Ecosystem engineering by bioturbation shapes ecosystems by physically modifying soil and sediment habitats, affecting microbial communities and biogeochemical processes. Although bioturbation is a key process for ecosystem health and functioning, its response to contaminants like microplastics (MPs) remains poorly explored. To address this gap, we conducted three microcosm experiments across terrestrial, freshwater, and marine ecosystems, using three species of ecosystem engineers: Aporrectodea caliginosa (earthworm), Tubifex tubifex (freshwater worm), and Hediste diversicolor (marine worm). Each ecosystem was contaminated by a mixture of polystyrene and polyamide MP fragments and fibers, ranging from 10 to 1000 μm, at two MP concentrations: 0 and 100 mg kg-1 soil/sediment dry weight. Tracer particles (luminophores) were used to quantify soil/sediment reworking activities of ecosystem engineers. After 21 days of exposure, distinct bioturbation proxies (i.e., maximum penetration depth, surface reworking, particle displacement coefficient, cast production, biodiffusion-like and non-local reworking coefficients) were measured in each microcosm experiment. Our results demonstrated contrasted effects of MPs on bioturbation across ecosystems/ecosystem engineer species. In the terrestrial ecosystem, surface sediment reworking by earthworms remained unaffected by MP contamination although the cast production by A. caliginosa tended to increase (+26 %) with MP contamination. Conversely, in the freshwater ecosystem, the presence of MPs significantly reduced bioturbation activity of tubificid worms, resulting in a nearly fourfold decrease in particle displacement and a substantial reduction in maximum penetration depth of the luminophores. In the marine system, although H. diversicolor maintained effective particle reworking activities with MP contamination, gallery-biodiffusion activity tended to decrease in presence of MPs. Overall, the impact of MP contamination on bioturbation process was context-dependent. It can be hypothesized that the impact of MPs on bioturbation process was dependent on the size of the ecosystem engineering species, with the strongest effect observed on the smallest organism (T. tubifex).

Biogenic sediment mixing is a key process in modern environments, which has played a major role in triggering macroevolutionary breakthroughs, including those that took place during the Ediacaran-Cambrian transition. In the modern, several procedures are used to quantify key metrics such as the thickness of the mixed layer, the maximum depth of sediment mixing, and the intensity of biogenic sediment reworking. Although assessing the extent and role of biogenic sediment mixing in the fossil record has been informed by our knowledge of bioturbation in modern oceans, extrapolating concepts and quantifying proxies is problematic. Complications arise from a series of conceptual barriers, which are sociological, epistemological, and ontological in nature. Sociological barriers reside in the fact that separate scientific communities deal with bioturbation in the modern and fossil record. These obstacles can be effectively removed through increased collaboration among marine benthic ecologists and ichnologists, which will result in enhanced cross-fertilization between fields. Epistemological barriers involve inconsistencies in terminology and conceptual frameworks, such as divergent interpretations of the term "mixed layer". These can be mitigated through the standardization of definitions, clarification of misconceptions, and adoption of unified methodological protocols. Ontological barriers, however, are the most difficult to overcome stemming from the fundamental differences between the nature of the modern and the fossil record, which impact on their corresponding datasets. This is illustrated by the need to adjust functional modes employed for modern bioturbators for the analysis of the fossil record and integration with paleobiology, and by the difficulties in quantifying biogenic sediment reworking in the fossil record. There are also notable differences in the availability of environmental and ecological correlations most closely associated with bioturbation, which lead to differences in the ability to determine and compare the relative importance of influential parameters reflected in the fossil record versus the modern. Hence, ancient bioturbated intervals do not fully represent a snapshot of the modern, precluding quantification of some parameters, most notably the thickness of the mixed layer. These limitations underscore the importance of contextualizing bioturbation within its sedimentological framework to better understand the unique nature/characteristics of trace fossil assemblages. Ultimately, a nuanced evaluation of the interplay of bioturbation and sedimentation is essential for advancing interpretations of paleoenvironmental and evolutionary dynamics and increase awareness of the idiosyncratic aspects of the trace-fossil record.

The importance of earthworms for soil functioning is widely accepted and is mainly linked to their burrowing, feeding and casting behaviours. However, our knowledge of earthworm behavior is still limited by the lack of efficient and easy-to-use methods. In this work, we describe and test a new marker of earthworm bioturbation. Dense particles of tungsten, visible in X-ray images, were located at a certain depth in repacked soil cores inoculated by either Lumbricus terrestris or Aporrectodea caliginosa, alone or in combination. This marker was compared to the classical luminophore method (i.e. colored sand particles) generally used in aquatic ecology. The dynamics of both the burrow systems and the casting activities was followed using X-ray tomography every two weeks for a period of 10 weeks. Below ground casting activities could be assessed since parts of the casts excreted by the earthworms were marked by tungsten and appeared white in the images. The time dynamics of both burrow and cast productions were almost linear and significantly influenced by the earthworm species and the presence of litter. As expected, L. terrestris created larger (up to 50 cm3) and deeper burrow systems and made fewer macropores compared to A. caliginosa. Surprisingly, both species were equally influenced by the presence of litter, and this highlighted their behavioral plasticity. For example, A. caliginosa decreased by 32 % the volume of burrows in the presence of litter and the resulting burrow system was significantly shallower which showed that this endogeic species is indeed able to partly feed on surface litter. The use of tungsten particles is a promising new tool to accurately characterize the casting activities of earthworms in the soil and to study behavioral plasticity under the influence of environmental factors.

An in-situ experiment was conducted in a young mangrove with no history of oil contamination (French Guiana). Control and oil-contaminated sediments were sampled one month after exposure and analyzed to a depth of 18 cm to assess natural oil depletion and changes in benthic communities. High biodegradation percentages (89-99 %) of n-alkanes and polycyclic aromatic hydrocarbons were measured. The microbiological results suggest that this degradation is strongly connected to several bacterial taxa. A 90 % decrease in the meso- (>250 mm) and macro-benthic organisms' (>1 mm) densities was observed. The oil has also significantly impacted the composition of the benthos, as well as the microorganisms responsible for mediating biogeochemical functions associated with nitrogen turnover. While chemical and microbiological analyses revealed a high bioremediation potential by the indigenous microbes, an oil spill would be a catastrophic event for the benthic fauna, which could, in turn, affect the microbial communities.

Martinique's mangroves, which cover 1.85 ha of the island (<0.1 % of the total area), are considerably vulnerable to local urban, agricultural, and industrial pollutants. Unlike for temperate ecosystems, there are limited indicators that can be used to assess the anthropogenic pressures on mangroves. This study investigated four stations on Martinique Island, with each being subject to varying anthropogenic pressures. An analysis of mangrove sediment cores approximately 18 cm in depth revealed two primary types of pressures on Martinique mangroves: (i) an enrichment in organic matter in the two stations within the highly urbanized bay of Fort-de-France and (ii) agricultural pressure observed in the four studied mangrove stations. This pressure was characterized by contamination, exceeding the regulatory thresholds, with dieldrin, total DDT, and metals (As, Cu and Ni) found in phytosanitary products. The mangroves of Martinique are subjected to varying degrees of anthropogenic pressure, but all are subjected to contamination by organochlorine pesticides. Mangroves within the bay of Fort-de-France experience notably higher pressures compared to those in the island's northern and southern regions. In these contexts, the microbial communities exhibited distinct responses. The microbial biomass and the abundance of bacteria and archaea were higher in the two less-impacted stations, while in the mangrove of Fort-de-France, various phyla typically associated with polluted environments were more prevalent. These differences in the microbiota composition led to the identification of 65 taxa, including Acanthopleuribacteraceae, Spirochaetaceae, and Pirellulaceae, that could potentially serve as indicators of an anthropogenic influence on the mangrove sediments of Martinique Island.

The increased frequency of heatwaves expected in the context of global warming will affect socio-ecological systems such as shellfish beds at intertidal seagrass meadows. A mesocosm experiment was performed to assess the effects of a simulated atmospheric heatwave during low tide on the bioturbation indicators and growth of the commercial juvenile native Ruditapes decussatus and the introduced clam R. philippinarum, and on their interactions with the seagrass Zostera noltei. Under the heatwave, heat dissipation at 5 cm depth was significantly greater in the sediments below Z. noltei than below bare sand, the photosynthetic efficiency (Fv/Fm) of Z. noltei decreased and the clams tended to grow less. Furthermore, after the heatwave clams below bare sand tended to burrow deeper than those below Z. noltei, indicating that seagrass provided a refuge for clams. Ruditapes phil-ippinarum grew less, and did not burrow as deeply as R. decussatus, which may imply greater vulnerability to desiccation and heat at low tide. The particle displacement coefficient (PDC) of R. philippinarum indicated lower bioturbation values in Z. noltei than in bare sand and was a suitable bioturbation indicator for juvenile Ruditapes spp. clams. In Z. noltei coexisting with R. philippinarum, the Fv/Fm values were higher than without clams after a recovery period, which may be linked to the assimilation of phosphate excreted by the clams and suggests a facilitative interaction. No such interaction was observed with R. deccusatus, probably because of its deeper burrowing depth. The findings suggest reciprocal facilitative interactions between R. philippinarum and Z. noltei and the potential contribution of Z. noltei to the sustainability of clams under global warming scenarios, which may support management actions aimed at enhancing the coexistence between shellfishing activities and sea -grass conservation.

Poplars establish on alluvial bars within sand and gravel-bed rivers. Alluvial bars also provide particularly suitable habitats for the proliferation of ants. We hypothesized that ants, by modifying substrate structure and resource availability in fluvial habitats, positively influence poplar growth during its establishment stage. We conducted a preliminary nine-month ex situ greenhouse experiment with one ant species (Lasius niger L.) and six different genotypes of poplar cuttings (Populus nigra L.), both collected on the Garonne River, SW France. Three main treatments: ‘P. nigra alone’, ‘P. nigra without ants and with ant food’ and ‘P. nigra with ants and ant food’ were applied. After one growing season, we tested differences in branching length and biomass of stems, roots and leaves. Certain genotypes showed significant differences in growth, but there were no significant differences in stem length, dry mass of stems and roots between the three treatments. The total biomass of poplars after the first growing season was positively affected by the initial size of the cuttings and was modulated by the genotype independently from the treatments. However, an increased poplar growth for the treatment without ants and with ant food was observed according to significant differences in dry weight of leaves and total biomass (i.e. dry mass of stems, roots and leaves) for the pooled genotypes across treatments. We discuss our results with the aim of serving as a reference for future in situ and ex situ experiments and field measurements exploring interactions between ants and poplars, specifically in riparian ecosystems.

The microbial communities inhabiting the Atlantic-East Pacific (AEP) mangroves have been poorly studied, and mostly comprise chronically polluted mangroves. In this study, we characterized changes in the structure and diversity of microbial communities of mangroves along the urban-to-rural gradient of the Cayenne estuary (French Guiana, South America) that experience low human impact. The microbial communities were assigned into 50 phyla. Proteobacteria, Chloroflexi, Acidobacteria, Bacteroidetes, and Planctomycetes were the most abundant taxa. The environmental determinants found to significantly correlated to the microbial communities at these mangroves were granulometry, dieldrin concentration, pH, and total carbon (TC) content. Furthermore, a precise analysis of the sediment highlights the existence of three types of anthropogenic pressure among the stations: (i) organic matter (OM) enrichment due to the proximity to the city and its wastewater treatment plant, (ii) dieldrin contamination, and (iii) naphthalene contamination. These forms of weak anthropogenic pressure seemed to impact the bacterial population size and microbial assemblages. A decrease in Bathyarchaeota, "Candidatus Nitrosopumilus", and Nitrospira genera was observed in mangroves subjected to OM enrichment. Mangroves polluted with organic contaminants were enriched in Desulfobacteraceae, Desulfarculaceae, and Acanthopleuribacteraceae (with dieldrin or polychlorobiphenyl contamination), and Chitinophagaceae and Geobacteraceae (with naphthalene contamination). These findings provide insights into the main environmental factors shaping microbial communities of mangroves in the AEP that experience low human impact and allow for the identification of several potential microbial bioindicators of weak anthropogenic pressure.

Caleta Valdés (CV) is a coastal lagoon of the Patagonian Atlantic coast located in the Península de Valdés declared as Humanity Mundial Patrimony due to its remarkable biodiversity, ecosystemic richness, and pristine state. Marine mammal populations are well documented in this area but few studies have been carried out on the local macrobenthic communities. The goals of this study were (a) to evaluate for the first time the seasonal variation of the structure and activity (i.e., sediment reworking) of the intertidal macrobenthic communities of CV, and (b) to validate an ex situ experimental protocol for future ecotoxicological studies. To do so, sedimentary (granulometry, water content, and organic matter) and biological (macrobenthic assemblages, biodiffusive-like and advective sediment reworking components) parameters were analyzed using a combination of in situ and ex situ measurements. Overall, polychaete and crustacean dominated the macrobenthic community. The highest abundances were found in spring–summer along with a predominance of biodiffusors versus conveyors. Ex situ and in situ measurements demonstrated similar results, thus allowing validation of an ex situ experimental procedure for macrobenthic community and functioning studies. In addition, these results provide a first baseline of benthic information on CV that will be helpful to monitor the effects of potential pollution in Patagonian coastal systems.

Particle mixing and irrigation of the seabed by benthic fauna (bioturbation) have major impacts on ecosystem functions such as remineralization of organic matter and sediment-water exchange. As a tribute to Prof. Gaston Desrosiers by the Nereis Park association, eighteen laboratories carried out a collaborative experiment to acquire a global snapshot of particle reworking by the polychaete Hediste diversicolor at 16 sites surrounding the Northern Atlantic. Organisms and soft sediments were collected during May - July at different geographical locations and, using a common laboratory protocol, particulate fluorescent tracers (`luminophores') were used to quantify particle transport over a 10-day period. Particle mixing was quantified using the maximum penetration depth of tracers (MPD), particle diffusive coefficients (D-b), and non-local transport coefficients (r). Non-local coefficients (reflecting centimeter scale transport steps) ranged from 0.4 to 15 yr(-1), and were not correlated across sites with any measured biological (biomass, biovolume) or environmental parameters (temperature, grain size, organic matter). Maximum penetration depths (MPD) averaged similar to 10.7 cm (6.5-14.5 cm), and were similar to the global average bioturbation depth inferred from short-lived radiochemical tracers. MPD was also not correlated with measures of size (individual biomass), but increased with grain size and decreased with temperature. Bio-diffusion (D-b) correlated inversely with individual biomass (size) and directly with temperature over the environmental range (Q(10) similar to 1.7; 5-21 degrees C). The transport data were comparable in magnitude to rates reported for localized H. diversicolor populations of similar size, and confirmed some but not all correlations between sediment reworking and biological and environmental variables found in previous studies. The results imply that measures of particle reworking activities of a species from a single location can be generally extrapolated to different populations at similar conditions.

Earthworms feed on organic matter present at the soil surface or within the soil. Thus, its distribution in the soil profile is likely to greatly influence earthworm behavior and, in turn, their burrow system. To test this idea, two anecic and two endogeic earthworm species were introduced into repacked soil cores (depth = 30 cm) upper half filled with a top soil containing 4% organic matter (0–15 cm) and lower half filled with a deep soil at 2% organic matter (15–30 cm). Earthworm behavior was studied using X-ray tomography combined with luminophores (colored particulate tracers of 63–125 μm size) placed at 0, 3, and 12 cm depth, a method widely used in sediment ecology. We observed that anecic and endogeic earthworms had contrasting reactions to the conditions with only endogeic species burrowing more intensively in the upper part. From a quantitative point of view, only a few percent of luminophores were displaced. However, luminophore displacements also provided qualitative information to complement the tomography: (i) endogeic species and especially Aporrectodea caliginosa bioturbated the most soil close to the surface (3 cm depth) and (ii) the two anecic species influenced the luminophore distribution differentially with Lumbricus terrestris displacing significantly more luminophores, whatever their initial depth, than Aporrectodea nocturna due to intense surface cast activity. Beyond methodological developments, our study found that endogeic earthworms burrow more in zones with higher organic matter contents and this explains why they are mainly found close to the soil surface in non-tilled soils.

The inventory and remediation of contaminated sites have emerged as top environmental priorities worldwide. A large body of evidence has accumulated to show how soil contamination affects biological communities and ecological processes. This knowledge has yet to be used for the development of indicators of soil quality that are meaningful to end-users and are easy to implement in soil quality assessment schemes. In this study, we used quantifiable measures of litter decomposition, a key biophysical process, as indicators of the ecological impact of soil contamination by trace metals and hydrocarbons. We conducted a litterbag experiment with coarse and fine mesh bags to compare highly vs. minimally contaminated sites within eight locations representative of a wide array of environmental conditions and types of pollution. Contrary to the common assumption that soil contamination hampers soil functions, idiosyncratic responses were detected for litter decomposition rate and decomposer activity metrics. A negative relationship between detritivore and microbial responses to soil contamination indicates that wherever the activity of one group of decomposers is reduced, increase in activity of the other group may ensure litter decomposition to proceed at rate similar or higher than baseline rate. This finding may indicate that compensatory dynamics in soil communities is important in determining ecosystem stability against chemical stressors. As litter decomposition may inform on the capacity of terrestrial ecosystems to cope with soil contamination, it may be a useful complement to chemical soil analyses in routine soil quality assessment schemes.

Bioindicators assess the mangroves ecological state according to the types of pressures but they differ with the ecosystem's specificities. We investigated benthic meiofauna diversity and structure within the low human-impacted mangroves in French Guiana (South America) in response to sediment variables with various distances to the main city. Contaminant's concentrations differed among the stations, but they remained below toxicity guidelines. Meiofauna structure (Foraminifera, Kinorhyncha, Nematoda) however varied accordingly. Nematode's identification brought details on the sediment's quality. The opportunistic genus Paraethmolaimus (Jensen, 1994) strongly correlated to the higher concentrations of Hg, Pb. Anoxic sediments were marked by organic enrichment in pesticides, PCB, and mangrove litter products and dominance of two tolerant genus, Terschellingia (de Man, 1888) and Spirinia (Gerlach, 1963). In each of these two stations, we found many Desmodora individuals (de Man, 1889) with the presence of epibionts highlighting the nematodes decreased fitness and defenses. Oxic sediments without contaminants were distinguished by the sensitive genera Pseudocella (Filipjev, 1927) and a higher diversity of trophic groups. Our results suggested a nematodes sensitivity to low contaminants concentrations. Further investigations at different spatio-temporal scales and levels of deterioration, would be necessary to use of this group as bioindicator of the mangroves' ecological status.

Temperature is known to stimulate metabolism with cascading effects on multiple biological processes. These effects may, however, vary across processes, types of organisms or levels of biological organisation. They can also vary with nutrient availability, with potentially stronger temperature effects when nutrients are not limiting. This context dependence of temperature effects on processes challenges our ability to anticipate their consequences on ecosystems in a changing world. In headwater streams, the decomposition of allochthonous leaf litter, driven by both microbial decomposers and invertebrates, is known to respond to both temperature and nutrient availability. These food webs are highly tractable and a useful model system to investigate the variations of temperature effects on processes across types of organisms (microbes versus invertebrates), resource availability levels (nutrient concentration), and levels of biological organisation (from individual to ecosystem). In a microcosm experiment, we measured the effects of temperature and nitrogen availability (four levels each) on respiration rates of litter-consuming microbes and invertebrates and their decomposition activity in different contexts of food web complexity. The latter included one treatment without invertebrate detritivore (microbial decomposers only), three single invertebrate taxa (Gammarus, Potamophylax, and Sericostoma) treatments, and one mixed invertebrate taxa treatment (three‐species altogether). Microbial processes increased nearly exponentially with temperature (Arrhenius model, activation energy (± 95% confidence interval) = 0.56 ± 0.53 and 1.00 ± 0.23 eV for litter decomposition and respiration), while invertebrate‐driven processes increased (activation energy from 0.47–1.15 eV) up to a maximal value at an intermediate temperature (c. 11–15°C depending on species and process), above which process rates decreased. By contrast, litter consumption in mixed invertebrate species treatments was not significantly influenced by temperature, because of a negative effect of species mixing occurring above 12°C. Nitrogen had a weaker influence, only slightly stimulating litter consumption by mixed‐species invertebrates, which limited the scope for synergies with temperature effects. Our results raise issues about how aquatic litter consumers meet their energy requirements at high temperature and suggest that a general consequence of warming could be loss of carbon through mineralisation in headwater stream food webs. In several aspects, our results deviate from expectations based on universal relationships between temperature and individual metabolism (e.g. metabolic theory of ecology), suggesting that we may need to develop less simplistic assumptions to predict the consequence of warming on ecosystem processes.

Mangrove forests are formed by mangrove trees and shrubs that grow in the intertidal zone at the sea-continent interface. They constitute major ecosystems of tropical to subtropical muddy coasts that perform several ecological functions, including: mitigation of coastal erosion and flooding hazards associated with storm waves, extreme tides and tsunami, providing nurseries for some estuarine and coastal species (e.g., shrimps, fishes), production and recycling of organic matter, carbon storage, functioning as long-term sinks for several contaminants. World mangroves face a number of threats with increasing habitat destruction caused by direct and indirect anthropogenic pressures coupled with global climate change. They are known to be extremely vulnerable to oil spills. Even if the fate and impact of oil spills in such ecosystems have been partially monitored and experimentally studied (e.g., 30-year TROPICS field experiment in Panama islands, replicated field trials conducted in central Queensland, Australia) significant gaps in knowledge remain. The oil dynamic in such ecosystem is complex and depends on the abiotic-biotic processes interactions. Understanding the fate and impact of the oil spill thus requires an integrated approach of the functioning of the whole mangroves system facing the pollution. The case of the French Guiana mangroves, subjected to intense hydromorpho-sedimentary dynamics under the direct influence of the massive discharge of suspended sediments from the Amazon River, will serve as conceptual model to highlight the importance of the need for a specific Ecosystem-based Management response in case of oil spill.

European Water Framework Directive is enforced in five tropical French Oversea Territories where mangroves are present. Developing bioindication tools to support the ecosystem-based management approach of the Directive is needed. A series of expert workshops was organized and led to the proposal of a strategy and of an applied research program to develop bioindication tools. The proceedings of the workshops are presented as a case study, as this is the first time such an integrative ecosystem-based approach is proposed in mangroves, combining structural and functional aspects, from forest structure to benthic community functioning.

Laboratory mesocosm incubations were undertaken to investigate the influence of burrowing shrimp Trypaea australiensis (marine yabby) on sediment reworking, physical and chemical sediment characteristics and nutrients in sandy sediments receiving mangrove (Avicennia marina) leaf litter. Mesocosms of sieved, natural T. australiensis inhabited sands, were continually flushed with fresh seawater and pre-incubated for 17 days prior to triplicates being assigned to one of four treatments; sandy sediment (S), sediment + yabbies (S+Y), sediment + leaf litter (organic matter; S+OM) and sediment + yabbies + leaf litter (S+Y+OM) and maintained for 55 days. Mangrove leaf litter was added daily to treatments S+OM and S+Y+OM. Luminophores were added to mesocosms to quantify sediment reworking. Sediment samples were collected after the pre-incubation period from a set of triplicate mesocosms to establish initial conditions prior to the imposition of the treatments and from the treatment mesocosms at the conclusion of the 55-day incubation period. Yabbies demonstrated a clear effect on sediment topography and leaf litter burial through burrow creation and maintenance, creating mounds on the sediment surface ranging in diameter from 3.4 to 12 cm. Within S+Y+OM sediments leaf litter was consistently removed from the surface to sub-surface layers with only 7.5% ± 3.6% of the total mass of leaf detritus added to the mesocosms remaining at the surface at the end of the 55-day incubation period. Yabbies significantly decreased sediment wet-bulk density and increased porosity. Additionally, T. australiensis significantly reduced sediment bio-available ammonium (NH4+bio) concentrations and altered the shape of the concentration depth profile in comparison to the non-bioturbated mesocosms, indicating influences on nutrient cycling and sediment-water fluxes. No significant changes for mean apparent biodiffusion coefficients (Db) and mean biotransport coefficients (r), were found between the bioturbated S+Y and S+Y+OM mesocosms. The findings of this study provide further evidence that T. australiensis is a key-species in shallow intertidal systems playing an important role as an ‘ecosystem engineer’ in soft-bottom habitats by significantly altering physical and chemical structures and biogeochemical function.

Coated sheets for car body are assembled by spot-welding and, more and more, by adhesive bonding. Thus, during life time, the coating endures stresses which can lead to the failure of the whole bonded assembly. The behavior of the zinc coating has then to be primarily studied during tension of flat samples. Several investigation techniques, including in-situ characterizations and 3D observations, are combined to observe and understand the damage mechanisms of the zinc coating during plastic deformation. A specific attention is paid to the influence of temper rolling which is usually applied on low-carbon steel sheets after annealing and hot-dip coating. Damage is mainly observed at the boundary of large zinc grains lying on the surface plateaus, non-deformed by rolling, and often nucleates at the defects due to dendritic zinc solidification.