Shell Accumulations Research Articles

Effects of climate change and extreme weather events on natural and archaeological landscapes in southwestern Puerto Rico

Recent archaeological fieldwork in the intertidal zone of southwestern Puerto Rico has revealed a unique landscape of ancient shell mounds (accumulations of marine shells deposited by prehistoric peoples). These mounds are, at present, protected from tidal inundation, storm surge, and storm-driven winds by a buffering arc of mangroves known as the Pitahaya Mangrove Forest (PMF). Concerns about the long-term health of these mangroves, and their continuing ability to shelter the shell mounds, motivated the current diachronic remote sensing study examining the effects of both long-term climatic factors (sea level rise, global climate change) and extreme weather events (droughts, hurricanes) on the recent and future health of the PMF. Ultimately, the analysis of NDVI change derived from multispectral satellite imagery, coupled with local climate and weather data and drone-based ground-truthing, revealed troubling trends in the health of the PMF that portend a rather grim future for both the mangroves and the unique ancient landscape they protect.

Shell-bearing Bivalvia and Gastropoda from a rocky shore in the Central Caribbean of Colombia

This study documents the natural accumulation of mollusk shells on an elevated rocky shore carved into the calcareous rocks of the La Popa formation at Punta Roca (Atlántico), covering an estimated area of 0.35 km2. Hydrodynamic transport and differential exposure to environmental conditions are the primary factors contributing to shell deposition. A total of 58 mollusk species were identified, including 30 bivalves and 28 gastropods. The Veneridae was the most prominent, with the highest number of species (7) and shells comprising 64.22 % of the total. Key species contributing to the accumulation include the bivalves Anomalocardia cf. flexuosa, Polymesoda cf. arctata, Leukoma pectorina, Tivela mactroides, Crassostrea rhizophorae, and the gastropod Vitta virginea. These species are primarily characteristic of estuarine environments, with the exception of T. mactroides. Notably, the first recorded occurrence of the non-native gastropod Naria turdus (Cypraeidae) on the Colombian Caribbean coast was documented. The accumulations exhibit varying degrees of abrasion, fragmentation, encrustation, and bioerosion, with some shells appearing almost intact, indicating differences in origin and transport mechanisms. The extraction of shells for ornamental purposes poses a significant challenge to this natural accumulation.

Carbonate microfacies reveal how Asturian shell middens formed in the Mesolithic

The littoral platform of eastern Asturias (northern Spain) is a coastal karst modeled by the sea. During the Early Holocene, this landscape was exploited by successfully coastal-adapted hunter-gatherers. Intense coastal foraging resulted in accumulation of large amounts of shellfish in numerous karstic rockshelters. A century ago, the Count of Vega del Sella established the post-Paleolithic age of the Asturian shell middens, carbonate-cemented deposits hanging from the walls of karstic cavities. He argued that these were remnants from past shell accumulations filling up completely the rockshelters, as result of direct waste disposal, while the occupations occurred outside. Our geoarchaeological approach tested this long-lasting site-formation model with micromorphology and carbonate microfacies analysis of two sites: El Alloru and El Mazo. Novel outcomes are: 1) the carbonate cements correspond to calcareous tufa resulting from spring activity; 2) the deposits show a stratigraphic framework related to successive phases of debris accumulations and stasis; 3) tufa formation and accumulation of anthropogenic debris are syn-depositional; 4) biogenic and diagenetic cements reveal phreatic conditions. All these contradict a priori expectations from Vega del Sella's widely accepted model of anthropogenic mound constructions preserved in the currently cemented deposits. Microcontextual evidence suggest that shells were likely processed and produced also inside the rockshelters, which might have been used as occupation spaces as well instead of just for waste disposal, while the analyses exterior deposits at El Alloru also present occupational signs. This study also supports further evidence for higher water-table levels in the early Holocene at regional level, despite most caves show no signs of spring activity today.

Mobility and the use of littoral resources in the Late Mesolithic of Northern Spain: the case of La Chora cave (Voto, Cantabria, N Spain)

Littoral resources have been consumed by humans since at least the Middle Palaeolithic. Examples of the use of molluscs have been documented along the shores of Europe during that period but it was not until many millennia later that European hunter-fisher-gatherer societies exploited those resources intensively—see the case of Nerja cave during the Younger Dryas. This economic activity caused the accumulation of shells at archaeological sites during the Mesolithic, resulting in the formation of the so-called shell middens, a very common type of deposit along the Atlantic seaboard of Europe. Despite the large number of research projects that have studied the exploitation of coastal environments and the way of life of Mesolithic populations, questions such as the relationship between human mobility and mollusc exploitation patterns still remain. The archaeomalacological study of the shell midden in La Chora cave (Cantabria, Spain) confirms that people foraged for shellfish at several places along the coast, mainly in the estuary of the River Asón. The main difference between La Chora and other Mesolithic sites is its longer shellfish collection radius as the inhabitants travelled over 10 km to the open coast to collect shellfish. This study has expanded the available data about the subsistence strategies of Mesolithic groups in a little-studied area and improved our knowledge of mobility patterns among Mesolithic societies in the northern Iberian Peninsula.

Impact of habitat engineering by invasive Corbicula clams on native European unionid mussels

Biological invasions cause biodiversity erosion on a global scale. Invasive species spreading beyond their natural range compete with native fauna for food and space, push native species to suboptimal habitats, impairing their behaviour and thus limiting their occurrence. Freshwater ecosystems are especially vulnerable to biological invasions and their ecological and economic impacts. The invasive Asian clams (Corbicula spp.), due to their opportunistic life style, can occur at densities of thousands ind. m−2. They act as ecosystem engineers transforming bottom substrata through accumulation of shells. Our goal was to determine the effect of substratum modification by living Corbicula and their shells on substratum choice and behaviour of Unio tumidus and Anodonta anatina, two European freshwater mussel species of the highly imperilled Unionidae family. We assessed their substratum selection in pairwise choice tests (pure sand vs. sand modified by living Corbicula or their shells, sand modified by shells vs. living Corbicula). Next, we tested locomotion and burrowing of unionids on pure substratum and substrata modified by Corbicula. Unionids avoided sand modified by living Corbicula and their empty shells, not distinguishing between these two types of substratum modification. In the presence of Corbicula, their burrowing was shallower or it took them longer to obtain the same depth as in the pure sand. Additionally, on sand modified by Corbicula shells, we observed a locomotion increase (U. tumidus) or slowing down (A. anatina). Our research showed a novel mechanism of negative impact of Corbicula on unionids, consisting in pushing them away from their optimal habitats. This may contribute to their habitat loss and future declines in invaded ecosystems.

Success and demise of exceptionally preserved terebratulide brachiopod accumulations in a Jurassic (early Pliensbachian) tropical lagoonal setting (Southern Alps, Italy): brachiopod response to environmental changes

During the Early Jurassic, the shallow marine carbonate platforms of the western-Tethys margins were characterized by highly diverse benthos including larger foraminifera, sponges, bivalves, gastropods, brachiopods, echinoderms, and dasycladalean calcareous algae. In this paper, we document examples of such assemblages within the lower Pliensbachian part of the Rotzo Formation (upper Orbitopsella Zone) of the Southern Alps, Italy. This carbonate succession was deposited in a complex mosaic of marine and brackish habitats within a tropical lagoon of the Trento Platform area. Large terebratulide brachiopod shells form autochthonous accumulations comprising exceptionally well-preserved monospecific assemblages of Lychnothyris rotzoana. These brachiopod-bearing successions were analysed in terms of biotic components, microfacies analysis, shell biofabric (three-dimensional arrangement of skeletal elements), and taphonomic signatures to understand brachiopod response to changing conditions within a highly variable lagoonal palaeoecosystem. Findings show that terebratulide shell accumulations are dominated by adult specimens and juveniles are rare. The brachiopods thrived during low energy conditions that resulted in the accumulation of highly temporally-condensed shell beds. Stabilized by microbialite encrustations, the shells were not re-oriented during the subsequent rapid burial. The abrupt demise of these communities was possibly related to rapid environmental change, and causal factors are discussed. The medium-term response of brachiopods to the relatively instable ecosystem of the tropical lagoon shows that they were not able to adapt to continuous perturbations, and that continuing stress severely compromised the resilience of benthic taxa.

Early Cretaceous bivalves of the Romualdo Formation, Araripe Basin, northeastern Brazil

The fossil-rich Romualdo Formation (late Aptian/early Albian), Araripe Basin, northeastern Brazil, contains world-renowned Fossillagerstätten characterized by exceptionally preserved fossils. Macroinvertebrates in this formation are primarily represented by mollusks, echinoids, and decapod crustaceans. Mollusk shells are abundant in certain stratigraphic intervals, forming coquinas or shell pavements. Despite recent advances in our understanding of the taxonomy of certain groups, comprehensive taxonomic studies are lacking for almost the entire bivalve fauna. Therefore, a detailed taxonomic analysis is presented here. The described bivalves include four new genera (Araripenomia, Ciceromya, Inversatella, Australoeocallista), and six new species (Araripenomia infirma, Inversatella cearensis, Ciceromya edentulosa, Australoeocallista juazeiroi, Legumen kaririense, and Corbulomima delicata), in addition to Musculus maroimensis, Crassatella maroimensis, “Myrtea” sp. and “Tellina” sp. This bivalve fauna mainly consists of cosmopolitan and endemic brackish/marine genera, with Tethyan affinities. The fauna is not homogeneously distributed in the sedimentary succession of the Romualdo Formation, but is constrained to the third order highstand systems tract. Bivalves recorded from muddy facies are strongly dominated by infaunal and semi-infaunal suspension feeders. Assemblages of the sand-dominated facies, with dense shell accumulations of semi-infaunal to epifaunal byssate and infaunal suspension feeders, were formed under shallow, higher energy conditions. Despite the degree of generic endemicity, the mytilids, anomiids, crassateliids, astartids, tellinids, and corbulids are related to the bivalve fauna of the Early Cretaceous Riachuelo Formation of the Sergipe-Alagoas Basin, as previously demonstrated for the bakevelliids and echinoids. Indeed, the Romualdo bivalve fauna is, in part, a modified and impoverished brackish/marine fauna of the Riachuelo Formation.

Auxetic Structure‐Assisted Triboelectric Nanogenerators for Efficient Energy Collection and Wearable Sensing

AbstractTriboelectric nanogenerators (TENGs) are recognized for energy conversion efficiency and applications including electronics and energy storage devices. This study introduces a groundbreaking development in TENG by incorporating negative Poisson's ratio metamaterials to fabricate auxetic‐assisted triboelectric nanogenerators (Auxetic‐TENG), subversively overcoming the low power density of traditional materials. Subtly, an integrated layer‐by‐layer‐assembly and core–shell accumulation strategy is employed to create a synclastic polytetrafluoroethylene negative friction shell‐skeleton, into which positive Poisson's ratio nature collagen aggregate (CA) foam is inwardly embedded as the positive friction core‐material. Surprisingly, the on‐demand introduction of metamaterials in synergy with CA significantly increases the contact area and mechanical energy absorption of the Auxetic‐TENG under pressure. This enhancement in the conversion efficiency of mechanical to electricity capitalizes on the contraction origins of negative Poisson's ratio metamaterials, integrated with the expansion characteristics of the positive Poisson's ratio materials within the structure, facilitating the synergistic compression of the positive and negative friction stratum. Consequently, Auxetic‐TENG achieves an open‐circuit voltage of 85 V, an overturning four times compared to conventional contact–separation TENG, and a power density of 4.2 W m−2. Application experiments demonstrate the superior performance of auxetic‐TENG under various compression ratios and stress conditions, highlighting its potential for real‐time monitoring in healthcare applications.

Ecological baselines in the Eastern Mediterranean Sea shifted long before the availability of observational time series.

Native biodiversity loss and invasions by nonindigenous species (NIS) have massively altered ecosystems worldwide, but trajectories of taxonomic and functional reorganization remain poorly understood due to the scarcity of long-term data. Where ecological time series are available, their temporal coverage is often shorter than the history of anthropogenic changes, posing the risk of drawing misleading conclusions on systems' current states and future development. Focusing on the Eastern Mediterranean Sea, a region affected by massive biological invasions and the largest climate change-driven collapse of native marine biodiversity ever documented, we followed the taxonomic and functional evolution of an emerging "novel ecosystem", using a unique dataset on shelled mollusks sampled in 2005-2022 on the Israeli shelf. To quantify the alteration of observed assemblages relative to historical times, we also analyzed decades- to centuries-old ecological baselines reconstructed from radiometrically dated death assemblages, time-averaged accumulations of shells on the seafloor that constitute natural archives of past community states. Against expectations, we found no major loss of native biodiversity in the past two decades, suggesting that its collapse had occurred even earlier than 2005. Instead, assemblage taxonomic and functional richness increased, reflecting the diversification of NIS whose trait structure was, and has remained, different from the native one. The comparison with the death assemblage, however, revealed that modern assemblages are taxonomically and functionally much impoverished compared to historical communities. This implies that NIS did not compensate for the functional loss of native taxa, and that even the most complete observational dataset available for the region represents a shifted baseline that does not reflect the actual magnitude of anthropogenic changes. While highlighting the great value of observational time series, our results call for the integration of multiple information sources on past ecosystem states to better understand patterns of biodiversity loss in the Anthropocene.

Oyster shell-modified lignite composite in globular shape as a low-cost adsorbent for the removal of Pb2+ and Cd2+ from AMD: Evaluation of adsorption properties and exploration of potential mechanisms

A low-cost composite adsorption material has been synthesized from fishery wastes and natural minerals to address challenges such as ecological balance destruction caused by high concentrations of Pb and Cd in acid mine drainage (AMD), unreasonable use of low-caloric lignite, and environmental pollution caused by idle accumulation of oyster shells. This new adsorbent can effectively treat AMD by improving acidity and adsorbing Pb2+ and Cd2+. In this study, oyster shell-modified lignite composite in globular shape (OSL-G) was synthesized by using pyrolyzed oyster shell and lignite, with the addition of bentonite adhesive. The adsorption properties of OSL-G on AMD were evaluated, and the potential mechanism of OSL-G repairing AMD was explored. The results showed that when the mass ratio of oyster shell to lignite was 1:1, oyster shell-modified lignite composite (OSL) was synthesized at 900 °C for 20 min. When the adhesive content was 15.50 %, the roasting temperature was 640 °C, and the roasting time was 2.35 h, OSL-G was synthesized and the adsorption effect was the best. The OSL-G could effectively treat AMD with pH 4 ∼ 5 and initial Pb2+ and Cd2+ concentrations of 10 mg/L within 600 min at a dosage of 4 g/L. The OSL-G adsorption process followed the quasi-second-order kinetic model and the Freundlich model. The maximum adsorption saturation capacities of Pb2+ and Cd2+ were 107.2821 mg/g and 8.3777 mg/g at 298.15 K, respectively. The adsorption process was a multistep controlled spontaneous endothermic process. The potential mechanism was mainly the adsorption-condensation coexistence results of electrostatic adsorption, neutralization precipitation, ion exchange, and surface complexation. The removal rates of Pb2+ and Cd2+ of the recovered OSL-G (ROSL-G) were still high, reaching 57.26 % and 50.38 % after 5 times of adsorption–desorption, respectively. The applicability of ROSL-G after adsorption–desorption for other heavy metal components in AMD proved its good application potential. This study suggested that OSL-G can be used as a promising environmentally friendly adsorbent for AMD. This study provided a broad picture of the management and reuse possibilities of fishery wastes and natural mineral resources, and addressed established, current, and potential strategic needs, particularly in terms of sustainability challenges and ecological civilization construction.

Taphofacies of coastal lakes based on mollusk death assemblages: a case study of Mirim Lake

Mirim Lake is the second-largest lacustrine body in Brazil, stretching for some 185 km and covering about 375 thousand hectares of water surface. This lake is part of the Patos-Mirim System, one of the world’s largest complexes of coastal lagoons, which is the result of the rise and fall of sea level over transgressive-regressive cycles triggered by glacio-eustasy during the Late Pleistocene and Holocene. Its characteristics and dynamics give it singular importance for studies on the genesis of shell accumulation in lagoons. This study aims to improve the knowledge of how the taphonomic signatures reflect the environmental characteristics and dynamics of Mirim Lake. Categorization of the arrangement and packing of death assemblages, as well as the orientation of shells, supported the biostratinomical approach. The taphonomic signatures included disarticulation, fragmentation, and corrosion of shells. Corrosion is the primary damage observed in the bioclasts, varying from a single loss of color to complete degradation. Differences in the characteristics of death assemblages observed in the dune fields and the lacustrine plain led to the recognition of two taphofacies. A more significant number of whole shells was observed in the dune field taphofacies, while sharp fragments and open-articulated bivalves in hydrodynamic unstable positions characterize the lacustrine plain taphofacies. The genesis of death assemblages and the taphonomic signatures of bioclasts were linked to three sedimentary dynamics attributed to the environment of Mirim Lake. Keywords: biostratinomy, taphonomic signatures, shell deposits, dune field, lacustrine plain.

Accumulations of Fossil Cephalopod Shells and Attached Epizoans from Some Late Ordovician Localities (Barrandian Area, Czech Republic)

Abstract As yet undescribed accumulations of shells of orthoconic cephalopods, which are in some aspects comparable to cephalopod limestones known from the Silurian and Lower Devonian of the Barrandian area and other regions of the world, occur in the Letná and Zahořany formations (middle Sandbian and lower Katian stages, Upper Ordovician, central Bohemia). These accumulated shells are often colonized by sessile organisms. Only a small proportion of these organisms could be attached to shells of alive cephalopods; the majority of them used empty shells as solid substrates. The most abundant epizoan is the cystosporate bryozoan of the genus Ceramopora that often overgrows the cephalopod shells extensively. Holdfasts of the genus Sphenothallus and problematic fossils assigned to the genus Conchicolites are common. Rarer epibionts include the bryozoan Spatiopora, the cystoid echinoderm Codiacystis and the brachiopod Ptychopeltis. Varying sizes of bryozoan colonies occurring on the same cephalopod shell point to several recurring attachment events, probably reflecting reproduction cycles.

Mussel Shells from Marine Aquaculture Act like Ecosystem Engineers: Legacy Effects on Benthic Communities

Ecosystem engineers are organisms that cause changes in the physical state of biotic and abiotic structures that modulate the availability of resources to other species, thus affecting biochemical cycles. Molluscs, especially bivalves such as mussels, are widespread in coastal environments and they are excellent ecosystem engineers because of the durability of their shells, which add complexity and heterogeneity to benthic environments. The presence of mussel farms favours the accumulation of shells in benthic environments and may influence surrounding bare sediments, with potential legacy effects on benthic communities. We studied the effects of the accumulation of mussel shells at finfish farms and mussel farms by experimentally comparing bare sediment and sediment with fragmented shells in terms of the abundance of the most relevant faunal groups, specifically polychaete families as well as physical–chemical variables in sediment water samples, specifically organic matter (OM), redox potential, and acid-volatile sulphides (AVS) NH4+ and PO43−. The experiment was replicated under two environmental conditions over a period of 35 days: eutrophic muddy sediments and oligotrophic sandy sediments. The OM and AVS values were significantly higher in the eutrophic sediment with mussel shells. Only NH4+ was positively affected by the mussel shells in the oligotrophic conditions. Differences between the two environments were observed, and the effect of the mussel shells on the polychaete assemblages was more significant in the oligotrophic conditions. Mussel shell accumulations affected the structure of benthic assemblages by modifying their heterogeneity and complexity, which suggests that the presence of mussel farms above bare sediment may affect ecosystem functioning. Aquaculture has potentially negative or positive effects that must be addressed on a large scale, considering the increased input of organic matter and also the simultaneous presence of mussel shell waste, both of which alter the surrounding environment. This is particularly important in oligotrophic sandy sediment.

Spatio-temporal evolution of the coastal shell accumulation in Villarino Peninsula, San Antonio Este, Argentina

Accumulations of mollusc shells occur frequently in modern coastal environments, including the large Holocene beach deposits at Villarino Peninsula, Argentina. The evolutive study of modern shell accumulations can be applied to predict and interpret ancient rocks formed by hardparts of mollusc shells. To study the spatio-temporal evolution of these accumulations, a mapping of the spatial boundaries using images acquired from Landsat 5™, 7E™, and 8OLI sensors in 1986, 1992, 1998, 2003, 2013, and 2020. This permitted the delimitation of the boundary between the shelly beach and the surrounding environments for each year. Eight cross-sections of the coastline were placed at geomorphologically representative locations to measure the respective displacements, and to reveal the deposition/progradation, erosion/retrogradation and stability zones. Through this study, it was possible to register the variability of the evolutionary behavior of the shells accumulation along the beach system through a period of 34 years. During this time, the sites with progradation (with a maximum value of +165.49 m) exhibit well-developed shore ridges, whereas the sites with retrogradation (with a maximum value of 53.8 m) and stability, show erosive features of escarpment and beaches with gentle ridges. The mapping of these geoindicators highlighted the coastal drift which occurs along the Villarino Peninsula in a clockwise circular pattern. The beach extensions show a more prominent progradation pattern than the retrogradational one.

Shell accumulation on seabed due to suspended coastal oyster farming and effects on burrowing capacity of the polychaete Perinereis aibuhitensis

Mariculture of bivalves (e.g., mussels, scallops, and oysters) is developing rapidly in coastal waters. This process releases shell debris that can accumulate on the seabed under farms. The ecological consequences of shell accumulation on the bioturbation of benthic macrofauna, which play a key role in the biogeochemical processes of sediment, are not yet fully understood. Thus, it is necessary to quantify the shell debris that accumulated under bivalves farms and evaluate whether the shell debris hinders the burrowing capacity of macrofauna. Oysters are common bivalve species cultured worldwide. However, no data are available on shell accumulation due to oyster farming and its possible effects on the burrowing capacity of polychaetes. Thus, we conducted a preliminary study on shells debris accumulation under an oyster farm in Daya Bay, southern China, and assessed the effects of shell accumulation on the burrowing activity of the polychaete Perinereis aibuhitensis in a mesocosm experiment for 32 days. The results showed that oyster farming significantly (p < 0.05) increased the accumulation of shell debris under the farm. The amount of shell debris under oyster farm (6.0 ± 1.3 kg (dry weight (DW)) m-2 or 130.0 ± 24.7 g (DW) kg-1 dry sediment) was approximately two times that in a non-culture area (3.5 ± 0.9 kg (DW) m-2 or 74.9 ± 10.5 g (DW) kg-1 dry sediment). The presence of shell debris did not affect the survival of P. aibuhitensis in experiment, but the animals in sediment with shell added exhibited greater losses of body weight compared with those without, indicating that the presence of shell causes animals to expend more energy in burrowing. The numbers of burrowing holes were lower in sediment with shell debris added compared with those in sediment without shell addition throughout the experiment. Whereas, this does not due to the P. aibuhitensis in +Shell treatment were less active in terms of their burrowing activities. The lower numbers of holes in +Shell treatment was mainly due to P. aibuhitensis were unable to use surface areas where shells were present, the amount of area occupied by shell material physically prevented P. aibuhitensis from forming burrows in these locations. The hindering effects of shells on the burrowing activity of P. aibuhitensis would decrease as the shells degraded into debris. Therefore, we recommend using small shells when conducting “shell addition” bioremediation strategies to avoid the possible negative effects of shells on burrowing by polychaetes.

Distribution of recent planktonic foraminifera in surface sediments of the Basque shelf (S Bay of Biscay): Oceanographic implications

In this work we describe for the first time the distribution of planktonic foraminifera assemblages preserved in recent surface sediments that cover the Basque shelf (southern Bay of Biscay), and their relationship with diverse oceanic currents that affect this area. In the 83 studied samples a total of 18 (morpho)species of planktonic foraminifera have been identified, being the most abundant species: Neogloboquadrina pachyderma dex., Globigerinoides ruber, Globigerina bulloides, Globoconella inflata, Orbulina universa and Turborotalita quinqueloba. These species represent the 92.8% of the total hand-picked specimens. The preferential accumulation of planktonic foraminifera shells in fine sediments deposited in the eastern margin of the Basque shelf, and the random distribution of the dominant species in this area, seem to respond to the general surface current that affect the Basque shelf, which flows eastward during most of the year. Moreover, the input of certain currents and deeper water masses in this area has an important impact on assemblage distribution. Thus, the presence of abundant individuals of Globigerinoides ruber indicates the entrance of the warm and salty Iberian Poleward Current (IPC). Likewise, the dominance of subpolar species Globigerina bulloides, Neogloboquadrina pachyderma dex. and Turborotalita quinqueloba, together with the occurrence, as accessories species, of Neogloboquadrina pachyderma sin., Globorotalia scitula, Globorotalia truncatulinoides and Neogloboquadrina dutertrei, suggest the impact of upwelling processes on the Basque shelf. In conclusion, in this work we have evidenced the useful application of planktonic foraminifera assemblages preserved in surface sediments as indicators of oceanic currents and water masses in shallow continental shelves, such as the Basque shelf.

Geo-archaeology and Haíɫzaqv oral history: Long-term human investment and resource use at EkTb-9, Triquet Island, N̓úláw̓itxˇv Tribal Area, Central Coast, British Columbia, Canada

Archaeological site EkTb-9 is located on Triquet Island in the N̓úláw̓itxˇv Tribal area of Haíɫzaqv (Heiltsuk) Nation territory, on the Central Coast of British Columbia, Canada. The results of radiometric dating and the analysis of palaeoenvironmental correlates indicate that the site was a persistent place of repeated human occupation spanning the early post-glacial period to the present day. This paper focuses on the paleogeographic and geomorphic setting of EkTb-9. Stratigraphic records show a complex array of site formation processes. Marine beach sediments are elevated above modern sea level, an extensive sand sheet consistent with a possible palaeotsunami event is present, as well as organic soils and peat deposits. Cultural strata are interbedded with these and include both shell-less and preserved shell accumulations. Results from our geo-archaeological and palaeoenvironmental assessments indicate that the outer coastal island changed from what was likely an open landscape during the early post-glacial period to the hypermaritime coastal temperate rainforest environs of the present day. Our interpretations are combined with Haíɫzaqv oral history and discussions are organized by Haíɫzaqv temporal phases identified for the N̓úláw̓itxˇv Tribal area. Combining Indigenous knowledge with our archaeological interpretations enhances our collective understanding of the long-term record of human occupation and investment at EkTb-9.

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.

Death Assemblages Record Significant Range Contraction in a Molluscan Species of Concern from the Eastern Gulf Of Mexico

Marine habitats are in decline due to increasing anthropogenic pressures, but baseline data on species distributions needed to manage and conserve populations are lacking. Incorporating death assemblages into species assessments can create a more accurate understanding of pre-anthropogenic communities than survey records alone. In this study, we conducted a live-dead analysis on mollusks from a new 2008-2018 dredge survey in the eastern Gulf of Mexico. We selected the predatory banded tulip snail, Cinctura hunteria, as a test case for assessment because this species is one of several designated by the Florida Fish and Wildlife as a species of concern. Using spatial count data for shells in our samples, we estimated density values for each taxonomic grade over the sampled area using IDW spatial interpolation. These maps reveal large areas of occupation across the west Florida shelf for two taxonomic grades of dead shells but loss of offshore occurrence for live records. One explanation for the lack of occurrences in offshore habitats is that, unlike dead shell records, there is no time averaging accumulation of live shells. Time averaging increases detectability of species in habitats where they are rare. However, independent fisheries data from live-only animal surveys not only mirror our live-dead results but suggest that habitat loss in our live-dead comparisons was rapid and occurred in the late 1980s or early 1990s. Thus, live-dead comparisons reveal both natural baselines as well as anthropogenic changes in distribution without being significantly distorted by time-averaging biases. Including live-dead data can greatly improve species assessments when long-term survey records are unavailable and provide a key tool in combatting biodiversity loss across marine ecosystems.

Concordant Spatial Gradients in Predation Intensity and Productivity Archived in Surficial Mollusk Shell Accumulations in Seagrass Meadows Along the Gulf Coast of Florida

Seagrass meadows are highly structured habitats of great socioeconomic value but are declining globally due to human impacts. The northern Gulf Coast of Florida contains one of the largest relatively unaltered seagrass habitats (~3,000 km2), making it a model system for acquiring baselines to better manage and monitor seagrass meadows. This project investigated spatial gradients in ecological and taphonomic attributes of surficial seagrass-associated benthic mollusk death assemblages. An updated analysis of water parameters (based on project COAST data) indicated that total dissolved phosphorous (TDP) and chlorophyll-a (CHL-a) concentrations increased steadily northward. To analyze the historical ecology of local seagrass meadows, mollusk assemblages were bulk sampled at 12 stations across multiple estuaries along the gradient. Radiocarbon dating of valves (n = 90) from several estuaries indicated that the assemblages represented a multi-millennial accumulation with a median shell age of 1760 AD. Focusing on two abundant bivalves found within all estuaries, Transennella spp and Crassostrea virginica, the study evaluated spatial trends in body size, traces of predation, and post-mortem shell alterations. The results, primarily focused on Transennella spp., indicated that ecological and taphonomic characteristics varied notably, both among and within estuaries. Relative abundance, body size, and taphonomic attributes did not appear to correlate significantly with productivity or drilling frequency. However, drilling frequency correlated significantly with TDP and CHL-a, suggesting that predator-prey interactions may co-vary tightly with productivity. These results suggest that spatial gradients in predation can be archived by drilling frequencies in death assemblages. Moreover, the consistency between the long-term record of predation and modern gradient conditions suggests that long-term spatial dynamics of predator-prey interactions may be hydrologically controlled.