Lithification with related diagenetic phenomena is an important step in a complex transition from living communities to fossil assemblages and a major taphonomic filter distorting the record of past biodiversity. Apart from direct diagenetic culling of fossils, cementation of fossiliferous deposits induces changes in sampling procedures used to extract paleontological data. This study explores the effects of this methodological shift on recorded fine-scale paleoecological patterns by using subfossil mollusk assemblages occurring in the unlithified and recently cemented storm-beach carbonate sands at Sand Dollar Beach, San Salvador Island, Bahamas, which experienced limited diagenetic alteration. Results show that consistent differences in relative abundance patterns of particular taxa can be observed between unlithified and lithified samples due to collection failure. Magnitude of this distortion is controlled in a large part by a degree of transport-related size sorting, with well-sorted assemblages dominated by small gastropods being more affected. This bias, however, is of limited importance and can be mitigated by selective exclusion of the smallest size classes (,5 mm) from the analysis. Moreover, unlithified and poorly lithified deposits record very similar rarefied richness estimates and patterns of diversity partitioning. This contrasts strongly with earlier estimates of lithification-related diversity loss, suggesting greater importance of diagenetic over methodological filters in creating lithification bias observed in the older rock record. Poorly lithified carbonate rocks-present in many late Neogene successions-may yield biodiversity data directly comparable to those recorded by unlithified sediments if careful collecting methods based on bulk samples are employed.

Palaeoecological data are unique historical archives that extend back far beyond the last several decades of ecological observations. However, the fossil record of continental shelves has been perceived as too coarse (with centennial-millennial resolution) and incomplete to detect processes occurring at yearly or decadal scales relevant to ecology and conservation. Here, we show that the youngest (Anthropocene) fossil record on the northern Adriatic continental shelf provides decadal-scale resolution that accurately documents an abrupt ecological change affecting benthic communities during the twentieth century. The magnitude and the duration of the twentieth century shift in body size of the bivalve Corbula gibba is unprecedented given that regional populations of this species were dominated by small-size classes throughout the Holocene. The shift coincided with compositional changes in benthic assemblages, driven by an increase from approximately 25% to approximately 70% in median per-assemblage abundance of C. gibba . This regime shift increase occurred preferentially at sites that experienced at least one hypoxic event per decade in the twentieth century. Larger size and higher abundance of C. gibba probably reflect ecological release as it coincides with an increase in the frequency of seasonal hypoxia that triggered mass mortality of competitors and predators. Higher frequency of hypoxic events is coupled with a decline in the depth of intense sediment mixing by burrowing benthic organisms from several decimetres to less than 20 cm, significantly improving the stratigraphic resolution of the Anthropocene fossil record and making it possible to detect sub-centennial ecological changes on continental shelves.

Aim The opening of the Suez Canal in 1869 re‐established the direct link between long‐separated biogeographic realms, allowing hundreds of marine species to spread from the Red Sea to the Mediterranean. We use marine bivalves to relate species‐level attributes to successful transition through successive stages of the invasion process. Location Mediterranean and Red Sea. Methods We compiled data on taxonomic composition, body size, life habit and geographic distribution of the Red Sea bivalve fauna from published literature, museum collections and our own field surveys. Using multimodel inference, we examined selectivity of the Lessepsian invasion and identify traits that distinguish successful species at three major stages of invasion: arrival, establishment and spread. Results The upper limit of bathymetric range and occurrence outside the tropical zone in other regions are the strongest predictors of successful transition through the Suez Canal. Establishment in the Mediterranean is positively correlated with earlier arrival and association with hard‐bottom habitats. Preference for hard substrates together with large body size is the primary factor distinguishing invasive aliens representing a significant threat to recipient ecosystems from other established species. Main conclusions The relative strength of abiotic and biotic filters changes along the course of the invasion: environmental affinity and climate match constrain the pool of potential invaders, while the establishment in the new region and invasive status depend on the habitat preferences and life history traits of aliens, affecting their interactions with resident species. Our results together with previous studies suggest that the eastern Mediterranean rocky shores are more susceptible to the establishment of Lessepsian species, many of which may induce strong pressure on recipient communities as ecosystems engineers and competitors of native species.

Abstract. Shallow and sheltered marine embayments in urbanized areas are prone to the accumulation of pollutants, but little is known about the historical baselines of such marine ecosystems. Here we study foraminiferal assemblages, geochemical proxies and sedimentological data from 1.6 m long sediment cores to uncover  ∼  500 years of anthropogenic pressure from mining, port and industrial activities in the Gulf of Trieste, Italy. From 1600 to 1900 AD, normalized element concentrations and foraminiferal assemblages point to negligible effects of agricultural activities. The only significant anthropogenic activity during this period was mercury mining in the hinterlands of the gulf, releasing high amounts of mercury into the bay and significantly exceeding the standards on the effects of trace elements on benthic organisms. Nonetheless, the fluctuations in the concentrations of mercury do not correlate with changes in the composition and diversity of foraminiferal assemblages due to its non-bioavailability. Intensified agricultural and maricultural activities in the first half of the 20th century caused slight nutrient enrichment and a minor increase in foraminiferal diversity. Intensified port and industrial activities in the second half of 20th century increased the normalized trace element concentrations and persistent organic pollutants (PAH, PCB) in the topmost part of the core. This increase caused only minor changes in the foraminiferal community because foraminifera in Panzano Bay have a long history of adaptation to elevated trace element concentrations. Our study underlines the importance of using an integrated, multidisciplinary approach in reconstructing the history of environmental and anthropogenic changes in marine systems. Given the prolonged human impacts in coastal areas like the Gulf of Trieste, such long-term baseline data are crucial for interpreting the present state of marine ecosystems.

Body size is a synthetic functional trait determining many key ecosystem properties. Reduction in average body size has been suggested as one of the universal responses to global warming in aquatic ecosystems. Climate change, however, coincides with human-enhanced dispersal of alien species and can facilitate their establishment. We address effects of species introductions on the size structure of recipient communities using data on Red Sea bivalves entering the Mediterranean Sea through the Suez Canal. We show that the invasion leads to increase in median body size of the Mediterranean assemblage. Alien species are significantly larger than native Mediterranean bivalves, even though they represent a random subset of the Red Sea species with respect to body size. The observed patterns result primarily from the differences in the taxonomic composition and body-size distributions of the source and recipient species pools. In contrast to the expectations based on the general temperature-size relationships in marine ectotherms, continued warming of the Mediterranean Sea indirectly leads to an increase in the proportion of large-bodied species in bivalve assemblages by accelerating the entry and spread of tropical aliens. These results underscore complex interactions between changing climate and species invasions in driving functional shifts in marine ecosystems.

Stratigraphic patterns of last occurrences (LOs) of fossil taxa potentially fingerprint mass extinctions and delineate rates and geometries of those events. Although empirical studies of mass extinctions recognize that random sampling causes LOs to occur earlier than the time of extinction (Signor–Lipps effect), sequence stratigraphic controls on the position of LOs are rarely considered. By tracing stratigraphic ranges of extant mollusc species preserved in the Holocene succession of the Po coastal plain (Italy), we demonstrated that, if mass extinction took place today, complex but entirely false extinction patterns would be recorded regionally due to shifts in local community composition and non-random variation in the abundance of skeletal remains, both controlled by relative sea-level changes. Consequently, rather than following an apparent gradual pattern expected from the Signor–Lipps effect, LOs concentrated within intervals of stratigraphic condensation and strong facies shifts mimicking sudden extinction pulses. Methods assuming uniform recovery potential of fossils falsely supported stepwise extinction patterns among studied species and systematically underestimated their stratigraphic ranges. Such effects of stratigraphic architecture, co-produced by ecological, sedimentary and taphonomic processes, can easily confound interpretations of the timing, duration and selectivity of mass extinction events. Our results highlight the necessity of accounting for palaeoenvironmental and sequence stratigraphic context when inferring extinction dynamics from the fossil record.

Mesopelagic fishes are an important element of marine food webs, a huge, still mostly untapped food resource, and great contributors to the biological carbon pump, whose future under climate change scenarios are unknown. The shrinking of commercial fishes within decades has been an alarming observation, but its causes remain contended. Here, we investigate the effect of warming climate on mesopelagic fish size in the eastern Mediterranean Sea during a glacial-interglacial-glacial transition of the Middle Pleistocene (marine isotope stages 20-18; 814-712 Kyr B.P.), which included a 4°C increase of global seawater temperature. Our results based on fossil otoliths show that the median size of lanternfishes, one of the most abundant groups of mesopelagic fishes in fossil and modern assemblages, declined by ~35% with climate warming at the community level. However, individual mesopelagic species showed different and often opposing trends in size across the studied time interval, suggesting that climate warming in the interglacial resulted in an ecological shift toward increased relative abundance of smaller-sized mesopelagic fishes due to geographic and/or bathymetric distribution range shifts, and the size-dependent effects of warming.

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