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Histograms showing age structure of Nassarius burchardi in relation to large scale habitats, in relation to the transects (reflecting the south to north gradient in the salinity fields), and aggregating all individuals sampled in the estuary. Data are presented only where n > 3. Histograms have been constructed where n =3 to n = 20 only to show the size distribution of animals in these very low density populations. A value of n = 0 indicates the site was sampled but no animals were collected. Each histogram represents data aggregated from several sites, either along a transect, or within a large scale habitat.
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Thirty-one species of mollusc were collected in Leschenault Inlet during 1982-1987. Seven species were common, with the remaining 24 species occurring sporadically, rarely or only once during the study. These seven most common species in order of general abundance were: Arthritica semen, Tellina deltoidalis, Nassarius burchardi, Spisula trigonella,...
Context in source publication
Context 1
... of size classes for N. burchardi for the various sites show a fairly uniform pattern of unimodal populations, with a mode centred on the 8 mm size class for most of the years of sampling (Fig 9). This mode occurred within all salinity fields and at all sites on all large scale habitats, indicating no growth, and persistence over several years of individuals in the population. ...
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Limacina helicina is the dominant pelagic gastropod mollusc species in temperate and polar ecosystems, where it contributes significantly to food webs and vertical flux. Currently, considerable uncertainty exists in the interpretation of L. helicina’s life cycle, hindering our understanding of its potential responses to environmental change. Here,...
Human patterns of subsistence and/or mobility may be reflected in the zooarchaeological record from estuarine mangrove shell mounds and other coastal ecotones. In a biogeographical domain, such as mangroves and their associated ecotones, the availability of much of the animal resources may increase due to seasonality and life cycle of organisms and...
Citations
... However, H. brazieri (4674 m −2 ) dominated on the 1-mm mesh in Oyster Harbour and there was a low density of A. semen (137 m −2 ). Semeniuk and Wurm (2000) examined molluscs in Leschenault Inlet, south of the Peel-Harvey Estuary, over 5 years from 1982 to 1987. As in the Peel-Harvey Estuary, A. semen (densities typically in the hundreds to thousands per square metre) and H. brazieri (tens to hundreds per square metre) were abundant estuarine species; Acteocina sp. was also common. ...
... At one site, H. brazieri was abundant, then was absent for over a year from February 1983 to May 1984, before reappearing. The substantial density variations in A. semen and H. brazieri recorded by Semeniuk and Wurm (2000) are similar to those recorded in the Peel-Harvey Estuary from March 1977 to February 1979 . Semeniuk and Wurm (2000) measured a number of physical parameters, and found no apparent relationship between any of the measured parameters and population fluctuations. ...
... The substantial density variations in A. semen and H. brazieri recorded by Semeniuk and Wurm (2000) are similar to those recorded in the Peel-Harvey Estuary from March 1977 to February 1979 . Semeniuk and Wurm (2000) measured a number of physical parameters, and found no apparent relationship between any of the measured parameters and population fluctuations. They did suggest that the absence of H. brazieri from one site from February 1983 until May 1984 may have been caused by a combination of high summer salinities (45 PSU) and temperatures at the site that caused the population to crash. ...
Context Eutrophication caused extensive macroalgal blooms in the Peel–Harvey Estuary, Western Australia, in the 1970s. Nutrient inputs were reduced and an artificial channel was constructed in 1994 to increase marine flushing. Aims This study examines benthic mollusc populations in the estuary in 1978, 2000 and 2020, to determine what changes have occurred in the estuaries over time. Methods Quantitative samples were made at 10 sites in autumn and spring of each year; physical and chemical parameters were measured in 2000 and 2020. Key results Species composition was stable, dominated by Arthritica semen and Hydrococcus brazieri; however, there have been substantial changes in abundance of these and less common species. Conclusions The exact cause(s) of density changes could not be determined, but it is likely to be due to a combination of factors. Implications Further changes in mollusc assemblages in south-western Australian estuaries are expected as the climate warms and dries and the estuaries are stressed by human population growth.
... In this study, we examine the Sr/Ca, Mg/Ca and Ba/Ca patterns in the micro-mollusc Arthritica helmsi to compare to the chemical and physical properties of the ambient waters. Abundant in south eastern Australian estuaries and also in the sediment record (Chamberlayne, 2015;Kanandjembo et al., 2001;Matthews and Constable, 2004;Semeniuk and Wurm, 2000), A. helmsi is an aragonitic micro-mollusc with a broad environmental tolerance (Wells and Threlfall, 1982a), short life span of ~1 year (Wells and Threlfall, 1982b), and continuous growth (Chamberlayne et al., 2020;Wells and Threlfall, 1982b). A previous geochemical analysis of this species from museum collections showed promising correlations between Sr/Ca and Mg/Ca and temperature (Chamberlayne et al., 2020), although water chemistry data were not available for that study. ...
Element-to-calcium ratios of bivalve shells are potentially useful proxies for environmental change, provided the relationship between the environmental variable and element ratio are calibrated using modern specimens. In this study we investigate the utility of trace elemental ratios in the estuarine micromollusc Arthritica helmsi as (palaeo)environmental proxies. Sr/Ca, Mg/Ca and Ba/Ca ratios were measured in waters (n = 137) and live bivalves (n = 125) were collected along a salinity gradient from fresh to hypersaline in the Coorong Lagoon and Lake Alexandrina, at the terminus of the Murray River, South Australia. Water Mg, Sr and Ca exhibited linear relationships with salinity, while Ba showed no relationship. Mg/Ca and Sr/Ca in water both showed positive logarithmic responses to increasing salinity, while the response of Ba/Ca was best explained by a negative power function. The Sr concentration and Sr/Ca of water collected between 2016 and 2018 were elevated compared to a previous study conducted between 2007 and 2008, possibly due to a higher river flow regime in the more recent period. The range of Sr/Ca, Mg/Ca and Ba/Ca measured in A. helmsi were in agreement with previous studies, as were the range of partition coefficients. However, the incorporation of Sr/Ca, Mg/Ca and Ba/Ca did not correlate with water elemental ratios, temperature, salinity or pH and are therefore likely to be more heavily influenced by biological processes. As a consequence, while the elemental composition of other carbonate fossils within the Coorong system may hold potential to reconstruct past climate and environmental change, the trace element geochemistry of A. helmsi aragonite shells, and possibly other similar micro-bivalve molluscs, should be treated with caution as a palaeoenvironmental tracer.
... Seven highly abundant taxa could not be assigned using this approach and were assigned based on their ecology. For example, two bivalve species, Arcuatula senhousia and Arthritica semen, were assigned to surficial modifiers based on the knowledge that A. senhousia forms byssal mats on the sediment surface (Mistri 2002) and A. semen inhabits the top 20 mm of sediment (Semeniuk & Wurm 2000). Some taxa could not be assigned as information on aspects of their ecology is unknown, which led four sites to have a proportion of unassigned taxa greater than 20%. ...
Microtidal estuaries are prone to anthropogenic degradation, with natural features of those in south-western Australia making them more susceptible. However, the benthic ecological health of these systems is rarely assessed, despite the importance of the benthos and frequent application of benthic indices in estuaries elsewhere, particularly macrotidal systems in the northern hemisphere. The aim of this research was to assess the current status of the benthic macroinvertebrate community and its role in the function and management of the microtidal Peel-Harvey Estuary. After accounting for the effects of natural hydrological conditions (e.g. salinity, temperature), the benthic macroinvertebrate community was shown to respond to anthropogenic stress as represented by sediment condition (i.e. oxygenation, organic enrichment, mud content, sulphide presence), demonstrating its potential utility for assessing estuarine health. However, existing benthic indices commonly used in macrotidal estuaries (e.g. the multivariate AZTI Marine Biotic Index) yielded results inconsistent with sediment condition, demonstrating their limitations when applied to highly adaptive, stress-tolerant macroinvertebrate communities that are common in microtidal estuaries. A new multi-metric Estuarine Benthic Community Index was developed, following a multivariate approach to select community metrics that showed greater responses to sediment condition than natural stress. Overall, the benthic macroinvertebrate community in the Peel-Harvey Estuary was typically in good to fair health, with decreased health in the summer and deeper depositional areas. It is largely dominated by small-bodied, opportunistic species, and apparently retained in early succession due to chronic natural and anthropogenic stress. This was further reflected by the community’s limited impacts on solute fluxes of benthic metabolism, nutrient exchange and denitrification, with sediment condition being more influential. These findings demonstrate that these benthic faunal communities do not play a substantial role in estuarine function, with the application of resulting benthic indices restricted to assessing more structural aspects (e.g. diversity) of benthic ecological health.
... Shell physiology means that juveniles are more tolerant of lower estuarine salinities (i.e. <15 g L -1 ) and deeper water than adults (Ludbrook 1984;Semeniuk & Wurm 2000). The presence of juvenile S.(N.) trigonella for the period c.7 750-7 450 years BP therefore suggests estuarine episodes in the centre of Lake Alexandrina; a peak in estuarine/marine diatoms at ~7 500 BP in Ax1 core indicates that these episodes may have extended into the northern part of the Lake periodically over that 300-year period (Fig. 2.4.2). ...
... The presence of juvenile S.(N.) trigonella for the period c.7 750-7 450 years BP therefore suggests estuarine episodes in the centre of Lake Alexandrina; a peak in estuarine/marine diatoms at ~7 500 BP in Ax1 core indicates that these episodes may have extended into the northern part of the Lake periodically over that 300-year period (Fig. 2.4.2). The lack of adult populations indicates only sporadic spikes in salinity, rather than persistently estuarine conditions, given that the species requires several years of optimal conditions (salinity >15 g L -1 ) to achieve maturity (Semeniuk & Wurm 2000). ...
... These bivalves are typical of low-energy coastal and lagoon environments along the southern Australian coast and are particularly well adapted to less dynamic areas in estuaries (Kanandjembo et al. 2001;Jespersen & Lützen 2009). This period is marked by increased abundances of estuarine/marine epiphytic diatoms, indicating that conditions at the site were most likely characterised by clear water with abundant coverage of aquatic plants, in keeping with the preferred habitat for these fauna of vegetated, sandy muds (Semeniuk & Wurm 2000). Diatom sampling during 2007, at the height of the Millennium Drought when connection with the marine environment was only possible through continued dredging at the Murray Mouth, failed to detect Paralia species at most sites in the Coorong in any but minor abundances ). ...
... Shell physiology means that juveniles are more tolerant of lower estuarine salinities (i.e. <15 g L -1 ) and deeper water than adults (Ludbrook 1984;Semeniuk & Wurm 2000). The presence of juvenile S.(N.) trigonella for the period c.7 750-7 450 years BP therefore suggests estuarine episodes in the centre of Lake Alexandrina; a peak in estuarine/marine diatoms at ~7 500 BP in Ax1 core indicates that these episodes may have extended into the northern part of the Lake periodically over that 300-year period ( Fig. 2.4.2). ...
... The presence of juvenile S.(N.) trigonella for the period c.7 750-7 450 years BP therefore suggests estuarine episodes in the centre of Lake Alexandrina; a peak in estuarine/marine diatoms at ~7 500 BP in Ax1 core indicates that these episodes may have extended into the northern part of the Lake periodically over that 300-year period ( Fig. 2.4.2). The lack of adult populations indicates only sporadic spikes in salinity, rather than persistently estuarine conditions, given that the species requires several years of optimal conditions (salinity >15 g L -1 ) to achieve maturity (Semeniuk & Wurm 2000). ...
... These bivalves are typical of low-energy coastal and lagoon environments along the southern Australian coast and are particularly well adapted to less dynamic areas in estuaries (Kanandjembo et al. 2001;Jespersen & Lützen 2009). This period is marked by increased abundances of estuarine/marine epiphytic diatoms, indicating that conditions at the site were most likely characterised by clear water with abundant coverage of aquatic plants, in keeping with the preferred habitat for these fauna of vegetated, sandy muds (Semeniuk & Wurm 2000). Diatom sampling during 2007, at the height of the Millennium Drought when connection with the marine environment was only possible through continued dredging at the Murray Mouth, failed to detect Paralia species at most sites in the Coorong in any but minor abundances ). ...
... 9, showed population structures typical of juvenile recruitment-based population maintenance (cf. Semeniuk & Wurm, 2000). For most of a year, the histograms are unimodal. ...
... Migration is ruled out as a source of recruits because the extensive tidal flat areas surrounding the soldier crab habitat in King Bay are free of soldier crabs (Semeniuk et al., 1982;Unno & Semeniuk, 2009). To some degree, the population structure of M. occidentalis largely follows traditionally established patterns for many invertebrate fauna elements, i.e., juvenile recruitment followed by incremental growth of individuals leading to the mode of the histograms generally shifting towards the larger size during the year, with a bimodal pattern emerging with the next period of juvenile recruitment (Potter & de Lestang, 2000;Semeniuk & Wurm, 2000). However, in detail, there are departures from traditional patterns in that there are multiple juvenile recruitment events within the year. ...
The previously undescribed population dynamics of the Western Australian soldier crab, Mictyris occidentalis Unno, 2008, in King Bay, north-western Australia are elucidated, with annual observations and sampling over a 30-year period from 1980 to 2010. This is the longest recorded study of a single inter-tidal brachyuran population and shows long-term persistence of soldier crab populations in stable, sheltered habitats. The life cycle of M. occidentalis follows a cryptic subsurface juvenile and immature adult (= adolescent) phase and an emergent adult phase. Population densities were generally 500 crabs/m2 for the early 1980s, late 1980s, and during the early 2000s. Maximum population densities were high in the mid 1980s (800 crabs/m2). The spatial and temporal variability in the distribution of the population was consistent over the study period. Juvenile recruitment extends for up to 7 months of a given year between May and November with the main influx of juveniles usually in June and occasional minor influxes in August or October. Juvenile recruitment is followed by incremental growth of individuals at a rate of 1 mm/month reaching sexual maturity in the first year at 6.0-6.9 mm carapace length (CL). Adult males are larger than females with a maximum size of 15.0 mm CL compared to 12.0 mm CL, respectively. Ovigerous females are low in numbers throughout most of the year but reach a peak in February. During swarming, M. occidentalis populations partition not only by size class, with surface crabs being adults only and subsurface crabs mainly adult females and juveniles, but also by sex in that swarms are male-dominated in varying ratios.
... It is well known, for instance, within a given biogeographic region and climate region, for marine environments, for example, that there are distinct benthic biotic assemblages in sandy environments, as compared to muddy sand, or mud environments ( Figure 6). Such assemblages are related to substrate types, salinity, and water depth (see Dampier Archipelago; Gulf of California, Gulf of Mexico, Leschenault Inlet estuary; Shark Bay; the Wadden Sea; the Woods Hole region; Semeniuk et al. 1982;Jones 2004;Parker 1960Parker , 1964Dürr & Semeniuk 2000; T A Semeniuk 2000; Semeniuk & Wurm 2000;Logan et al. 1970Logan et al. , 1974Wolff 1983;Parker 1975). Similar patterns of assemblageto-habitat relationships exist on tidal flats (sand, muddy or sand-to-mud graded tidal flats), often with biota exhibiting zonation in relationship to environmental gradients (cf. ...
... This diagram does not address depth occurrence, or (wave and tidal) energy effects on species occurrence. Information on molluscan fauna adapted from Abbott & Dance 2000; Beesley et al. 1998;Semeniuk & Wurm 2000;Wells 1984;Wells & Bryce 2000;Wilson 1993Wilson , 1993bWilson & Gillett 1974). showing key species within contrasting but adjoining sediment types, viz., sand versus mud, and the complexity of species composition within habitats. ...
Biological evolution can be reconstructed from a number of pathways, including analysis of synoptic species variation, developmental biology (or embryology), palaeontology, and in more recent times use of microbiology and genetic science. The modern environment provides mechanisms and drivers that underpin biological evolution, viz., predation, inter-species competition, infra-species competition, changes in environment, changes in food sources, expansion of species population into neighbouring niches, amongst others. Using the modern environment as an example, there are innumerable and complex processes that result in complexity of stratigraphic sequences and biostratigraphic sequences. If properly addressed and categorised, and applied to the geological record, such information provides a reliable and robust interpretation of the fossil record, and while the synoptic approach for extant and fossil species is useful and has provided insights into speciation, the palaeontologic approach combined with stratigraphy, which is diachronous, holds to be the most useful because it involves tens to hundred of millions of years, and thousands of species. In this paper, the focus is on the use of palaeontology and the use of stratigraphy within which changes in species are recorded, but to begin with we describe some key background principles, processes and factors of geology, biology and evolution that underpin modern ecology, biological evolution, sedimentology and stratigraphy and the use of stratigraphy in evolutionary palaeontological studies; these include: uniformitarianism; gradations; mutations in organisms; biotic assemblages and ecology with respect to habitat; lateral habitat tolerance of organisms and its implications for evolution; skeletal contribution to sediments; the relatively poor record (contribution) of modern assemblages to the fossil record; ecological and population processes underpinning evolution as "drivers" and "determinants"; differential response of organisms to pressures and environmental changes; sedimentology, fades, and habitats; changes in fades laterally and vertically to develop stratigraphic sequences; changes in lithology macrostratigraphically, microstratigraphically, geochemically, or isotopically driven, for instance, by climate and tectonism; and geological processes and the incompleteness of the stratigraphic record. The different types of stratigraphic sequences are explored in their usefulness in interpreting the palaeontological record in terms of trends in biological evolution, and several of the best documented fossil sequences are noted and discussed. Stratigraphy is a powerful and important tool to set the geological stage for inferring evolutionary lineages, understanding evolutionary changes, and separating types of palaeontological sequences useful for interpreting lineages because it helps identify the framework in which the fossils occur, e.g., is a vertical sequence of fossils illustrating anatomical changes the result of stacking of facies and hence a stacking of the synoptic assemblages, or is it the result of diachronous changes?
... Recent research on Australian amphibolids has been limited to ecological studies, which have demonstrated their high abundance (Roach 1996;Roach & Lim 2000;Semeniuk & Wurm 2000). For example, Morgan & Hailstone (1986) recorded juvenile Salinator fragilis at very high densities (3000 per m 2 ) in a Queensland mangrove forest. ...
The taxonomy of the pulmonate superfamily Amphiboloidea is investigated with particular reference to Australasian taxa. Anatomical features of the alimentary, reproductive and central nervous systems differ substantially between taxa, and conchological, opercular and radular characters are also described. Four genera are recognised in Amphibolidae; Amphibola Schumacher, 1817, Salinator Hedley, 1900, Lactiforis gen. nov. and Naranjia gen. nov.. Two additional genera are assigned to new families; Phallomedusa gen. nov. (Phallomedusidae fam. nov.) and Maningrida gen. nov. (Maningrididae fam. nov.). Phallomedusidae fam. nov. is characterised by a paucispiral, keeled operculum and syntremous diaulic reproductive system with a complex, spiral penis. Maningrididae fam. nov. has an expanded operculum with a marginal nucleus and a syntremous diaulic reproductive system with two novel copulatory structures at the genital aperture. Taxonomic descriptions and a key are provided for eight Australian species; Salinator fragilis (Lamarck, 1822), Salinator tecta sp. nov., Salinator rhamphidia sp. nov., Salinator rosacea sp. nov., Lactiforis tropicalis sp. nov., Phallomedusa solida (Martens, 1878), Phallomedusa austrina sp. nov., and Maningrida arnhemensis sp. nov. and three non-Australian taxa; Amphibola crenata (Martyn, 1786), Lactiforis takii (Kuroda, 1928) and Naranjia cf. swatowensis (Yen, 1939).
... This study of the habitat features of Leschenault Inlet is part of a larger study that also described and monitored benthic fauna at sites used for habitat measurement and monitoring. These data are presented by Semeniuk & Wurm (2000) and Wurm (1987). ...
The Leschenault Inlet estuary has a distinctive pattern of bathymetry, water salinity and sediment types. The estuary is a flat, elongate central basin, flanked to east and west by shallow, shore-parallel platforms. The central basin grades into a shallow-water flat in the north, and adjoins deltas in the south. The estuary is underlain by mud in the central basin and northern flat, sand and muddy-sand on the eastern platform, mud, muddy-sand, sandy-mud and sand on the western platform, and predominantly sand under the deltas. The estuarine waters undergo seasonal changes in salinity as a result of restricted oceanic exchange, freshwater inflow during winter and evaporation in summer. Various salinity fields were identified in this study, based on the mean and range of salinity values occurring within the annual hydrological cycle. Hypersaline to mesosaline waters occur to the north, and increasingly more hyposaline to mesosaline waters occur to the south. Each of the large-scale geomorphic units in the estuary can further be subdivided on the basis of water salinity, bathymetry, substrate and presence of macrophytes. Based on these physical features, nineteen small-scale habitats units were proposed for Leschenault Inlet. These smaller scale habitat units provide a framework within which to study the distribution and ecology of benthic fauna.
Arthritica korniushini n. sp. is described from three groups of artesian mound springs in the southwestern part of the Lake Eyre Spring Supergroup. All other described species of Arthritica are oceanic or estuarine. The four previously described Australian species referrable to Arthritica are reviewed.
