Shell Assemblages Research Articles

Freshwater Mussel (Unio pictorum) Shells Reveal Hydrological and Environmental Change From 1300 BC to the Present Day.

Preserved biological communities can provide baseline data about the historical ecosystems and environmental conditions that preceded recent anthropogenic alteration. Freshwater mussel shells show particularly good preservation, and the shell assemblages commonly found during archaeological excavations can offer insights into past ecosystems. We studied assemblages of Unio pictorum mussel shells from palaeochannel silts associated with the Late Bronze Age site of Must Farm in eastern England (c. 850 BC), on an ancient tributary of the modern-day River Nene. We compared archaeological shells from two sediment horizons (broadly 1300-700 BC) to live individuals collected from two analogous sites on the present-day Nene. Size and growth rate, interannual growth variability and stable isotope (δ18O and δ13C) composition were compared between the populations. Size and the von Bertalanffy growth parameter L∞ differed among all four populations. Mean lengths and L∞ were higher in the two modern populations (mean lengths 77.3 ± SE 0.8 and 73.8 ± SE 1.1 mm, L∞ 91.8 ± 5.4 and 79.0 ± 8.1 mm) than the ancient populations (mean lengths 58.1 ± SE 1.6 mm and 68.4 ± SE 0.9 mm; L∞ 71.5 ± 16.9 and 76.8 ± 6.2 mm). Modern individuals also showed greater variation in age-corrected year-to-year growth. δ13C was lower in modern shells (-11.8‰ for modern shells, -9.03‰ and -9.02‰ for ancient shell populations), potentially reflecting altered hydrological and nutrient regimes. δ18O and δ13C were positively correlated for all but one sampled ancient shell, but not modern shells. These results reflect changes in local environmental conditions, particularly the transition from a shallow, slow-flowing tributary to a deeper, canalised river with faster flow, as well as effects of anthropogenic nutrient enrichment. The findings demonstrate the importance of long-term data in studying anthropogenic ecosystem alteration and avoiding shifting baseline syndrome in conservation planning.

Living in the shore: changes in coastal resource intensification during the Mesolithic in northern Iberia

Recent research on human exploitation of molluscs, echinoderms and crustaceans during the Mesolithic in the Cantabrian region (northern Iberia) has shown significant variability in the intensity of the use of coastal resources by the last hunter-fisher-gatherers throughout the ~ 4000-year expanse of the Mesolithic (10,700 – 6,700 cal BP). Previous studies have proposed hypotheses related to demographic changes to explain intensification events. In this paper we aim to unravel whether climatic and environmental changes, or other social factors, such as demography, were involved in the increase in the use of marine resources at certain times. We employed species representation, quantification and biometric analysis of the shell assemblages from the El Toral III archaeological site (Asturias, northern Iberia) to identify patterns in shell exploitation throughout the stratigraphic sequence. To establish the chronology and distinguish occupation phases of the site, we employed Bayesian modelling of radiocarbon measurements. Faunal results show that marine gastropods such as limpets of the Patella genus and topshells Phorcus lineatus (da Costa, 1778) were the most exploited species, while bivalves, echinoids and crustaceans were present in smaller quantities. The comparison of the results for El Toral III with other Mesolithic sites in the region reveals significant temporal differences in the intensity of collection of marine shell species. Results showed that intensification processes are not clearly related to climate change but to other social factors, such as demography, suggesting that intensification and relaxation in shell collection events were strategies adopted depending on the needs of the human groups at different times.

ONSHORE-OFFSHORE TRENDS IN THE TEMPORAL RESOLUTION OF MOLLUSCAN DEATH ASSEMBLAGES: HOW AGE-FREQUENCY DISTRIBUTIONS REVEAL QUATERNARY SEA-LEVEL HISTORY

Abstract Surficial shell accumulations from shallow marine settings are typically averaged over centennial-to-millennial time scales and dominated by specimens that died in the most recent centuries, resulting in strongly right-skewed age-frequency distributions (AFDs). However, AFDs from modern offshore settings (outer shelf and uppermost continental slope) still need to be explored. Using individually dated shells (14C-calibrated amino acid racemization), we compared AFDs along an onshore-offshore gradient across the southern Brazilian shelf, with sites ranging from the inner shelf, shallow-water (< 40 m) to offshore, deep-water (> 100 m) settings. The duration of time averaging is slightly higher in deeper water environments, and the AFD shapes change along the depositional profile. The inner shelf AFDs are strongly right-skewed due to the dominance of shells from the most recent millennia (median age range: 0–3 ka). In contrast, on the outer shelf and the uppermost continental slope, AFDs are symmetrical to left-skewed and dominated by specimens that died following the Last Glacial Maximum (median age range: 15–18 ka). The onshore-offshore changes in the observed properties of AFDs—increased median age and decreased skewness, but only slightly increased temporal mixing—likely reflect changes in sea level and concurrent water depth-related changes in biological productivity. These results suggest that on a passive continental margin subject to post-glacial sea-level changes, the magnitude of time-averaging of shell assemblages is less variable along the depositional profile than shell assemblage ages and the shapes of AFDs.

Crushed turtle shells: Proxies for lithification and burial-depth histories

Abstract We propose a new proxy that employs assemblages of fossil turtle shells to estimate the timing and depth at which fossilization and lithification occur in shallowly buried terrestrial strata. This proxy, the Turtle Compaction Index (TCI), leverages the mechanical failure properties of extant turtle shells and the material properties of sediments that encase fossil turtle shells to estimate the burial depths over which turtle shells become compacted. Because turtle shells are one of the most abundant macroscopic terrestrial fossils in late Mesozoic and younger strata, the compactional attributes of a suite of turtle shells can be paired with geochronologic and stratigraphic data to constrain burial histories of continental settings—a knowledge gap unfilled by traditional burial-depth proxies, most of which are more sensitive to deeper burial depths. Pilot TCI studies of suites of shallowly buried turtle shells from the Denver and Williston basins suggest that such assemblages are sensitive indicators of the depths (~10–500 m) at which fossils and their encasing sediment become sufficiently lithified to inhibit further shell compaction, which is when taphonomic processes correspondingly wane. This work also confirms previously hypothesized shallow Cenozoic burial histories for each of these basins. TCI from mudstone-encased turtle shells can be paired with thicknesses and ages of overlying strata to create geohistorical burial curves that indicate when such post-burial processes were active.

Documenting the Evolution of a Southern California Coastal Lagoon during the Late Holocene

Coastal wetlands are declining globally, and although wetland restoration looks to offset these losses, its success relies on anticipating environmental response to external forces. The purpose of this study is to investigate the sedimentological record of Los Peñasquitos Lagoon to determine the processes that drive environmental transitions in a Southern California coastal wetland. For this project, we analyze three sediment cores from the wetland for grain size, total organic matter, and shell assemblages to reconstruct environmental change over the past ~4000 years. From the results, we find that the lagoon was initially an open embayment that persisted for >2000 years; however, at ~1000 cal yrs BP, a short-lived wet climatic period triggered a fluvial deltaic progradation at the head of the lagoon. As the wet period ended and drier conditions returned, the delta began to retreat, and the lagoon infilled as the estuarine mouth bar was permanently established. The permanent establishment of the mouth bar resulted in a transition to a marsh-dominated environment throughout the wetland. Ultimately, these environmental transitions were driven by climate variability, although evidence of human impacts was observed more recently in the record. Therefore, future restoration efforts must consider both natural climatic variability and anthropogenic influences if they intend to sustain coastal wetlands.

Mont Saint-Aubin in Oisy (Nièvre, France): a Badegoulian manufacturing site for shell ornaments

Abstract. The Badegoulian open air site of mont Saint-Aubin at Oisy (Nièvre) yielded 353 marine mollusc shell remains (gastropods, scaphopods and bivalves) which testify of on-site shell bead manufacturing activities. The large conchyliological spectrum (31 taxons) includes many fossils from the Parisian Basin and a few shells that must have been collected on the Atlantic coast, indicating a distance of several hundreds of kilometres between the shell sources and the production site. The shell assemblage is composed of unmodified raw material, waste products and finished beads with intense use wear traces and sometimes repaired suspension holes. The identified manufacturing processes (morphometrical choices, perforation and segmentation methods, and systems of attaching the beads) reveal that the finished ornamental displays must have been varied, playing with different bead morphologies and -sizes as well as with different ways of attaching the beads (string, braiding). Providing information on the ways and means of marine shell exploitation for beadwork (territories of procurement and circulation of shells, storage, craftsmanship, recycling) this study offers new insights on Badegoulian techno-economic behaviour.

RURAL SOCIAL DIFFERENTIATION IN EARLY CLASSIC CHUNHUAYUM, YUCATAN, MEXICO

AbstractThis article examines rural social differentiation in Chunhuayum, Yucatan, a rural village continuously occupied from approximately 800 b.c.–a.d. 1000. Focusing on the late Early Classic (a.d. 400/500–600/630), a time when other settlements of the Uci polity experienced political and population disruptions, I examine how households shaped and expressed local social differentiation, particularly wealth, occupation, and social connectivity. Residential architecture provides the most salient marker of wealth differences at Chunhuayum, while ceramic, shell, and obsidian assemblages indicate that households also varied in terms of their occupations and external social networks. Within this predominantly agrarian village, two households attempted to improve their economic and immaterial well-being through locally innovative strategies—shell crafting and group-oriented ritual orchestration. Such strategies ultimately had different outcomes both for the household and community. These points underscore the heterogeneity of the rural ancient rural Maya, and that social differentiation was actively constructed by rural people rather than a trickling-down of the normative hierarchical social order. Through habituated practice and innovative action, Chunhuayum's Early Classic residents continued participating in external networks while shaping locally meaningful relations of differences.

Taxonomy, palaeoecology and palaeobiogeography of upper Cenomanian (Upper Cretaceous) oysters and plicatulids from southern Algeria

ABSTRACT Palaeontological investigation of four lithostratigraphic sections documenting the upper Cenomanian shallow marine carbonates of three palaeogeographic domains of southern Algeria (western Saharan Atlas, Guir Basin and Tinrhert Hamada) has produced a comprehensive collection of large bivalve assemblages for taxonomic purposes. A first inventory list of late Cenomanian oysters and plicatulids from southern Algeria is now available and consists of 15 taxa as follows: Lopha syphax, Ostreidae gen. et sp. indet., Curvostrea rouvillei, Flemingostreidae gen. et sp. indet., Costagyra olisiponensis, Amphidonta obliquata, Ceratostreon flabellatum, Ilymatogyra africana, Rhynchostreon suborbiculatum, Gyrostrea delettrei, Gyrostrea sp. indet., Pycnodonte (Phygraea) vesicularis vesiculosa, Plicatula (Plicatula.) auressensis, Plicatula (Plicatula) batnensis, and Chondrodonta? sp. indet. These taxa build five distinctive oyster-facies patterns, all purportedly recognisable in the field for stratigraphic assignment and regional correlation. Scarce sclerobiontic assemblage (borings: Entobia, Gastrochaenolites and Oichnus; and epibionts: juvenile oysters, serpulid tubes and Berenicean-type bryozoa) observed within these oyster shell assemblages is also identified, briefly described and adressed. This first taxonomic analysis highlights three main palaeogeographic components within these oyster- and plicatuloid-assemblages: endemic Mediterranean, Tethyan-Atlantic and cosmopolitan taxa. Moreover, the present study on these late Cenomanian oyster assemblages provides a first inventory list and stratigraphical baseline data towards further datation and correlation at the regional scale.

Marine Shell Working at Harlaa, Ethiopia, and the Implications for Red Sea Trade

Abstract Twelve species of marine shell were transported in significant quantities from the Red Sea to the trade centre of Harlaa in eastern Ethiopia between the eleventh and early fifteenth centuries AD. Initially, it was thought that species such as the cowries were imported from the Indian Ocean. Subsequent research has found that all were available from the Red Sea and the Gulf of Aden, c. 120 km east of Harlaa. This suggests that a hitherto largely unrecognised source of marine shells was available, and the Red Sea might have supplied not only the Horn of Africa, but other markets, potentially including Egypt, and from there, elsewhere in North Africa and ultimately West Africa via trans-Saharan routes, as well as Nubia and further south on the Nile in the Sudan, the Arabian Peninsula, and the Arabian/Persian Gulf. This is explored with reference to the shell assemblage from Harlaa, and selected shell assemblages from elsewhere in the Horn of Africa, and trading centres on the Red Sea.

Substrate temperature as a primary control on meiofaunal populations in the intertidal zone: A dead zone attributed to elevated summer temperatures in eastern Bahrain

Summer temperatures in excess of 52°C, have been measured at the high tide mark in surficial substrates in the exposed areas of an intertidal mudflat in Bahrain. The incoming flood tide may have a temperature as high as 42°C. As a result, large swaths of the upper intertidal zone are barren of living meiofauna (e.g., foraminifera, ostracods, gastropods, and worms) during the hottest months of the year. Samples collected from the intertidal zone in August present only dead assemblages of foraminifera, ostracods, and gastropod shells. Dead assemblages of the foraminifer Peneroplis collected from the upper reaches of the intertidal zone consist largely of juvenile specimens, implying that the living populations, when present, do not reach maturity. The full range of living meiofaunal organisms is only observed in tidal channels that remain submerged during low tide. The presence of a summer dead zone for intertidal meiofaunal organisms is consistent with predictions of climate models that suggest portions of the Arabian Gulf may become too extreme to support eukaryotic life.

Miocene shells in Late Neolithic and Early Bronze Age burials in Poland

AbstractThe present study provides an archaeological interpretation of shell assemblages from Neolithic and Early Bronze Age burials found in Poland based on the identification of fossil shell type and provenience. The taxonomic identification of shells directly points to their source of procurement, which facilitates the understanding of why only some societies used shell ornaments and why only certain species were selected for use in this way. Focusing on artefacts, we present the results of standard methods of analysis used in archaeomalacological research. Strontium isotope analysis 87Sr/86Sr was furthermore applied in the cases for which the exact recognition of species was impossible based on standard methods. The research shows that for the periods discussed, one can observe both the phenomena of the transfer of prestigious objects (Quaternary shells obtained from the Mediterranean) and the transmission of ideas with subsequent local adaptation (the use of local Miocene fossil shells similarly to Quaternary Mediterranean shells). The shells constitute a part of the Neolithic tradition of body ornamentation seen during this period across Europe. The study indicates that fossil shells were only used by some of the communities inhabiting the area of southern Poland in the Neolithic and Early Bronze Age and suggests chronological and regional differentiation.

Contributions of temporal and spatial variation to the diversity of soil-dwelling testate amoeba assemblages in a swampy forest

Understanding the spatial and temporal variation in protist communities is essential for comprehensive studies on diversity and biogeography, yet most research focuses on either spatial or temporal processes, ignoring their combined effects. Here we use an additive partitioning approach to estimate the contribution of temporal and spatial components to the total taxonomical (morphospecies) diversity of testate amoebae in a swampy forest (the forest-steppe zone, Russia) during a snow-free season (from April to November). Testate amoebae have been chosen as model organisms for the study because they are a diverse and abundant group of protists that play important roles in soil communities mostly as consumers in decomposer food webs. Our results indicate that seasonality considerably contributed to the variation in the total species richness (γ) of both live and empty shell assemblages of testate amoebae (48 and 38 %, respectively). The beta component of species richness related to the spatial variation among sampling plots explained 22 % of γ-diversity in live assemblages and 28 % in empty shell assemblages. Beta diversity (both as species richness and species composition) decreased towards the end of the snow-free season. Spring assemblages were dominated by hydrophilous species of testate amoebae, whereas xerophilic species were more abundant in autumn. Our results imply that the snowmelt phase could be an important factor setting the heterogeneity of testate amoeba assemblages in the early spring, whereas in the rest of snow-free season the assemblages were considerably controlled by substrate moisture. Overall, temporal sampling is essential for adequate estimates of species diversity of soil-dwelling testate amoebae.

CUENTAS Y TEMBETÁS MALACOLÓGICOS DE LOS GRUPOS CAZADORES-RECOLECTORES PREHISPÁNICOS DEL HUMEDAL DEL PARANÁ INFERIOR

Entre los grupos cazadores-recolectores que ocuparon el humedal del río Paraná inferior durante el Holoceno tardío, el conjunto más numeroso de adornos es el de las cuentas y tembetás hechos sobre valvas de moluscos. En trabajos previos observamos que estos elementos presentan similitudes morfológicas a nivel intersitio, con pequeñas variaciones formales. En este trabajo evaluamos la posibilidad de que estos elementos hayan funcionado como demarcadores sociales. En este sentido esperamos un patrón homogéneo tanto en la forma general y sus atributos, como en el tamaño. Para ello analizamos métrica y morfológicamente los conjuntos malacológicos provenientes de diez sitios arqueológicos del área. Los resultados muestran tendencias diferentes para las cuentas y los tembetás. Las primeras se distribuyen de manera homogénea en el espacio con un patrón morfológico y métrico compartido que sólo excluye uno de los sitios arqueológicos. Los tembetás, por su parte, son menos frecuentes y presentan dos variantes morfométricas que pueden responder a variaciones individuales o reflejar parcialidades étnicas.

Invasive mollusc faunas of the River Thames exemplify biostratigraphical characterization of the Anthropocene

Profound changes to the species configuration of ecosystems globally during the 19th to 21st centuries, resulting from the introduction of neobiota, have produced a distinctive palaeontological signature in sedimentary deposits, here exemplified by those of the River Thames. Coring near Teddington Lock (ca. 4.3 m above sea level, ca. 89 km upstream from the mouth of the Thames estuary) yielded dense assemblages of shells of the invasive Asian clam Corbicula fluminea (recently invaded in 2004) and the zebra mussel Dreissena polymorpha (invaded 1824), which together accounted for 96% of individuals sampled. Population densities of C. fluminea of over 6000 individuals per m2 were maintained for a depth of 1 m indicating that the Asian clam is an important biostratigraphical marker in the Thames for sedimentary deposits accumulating since 2004. The first modern European occurrence of C. fluminea was in Portugal in 1980. In 1987, the first occurrence of C. fluminea on the northern coast of South America was observed in the Caripe River, Venezuela. The non-native range of D. polymorpha was restricted to continental Europe for over 200 years until it appeared in the Great Lakes, USA, in 1986 having been transported in ballast water. Within three years, it reached populations of over 750,000 individuals per m2 and it is presently recorded in 35 states. Therefore, the pan-Atlantic range expansion of D. polymorpha, coupled with the recent invasion history of C. fluminea in Venezuela and Portugal, identifies a biostratigraphical interval in sedimentary deposits forming from the early 1980s that can be correlated between Europe and the Americas.

Palaeoecological Analysis of Benthic Molluscs from the Eocene of Kutch, Gujarat Reveals an Event of Storm Induced Concentration of Shells in a Quiet Marginal Marine Environment

The Eocene deposits of the Kutch basin are characterized by predominance of plane-laminated shales and low diversity mollusc faunas. These features reflect a low energy, restricted environment. A thin molluscan shell bed stands out in this backdrop because it produced a very diverse assemblage of bivalves and gastropods. Palaeosynecological analysis of the benthic mollusc assemblages from different stratigraphic levels of the Eocene of Kutch, including the shell bed, was carried out by testing for standard ecological models of rank-abundance. The specific abundance data from the shell bed c onform to the log-normal model indicating stable, resource-rich environment. On the other hand, low diversity and often high abundance of opportunist species from other levels reflect harsh ecological conditions for molluscs. Analyses of habitat preferences and habits of the genera from the shell bed indicate shallow to very shallow shelf environment. It is inferred that this exotic assemblage of shells was brought in this quiet, restricted environment by storm surges from open part of the sea. High degree of shell fragmentation and high content of micrite matrix corroborate this interpretation.

UNVEILING THE CONSEQUENCES OF ENVIRONMENTAL VARIATION AND SPECIES ABUNDANCES ON BEACH TAPHOFACIES IN BAHAMAS: THE ROLE OF CEMENTATION AND EXHUMATION

Although environmental variability generates differences in the preservation of shell assemblages, intrinsic variations in shell characteristics can confound the effects of environment on preservation. However, several studies proposed that the composition of shell supply only affects the intensity of alteration but not its preservation trend along the environmental gradient and that environmental variability represents a major driver of taphofacies preservation. Here, we examine whether taphonomic differences among four infaunal and aragonitic bivalve species differing in shell thickness affect the definition of beach taphofacies in tropical carbonate environments on San Salvador Island (Bahamas). We show that (1) taphofacies can be discriminated with respect to (a) wave and storm activity as a function of exposure to Trade Winds, and (b) sandy beaches versus beaches with a mixture of sands and beach rock (representing a source of exhumed and cemented shells), and (2) species-specific bivalve assemblages show similar gradients in preservation, documenting that differences in preservation between species have minor effects on taphonomic discrimination of beach environments. Environments with a mixture of sands and beach rock are characterized by higher frequency of external cementation and abrasion than sandy beaches. Shells from low-energy beaches are more fragmented and discolored than shells from high-energy beaches. Previous studies showed that shells from San Salvador sandy beaches are more time-averaged than shells from rocky beaches. Differences in preservation between these two environments indicate two pathways: (1) assemblages on sandy beaches are degraded at higher rate but are enriched by old exhumed and lithified shells, and (2) assemblages on rocky beaches are cemented at higher rate. Old and lithified shells on sandy beaches are probably derived from submerged or exposed beach rock patches, leading to the mixture of young, well-preserved shells with old, poorly preserved shells. Shells on sandy beaches thus experience a complex history of burial and exhumation before their final deposition. Therefore, shell assemblages in lower energy carbonate environments from San Salvador Island are highly time-averaged, with the presence of old, poorly preserved shells. The depositional environment is thus the dominant factor controlling the structure of San Salvador beach taphofacies.

Fishing together, fishing on its own: Fish exploitation patterns at the Neolithic Alepotrypa cave (Diros, Greece) and Aegean prehistoric fishing traditions

AbstractVarious marine animal assemblages from prehistoric contexts across the Mediterranean suggest a focus on the exploitation of marine resources by coastal populations as early as the Mesolithic. Along with the harvesting of nearshore coastal resources (fish and invertebrates), a more organised fishing activity that targeted pelagic species, traditionally considered migratory, is evident in several Mesolithic assemblages. With the advent of the Neolithic, marine‐related subsistence activities seem to be gradually restricted to the exploitation of coastal year‐round resources. The cave of Alepotrypa in the Peloponnese, Greece, provides an opportunity to ascertain the exploitation practices of a coastal Late/Final Neolithic community in which a combination of fishing strategies and a diversified connection to the sea were apparent. The abundant shell assemblage demonstrates the importance of molluscs for consumption, as well as the various uses of their shell. This paper focuses on the fish remains from the cave. Fish assemblages from this period are rather sparse in the Aegean. The study of the fish assemblage highlights the exploitation of pelagic fish species as well as the harvesting of a wide range of coastal fish species. A shift from pelagic to coastal resources and an intensification of fishing are also observed from the Late to Final Neolithic. These trends are discussed in the perspective of social organisation and technological adaptations, with an emphasis on the engagement of Neolithic fishermen in communal and individual fishing strategies and the seasonally important role of these activities. The choice of specific exploitation strategies and the diachronic trends observed suggest that earlier Mediterranean fishing traditions persisted until the end of the Neolithic.

Aboriginal marine subsistence foraging flexibility in a dynamic estuarine environment: The late development of Tin Can Inlet (southeast Queensland) middens revisited

Although the sea arrived in southeast Queensland around 8000 years ago, most estuarine middens date to the past 1000 years. An example is midden deposits dating to the past 400 years forming the upper levels of Sites 62 and 75b from Tin Can Inlet located immediately south of the Fraser Island (K’gari) World Heritage Area. Both sites were excavated and analysed in the 1980s. This paper revisits these results following a detailed re-analysis of midden materials and new insights on regional sea level changes. Taking an historical ecology approach, species-specific habitat requirements and associated substrate sediment dynamics help explain similarities and differences between the two midden shell assemblages. Environmental factors and the location of both sites on landforms that formed following sea level fall over the past 2000 years help explain why the basal levels of both sites are probably <1000–1500 years old. Documenting pre-2000-year-old Aboriginal use of Tin Can Inlet will need to target more elevated inland dune deposits (>5m ASL) fronting the mid-Holocene sea level highstand palaeoshoreline.

Mollusk shell assemblages as archives of spatial structuring of benthic communities around subtropical islands

Surficial assemblages of mollusk shells provide minimally invasive, quantitative data that are potentially adequate for assessing spatial organization of local benthic ecosystems. This study evaluates distribution and ecological characteristics of mollusk-dominated benthic communities around San Salvador Island (Bahamas). A total of 60 bulk samples collected along 12 onshore-offshore transects around the island yielded 20,301 specimens representing 180 mollusk species. Radiocarbon dating of individual shells (n = 30) indicated that these surficial accumulations represented a multi-millennial (time-averaged) record of local communities. Indirect multivariate ordinations (NMDS) separated mollusk death assemblage samples by locality, local habitat types, and regional context. Even in the case of comparable habitats within the same bay, samples clustered by transect location suggesting that surficial shell accumulations faithfully archive local differences in mollusk communities despite time-averaging and post-mortem shell transport. At the regional scale, a clear faunal separation is observed between windward and leeward sides of the island, suggesting that water energy represents an overriding regional driver that controls local composition of mollusk assemblages. Within each water energy regime, the faunal composition appeared to be primarily controlled by habitat type (seagrass versus sand habitats). Moreover, consistent with theoretical predictions that structured habitats enhance faunal stability of local communities, death assemblages from seagrass habitats were less variable in faunal composition than open sand habitats. Results indicate that San Salvador Island benthic communities are characterized by a predictable spatial organization controlled primarily by regional physical and, secondarily, biological processes. Also, the fact that extensively time-averaged shell assemblages have retained an interpretable spatial pattern suggests that regional physical processes, local habitat distribution, and structuring of mollusk associations must have been stable over multi-centennial time scales. This case study suggests that non-invasive sampling of dead mollusks can be an effective strategy for assessing prevalent long-term patterns in spatial distribution of regional faunal associations and examining processes that drive spatial structuring of marine communities.

Prehistoric Shellfish Utilization and Settlement Systems on Western Santa Cruz Island

Archaeologists generally have not taken advantage of the distinctive characteristics of assemblages of shellfish remains from prehistoric sites to gain information about movement of people between sites within their territory. I attempt to demonstrate this potential through analysis of shell assemblages obtained through small-scale test excavation at 2 archaeological sites in the interior of Santa Cruz Island: CA-SCRI-796 in the western sector of the island and CA-SCRI-758 at an upland location in the central sector. An aspect of the data analysis focused on strata containing an abundance of red abalone shells, dating sometime between 3700 and 3350 cal BC at CA-SCRI-796 and sometime between 4900 and 4325 cal BC at CA-SCRI-758. Also considered are assemblages from later strata at CA-SCRI-758, dating between 2600 and 1600 cal BC. Alternative hypotheses to account for the differences between the sites in proportions of shellfish taxa represented are the following: differences in proportional abundances of taxa at the localities where site inhabitants collected shellfish, changes over time in the character of shellfish communities, different distances of the sites from sources of shellfish, and variation in the intensity of shellfish collecting. The first alternative appears to account for most of the differences between assemblages, thus providing information about the geographic extent of settlement systems.