Death Assemblages Research Articles

Death assemblages of the freshwater mussels Unio crassus and U. tumidus (Bivalvia, Unionidae) from southern Finland: comparing taphonomical data with 14C dates

Death assemblages of the freshwater mussels Unio crassus and U. tumidus (Bivalvia, Unionidae) from southern Finland: comparing taphonomical data with 14C dates

Mollusk death assemblages in 210Pb-dated marine sediment cores reveal recent biotic changes in the Gulf of Guanahacabibes, NW Cuba

We investigated stratigraphic changes in mollusk death assemblages and geochemistry in sediment cores from four seagrass beds and one unvegetated site in the Gulf of Guanahacabibes (GG), NW Cuba. There was a transition from mangrove to seagrass beds, associated with sea level rise ∼6000 years ago. Sediment accumulation rates during the last century showed a general rise, but increased sharply after ∼1980, likely because of human activities. The GG displayed overall high mollusk γ-diversity, and our estimate of 189 species is biased toward the low end. High β-diversity was driven by inter-site differences in grain size, vegetation cover, and nutrient input. Spatial heterogeneity within the basin influenced downcore abundance and diversity metrics, highlighting the influence of local drivers. Herbivorous gastropods dominated in seagrass beds and suspension feeder bivalves were dominant on sandy bottom. In the top parts of cores, species richness declined at two sites that were subject to high, human-mediated bulk sedimentation rates and eutrophication. Conservation measures are needed to preserve this hotspot of marine diversity.

Accounting for uncertainty from zero inflation and overdispersion in paleoecological studies of predation using a hierarchical Bayesian framework

AbstractThe effects of overdispersion and zero inflation (e.g., poor model fits) can result in misinterpretation in studies using count data. These effects have not been evaluated in paleoecological studies of predation and are further complicated by preservational bias and time averaging. We develop a hierarchical Bayesian framework to account for uncertainty from overdispersion and zero inflation in estimates of specimen and predation trace counts. We demonstrate its application using published data on drilling predators and their prey in time-averaged death assemblages from the Great Barrier Reef, Australia.Our results indicate that estimates of predation frequencies are underestimated when zero inflation is not considered, and this effect is likely compounded by removal of individuals and predation traces via preservational bias. Time averaging likely reduces zero inflation via accumulation of rare taxa and events; however, it increases the uncertainty in comparisons between assemblages by introducing variability in sampling effort. That is, there is an analytical cost with time-averaged count data, manifesting as broader confidence regions. Ecological inferences in paleoecology can be strengthened by accounting for the uncertainty inherent to paleoecological count data and the sampling processes by which they are generated.

Phyllozoon and Aulozoon: key components of a novel Ediacaran death assemblage in Bathtub Gorge, Heysen Range, South Australia

AbstractThe recognition of fossiliferous horizons both below and above the classical Ediacara levels of the Flinders Ranges, South Australia, significantly expands the potential of this candidate World Heritage succession. Here we document a small window into the biology and taphonomy of the late Ediacaran seafloor within the new Nilpena Sandstone Member of the Rawnsley Quartzite in Bathtub Gorge, northern Heysen Range. A 1 m2 slab extracted from the gorge, now on permanent display at the South Australian Museum, has a death assemblage dominated by the erniettomorph Phyllozoon hanseni Jenkins and Gehling 1978 and a newly named macroscopic tubular body fossil – Aulozoon soliorum gen. et sp. nov. – on its fine sandstone bed sole. The orientations and juxtaposition of these taxa suggest overprinting of an in situ benthic Phyllozoon community by sand-filled tubes of Aulozoon carried in by a storm wave-base surge. Phyllozoon hanseni is a widespread species that is restricted to the Nilpena Sandstone Member of the Rawnsley Quartzite, whereas Dickinsonia costata ranges from the underlying Ediacara Sandstone Member into the Nilpena Sandstone Member. Fundamental differences in the ways these two vendobiont taxa are constructed and preserved may provide insights into their biology and phylogenetic affinities. In the Nilpena Sandstone Member, D. costata is joined by Dickinsonia rex Jenkins 1992, which appears to be confined to the member, and is here re-described to clarify its taxonomic status and stratigraphic distribution.

EVALUATING COMPOSITIONAL FIDELITY AND SOURCES OF MORTALITY OF SHORELINE FISH CARCASSES IN A FRESHWATER LAKE COMMUNITY IN WESTERN CANADA

ABSTRACT Taxonomic comparisons of death assemblages with extant communities continue to provide insight for ecological studies but whether demographic aspects such as age structure, sex ratio, and causes of mortality are accurately captured by the former remains little studied. At a 110 ha dystropic lake in western Canada, seasonal shoreline accumulations of fish carcasses were collected annually for 12 years (N=4499) during 95 full lake-circuits and analyzed for taxa, body size frequencies, sex ratio relative to live-captures and sources of mortality. Rank order of the four fish species (Gasterosteus aculeatus, Oncorhynchus clarki, O. keta, Salvelinus malma) was similar for live-captures and carcasses. Of the dominant species (G. aculeatus), modal adult body length (∼80 mm SL) was the same for carcasses and live-captures and shifted by about 10% over 30 years with parallel trends between the groups for both sexes. Age-specific body size was about 5% larger (P<0.001) in carcasses than live-captures. Carcasses were significantly female-biased (2:1) each year relative to a population sex ratio of 1:1 in the lake. There was a complete absence of juvenile fish (<30 mm) among carcasses but these constituted 70% of the live population. Estimated relative contributions to mortality for the carcasses include starvation (<1%), parasitism (3%), senescence (4%) and lethal injuries from predator attack (70–80%). If these carcasses are representative of a fossil series in freshwater lake sediments, then several demographic parameters including age-specific body size, age-class frequencies and sex ratio depart substantially from the live population. As well, the virtual absence of avian piscivores in the carcass assemblage, the major source of predation on the fish population, warrants additional attention in paleoecological studies.

The Distribution Pattern of Marine Bivalve Death Assemblage From the Western Margin of Bay of Bengal and Its Oceanographic Determinants

The global pattern of shallow marine biodiversity is constructed primarily using the data from extra-tropical sites. A severe knowledge gap in the shallow benthic diversity exists for the tropical Indian Ocean, especially along the coastline of peninsular India. Latitudinal biodiversity gradient (LBG)—a poleward decrease in diversity, even though accepted as a pervasive global pattern, often differs from regional trends. Although several oceanographic variables are known to influence regional patterns, their relative effect in shaping the shallow benthic community in tropical seas remains unclear. The east coast of India bordering the Bay of Bengal (BoB) presents a 2,500 km stretch (8–22°N) of tropical coastline with a spatial variation in oceanographic parameters including freshwater mixing, primary productivity, temperature, and shelf area. Here, we documented the marine bivalve distribution using spatially-temporally averaged beach samples and evaluated their relationship with the oceanographic variables. Our data reveal the existence of a highly diverse fauna, comparable to other tropical shallow marine sites. Overall species composition reflects a typical assemblage of the Indian Ocean, dominated by Veneridae but shows an uncharacteristically low proportion of Tellinidae and Lucinidae. The latitudinal variation in diversity shows a mid-latitude drop at around 14°N—a pattern inconsistent with the prediction of latitudinal biodiversity gradient (LBG). The functional groups are dominated by infauna (65%), unattached groups (69%), and suspension feeders (87%). There is only a slight difference in species composition between southern and the northern sites pointing to a predominantly continuous circulation and considerable mixing within the BoB. Productivity range, shelf area, and salinity emerge as best predictors of the species richness. All environmental variables together explain the species composition across the latitudinal bins satisfactorily. The species composition of the east coast shows no distinct nature in comparison to the Indo-Malayan biodiversity hotspot; the proximity to this hotspot and biological exchange with it may have contributed to the high diversity of the east coast fauna. Our study highlights the complex interplay between multiple oceanographic variables in determining the distribution and diversity of tropical shallow marine benthos at a regional scale generating biodiversity patterns that are at odds with global trends such as LBG.

MOLLUSCAN LIVE-DEAD FIDELITY OF A STORM-DOMINATED SHALLOW-MARINE SETTING AND ITS IMPLICATIONS

ABSTRACT Actualistic studies are important for evaluating the fidelity of fossil assemblages in representing the living community. Poor live-dead (LD) fidelity in molluscan assemblages may result from transport-induced mixing. Large-scale mixing is more common in siliciclastic settings with a narrow shelf, high sedimentation rate, and those that are frequented by episodically high-energy events. Chandipur-on-sea, on the east coast of India has an optimal setting to promote such conditions. By studying the LD fidelity and modeling size-frequency distribution (SFD) of the fauna, we attempted to evaluate the contribution of “out-of-habitat” versus “within-habitat” mixing in developing the molluscan death assemblage. The correlation between the composition of live (LA) and death assemblages (DA) was insufficient; unlike LAs, the DAs do not show environmental partitioning in ordination space. A numerical simulation of the shell size frequency distribution (SFD) for DAs from LAs was compared with the observed SFD of the DAs. The results of this simulation indicate that DAs are not likely to be a product of within-habitat mixing. DAs probably received considerable input via regional transport, facilitated by frequent tropical cyclones affecting the coast of Odisha. Chandipur receives a large proportion of cyclones originating above 15°N, which causes a high degree of lateral transport and shell mixing between 15° to 21°N, explained by the high compositional similarity of species within this latitudinal extent. Our study highlights the significance of out-of-habitat transport in shaping the regional distribution of marine fossil assemblages, especially in storm dominated siliciclastic shallow-marine settings.

Numerous new records of tropical non-indigenous species in the Eastern Mediterranean highlight the challenges of their recognition and identification.

New data on 52 non-indigenous mollusks in the Eastern Mediterranean Sea is reported. Fossarus sp. (aff. aptus sensu Blatterer 2019), Coriophora lessepsiana Albano, Bakker & Sabelli, sp. nov., Cerithiopsis sp. aff. pulvis, Joculator problematicus Albano & Steger, sp. nov., Cerithiopsis sp., Elachisina sp., Iravadia aff. elongata, Vitrinella aff. Vitrinella sp. 1 (sensu Blatterer 2019), Melanella orientalis, Parvioris aff. dilecta, Odostomia cf. dalli, Oscilla virginiae, Parthenina cossmanni, Parthenina typica, Pyrgulina craticulata, Turbonilla funiculata, Cylichna collyra, Musculus coenobitus, Musculus aff. viridulus, Chavania erythraea, Scintilla cf. violescens, Iacra seychellarum and Corbula erythraeensis are new records for the Mediterranean. An unidentified gastropod, Skeneidae indet., Triphora sp., Hypermastus sp., Sticteulima sp., Vitreolina cf. philippi, Odostomia (s.l.) sp. 1, Henrya (?) sp., and Semelidae sp. are further potential new non-indigenous species although their status should be confirmed upon final taxonomic assessment. Additionally, the status of Dikoleps micalii, Hemiliostraca clandestinacomb. nov. and H. athenamariaecomb. nov. is changed to non-indigenous, range extensions for nine species and the occurrence of living individuals for species previously recorded from empty shells only are reported. Opimaphora blattereri Albano, Bakker & Sabelli, sp. nov. is described from the Red Sea for comparison with the morphologically similar C. lessepsiana Albano, Bakker & Sabelli, sp. nov. The taxonomic part is followed by a discussion on how intensive fieldwork and cooperation among institutions and individuals enabled such a massive report, and how the poor taxonomic knowledge of the Indo-Pacific fauna hampers non-indigenous species detection and identification. Finally, the hypothesis that the simultaneous analysis of quantitative benthic death assemblages can support the assignment of non-indigenous status to taxonomically undetermined species is discussed.

Native biodiversity collapse in the eastern Mediterranean.

Global warming causes the poleward shift of the trailing edges of marine ectotherm species distributions. In the semi-enclosed Mediterranean Sea, continental masses and oceanographic barriers do not allow natural connectivity with thermophilic species pools: as trailing edges retreat, a net diversity loss occurs. We quantify this loss on the Israeli shelf, among the warmest areas in the Mediterranean, by comparing current native molluscan richness with the historical one obtained from surficial death assemblages. We recorded only 12% and 5% of historically present native species on shallow subtidal soft and hard substrates, respectively. This is the largest climate-driven regional-scale diversity loss in the oceans documented to date. By contrast, assemblages in the intertidal, more tolerant to climatic extremes, and in the cooler mesophotic zone show approximately 50% of the historical native richness. Importantly, approximately 60% of the recorded shallow subtidal native species do not reach reproductive size, making the shallow shelf a demographic sink. We predict that, as climate warms, this native biodiversity collapse will intensify and expand geographically, counteracted only by Indo-Pacific species entering from the Suez Canal. These assemblages, shaped by climate warming and biological invasions, give rise to a ‘novel ecosystem’ whose restoration to historical baselines is not achievable.

Basin-wide infaunalisation of benthic soft-bottom communities driven by anthropogenic habitat degradation in the northern Adriatic Sea

Shallow coastal seas play an important role in the economy of many countries by sustaining fisheries, tourism, aquaculture and other economic activities. Their exploitation has large-scale ecosystem effects that are easily overlooked, as they often built up over decades or centuries, and historical ecological reference data are rarely available. Here, we assess these effects by comparing live and surface death assemblages (recording historical community states) of soft-bottom molluscs across a range of habitats in the northern Adriatic Sea, using the degree of mismatch between the 2 assemblages as a proxy for ecological change. We found a consistent live-dead mismatch at all stations. Although the degree of mismatch varied between stations with low and high time-averaging (i.e. the range of post-mortem shell ages), the community change followed the same trend over the entire Adriatic basin regardless of the type of sedimentary environment, with a loss of epifaunal species and the reduction of grazers, carnivores, and herbivores. In turn, the abundance of infaunal and opportunistic species feeding on plankton or detritus strongly increased in the living communities. Directionality and magnitude of these changes cannot be explained by time-averaging or by differences in species durability, but reflect a true ecological shift in response to multiple, long-lasting anthropogenic pressures, mainly bottom trawling, eutrophication and hypoxia. The original heterogeneous assemblages characteristic of different sedimentary habitats are thus replaced by a more infaunal, functionally impoverished and less diverse benthic community representing a new ecological baseline shaped by human impact.

Taphonomic information from the modern vertebrate death assemblage of Doñana National Park, Spain.

Modern death assemblages provide insights about the early stages of fossilization and useful ecological information about the species inhabiting the ecosystem. We present the results of taphonomic monitoring of modern vertebrate carcasses and bones from Doñana National Park, a Mediterranean coastal ecosystem in Andalusia, Spain. Ten different habitats were surveyed. Half of them occur in active depositional environments (marshland, lake margin, river margin, beach and dunes). Most of the skeletal remains belong to land mammals larger than 5 kg in body weight (mainly wild and feral ungulates). Overall, the Doñana bone assemblage shows good preservation with little damage to the bones, partly as a consequence of the low predator pressure on large vertebrates. Assemblages from active depositional habitats differ significantly from other habitats in terms of the higher incidence of breakage and chewing marks on bones in the latter, which result from scavenging, mainly by wild boar and red fox. The lake-margin and river-margin death assemblages have high concentrations of well preserved bones that are undergoing burial and offer the greatest potential to produce fossil assemblages. The spatial distribution of species in the Doñana death assemblage generally reflects the preferred habitats of the species in life. Meadows seem to be a preferred winter habitat for male deer, given the high number of shed antlers recorded there. This study is further proof that taphonomy can provide powerful insights to better understand the ecology of modern species and to infer past and future scenarios for the fossil record.

Shell strength of freshwater molluscs and its implication on preservation potential

ABSTRACT Shell strength of the modern freshwater molluscs Heleobia parchappii, Biomphalaria peregrina, Uncancylus concentricus, Musculium argentinum, Physa acuta, Succinea meridionalis and Pomacea canaliculata was quantified through load measurements and analysed using Weibull distribution, a statistical method used for brittle materials. In this study, we defined shell strength as the maximum compressive force required to break a shell per unit of resistant area, which is known as mechanical tension or stress. Intrinsic properties of shells were also measured through mineralogical and morphological characterisation. Shells were mainly composed of aragonite and varied in size and shell thickness, being P. canaliculata (biovolume = 104 mm3) the largest and H. australis and H. parchappii (3.35 and 7.93 mm3, respectively) the smallest ones. The dominant microstructure was cross-lamellar, with layers that varied between one and four. The organic matter of the matrix varied between 1.58% and 4.24%. Shell strength differs among mollusc species. Smallest species have higher shell strength than larger ones because they have a smaller resistant area on which the load is applied, and therefore the resulting value of fracture stress increases abruptly. This may explain the dominance of H. parchappii in death and fossil assemblages from Pampa sediments.

U-Th dating of Holocene age Acropora prolifera (Lamarck, 1816) colonies confirms coral hybridization is not a recent phenomenon.

To confirm previous findings that hybridization of Caribbean acroporid corals occurred in the recent geologic past, we determined the uranium-thorium (U-Th) ages of two subfossil Acropora prolifera samples collected from nearshore coral death assemblages located off the coast of southeastern Florida. Our results indicate that A, prolifera existed in southeastern Florida during the late Holocene, confirming that Caribbean acroporid hybridization occurred prior to their region-wide die off in the 1970s and 1980s.

A camera trap record of scavengers at a kudu carcass: implications for archaeological bone accumulations

A camera trap was set near a greater kudu bull carcass for 3 weeks at the start of winter. The carcass lay in an open savanna setting on a game farm in Limpopo, and it was visited by leopard, brown hyena, black-backed jackal, African civet, honey badger, bushpig and warthog. At the end of a month there were no visible remains of the carcass save the skull and damaged horns. After a week, when decomposition was pronounced, suids spent more time at the carcass than other animals. They may have been responsible for much of the on-site bone consumption. Bone and meat portions not eaten directly at the death scene were probably carried away by scavengers like brown hyena and jackal. The area was excavated and sieved to collect bone debris that might have been trampled into sediment. Only a few small bone fragments were recovered, one of which had a tooth mark. Several outcomes are of interest to archaeologists. Firstly, the diversity of scavengers at the kudu carcass (including some animals not normally classified as scavengers) suggests that damage on surviving bone at some archaeological sites may be from an assortment of animals not normally considered to be scavengers. Comparative collections must accommodate such variety. Secondly, under certain environmental conditions, death assemblages in the wild may disappear without trace when predators can move freely and feed without disturbance. Thirdly, is possible that some bone fragments survive at archaeological sites because they were protected (possibly unintentionally) by human presence, and because they were on occasion processed in ways that made them less attractive to predators.

High-resolution (centimetre-scale) GPS/GIS-based 3D mapping and spatial analysis of in situ fossils in two horned-dinosaur bonebeds in the Dinosaur Park Formation (Upper Cretaceous) at Dinosaur Provincial Park, Alberta, Canada

Mapping of fossil sites represents an important aspect of palaeontology, because the data collected are required for interpreting the taphonomic and depositional history of the site, as well as the palaeoecology and behavior of the organisms. Methods for mapping and documenting certain vertebrate fossil sites, such as trackways, have drastically changed in recent years, with the integrated technologies of photogrammetry, laser scanning, and geographic information systems becoming standard practice, and providing digital, three-dimensional, and georeferenced data for analyses. Contrasting this technological revolution, the methods for mapping vertebrate bone accumulations, such as bonebeds, have changed little in recent decades, and are largely limited to two dimensions, are non-georeferenced, and produce static maps. Here, we present a novel test case in the mapping of two ceratopsid (Dinosauria: Ornithischia) monodominant bonebeds (mass death assemblages) that are documented digitally, fully georeferenced, and in three dimensions, using a combination of high-resolution (at centimetre-scale) global positioning system, photogrammetry, and geographic information systems. Importantly, accompanying spatial data (i.e., size and orientation) are collected in the field in the traditional manner and directly compared with values calculated from the digital map. Parameters describing bone length and orientation exported from the digital map are largely reflective of measured field data, with both size and orientation distributions being statistically indistinguishable, but with disproportionate error for elements smaller than 10 cm. Protocols and methods tested here will hopefully add to the discussion about the future of fossil bonebed mapping, specifically incorporating digital, three-dimensional, and fully georeferenced data into a powerful analytical tool.

Relationship of sediment influx to ostracode populations on the variably deforested Luiche and Mahale platform coasts of Lake Tanganyika, Tanzania

We investigated the hypothesis that ostracode populations are sensitive to variations in sediment discharge related to watershed differences at Lake Tanganyika. Many ostracode species are documented to be sensitive to high turbidity which increases during runoff from strong rainfall events and changes in ostracode populations can impact organisms higher in the food web. We compared surficial death assemblages of ostracodes around two sites with extensive shell beds, the highly deforested Luiche Platform area, heavily populated since the 20th Century, and the less deforested Mahale Platform area, with recent population increases, to understand the impacts of increasing sedimentation within and between sites. The study found that whereas the Mahale Platform area is less disturbed, the faunal differences between sites is not large. The data showed high species richness and abundance of ostracodes at 10–20 m depth at both sites, within shell bed zones, with no statistical difference in raw species richness between the sites. The Mahale Mountain area ostracode populations were however statistically more diverse (Shannon H) than at Luiche. We conducted a multi-response permutation procedure and found that the sites are statistically different, but with very small differences in species richness and ostracode abundance. Non-metric multidimensional scaling ordination of species assemblages shows that most samples overlap on both major axes. This study synthesized with ongoing research about shell bed communities in less disturbed regions of the lake will give insights into how conservation projects can be optimized to preserve the lake’s benthic ecosystem from the effects of deforestation.

Live, dead, and fossil mollusks in Florida freshwater springs and spring-fed rivers: Taphonomic pathways and the formation of multisourced, time-averaged death assemblages

AbstractTaphonomic processes are informative about the magnitude and timing of paleoecological changes but remain poorly understood with respect to freshwater invertebrates in spring-fed rivers and streams. We compared taphonomic alteration among freshwater gastropods in live, dead (surficial shell accumulations), and fossil (late Pleistocene–early Holocene in situ sediments) assemblages from two Florida spring-fed systems, the Wakulla and Silver/Ocklawaha Rivers. We assessed taphonomy of two gastropod species: the native Elimia floridensis (n = 2504) and introduced Melanoides tuberculata (n = 168). We quantified seven taphonomic attributes (aperture condition, color, fragmentation, abrasion, juvenile spire condition, dissolution, and exterior luster) and combined those attributes into a total taphonomic score (TT). Fossil E. floridensis specimens exhibited the greatest degradation (highest TT scores), whereas live specimens of both species were least degraded. Specimens of E. floridensis from death assemblages were less altered than fossil specimens of the same species. Within death assemblages, specimens of M. tuberculata were significantly less altered than specimens of E. floridensis, but highly degraded specimens dominated in both species. Radiocarbon dates on fossils clustered between 9792 and 7087 cal BP, whereas death assemblage ages ranged from 10,692 to 1173 cal BP. Possible explanations for the observed taphonomic patterns include: (1) rapid taphonomic shell alteration, (2) prolonged near-surface exposure to moderate alteration rates, and/or (3) introduction of reworked fossil shells into surficial assemblages. Combined radiocarbon dates and taphonomic analyses suggest that all these processes may have played a role in death assemblage formation. In these fluvial settings, shell accumulations develop as a complex mixture of specimens derived from multiple sources and characterized by multimillennial time-averaging. These findings suggest that, when available, fossil assemblages may be more appropriate than death assemblages for assessing preindustrial faunal associations and recent anthropogenic changes in freshwater ecosystems.

Holocene fish assemblages provide baseline data for the rapidly changing eastern Mediterranean

The eastern Mediterranean marine ecosystem is undergoing massive modification due to biological invasions, overfishing, habitat deterioration, and climate warming. Our ability to quantify these changes is severely hindered by the lack of an appropriate baseline; most ecological datasets date back a few decades only and show already strong signatures of impact. Surficial death assemblages (DAs) offer an alternative data source that provides baseline information on community structure and composition. In this study, we reconstruct the marine fish fauna of the southern shallow Israeli shelf before the opening of the Suez Canal based on fish otoliths. We quantify the age of the otolith DAs by radiocarbon dating, and describe its taxonomic composition, geographic affinity, and trophic structure. Additionally, we test by radiocarbon dating the hypothesis that Bregmaceros, a presumed Lessepsian invader with continuous presence in the Mediterranean throughout the late Cenozoic, is a relict species. The otolith DA dates back to the mid-Holocene because 75% of the dated otoliths of the native species are older than the opening of the Suez Canal in 1869, suggesting that the DA is a proper baseline for quantifying modern impacts. Consistently, 97% of the otoliths and 88% of the species we collected belong to native Mediterranean species. The native anchovy Engraulis encrasicolus dominates the DAs, although gobiids are the most diverse group (14 species, 28%). The DAs show similar trophic structure to present-day pristine Mediterranean coastal fish assemblages. Two non-indigenous species are recorded here for the first time in the Mediterranean Sea, Amblygobius albimaculatus and Callogobius sp., highlighting the importance of DAs for detecting non-indigenous species. Finally, Bregmaceros otoliths are modern, not supporting the previous hypothesis that the taxon is a Pleistocene relict.

Historic and contemporary anthropogenic effects on granulometry and species composition detected from sediment cores and death assemblages, Nelson Bays, Aotearoa-New Zealand

To effectively manage anthropogenic stressors causing widespread and pervasive habitat change, resource managers and policy makers require advice on priority stressors to optimally target conservation and restoration outcomes. This is difficult in soft sediment ecosystems affected by multiple stressors operating across centuries with possible legacy interactions. Using tools from the emerging discipline of conservation paleobiology, we attempted to disentangle the effects of two stressors: i) changes to sediments (sedimentation rate, composition) and ii) fishing disturbance across pre-human to contemporary timescales by analysing death assemblages (DA) at a rare location protected from power fishing methods for ca. 30 yr in Nelson Bays, Aotearoa-New Zealand. Replicate sediment cores and surface grab samples were collected at paired stations, spread across three depth profiles (25, 30, 35 m), split inside and outside the fishing exclusion zone. Sediment core geochronologies were established using radioisotope dating and analysis of terrestrial plant palynomorphs (spores, pollen, starch) associated with Māori and European introduction to Aotearoa-New Zealand. Results unearthed a complex of brachiopods, molluscs, crustacea, bryozoan, and Māori-introduced pollen and starch remains – the latter a marine first. Following human arrival in the region (ca.1500AD) statistical models revealed separation of DAs between time periods were correlated with a 10–15% increase in sediment silt content following a ca.11-fold increase in Sediment Accumulation Rates (SAR). In contrast, separation of recent surface DAs (ca. 60yr) are now more strongly correlated with sediment mixing, detected by discordance in radioisotope profiles, consistent with exposure to homogenising effects of fishing disturbance outside the exclusion zone. We conclude that historic legacy effects, ongoing sedimentation and fishing disturbance have synergistically modified the sediment characteristics from “natural” baseline conditions. Those changes have likely contributed to the collapse and lack of recovery of Nelson Bays shellfish fisheries.

Radiocarbon dating supports bivalve-fish age coupling along a bathymetric gradient in high-resolution paleoenvironmental studies

Abstract Studies of paleocommunities and trophic webs assume that multispecies assemblages consist of species that coexisted in the same habitat over the duration of time averaging. However, even species with similar durability can differ in age within a single fossil assemblage. Here, we tested whether skeletal remains of different phyla and trophic guilds, the most abundant infaunal bivalve shells and nektobenthic fish otoliths, differed in radiocarbon age in surficial sediments along a depth gradient from 10 to 40 m on the warm-temperate Israeli shelf, and we modeled their dynamics of taphonomic loss. We found that, in spite of the higher potential of fishes for out-of-habitat transport after death, differences in age structure within depths were smaller by almost an order of magnitude than differences between depths. Shell and otolith assemblages underwent depth-specific burial pathways independent of taxon identity, generating death assemblages with comparable time averaging, and supporting the assumption of temporal and spatial co-occurrence of mollusks and fishes.