Hard Substrates Research Articles

High Vulnerability of Rhodolith Bed Frameworks and Underlying Sediment to Ongoing Ocean Climate Change

ABSTRACTRhodoliths are non‐geniculate, free‐living coralline red algae that can accumulate on the seafloor and form structurally complex habitats supporting highly biodiverse communities termed rhodolith beds. Limited understanding of key rhodolith kinetical attributes and how they scale with environmental variability limits ability to predict changes in rhodolith bed distribution and abundance in a globally changing ocean climate. We carried out two experiments in an oscillatory wave tank to test the effects of (1) rhodolith (Boreolithothamnion glaciale) density and wave velocity on rhodolith displacement and abrasion over a hard substratum and (2) rhodolith density on rhodolith displacement and the stability of underlying sediment. We established that on a hard substratum, (1) a threshold wave velocity of ~0.3 m s−1 is required to induce noticeable displacement in average‐sized rhodoliths and (2) rhodolith abrasion increases (quasi‐linearly) with wave velocity up to this threshold. We also showed that (3) for a same rhodolith density, rhodolith displacement is at least two times smaller on a sedimentary than hard substratum and (4) the loss of sediment underneath rhodoliths decreases (quasi‐linearly) with an increase in rhodolith density. Rates documented and strong scaling with changes in water motion and rhodolith density indicate that relatively small changes in the density of rhodoliths or hydrodynamic forces can quickly destabilize rhodolith bed frameworks and underlying sediment. These rates can be used to develop predictive models of change in rhodolith bed distribution and abundance that can in turn inform development of more accurate, science‐based rhodolith bed conservation strategies.

Linking fish bioturbation to life history in a eutrophic wetland: An analysis of fish contributions to internal nutrient loading

Abstract Bioturbation (sediment disturbance by animal actions) effects on nutrient cycling and nutrient levels in surface waters are difficult to quantify, in part because the diversity and magnitude of species‐specific influences are poorly understood. These influences may have consequences for the management of the trophic state of freshwater ecosystems. Fish cause bioturbation in freshwater and marine ecosystems by digging in benthic sediments, manipulating periphyton mats while searching for prey and scraping hard substrates while feeding. We used experimental enclosures (2.25 m2) to quantify bioturbation‐mediated phosphorus (P) and nitrogen (N) regeneration from sediment by three species of fish that differ in interactions with the benthos (largemouth bass, Micropterus salmoides; tilapia, Oreochromis spp.; and sailfin catfish, Pterogoplichthys spp.) in shallow eutrophic wetlands in Southern Florida. Tilapia are omnivores that include detritus in their diet (winnowing or ingesting sediments) and dig nests in soft sediments year round, sailfin catfish actively burrow into substrate and consume detritus (digging and ingesting sediments), and largemouth bass are piscivores that do not routinely interact with the benthos when feeding but may dig nests in soft sediment in spawning season (January–April). We quantified the amount of suspended flocculent organic matter and changes in water column nutrients (total phosphorus [TP] and total nitrogen [TN]) in 2‐week trials for each species and estimated the portion of nutrient increases relative to fishless controls that could be attributed to bioturbation‐mediated internal nutrient loading through suspension of organic matter (as opposed to excretion or other sources of nutrient loading). Water column nutrient concentrations increased with increasing biomass for all species, but the bioturbation contribution differed by species. Largemouth bass increased water column nutrient concentrations (TP: 86% and TN: 5% relative to controls) but did not influence water column suspended particulate matter through bioturbation of sediment. Tilapia increased water column nutrients a modest amount (TP: 8%; TN: 15%), of which a small portion was attributed to bioturbation (c. 18% of TP). Sailfin catfish raised water column nutrients substantially (TP: 105%; TN: 46%) and up to 100% of the increased TP was attributed to bioturbation. Sailfin catfish also suppressed algal growth and TP accumulation on the sides of the enclosures and reduced nutrient concentrations of the flocculent sediments. Our results were consistent with our hypothesis that behaviour and foraging traits affect bioturbation contributions to nutrient loading. The results also demonstrated that species with similar net effects like largemouth bass and sailfin catfish, added nutrients via different mechanisms (i.e. excretion vs. bioturbation). Considering the feeding strategies and interactions with the substrate of common fish species may assist managers in meeting nutrient reduction goals for eutrophic wetlands and managed freshwater systems.

Spatial Variation in Upper Limits of Coral Cover on the Great Barrier Reef

ABSTRACTAimIdentifying the maximum coral cover that a coral community can sustain (i.e., its ‘upper limit’) is important for predicting community dynamics and improving management strategies. Here, we quantify the relationship between estimated upper limits and key environmental factors on coral reefs: hard substrate availability, temperature and water clarity.LocationGreat Barrier Reef (GBR), Australia (over 1400 km).Time Period1990 to 2022.Major Taxa StudiedScleractinian corals.MethodsWe used 32 years of data on coral cover around reef perimeters. Each reef was divided into four wave‐exposure habitats depending on prevailing wind conditions. For each site, we determined if hard coral cover had reached a plateau or upper limit. Next, we extracted existing estimates of hard substrate availability, modelled water temperature and Secchi depth. Then, we quantified the relationship between these environmental variables and the upper limits.ResultsWe found varying upper limits across the GBR, with a median of 33% coral cover and only 17% of the estimated upper limits exceeded 50% coral cover. Upper limits increased towards the southern reefs. Our results show that upper limits increased with increasing hard substrate availability and decreased with temperature and, to a lesser extent, with water clarity.Main ConclusionsThe upper limits estimated in this study are much lower than what is commonly assumed when modelling ecological dynamics, most likely resulting in predicted recovery rates being inappropriately high. Although hard substrate ultimately restricted upper limits, there are mechanisms constraining the proportion of hard substrate that is covered by hard corals. The negative relationship between temperature and upper limits cannot be explained by changes in macroalgal abundance but may be related to changes in species composition. The quantitative relationships between the upper limits of coral cover and environmental variables will provide critical information to prioritise sites for management interventions.

Research on wafer-level SiC microgroove array process via integrated molding-etching process

Silicon carbide (SiC) microgroove arrays (MGAs) play a pivotal role as optical components in modern optical engineering. This paper introduces an innovative approach for the fabrication of MGAs on hard materials. This method integrates hot embossing (HE) and inductively coupled plasma (ICP), utilizing polydimethylsiloxane (PDMS) as the intermediary mold due to its excellent demolding performance and shape replication qualities. The process involves transferring the MGAs from the Ni-P master mold to the PDMS mold, followed by replication onto the photoresist surface by hot embossing. Subsequently, the MGAs on the photoresist mask is etched into the hard substrate material using ICP etching. For efficient customization of MGAs, a reliable geometrical model based on angular dependence theory is developed to assist in selecting process parameters and designing masks. The correlation between etching selectivity and characteristic dimension is elucidated. Experimental results demonstrate that the sidewall angle decreases with higher selectivity and increases with a greater sidewall angle on the patterned mask. Plasma etching reveals unaffected areas in convex corners and the forming errors in concave corners, highlighting a high angular dependence of the etch rate. Moreover, minimizing microdefects can be achieved by optimizing process parameters and reducing etch time.

Addition of mussel shells enhance marine benthic biodiversity in two degraded coastal soft sediment ecosystems

The decline in coastal shellfish populations, attributed to anthropogenic stressors such as harvesting via dredging, can deplete the seabed of vital biogenic habitat. This removal of shellfish significantly reduces habitat complexity, biodiversity, and the hard substrate required for the natural recovery of some key species. A common method for oyster restoration involves deploying oyster shell material to provide habitat and substrate for settling larval oysters. In contrast, hard substrate is not required for the mussel lifecycle and as a result the deployment of mussel shell for seabed restoration has received minimal attention, with the effects of reintroducing this material poorly understood. Deploying mussel shell material has the potential to aid in ecosystem recovery, including reviving seabed biodiversity, especially in areas that have been depleted of shellfish via damaging methods such as dredging. This study aimed to investigate the ecosystem effects of returning mussel shells onto two locations with differing soft sediment (sand and mud) in areas historically subjected to excessive dredging of mussel populations and sedimentation. Within 2 years 4 months the infaunal taxa richness was higher in the shell areas compared to the reference areas in both locations, while abundance of infauna was higher in only the sand location and infaunal diversity did not differ at either location. Epifaunal diversity was also higher in the shell area compared to the reference areas at both locations, while the abundance and richness did not differ. Few significant differences were seen in benthic biogeochemical variables between the reference and shell areas and those observed were likely the result of the addition of the shell material changing the sediment composition. These findings demonstrate that mussel shells are a restoration tool that can enhance epifaunal biodiversity and infaunal taxa richness in soft sediment ecosystems historically impacted by shellfish overharvesting and sedimentation.

The diversity of commercial marine bivalves in the Nha Phu Lagoon, Khanh Hoa Province, south-central Vietnam

The study was conducted as part of the Joint Vietnam–Russia Tropical Science and Technology Research Center’s project on indicator organisms in the marine environment of south-central Vietnam. The research focused on coastal areas with significant anthropogenic impacts, revealing that biological resources directly affect the livelihood and activities of coastal populations. These resources are dynamic and subject to both human and natural factors. The material from the soft-bottom zone was collected using a grab rake with a mesh bag at the end. Scuba diving equipment was used in areas with a hard substrate and mudflats. In addition, during sample collection, several mollusc specimens were acquired from fishermen who cought marine organisms in that lagoon. Comparing the results with previous studies on bivalve resources in the area, the Nha Phu Lagoon was found to harbour a wide range of economically valuable bivalve species. A total of twenty-seven bivalve species from thirteen families were identified, with the family Veneridae having the highest number of species (eight). The most abundant catches were from the families Ostreidae and Mytilidae, primarily consisting of Magallana gigas (Thunberg 1793) and Perna viridis (Linnaeus 1758), both cultured in the lagoon. Apart from their economic value, these two species also play crucial roles in the ecosystem by filtering water and retaining organic debris in the environment.

The investigation of support effect from hard substrate to soft coating of PI/EP-PTFE under different coating thicknesses and frictional contacts

Engine bearings on ships can experience rapid failure under extreme conditions, such as when seawater infiltrates the engine compartment due to collisions with reefs or missile attacks. To enhance the self-lubrication and wear resistance of these bearings, a composite coating consisting of ZrO2-PI/EP-PTFE has been designed. This coating was applied using liquid spraying technology onto the surfaces of A370 aluminum alloy, CuPb22Sn2.5 copper alloy, and 15# carbon steel. Three different coating thicknesses—20 μm, 30 μm, and 40 μm—were applied to each substrate. The tribological properties of these coatings on the three substrates were investigated under both dry sliding wear and seawater corrosion conditions. The results indicated that the tribological performance of the coatings is influenced by factors such as the coating hardness, frictional contacts, and the supporting effect of the substrate. The hardness and elastic modulus of the coatings decreased as the coating thickness increased. A thicker coating results in reduced support from the substrate. The adhesive wear of these coatings under dry sliding wear conditions on the different substrates is also presented. The coefficients of friction (CoFs) of these coatings increased with coating thickness on all three substrates. In contrast, the wear rates decreased as the coating thickness increased. The hardness of the coating was influenced by the support effect of the substrate. The primary factors governing the tribological performance of the coating under dry sliding conditions are the pinch action of the hard grinding ball against the soft coating on the hard substrate and the contact pressure. Abrasive wear, spalling wear, plough grooves, and spalling pits were observed under seawater corrosion conditions. These findings suggest that increased coating thickness is associated with lower coefficients of friction (CoFs) and wear rates. The main contributing factors are seawater corrosion and the scouring effect of high-frequency reciprocating friction.

The influence of temperature on oxygen uptake of red alga Hildenbrandia rivularis – the next step of the indicatory potential revision

Hildenbrandia rivularis belongs to the freshwater red algae and is cosmopolitan. In some European countries, this species is protected, e.g., in Poland, where it mainly inhabits highly oxygenated, fast-flowing ecosystems. This alga is often considered both a bioindicator of oligotrophic waters and a relatively rare species in Europe. However, the expansion and ecological tolerance of H. rivularis have increased over the last decades; thus, there is an urgent call to retest its environmental optima and significance for bioindicative potential. In this paper, H. rivularis from Welna River (Poland) growing on hard substrates was tested. In addition to genetic, microscopic, and physicochemical analyses, we also delivered for the first time the relationship between the transient temperature changes (15 – 45 °C, with 5 °C intervals) and oxygen uptake of H. rivularis (based on ex situ measurements of O2 consumption by thalli). Interestingly, for the eurythermal H. rivularis, at the lowest temperature (15 °C) treatment, the O2 uptake was undetectable, but the respiratory rate reached maximal velocity at the two highest temperatures (40 and 45 °C). Importantly, the respiration of this alga was relatively stable across temperature gradient 20 – 35 °C. This observation could explain why this species has been disappearing from colder waters of uplands and mountains and started to prefer warmer lowland water ecosystems. The further increase in global warming can significantly accelerate this tendency, thus causing a significant change in the H. rivularis distribution pattern known from the previous literature. Finally, our research sheds new light on the bioindicative potential of H. rivularis.

Cryptofaunal communities are influenced by benthic cover and fish abundance in a large Caribbean coral reef system

Abstract Small-sized invertebrates inhabiting hard substrates in coral reefs (a.k.a. cryptofauna) contribute substantially to reef biodiversity, but their patterns of distribution and ecological controls are poorly understood. Here, we characterized the cryptofauna community and explored “bottom-up” and “top-down” controls by benthic cover and fish abundance, respectively. We sampled the cryptofauna inhabiting the reef terrace from 13 sites along 200 km in Jardines de la Reina (Cuba), a well-preserved and protected area in the Caribbean. We counted 23,959 invertebrates of 14 higher taxa, being the most abundant Copepoda (54%), Nematoda (21%), Mollusca (7%), Ostracoda (5%), Polychaeta (5%), and Amphipoda (3%). Richness, abundance, and community structure varied across the reefs without any geographical gradient of distribution. One-third of the variance occurred at site scale (~ 10 km), and half occurred at quadrat scale (~ 1 m). Algal cover promoted cryptofauna richness and abundance likely providing substrate and food, while live coral cover negatively influenced nematode abundances, potentially due to coral defenses. Relationships between cryptofauna and reef fishes were also present, with invertivores and herbivores negatively affecting cryptofauna abundance likely due to direct or indirect predation pressures. This research highlights the important roles of bottom-up and top-down controls, by algal/coral cover and fishes, respectively, on cryptofauna and in extension to coral reef biodiversity. Current threats by climate change are expected to alter these controls on cryptofauna resulting in changes to diversity, trophodynamics and energy flows of coral reefs.

Boring into rock and hard substrates by the midge, Axarus (Diptera; Chironomidae).

Boring into rock and hard substrates by the midge, Axarus (Diptera; Chironomidae).

Ecological shifts underlie parallels between ontogenetic and evolutionary allometries in parrotfishes.

During ontogeny, animals often undergo significant shape and size changes, coinciding with ecological shifts. This is evident in parrotfishes (Eupercaria: Labridae), which experience notable ecological shifts during development, transitioning from carnivorous diets as larvae and juveniles to herbivorous and omnivorous diets as adults, using robust beaks and skulls for feeding on coral skeletons and other hard substrates. These ontogenetic shifts mirror their evolutionary history, as parrotfishes are known to have evolved from carnivorous wrasse ancestors. Parallel shifts at ontogenetic and phylogenetic levels may have resulted in similar evolutionary and ontogenetic allometric trajectories within parrotfishes. To test this hypothesis, using micro-computed tomography (μCT) scanning and three-dimensional geometric morphometrics, we analyse the effects of size on the skull shape of the striped parrotfish Scarus iseri and compare its ontogenetic allometry to the evolutionary allometries of 57 parrotfishes and 162 non-parrotfish wrasses. The young S. iseri have skull shapes resembling non-parrotfish wrasses and grow towards typical adult parrotfish forms as they mature. There was a significant relationship between size and skull shapes and strong evidence for parallel ontogenetic and evolutionary slopes in parrotfishes. Our findings suggest that morphological changes associated with the ecological shift characterizing interspecific parrotfish evolution are conserved in their intraspecific ontogenies.

Substrate stiffness modulates extracellular vesicles’ release in a triple-negative breast cancer model

Aim: The microenvironment effect on the tumoral-derived Extracellular Vesicle release, which is of significant interest for biomedical applications, still represents a rather unexplored field. The aim of the present work is to investigate the interrelation between extracellular matrix (ECM) stiffness and the release of small EVs from cancer cells. Here, we focus on the interrelation between the ECM and small extracellular vesicles (sEVs), specifically investigating the unexplored aspect of the influence of ECM stiffness on the release of sEVs. Methods: We used a well-studied metastatic Triple-Negative Breast Cancer (TNBC) cell line, MDA-MB-231, as a model to study the release of sEVs by cells cultured on substrates of different stiffness. We have grown MDA-MB-231 cells on two collagen-coated polydimethylsiloxane (PDMS) substrates at different stiffness (0.2 and 3.6 MPa), comparing them with a hard glass substrate as control, and then we isolated the respective sEVs by differential ultracentrifugation. After checking the cell growth conditions [vitality, morphology by immunofluorescence microscopy, stiffness by atomic force microscopy (AFM)], we took advantage of a multi-parametric approach based on complementary techniques (AFM, Nanoparticle Tracking Analysis, and asymmetric flow field flow fractionation with a multi-angle light scattering detector) to characterize the TNBC-derived sEV obtained in the different substrate conditions. Results: We observe that soft substrates induce TNBC cell softening and rounding. This effect promotes the release of a high number of larger sEVs. Conclusion: Here, we show the role of ECM physical properties in the regulation of sEV release in a TNBC model. While the molecular mechanisms regulating this effect need further investigation, our report represents a step toward an improved understanding of ECM-cell-sEVs crosstalk.

Crustacean species off the coast of Kıyıköy (Black Sea, Türkiye) with a new record

Examination of hard- and soft-bottom samples collected off the coast of Kıyıköy (Black Sea, Türkiye) using grabs, quadrats and trawls revealed a total of 39 crustaceans belonging to eight orders. Among the species, Medorippe lanata was recorded in the Black Sea for the first time. Amphipoda dominated on hard and soft substrates in terms of the number of species and individuals. A total of 898 individuals belonging to 27 species were identified on the hard bottom, of which Ampithoe ramondi was the most dominant species (47.4%). On the other hand, a total of 123 individuals belonging to 16 species were recorded on the soft bottom, with Diogenes pugilator (21.1%) being the most dominant species (21.1%). A total of 441 individuals belonging to nine species were found following bottom and beam trawl hauls, with Liocarcinus navigator and L. depurator being the most frequent species. Community parameters were estimated in both hard- and soft-bottom samples.

Expanded distribution and a new genus for rock-inhabiting sea pens (Cnidaria, Anthozoa, Octocorallia, Pennatuloidea)

Sea pens (Superfamily Pennatuloidea) are a specialized group of octocorals that evolved to live embedded in a soft-sedimented seafloor using their peduncles as anchors. Rock-inhabiting sea pens (“rock pens”) were first described in 2011; their peduncle is modified into a suction cup-like structure that allows them to attach onto the surface of hard substrates, an adaptation previously unknown in sea pens. There are currently four species that have been identified as rock pens based on their peduncular morphology: three of these are in the genus Anthoptilum (Anthoptilidae), and one in the genus Calibelemnon (Scleroptilidae). Herein, we explore the geographic distribution and depth ranges of rock pens using observations from remotely operated vehicles and investigate the evolutionary origins of the rock pens. We present a phylogenomic study of sea pens, based on DNA sequences from hundreds of ultraconserved elements (UCE) and compare these trees to those constructed using mitochondrial gene regions. Our results show that the ancestral sea pen had a typical elongated peduncle. The adaptation to attach onto hard, rocky substrates using the special suction cup-like peduncle evolved along a single derived lineage that is sister to a lineage comprising the genus Anthoptilum. We propose all known rock pen species be grouped into a single new genus, described herein, in the family Anthoptilidae, to reflect the phylogenetic history.

Late Ordovician cornulitid tubeworms from high-latitude peri-Gondwana (Sardinia and the Pyrenees) and their palaeobiogeographic significance

Seven Cornulites species, including a new one — Cornulites leonei n. sp., are described from the Upper Ordovician Portixeddu Formation (Katian, stage slices Ka2–3) of Sardinia and the Cavá (lower Katian, stage slice Ka2) and Estana (upper Katian, stage slices Ka3–4) formations of the Pyrenees. The Sardinian and Pyrenean cornulitids represent an adaptation to live in environments with high sedimentation rates and limited hard substrates availability. Their prominent annuli could have had a stabilizing function in the soft sediment that helped cornulitids to keep a favourable position in the sediment to enable suspension feeding. The known Late Ordovician cornulitid diversity in different Gondwana areas is low, usually ranging from one to three taxa, being higher (seven) in Sardinia. Like other benthic groups during the Late Ordovician, the cornulitid tubeworm faunas within the high-latitude peri-Gondwana Province indicate a certain endemism and share morphological and ecological affinities, such as a small body size and tubes with a strikingly small apical angle. Although essentially endemic, some links with cornulitids from the Late Ordovician of Scotland are revealed.

Formation mechanism of radial and circular cracks promoted by delamination in drying silica colloidal deposits.

Cracks with radial and circular patterns are appealing in nature and industry. Although morphologies and propagation conditions of cracks are extensively studied, the formation mechanism of crack pattern by the interaction of channel fracture and interfacial delamination remains elusive. Here, we present the transition of radial to coexisting radial and circular crack patterns when the thickness of colloidal deposits on both hard and soft substrates exceeds a critical value, through the colloidal volume fraction dependence. In addition, a thickness-dependent phase diagram from radial crack to coexistence of radial and circular cracks was constructed with respect to the radius and the volume fractions of silica colloidal deposits. A phase-field fracture model is developed to elucidate how the formation of radial cracks is facilitated by simultaneous delamination. The warping-induced radial tensile stress at the bottom surface of the striped deposit is proportional to the thickness. It leads to subsequent nucleation and growth of circular cracks in thick deposits. This work provides insight into the formation mechanism of complex crack patterns in drying colloidal deposits and revolutionizes the design space of crack-based micro-nano structures.

Effect of overlapping deposition strategy on microstructure and mechanical properties of Al-clad steel by AFSD

Cladding of the aluminum (Al) layer on steel was successfully implemented via additive friction stir deposition (AFSD). We revealed the relationship between the overlapping deposition strategy of AFSD and the resultant microstructure and mechanical properties of Al-clad steel for the first time. Overlapping deposition strategies efficiently improved the adhesion of the Al layer on steel in the boundary region owing to the sufficient material flow and large plastic deformation. This is in contrast to the sample without overlapping where the Al/steel interface in the boundary region is characterized by holes and weak bonding. In particular, the maximum shear strength (109.0 MPa) was obtained for the sample with an overlap of 8 mm, even higher than that of the single-pass sample. This study provided a novel approach to the fabrication of large-scaled clad layers on hard substrates, and this strategy is expected to greatly contribute to the adoption of AFSD in the fields of cladding, joining, and coating.

Self-assembled magnetic particles on hard magnetic materials substrate for simple and rapid SERS detection of organic dye

In this paper, a detection strategy based on Surface-enhanced Raman Scattering (SERS) was proposed to quickly and simply separate target molecules from samples. Fe3O4@SiO2@Ag (FSA) magnetic particles modified with flower-like silver nanosheets were employed for efficient enrichment of target molecules, followed by their self-assembly onto the NdFeB substrate surface in fluid medium. The SERS sensitivity was indirectly adjusted by changing the reaction time to control the morphology of flower-like silver nanosheets on the surface of magnetic particles. SERS experiment showed that the substrate prepared by this detection strategy had high sensitivity, Rhodamine 6G (R6G) could be detected at the concentration of 10−8M and Methylene Blue (MB) could be detected at the concentration of 10−7M, the calculated enhancement factor was 1.34 × 105. In addition, the uniformity of the substrate was evaluated by SERS mapping using 10-6 M R6G, the RSD value of 8.89% was obtained. This detection strategy provides a new idea for simple and rapid SERS detection of organic dye.

Bioerosion and encrustation in Late Triassic reef corals from Iran

Hard substrate communities can impact coral reef growth by adding or removing calcium carbonate when they act as encrusters or bioeroders, respectively. Although such sclerobiont communities are known across the Phanerozoic, the Triassic saw a substantial increase in reef macrobioerosion. This study provides the first quantitative assessment of sclerobionts in a Late Triassic (Norian) reef coral community (from the Nayband Formation in central Iran) and establishes some post-Paleozoic trends in reef bioerosion. Sclerobionts were common on the dominant coral Pamiroseris rectilamellosa and covered between 0 and 26.4% of total coral surface area among the 145 colonies investigated. Encrustation was significantly more prevalent (1.78% of total area) than bioerosion (0.36% of total area). The underside of corals was 3.5 times more affected by sclerobionts than the upper surfaces. This suggests that the sclerobionts preferentially colonized dead parts of the corals. The main encrusting taxa were polychaete worms (76.2%), followed by bivalves (11.9%). The main bioeroders were Polychaeta (51.4%), Porifera (22.2%), and Bivalvia (20.7%). The lack of a correlation between encrustation and bioerosion intensity suggests that the number of sclerobionts is not simply a function of exposure time before final burial. Our review of the published literature suggests a declining trend in the relative importance of bivalves, polychaetes and cirripeds in reefs, whereas sponges increased in importance from the Triassic until today.

Quantifying T cell receptor mechanics at membrane junctions using DNA origami tension sensors.

The T cell receptor (TCR) is thought to be a mechanosensor, meaning that it transmits mechanical force to its antigen and leverages the force to amplify the specificity and magnitude of TCR signalling. Although a variety of molecular probes have been proposed to quantify TCR mechanics, these probes are immobilized on hard substrates, and thus fail to reveal fluid TCR-antigen interactions in the physiological context of cell membranes. Here we developed DNA origami tension sensors (DOTS) which bear force sensors on a DNA origami breadboard and allow mapping of TCR mechanotransduction at dynamic intermembrane junctions. We quantified the mechanical forces at fluid TCR-antigen bonds and observed their dependence on cell state, antigen mobility, antigen potency, antigen height and F-actin activity. The programmability of DOTS allows us to tether these to microparticles to mechanically screen antigens in high throughput using flow cytometry. Additionally, DOTS were anchored onto live B cells, allowing quantification of TCR mechanics at immune cell-cell junctions.