of
these microgastropods within each habitat is at small
spatial scales, i.e. processes influencing small gas-
tropods operate with a similar overall influence of
small-scale processes; (2) closely related species show
similar patterns of variation because of their similar
responses to ecological processes; and (3) patterns of
variation are similar across different habitats because
similar processes occur in different habitats. This in-
formation is essential in characterizing variation in
this assemblage and necessary for its use as ‘indicators’
of environmental change. In addition, this study is part
of a larger study of natural temporal change in popula-
tions of individual species and the assemblage and
relations of these patterns to aspects of life histories.
MATERIALS AND METHODS
Sampling design. The samples were collected on an
intertidal shore in the Cape Banks Scientific Marine
Research Area on the northern headland of Botany
Bay, New South Wales, Australia (Fig. 1). Two different
sheltered mid-shore habitats were chosen: coralline turf
on intertidal rock platforms and patches of sandy sedi-
ment among intertidal boulders adjacent to the plat-
forms. The turf was composed of tightly packed
upright branches of coralline algae, primarily Corallina
officinalis Linnaeus, forming a stiff matrix that held
significant quantities of sand. Some patches of turf also
included other taxa of articulated coralline algae (e.g.
Jania spp., Amphiroa spp.).
The design incorporated 4 spatial scales in each of
the 2 habitats. Two different locations were chosen to
represent shores with orientations, slopes and wave
exposures that are typical for the area (Fairweather &
Underwood 1991). Location 1 was oriented to the
south-west with a slope of 10° whereas location 2 was
oriented to the west and a slope of 30°. Both locations
were sandstone platforms and were separated by
about 300 m. In each location, 2 sites (patches within
each of these locations) were randomly selected, 50 m
apart. In each site, there were 2 randomly chosen repli-
cate plots (smaller-scale patches that, in the case of the
algal turf, were physically isolated from each other),
10 m apart. Finally, in each plot (approximately 2 m
2
),
3 replicate cores (potentially patches of habitat of dif-
ferent quality within each plot) were sampled. Each
plot was sampled twice, 2 wk apart, in February 2000.
Previous studies in soft-sediments (Nichols & Thomp-
son 1985, Livingston 1987, Morrisey et al. 1992b) and
in mangroves (Underwood & Chapman 1999) have
shown large variability in the abundance and composi-
tion of fauna over periods of days, weeks or months.
Therefore, the replicate cores were sampled to test the
hypothesis that the patterns of abundance were consis-
tent over short periods of time and to identify the scale
of any spatio-temporal interactions.
Sampling methods. Samples were collected using a
10 cm diameter plastic corer. The corer was pushed
203
Fig. 1. Map of Australia showing the sampling locations within
the study area
Mar Ecol Prog Ser 220: 201211, 2001
into the sediment to a depth of 5 cm. In coralline turf,
the corer was pushed into the turf and the algae and
sediment inside the corer scraped off at the level of the
rock. Because no direct statistical comparisons were
made between habitats, it was not necessary to sample
exactly the same volume of each habitat. Nevertheless,
the turf was approximately 5 cm thick. A 10 cm corer
was used because previous studies of the fauna in
coralline turf in this area showed that the precision
of the estimates of abundance obtained with this size
of core was acceptable (SE/x <0.06; B. Kelaher pers.
comm.).
A pilot experiment was done on the fauna in
coralline turf in order to evaluate the optimal number
of replicates needed to provide a good estimate of
spatial and temporal variability, while minimizing the
amount of time taken to sort the samples. Twelve
cores were taken from each of 2 plots (10 m apart) in
each of 2 sites (50 m apart) in 1 location. The 5 most
abundant species were sorted and the abundances
analyzed by ANOVA. The purpose was to determine
the minimal size of sample that could reliably mea-
sure abundance at a specific time. If estimates at a
single time were imprecise, differences from time to
time in any analysis of temporal change would be
confounded with equally large spatial variation. For
each analysis, the factors were ‘sites’, ‘plots’ nested
within sites and ‘times’, i.e. different subsets of repli-
cates chosen randomly from the sample of 12 to repre-
sent different times of sampling (although all repli-
cates were, in fact, collected at the same time). For
each set of analyses, different numbers of replicates
were used, i.e. n = 2, n = 3, n = 4 and n = 6, picked at
random from the 12 available (each with 1000 ran-
domizations for each species and each experimental
design). The frequency of significant temporal varia-
tion in these analyses provided information about the
probability of detecting real temporal variation with-
out confusion from spatial variability of very patchily
distributed animals using small sample sizes. These
data also allowed comparison of the spatial patterns
using different numbers of replicates.
Samples were fixed in 7% formalin in seawater and
sieved through a 63 µm mesh. Eleven species of micro-
gastropods from a variety of families were selected for
analysis because they occurred in the 2 habitats, were
relatively abundant in at least 1 of these habitats dur-
ing this study and represent different species within a
range of families (Table 1). Despite their large abun-
dances in some habitats, there is little information
about their basic ecology (Beesley et al. 1998). Most
are thought to feed on micro-algae, diatoms and detri-
tus, as inferred from the structure of their radulae,
although Omalogyra liliputia probably feeds on the
cell contents of larger algae, such as Ulva spp. (Ponder
& Keyzer 1998).
Analyses of data. Abundances of each species in
each habitat and for each time were separately ana-
lyzed using nested ANOVA (locations, sites[locations]
and plots[sites]) to get 2 independent measures of:
(1) the scales at which there was significant spatial
variability, and (2) the components of variation at each
spatial scale. In addition, the data were re-analyzed
with time of sampling as a 4th factor to measure the
spatial scale(s) at which there was short-term (2 wk)
temporal interaction in these populations. All factors,
spatial and temporal, were random. Homogeneity of
variances was examined using Cochran’s test, and in
no case was it necessary to transform the data.
RESULTS
Pilot experiment
For all the species analyzed, the frequencies of sig-
nificant temporal variation were low (<6.5%) and were
very similar when using different numbers of repli-
cates (i.e. n = 2, n = 3, n = 4 and n = 6). These results
indicated that whatever samples we used we obtained a
204
Superfamily Family Species
Cingulopsoidea Eatoniellidae Eatoniella atropurpurea (Frauenfeld 1867)
Crassitoniella flammea (Frauenfeld 1867)
Cingulopsidae Eatonina rubrilabiata Ponder & Yoo 1980
Pseudopisinna gregaria gregaria Laseron 1950
Rissooidea Anabathridae Amphithalamus incidata (Frauenfeld 1867)
Scrobs luteofuscus (May 1919)
Scrobs elongatus Powell 1927
Pisinna olivacea (Frauenfeld, 1867)
Anabathron contabulatum (Frauenfeld 1867)
Rissoelloidea Rissoellidae Rissoella confusa roberstoni Ponder & Yoo 1977
Omalogyroidea Omalogyridae Omalogyra liliputia (Laseron 1954)
Table 1. Taxonomic relations of the species of microgastropods selected for this study
Olabarria & Chapman: Spatial variation of microgastropods
good estimate of spatial variability of
these patchy snails, without the risk
of confounding with temporal varia-
tion. Moreover, the mean squares
obtained in these analyses showed
a consistent spatial pattern of the
species, independent of the number
of replicates used. Taking this into
account and trying to minimize the
costs and sorting times, we consid-
ered a sample size of n = 3 to be suit-
able for obtaining a good estimate of
variability.
Scales of spatial variation
All except 1 species, Scrobs luteo-
fuscus, showed significant variation
in abundances at some spatial scale
in at least 1 of the 4 experiments
(2 experiments in each of 2 habi-
tats). Nevertheless, scales of varia-
tion differed among species and
habitats, and between the 2 times
of sampling.
For example, abundances of 8 of the 11 species
showed significant variation among plots in the coralline
turf, but only for Crassitoniella flammea and Pseudo-
pisinna gregaria gregaria was this scale significant on
each of the 2 sampling periods, even though these were
only 2 wk apart (Table 2). In addition, for each of these
species, the relative differences in abundances among
the plots varied from one time to the next, i.e. different
plots did not consistently have larger or smaller densi-
ties than other plots (Fig. 2a,b). Similar variability in
plot-to-plot differences were shown for the other spe-
cies, irrespective of whether differences among plots
were significant (e.g. Scrobs luteofuscus Fig. 2c, Eaton-
ina rubrilabiata Fig. 2d). Therefore, as predicted, in
coralline most species showed small-scale variability in
abundances, but these patterns varied across plots and
sites and times of sampling.
Only 3 species, Scrobs elongatus, Rissoella confusa
robertsoni and Omalogyra liliputia, showed significant
variation in abundance in coralline turf at the scale of
205
Family Species Coralline turf Sediment
Location Site Plot Location Site Plot
T1 T2 T1 T2 T1 T2 T1 T2 T1 T2 T1 T2
Eatoniellidae E. atropurpurea ns ns ns ns ns * ns ns ns ns ns ns
C. flammea ns ns ns ns * * X ns X ns X ns
Cingulopsidae E. rubrilabiata ns ns ns ns ns * ns ns ns ns ns ns
P. gregaria gregaria ns ns ns ns * * ns ns ns ns ns ns
Anabathridae A. incidata ns ns ns ns ns * ns ns * ns ns ns
S. luteofuscus ns ns ns ns ns ns ns ns ns ns ns ns
S. elongatus ns ns ns * * ns ns * ns ns ns ns
P. olivacea ns ns ns ns * ns ns X * X ns X
A. contabulatum ns ns ns ns ns * * * ns ns ns ns
Rissoellidae R. confusa robertsoni *ns ns* nsns ns ns ns ns ns ns
Omalogyridae O. liliputia ns * ns ns ns ns ns ns ns ns ns ns
Table 2. Results of ANOVA for abundances of 11 species of microgastropods in each of 2 habitats measured on 2 occasions (T1
and T2), 2 wk apart. *p < 0.05; ns: p > 0.05; X: insufficient data for analyses. See Table 1 for species abbreviations
Fig. 2. Mean ± SE numbers of individuals per core (n = 3) at each of the 2 times of
sampling (empty and filled bars) for each plot in each location in the coralline algal
turf. (a) Crassitoniella flammea, (b) Pseudopisinna gregaria gregaria, (c) Scrobs
luteofuscus, (d) Eatonina rubrilabiata, (e) Scrobs elongatus. L1: Location 1; L2:
Location 2; p1 to p8: Plots 1 to 8; S1 to S4: Sites 1 to 4
Mar Ecol Prog Ser 220: 201211, 2001
sites and locations and, again, these patterns differed
between the 2 sampling periods. These differences
were generally due to large abundances at only 1 site
in one of the locations (illustrated for S. elongatus in
Fig. 2e). In no single experiment was there significant
variation at more than 1 scale for any species.
There was very little variation in abundance of snails
at any scale in the sediment. Four species showed sig-
nificant differences in abundances at the scale of sites
or locations, but only Anabathron contabulatum
showed similar patterns of significance over the 2
experiments. Nevertheless, for this species, the differ-
ences in abundances differed between locations from
one time of sampling to the next
(Fig. 3a). No species showed signifi-
cant differences between plots in the
sandy substratum, although many of
the species were found in only 1 or
a few plots (illustrated for Pseudo-
pisinna gregaria gregaria and Eaton-
ina rubrilabiata in Fig. 3b and Fig. 3c,
respectively). The only species that
was consistently found across plots in
the sandy substratum was Amphi-
thalamus incidata (Fig. 3d).
The components of variation for
each of the 4 spatial scales investi-
gated (i.e. <1 m between cores [=
residual], 10 m [between plots], 50 m
[between sites] and 300 m [between
locations]) were independently cal-
culated from the mean square esti-
mates for each habitat, each species
and each time of sampling. There
was very large variability in these estimates between
the 2 times of sampling, and many of the estimates at
the scales of sites or locations were negative, indicat-
ing that the spatial variability at these scales was
underestimated relative to that at the scale of plots
(Underwood 1997). These components of variation
were therefore not formally compared among species
or habitats.
Nevertheless, for all species, very large proportions
of the total variance were found at the scale of cores
within plots (the Residual Mean Squares). These aver-
aged (±SE) 52 ± 5 and 82 ± 4% for the algal habitat
and sediment, respectively (averaged across all species
and the 2 times of sampling). Therefore,
most of the variation in abundances was
at the smallest spatial scale measured
(Table 3). In the coralline algal turf, an-
other 29 ± 4% of the total variation was
found at the scale of plots (ignoring 2
estimates out of 22 that were negative
and, therefore, slightly overestimating
this estimate). Similar calculations were
not done for the sediment because of
the larger number of negative esti-
mates. For all species in each habitat,
therefore, most variation was at the
smallest spatial scales, particularly for
the sediment (Table 3).
Because most of the variation in
abundances was at the smallest spatial
scale measured, the tests of the hy-
potheses that densities of the different
species are spatially correlated used
the number of individuals per core
206
Fig. 3. Mean ± SE numbers of individuals per core (n = 3) at each of the 2 times
of sampling (empty and filled bars) for each plot in each location in the sandy sed-
iment. (a) Anabathron contabulatum, (b) P. gregaria gregaria, (c) E. rubrilabiata,
(d) Amphithalamus incidata. See Fig. 2 for species and other abbreviations
Coralline turf Sediment
Time 1 Time 2 Time 1 Time 2
Plot Residual Plot Residual Residual Residual
(L × S) (L × S)
E. atropurpurea 24.91 51.69 40.69 20.76 66.66 97.64
A. incidata 29.21 54.29 32.25 51.24 83.33 73.49
E. rubrilabiata 37.88 45.84 18.91 27.92 64.28 94.44
S. luteofuscus 8.04 91.96 0 94.44 79.38 82.21
S. elongatus 26.06 27.67 59.09 88.13 76.74
P. gregaria gregaria 35.89 57.02 65.26 19.14 70.73 100
P. olivacea 40 60 33.33 66.66 42.10 No test
R. confusa roberstoni 15.38 61.53 36.73 100 100
O. liliputia 4.61 84.61 22.35 63.41 76.54 63.62
C. flammea 60 20 37.03 59.25 No test 90.1
A. contabulatum 33.30 58.33 53.60 22.68 99.92 90.1
Table 3. Variance estimates (%) derived from ANOVA for selected taxa from the
2 types of habitats (calculated according to Underwood 1997; –: negative esti-
mates). Only variance estimates at small scale of cores (the residual) and plots
from algal turf, and cores from sediment are shown. L: Location; S: Site.
See Table 1 for species abbreviations
Olabarria & Chapman: Spatial variation of microgastropods
(tested for correlation using Pearson’s r). Because
many species were very patchy and present in only a
few cores at any one time, these tests were restricted
to those species that were relatively widespread, i.e.
found in 75% or more of the cores in any habitat at
either time of sampling. These species were Amphi-
thalamus incidata, Eatoniella atropurpurea, Pseudo-
pisinna gregaria gregaria, Omalogyra liliputia and
Eatonina rubrilabiata.
Only 3 of the correlations were significant; numbers
of Amphithalamus incidata and Eatoniella atropur-
purea were positively correlated at each time of sam-
pling (r = 0.49, p < 0.05 and r = 0.70, p < 0.01, respec-
tively; Fig. 4a) and A. incidata and Pseudopisinna
gregaria gregaria were positively correlated during the
second sampling period (r = 0.80, p < 0.001; Fig. 4b).
For most species, despite very patchy distributions at
very small spatial scales, densities were not correlated
among species or abundances were too patchy for
analysis, especially in the sediment.
Despite this small-scale patchiness (Figs 2 & 3), there
were substantial differences among species in their
distributions and abundances in the 2 different habi-
tats (Table 4). All species except Scrobs luteofuscus
were more abundant in coralline turf than in sediment,
although the magnitude of these differences varied
markedly. These patterns showed no relation to the
taxonomic relations of the different species. For exam-
ple, the increase in abundance between the algal and
sediment habitat for the 2 species in the Eatoniellidae
varied between 700× for Eatoniella atropurpurea and
15× for Crassitoniella flammea (Table 4). Similarly, the
2 species of Scrobs showed different patterns, with S.
luteofuscus more abundant in sediment and S. elonga-
tus more abundant in coralline turf. In general, E.
atropurpurea, Amphithalamus incidata and Pseudo-
pisinna gregaria gregaria were the dominant species
in coralline turf, while A. incidata and S. luteofuscus
were the only 2 relatively abundant and widespread
species in sediment.
Although temporal variability at different temporal
scales is the focus of a related study, the consistency
of these spatial scales of variation over a 2 wk period
was examined using ANOVA for each species and
each habitat separately. There were significant inter-
actions among patterns in time and space in 6 spe-
cies (Eatoniella atropurpurea, Crassitoniella flammea,
Pseudopisinna gregaria gregaria, Pisinna olivacea,
Anabathron contabulatum and Rissoella confusa ro-
bertsoni). All showed significant interactions in abun-
dances in the coralline turf, except for P. olivacea,
which showed similar interactions in sediment, so
patterns of spatial variability in this latter habitat
were more consistent through time. Moreover, most
interactions were at the ‘plot’ scale (E. atropurpurea,
F
4, 32
= 3.71, p < 0.05; C. flammea, F
4, 32
= 5.37, p <
0.01; P. g. gregaria, F
4, 32
= 9.77, p < 0.001; A. contab-
ulatum, F
4, 32
= 2.70, p < 0.05), except for P. olivacea
(F
2, 36
= 9.01, p < 0.001) and R. confusa robertsoni
(F
2, 36
= 6.93, p < 0.01), which varied temporally at
the ‘site‘ scale.
207
Fig. 4. Significant correlations between (a) the numbers of A.
incidata and E. atropurpurea and (b) A. incidata and P. gre-
garia gregaria per core in coralline turf at the 2 times of sam-
pling (time 1: empty symbols, time 2 filled symbols. See Fig. 2
for species abbreviations
Species Coralline turf Sediment
E. atropurpurea 349.7 ± 40.9 0.5 ± 0.2
C. flammea 1.5 ± 0.6 0.1 ± 0.1
E. rubrilabiata 16.4 ± 2.5 1.1 ± 0.6
P. gregaria gregaria 35.6 ± 7.2 0.2 ± 0.1
A. incidata 51.2 ± 8.0 4.1 ± 0.4
S. luteofuscus 1.3 ± 0.4 6.8 ± 4.2
S. elongatus 1.3 ± 0.5 0.0 ± 0.0
P. olivacea 2.0 ± 0.4 0.0 ± 0.0
A. contabulatum 2.7 ± 1.0 0.1 ± 0.1
R. confusa roberstoni 2.8 ± 0.7 0.1 ± 0.0
O. liliputia 12.4 ± 1.7 0.6 ± 0.2
Table 4. Mean ± SE number of individuals per core for each
species, averaged over the 2 times of sampling and all spatial
scales (n = 48). See Table 1 for species abbreviations
Mar Ecol Prog Ser 220: 201211, 2001
DISCUSSION
This mensurative study showed that abundances of
microgastropods in coralline turf and sandy habitats
are patchy at a number of different spatial scales, and
this varied according to habitat. In each habitat, most
variation was, as predicted, at the smallest spatial
scale, i.e. among small cores of each habitat, spaced
approximately 1 m apart. This was particularly the
case in the sediment where more than 80% of the vari-
ation was found among replicate cores within 2 m
2
sites. This small-scale variability is similar to patterns
shown for other intertidal gastropods (e.g. Underwood
& Chapman 1996) and benthic macrofauna (e.g. Mor-
risey et al. 1992a) and re-emphasizes the need to accu-
rately quantify patterns of abundance at a hierarchy of
scales for understanding ecological processes (Bourget
et al. 1994), measuring patterns of biodiversity (Under-
wood & Chapman 1998a) and assessing environmental
impacts (Underwood 1996a,b).
With respect to the consistency of patterns of varia-
tion across species and habitats, there were relatively
consistent patterns between the 2 types of habitat. Ten
of 11 species were more abundant in coralline turf
than in sediment. For most species, despite the large
amounts of small-scale variability among cores in each
plot, there were also significant differences in abun-
dances between plots (10 m apart) in turf in at least one
of the sites during one or both experiments. In sedi-
ment, significant spatial variation was less common, but
when found, was generally at the larger spatial scales
of sites and locations. Nevertheless, examination of the
mean abundances indicated that most species in sedi-
ment were common in only one or a few sites; no spe-
cies was consistently found in greater numbers in all
sites in one location compared to another location.
In addition, patterns of variability varied from
one period of sampling to another, 2 wk later, in the
coralline algal habitat where the animals were abun-
dant, but not in the sediment. Again, this was generally
manifested at the smallest spatial scale, i.e. densities
varied from time to time at the scale of plots. With more
detailed sampling designs, such small scales of spatio-
temporal interaction are becoming more apparent as
an essential feature of natural ecological variation (e.g.
Morrisey et al. 1992b, Thrush et al. 1994, Underwood &
Chapman 1998b).
The spatial patterns of abundance therefore varied
among species, habitats and times of sampling, and
there was no close correlation between spatial patterns
of abundance and taxonomic relations of the different
species. The species responded to the spatial arrange-
ment of habitats in a landscape according to the patch-
iness of habitat at a number of spatial scales, the type
of habitat, environmental conditions (times of sam-
pling) and characteristics of the species (e.g. McNeill &
Fairweather 1993, Egglestone et al. 1999).
At the scale of habitat, although all species were
found in each habitat, only 1 of the 11 was more com-
mon in the sediment than in the coralline turf.
Coralline turfs are structurally complex matrices,
offering invertebrate animals refuges from predation
(Akioka et al. 1999) and potentially a greater diversity
and quantity of food (Edgar 1990, Bell et al. 1993).
Coralline turf can result in greater rates of survival
than in unvegetated habitats for many small organisms
(Heck & Crowder 1991). Whether the differences in
abundance between the 2 types of habitat identified in
this study are due to differences in mortality, recruit-
ment or emigration and immigration is not, at this
stage, known.
Numerous factors influence spatial heterogeneity in
the distribution of organisms within habitats. Com-
monly, large-scale abiotic factors are considered im-
portant in defining broad patterns of distribution
(Lewis 1964, Barry & Dayton 1991). The large differ-
ences in and changes to abundances of microgastro-
pods among patches of the same type of habitat a few
meters apart may also be influenced by recruitment or
mortality. Therefore, variation in the quality of habitat
and limited dispersal may also partly explain their
patchy patterns of abundance, although the patterns
are likely to be modified by the adult animals redistrib-
uting themselves among patches of habitat (Under-
wood & Chapman 1996). Although there are few data
on rates of movement of adult microgastropods among
patches of habitat, the adults appear to be active dis-
persers. New intertidal boulders are colonized by adult
microgastropods within a few days of deployment (M.
G. Chapman unpubl. data) and hundreds of small gas-
tropods appear in new patches of algal turf within a
couple of weeks (B. Kelaher pers. comm.). Many gas-
tropods respond to small-scale features of their habi-
tats and aggregate in response to cues from the habitat
and each other. As a result, a change or difference in
density in any area can potentially result in quite dif-
ferent responses and patterns of variance (Underwood
& Chapman 1992, Underwood 1996a). Short-term, dy-
namic patterns of immigration and emigration among
patches of habitat are an important aspect of the eco-
logy of small benthic animals, with strong local influ-
ences on patterns of abundance and distribution (e.g.
Barnes 1998). Moreover, variations in recruitment
rates can be a major cause of spatio-temporal variabil-
ity among different habitats (e.g. Littorina acutispira;
Underwood & McFadyen 1983).
The heterogeneity of coralline turf is likely to affect
the patchy distribution and abundance of microgas-
tropods that associate with fronds or live among the
trapped sediment. Most of the microgastropods in this
208
Olabarria & Chapman: Spatial variation of microgastropods
study appeared to be associated with the sediment
among Corallina, except for Eatoniella atropurpurea
and Omalogyra liliputia. In the study area, the co-
ralline turfs showed a great variability in compactness,
which may influence detrital accumulation, thereby
affecting sediment-dwelling populations. Small-scale
changes in physical characteristics associated with
such algae, such as accumulation of detritus and
changes in water flow, have also been reported to
directly or indirectly alter faunal abundance (Eckman
1987, Edgar et al. 1994).
Patchiness in the distribution of invertebrates in
sediments has also been reported at small scales (e.g.
Volckaert 1987, Morrisey et al. 1992a,b). Processes
influencing distributions of organisms may change
with scale (Thrush et al. 1994, 1997). For example,
Hewitt et al. (1997) identified variable relations
between adult and juvenile bivalves with changes in
spatial scales in sediment. Although this variability is
sometimes attributable to small-scale environmental
or biological variables (e.g. Bell et al. 1978, Bell &
Coen 1982, Thrush 1986), much is still inexplicable
with no clear environmental correlate(s). Similarly,
patchiness and short-term variation in abundance and
distribution of organisms have been shown in man-
groves (Underwood & Chapman 1999) and intertidal
rocky shores (Underwood & Chapman 1996, 1998b),
although the latter have been focussed on large com-
ponents of macrofauna. Nevertheless, studies on the
spatio-temporal variability of faunal assemblages in
algal turf have rarely been investigated or have been
poorly done. As 2 examples of many, Hull (1997)
examined seasonal changes of ostracods in only 1
patch of habitat, ignoring any potential variability at
other spatial scales. In addition, Davenport et al.
(1999) compared epifauna associated with 4 species of
algae with each collected in a different patch (<5 m
apart), thus confounding species-specific and small-
scale spatial variability.
This well-replicated mensurative experiment com-
paring a number of different species showed 2 strik-
ing features: first, the difference in the scales of spa-
tial variance for 1 species from habitat to habitat; and
second, the different spatial patterns of variation
among closely related species, which (according to
the limited literature available) were expected to have
similar requirements for resources. Although all spe-
cies examined occur in sediment and algal turfs, these
obviously provide a different quality of habitat for the
different species, but this is reflected in different pat-
terns of variability. Spatial variation of invertebrates
at different scales among habitats may be due to a
real difference in the ecological processes operating
from habitat to habitat, or simply spatial variation
due to stochastic variability from one site to another
(Underwood 1996a). Furthermore, the lack of correla-
tion between patterns of variability and taxonomic
relations of the different species indicate that each
species responded differently to ecological processes.
These results underline the need to incorporate com-
parisons across habitats and species-level discrimina-
tion in any study about spatio-temporal variability at
small scale.
Therefore, the present study has important conse-
quences for studies of the distribution of microgas-
tropods in different intertidal habitats, including those
concerned with environmental monitoring. Coherent
predictions about potential changes to populations in
response to disturbances require understanding of
interactive variances. An impact is definable in terms
of change in the variance component that is associated
with differences between abundances of populations
in disturbed and control sites before and after the dis-
turbance (Underwood 1996b). As a first step to mea-
suring impact it is necessary to have quantitative data
on natural patterns of spatial and temporal variation.
Furthermore, to understand how and to predict under
what circumstances impacts occur, it is necessary to
know how and why the populations vary from place to
place or time to time.
As mentioned above, many ecological and environ-
mental studies are unreplicated or confounded be-
cause of inadequate attention to spatial and temporal
scales of variance. When the scales at which variation
occurs are not known in advance, sampling using
nested designs can identify the relevant scales of vari-
ability to be incorporated into further research (Caffey
1985, Phillips & Fleeger 1985, Jones et al. 1990, Mor-
risey et al. 1992a,b, Underwood 1997, Underwood &
Chapman 1998b). The scales can be chosen arbitrarily
and adapted to the objectives of the particular study,
although it is often useful to do a pilot study to identify
scales at which variation is significant (Underwood
1997). The importance of the small spatial scales in
patterns of abundance re-emphasizes the need to
incorporate hierarchical scales of variability within
locations for any comparisons among locations, be they
to increase understanding of ecological patterns and
processes, or to identify changes in assemblages in
response to human disturbances.
Acknowledgements. This work was supported by funds from
the Australian Research Council, the Institute of Marine Ecol-
ogy and the Centre for Research on Ecological Impacts of
Coastal Cities. We are grateful to many people for help with
sampling, but particularly Stefanie Arndt, who worked hard
in the field and laboratory. We thank Vanessa Mathews and
Michelle Button for help with the graphics, and L. Benedetti-
Cecchi and A. J. Underwood for commenting on an earlier
draft of this paper. We also thank 3 anonymous referees for
comments that improved the manuscript.
209
Mar Ecol Prog Ser 220: 201211, 2001
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Editorial responsibility: Otto Kinne (Editor),
Oldendorf/Luhe, Germany
Submitted: September 15, 2000; Accepted: February 27, 2001
Proofs received from author(s): September 4, 2001
... These and other studies raise the issue concerning the discrimination of scale-dependent patterns from those due to other concomitant causal processes (see also Bishop et al., 2002;Bertocci et al., 2012;Oliveira et al., 2014). Patterns of variability at multiple spatial scales have been described among contrasting habitat types (Olabarria and Chapman, 2001;Balata et al., 2007;Magni et al., 2017), geographic regions (Fraschetti et al., 2005;Giménez et al., 2005;Dal Bello et al., 2017) and seasons (Maggi et al., 2017), as well as along environmental gradients (Benedetti-Cecchi, 2001;Benedetti-Cecchi et al., 2001;Ysebaert and Herman, 2002;Terlizzi et al., 2007;Kraufvelin et al., 2011) and between putatively impacted vs. reference areas (Bishop et al., 2002;Balestri et al., 2004;Bertocci et al., 2012Bertocci et al., , 2017Oliveira et al., 2014). Despite an increasing interest in assessing patterns of spatial variability, such observations have been carried out for a much larger extent in rocky shore habitats than in soft-bottom systems (Ysebaert and Herman, 2002;Giménez et al., 2005;Kraufvelin et al., 2011;Magni et al., 2017;Bertocci et al., 2019;Datta and Bertocci, 2023). ...
... Marine ecologists have often described the spatial pattern of biological descriptors among contrasting environmental conditions, such as those across different habitats or seasons and across multiple scales (Kelaher et al., 2001;Olabarria and Chapman, 2001;Balata et al., 2007;Dal Bello et al., 2017;Magni et al., 2017). These studies have provided the observational background for developing explanatory models and testable hypotheses about causal processes, including biological and environmental factors and human-induced stressors (Olabarria and Chapman, 2001; Bishop et al., 2002;Terlizzi et al., 2007;Bertocci et al., 2012;Kraufvelin et al., 2011). ...
Article
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A B S T R A C T Studies focusing on patterns of spatial variation in marine soft-bottom assemblages suggest that variability is mainly concentrated at small spatial scale (from tens of centimeters to few meters), but there is still a lack of knowledge about the consistency of this spatial pattern across habitats and seasons. To address this issue, we quantified the variability in the structure of macrozoobenthic assemblages and in the abundance of dominant macroinvertebrate species in the Mellah Lagoon (Algeria) at three spatial scales, i.e., Plot (meters apart), Station (10’s m apart) and Site (kms apart) scale, in Ruppia maritima (Ruppia) beds and unvegetated sediments (Unvegetated), and in two dates in winter and two dates in summer 2016. Spatial variability of the most dominant bivalve Mytilaster marioni varied significantly between habitats, but consistent across the two seasons, with a more heterogeneous distribution in Ruppia than in Unvegetated at the Station scale. Furthermore, a second-order interaction among the hierarchical nature of spatial variability, season and habitat emerged for the assemblage structure. Spatial variability between habitats varied significantly in winter, with the largest variation at the Plot scale in Unvegetated and more heterogenous assemblages at the Plot and Site scales than at the Station scale in Ruppia, but did not vary in summer when most of the variance was at the Site scale. We demonstrate that the scales of influence of the processes operating in the Mellah Lagoon are contingent on the specific habitat and/or period of the year at which the study was conducted, highlighting the importance of examining all these sources of variation simultaneously to increase the accuracy of explanatory models derived from the observed patterns in sedimentary environments. Keywords: Spatial variation Seasonal-changes Spatial scale Distribution patterns Benthic macroinvertebrates Seagrass Structuring factors Aquatic vegetation Biodiversity Coastal lagoons
... On Botany Bay's shorelines, studies of microgastropods (gastropods with adult body size < 2 mm) showed that there were substantial spatiotemporal interactions contributing to observed patchy densities (Olabarria andChapman, 2001, 2002;Olabarria, 2002). Spatial variation in the distribution of eleven intertidal microgastropods across sandy sediment between intertidal boulders or coralline turf on intertidal rock platforms occurred mainly at small scales, ranging from less than one metre to ten metres (Olabarria and Chapman, 2001). Ten of the eleven microgastropods were more abundant in the coralline turf than sediment habitat, being generally sparse on the sediment (Olabarria and Chapman, 2001). ...
... Spatial variation in the distribution of eleven intertidal microgastropods across sandy sediment between intertidal boulders or coralline turf on intertidal rock platforms occurred mainly at small scales, ranging from less than one metre to ten metres (Olabarria and Chapman, 2001). Ten of the eleven microgastropods were more abundant in the coralline turf than sediment habitat, being generally sparse on the sediment (Olabarria and Chapman, 2001). Also, there was inconsistency in the temporal variability of densities of the coexisting microgastropods in patches of coralline turf or sediment in the intertidal zone (Olabarria and Chapman, 2002). ...
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This paper provides a synopsis of the ecological structure and function of waterways in the Botany Bay catchment, informed by a comprehensive review of literature. Botany Bay is one of Australia’s best known and most studied waterways. It is a large sheltered embayment with a marine-dominated estuary that receives freshwater discharges mainly from the Georges and Cooks Rivers. The catchments of those rivers, and much of the northern shoreline of the bay, have been intensively developed over the past two centuries. Thus, the structure and functioning of all ecosystems in the region have been modified to varying extents. However, some natural features have been retained across the Botany Bay catchment, particularly in protected areas in and around Towra Point Nature Reserve and the National Parks in the upper Georges River catchment. Studies of those natural features have provided valuable information about community structure, fish behaviour and food webs in a range of estuarine habitats (particularly seagrass, mangroves and saltmarsh). In contrast to the extensive information about estuarine ecology, there is minimal published information about the natural features of freshwater ecosystems in the catchment.
... Los organismos más frecuentes en esta zona son las macroalgas (Lee, 2008), mismas que proporcionan refugio y alimento para numerosos grupos de invertebrados (García-Robledo et al., 2008;Jover-Capote y Diez, 2017;Moreno, 1995;Steneck y Watling, 1982;Yang et al., 2007). Las macroalgas son un ambiente espacialmente heterogéneo, lo que hace posible que puedan albergar distintos grupos de invertebrados a lo largo del tiempo Olabarria y Chapman, 2001). Los anfípodos, poliquetos y moluscos son los grupos más importantes al interior de la comunidad de macroalgas, ya que representan 70% de la abundancia en éstas (Aguilera, 2011;Colman, 1940). ...
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Intertidal macroalgae provide food and shelter for different organisms. The objective of this work was to analyze the bivalves associated with macroalgae. Sampling was carried out in January, May, July, and November 2014, 72 samples of macroalgae and their associated bivalves were manually collected within 400 cm2 in 2 locations in Guerrero: El Palmar and Las Gatas beaches. The community structure of bivalves was determined from specific richness, composition, abundance, distribution, and community indices: Shannon diversity, Pielou evenness and Simpson dominance. Each macroalgal species (59 spp.) was associated with proposed morphofunctional groups. Macroalgal cover, bivalve abundance and retained sediment were analyzed. Of the total number of individuals (873), 17 bivalve species were recognized. The Shannon index was 2.15 bits/individual. Bivalves were associated with 3 morphofunctional groups of macroalgae. Bivalve abundance and retained sediment decreased by month, while abundance, cover, and sediment decreased with increasing tide level. Studies like this provide important information for understanding coastal diversity, in this case of a tourist area in Guerrero.
... Many organisms can use detritus directly as food, because shortly after microorganisms colonize that detritus, its nutritional value increases significantly [55]. It was observed that differences in density, branching and overall compactness of the genus Corallina have different effects on the accumulation of detritus, and thus on the species living in the intertidal sediments [56]. Small changes in such morphological characteristics, as well as changes in water currents, also affect the abundance of fauna. ...
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Available research on invertebrates in Corallina officinalis settlements shows a high level of biodiversity due to a complex habitat structure. Our aim was to examine seasonal changes in the invertebrate population, considering the algae’s growth patterns. Nine locations with over 90% algal coverage were selected in southern Istria, where quantitative sampling was performed using six replicates of 5 × 5 cm quadrats in each location. Results showed that 29,711 invertebrates were found during winter (maximum algae growth) and 22,292 during summer (minimum algae growth), with an extrapolated average density of 220,000 and 165,200 individuals per square meter, respectively. The total number of individuals showed a linear increase as the algae biomass increased. The highest density, 586,000 individuals, was recorded in the Premantura area during winter. Dominant groups such as amphipods, polychaetes, bivalves and gastropods made up over 80% of the invertebrates. Our study confirms high invertebrate richness in the C. officinalis settlements, with the maximum density being the highest when compared to previously published data.
... Los micromoluscos adultos miden máximo 10 mm, y algunos son casi invisibles a simple vista, por lo que la clasificación de los individuos de los sedimentos marinos es laboriosa. Como resultado, la mayor parte de la información sobre los moluscos se ha centrado en los macromoluscos y ha ignorado o subestimado la abundancia and Chapman 2001). Therefore, the search for micromollusks needs to expand in environments that have yet to be studied well and may harbor a great diversity and richness of species. ...
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Marine mollusks provide important ecosystem services. They create habitats for benthic organisms, filter water, biodeposit organic carbon in the seafloor, and serve as food sources for other organisms. Studies of mollusk diversity require time-consuming methods to process samples and identify species. Thus, it is not surprising that most studies have focused on macromollusks that can be collected and processed easily, ignoring micromollusk species. Without understanding the ecology and distributions of micromollusks properly, it is impossible to assess their populations and implement adequate conservation measures. Here we present microgastropods collected in Bahia de los Angeles at the family level for September 2013 (summer) and February 2014 (winter). During each season, we sampled 6 coastal sediment stations, and analyzed depth, salinity, temperature, granulometry, and organic matter. A total of 20,353 specimens were collected: 15,310 in summer and 5,043 in winter. Seven micromollusk families were identified: Barleeidae, Caecidae, Cerithiidae, Eulimidae, Pyramidellidae, Rissoidae, and Tornidae. Caecidae and Barleeidae exhibited the highest densities among all families in summer and winter, respectively (278,044 ind·m–2, 142,222 ind·m–2). The lowest densities for summer and winter were observed for the Tornidae family (~1,867 ind·m–2, ~1,411 ind·m–2). Barleeidae, Caecidae, Cerithiidae, Rissoidae, and Tornidae were classified as herbivorous and detritivorous; Eulimidae and Pyramidellidae, as carnivorous and ectoparasitic. Tornidae and Eulimidae showed symbiotic relationships with various invertebrate species. The Bayesian analysis of variance indicated a high probability of differences only in summer (BF > 3). When comparing the stations in both periods, all stations, except station 6, showed differences between periods (BF > 3). The canonical correlation analysis indicated some associations between family abundances and temperature. This study provides valuable information that expands the knowledge of micromollusk biodiversity in the coastal area of Bahia de los Angeles, an important site for conservation in Mexico.
... The patterns of distribution have been shown to be substantially different in a spatial scale, ranging from some centimeters to hundreds of meters, regarding intertidal mollusks [8]. Temporally, the dispersion pattern of these organisms can significantly change seasonally, but also over longer periods of time [9,10]. ...
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The present study is the first to examine spatio-temporal variations in the densities and morphometrics of three shallow water Polyplacophora species (Rhyssoplax olivacea, Acanthochitona fascicularis and Lepidopleurus cajetanus), native to the eastern Mediterranean, while also estimating several growth parameters. Two intertidal boulder fields located in the Pagasitigos gulf (central Aegean) were sampled monthly with SCUBA diving using quadrant sampling, to compare the spatial and temporal (month, season) effects on their size, population density and dispersion pattern. Region was the most significant factor influencing the abundance and size for all three species, while the temporal scales affected mostly Rhyssoplax olivacea. The effect of a boulder under the surface was only significant for the density of Lepidopleurus cajetanus. The standardized major axis method showed that the three species exhibited different allometric relationships between length, width and weight, while a slope comparison between regions yielded significant, in most cases, results. Using the standardized Morisita index for dispersion, a clustered pattern was observed for all species seasonally, with the exception of Acanthochitona fascicularis in Plakes in autumn and winter. To estimate the growth parameters, a bootstrapped Electronic Frequency Analysis (ELEFAN) utilizing a genetic algorithm was employed on pooled populations. L∞ and K varied among the three species with A. fascicularis exhibiting the highest L∞ and L. cajetanus the lowest K value.
... A comparison of mollusk species isolated from C. officinalis turfs with previously recorded species conducted throughout the world confirms this algal settlement as a biodiversity reservoir for marine mollusks. Most commonly recorded genera for gastropods are Alvania, Eatonina, Odostomia, Rissoa, Rissoella and the family Rissoidae in general, and for bivalves Hiatella, Lasaea, Musculus and Mytilus [2,[12][13][14][15][16][17][18][19][20][21]23,[93][94][95] which were all recorded in considerable numbers in our study as well. Even though C. officinalis turfs have been investigated for years, there are still many unknowns regarding its settlements, which is further substantiated by the fact that we identified one gastropod genus (Episcomitra) and three bivalve genera (Gregariella, Lucinella, Striarca) that were not documented in previous studies. ...
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Presence of mollusk assemblages was studied within red coralligenous algae Corallina officinalis L. along the southern Istrian coast. C. officinalis turfs can be considered a biodiversity reservoir, as they shelter numerous invertebrate species. The aim of this study was to identify mollusk species within these settlements using DNA barcoding as a method for detailed identification of mollusks. Nine locations and 18 localities with algal coverage range above 90% were chosen at four research areas. From 54 collected samples of C. officinalis turfs, a total of 46 mollusk species were identified. Molecular methods helped identify 16 gastropod, 14 bivalve and one polyplacophoran species. COI sequences for two bivalve species (Musculus cf. costulatus (Risso, 1826) and Gregariella semigranata (Reeve, 1858)) and seven gastropod species (Megastomia winfriedi Peñas & Rolán, 1999, Eatonina sp. Thiele, 1912, Eatonina cossurae (Calcara, 1841), Crisilla cf. maculata (Monterosato, 1869), Alvania cf. carinata (da Costa, 1778), Vitreolina antiflexa (Monterosato, 1884) and Odostomia plicata (Montagu, 1803)) represent new BINs in BOLD database. This study contributes to new findings related to the high biodiversity of mollusks associated with widespread C. officinalis settlements along the southern coastal area of Istria.
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Mollusca, the second-most diverse animal phylum, is estimated to have over 100,000 living species with great genetic and phenotypic diversity, a rich fossil record, and a considerable evolutionary significance. Early work on molluscan system-atics was grounded in morphological and anatomical studies. With the transition from oligo gene Sanger sequencing to cutting-edge genomic sequencing technologies, molecular data has been increasingly utilised, providing abundant information for reconstructing the molluscan phylogenetic tree. However, relationships among and within most major line-ages of Mollusca have long been contentious, often due to limited genetic markers, insufficient taxon sampling and phylogenetic conflict. Fortunately, remarkable progress in molluscan systematics has been made in recent years, which has shed light on how major molluscan groups have evolved. In this review of molluscan systematics, we first synthesise the current understanding of the molluscan Tree of Life at higher taxonomic levels. We then discuss how micromolluscs, which have adult individuals with a body size smaller than 5 mm, offer unique insights into Mollusca's vast diversity and deep phylogeny. Despite recent advancements, our knowledge of molluscan systematics and phylogeny still needs refinement. Further advancements in molluscan systematics will arise from integrating comprehensive data sets, including genome-scale data, exceptional fossils, and digital morphological data (including internal structures). Enhanced access to these data sets, combined with increased collaboration among morphologists, palaeontologists, evolutionary developmental biologists, and molecular phylogeneticists, will significantly advance this field.
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Increasing coastal development and global warming have resulted in large-scale habitat changes, with artificial coastal structures replacing extensive tracts of natural shores. In Singapore, for example, more than 63% of the natural coastline has been replaced by seawalls. Multiple studies from both temperate and tropical regions have compared species diversity supported by these artificial structures with natural rocky shores. Few, however, have estimated and compared the population size and movement of common intertidal species between these two habitat types. Using mark–recapture techniques, this study investigated: (1) the population size of three common gastropod genera (Nerita spp., Trochus spp. and Turbo spp.) and (2) differences in displacement of Nerita spp. and Trochus spp., two common species found on natural rocky shores and seawalls in Singapore. The results of our mark–recapture surveys indicated that seawalls supported large densities of Nerita spp.—more than 50 times greater than that on adjacent rocky shores. The mark–recapture data also revealed that movement of the gastropod species differed between the two habitats, with individuals on seawalls generally travelling longer distances.
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Benthic and pelagic marine habitats, like terrestrial landscapes, can be viewed as mosaics of environmental quality produced by spatial and temporal variation in the physical and biological constraints encountered by populations. In marine systems hydrodynamic processes (water column stability, temperature and nutrient gradients, turbulent oceanographic features, storm disturbances) and biological processes (competition, grazing, predation) affect the recruitment and survival of populations. The emerging view of the dynamics of communities and populations as nonequilibrium systems (Chesson and Case, 1986; DeAngelis and Waterhouse, 1987) increases the interest in processes that generate or perpetuate heterogeneity. That variable environmental parameters cause gradients in community structure or the distribution of species is by no means a novel observation. Merriam’s (1898) concept of life zones relating plant distributions to changes in air temperature along an elevation gradient was an early explanation of environmentally controlled community patterns. Terrestrial biomes (Clements and Shelford, 1939) are defined by large-scale changes in physical and biological characteristics of the landscape. In some marine habitats, however, these divisions may be less apparent, but they are nevertheless similarly heterogeneous over many scales in space and time.
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The study of heterogeneity in the biological components of aquatic ecosystems has been an important part of ecology for more than a century. Although many early ecologists (see review by Lussenhop, 1974) perceived especially the pelagic milieu to be uniform [hence the term plankton or “wanderers” for its inhabitants (Ruttner, 1953)], early quantitative limnologists such as Birge (1897) found the aquatic habitat to be highly heterogeneous in factors such as light, temperature, oxygen, and limiting nutrients. The physical heterogeneity of the aquatic habitat has long been known to be reflected in the spatial patterns of aquatic populations.
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