Dead Shells Research Articles

Marine biotopes of Askar coastal area, east of Bahrain

The scope of the present work has covered the area located at the east coast of Bahrain along the Askar coast associated with depth mostly < 10 m, extending for approximately 5Km. This coastal area is subjected to several sources of industrial and domestic pollution. The marine survey was conducted in May 2018 within an area of ∼5.27 km2 covering the intertidal and subtidal zones. A drop-down video camera (DDV) was used within an equidistant station grid spaced by 300 m and entailed 69 stations. SCUBA diving was performed at eight locations representing different biotopes for qualitative and quantitative analysis based on epi-benthic flora and fauna. Five biotopes were identified representing silty sand, silty sand with seagrass, mud, rock with sand veneer and macroalgae. A lack of conspicuous flora and fauna characterized most of the sites investigated. The seagrass habitat was found to be of less cover across the study area represented by patchy forms (<1%). The high concentration of alluvium discharged by the sand wash plant heavily impacted the water clarity, where fine particles were driven by currents during the ebb cycle toward the Askar coast. The DDV survey showed that most of the bottom layers are turbid and numerous dead bivalve shells of Pinctada sp. were observed. The current monitoring program needs to be rescheduled to cover further locations to minimize the vulnerability of traditional fisheries.

Historical biogeographic range shifts and the influence of climate change on ocean quahogs (Arctica islandica) on the Mid-Atlantic Bight

The Holocene, starting approximately 11.7 cal ka, is characterized by distinct periods of warming and cooling. Despite these known climate events, few temperature proxy data exist in the northwestern Atlantic Ocean. One potential record of past water temperatures is preserved in the marine fossil record. Shell growth of ocean quahogs ( Arctica islandica), a long-lived bivalve, can provide records of past environmental conditions. Arctica islandica habitat includes the Mid-Atlantic Bight (MAB), an area rapidly warming as a consequence of climate change. The Cold Pool, a bottom-trapped water mass on the outer continental shelf within the MAB, rarely rises above 15°C. Ocean quahogs inhabiting the MAB are confined to the Cold Pool as a consequence of an upper thermal limit for the species of ~15–16°C. Recently, dead A. islandica shells were discovered outside of the species’ present-day range, suggesting that the Cold Pool once extended further inshore than now observed. Shells collected off the Delmarva Peninsula were radiocarbon-dated to identify the timing of habitation and biogeographic range shifts. Dead shell ages range from 4400 to 60 cal BP, including ages representing four major Holocene cold events. Nearly absent from this record are shells from the intermittent warm periods. Radiocarbon ages indicate that ocean quahogs, contemporaneous with the present MAB populations, were living inshore of their present-day distribution during the past 200 years. This overlap suggests the initiation of a recent biogeographic range shift that occurred as a result of a regression of the Cold Pool following the Little Ice Age.

Potential Recovery of the Mussel Fauna of the Clarion River, Pennsylvania

The Clarion River, a tributary of the Allegheny River in northwestern Pennsylvania, underwent heavy industrialization during the late 19th and early 20th centuries. In the early 1900s, eight tanneries, 11 wood chemical plants, and a large paper mill operated on the Clarion River, releasing a cumulative 98 million liters of industrial effluent daily, in addition to the discharge of coal-mining wastes. By 1911, aquatic life was considered eliminated from the river, but its original mussel fauna was never recorded. In 1993, four living individuals of Strophitus undulatus, the Creeper, were discovered by chance near Clarington, Forest County, which constituted the first documented collection of mussels from the river. I conducted qualitative shell surveys from 2007 to 2019 at 157 sites to document past and present mussel distribution along a 55-km reach of the river. Recently dead shells, weathered shells, or living individuals of S. undulatus were encountered at 146 sites within the study reach. Relic shells of Actinonaias ligamentina were found at 12 sites, recently dead shells and one living individual of Lampsilis fasciola were found at five sites, and a single recently dead shell of Lampsilis ovata was collected. Ages of a subsample of 60 recently dead S. undulatus ranged from 2 to 16 yr (mean = 8.0 yr) and length ranged from 26.8 to 81.7 mm (mean = 29.8 mm), suggesting that natural recruitment may be occurring in the river. Source populations for recolonization of the river are unknown, but tributaries of the Clarion River are a possibility. My results suggest that the Clarion River now supports a substantial mussel population, but additional surveys are needed to provide a baseline for monitoring future recovery.

Differences in resident prey survival on newly created shell and established natural intertidal oyster reefs

Established natural oyster reefs historically provide a three‐dimensionally complex habitat utilized by a variety of resident and transient species, but newly created reefs designed to counter the loss of natural reefs initially may lack similar complexity. The loosely stacked shells of newly created reefs little resemble the vertically interconnected live and dead shell matrix typical of older reefs. Reduced complexity on created reefs may alter predator–prey dynamics and negatively affect ecological functions typically associated with natural reefs. We examined select physical characteristics (e.g. shell morphology) and short‐term survival of reef‐resident prey to determine if differences exist between newly created (&lt;1‐year‐old shell bags) and established natural intertidal reefs in South Carolina. Shell physical characteristics differed consistently between reefs, with greater numbers of smaller and lighter shells found on natural reefs. However, short‐term survival of crabs (Panopeid sp.) and mussels (Geukensia demissa) generally was not dependent on reef type. The few instances of reef dependent prey survival were either inconsistent with expected results, assuming reduced complexity on created reefs, or not supported by effect size analyses. Evidence indicates that adding shell bags to create oyster reefs in intertidal environments almost immediately increases resident species survival similar to that on existing natural reefs and leads to the rapid return of a major ecosystem service associated with coastal oyster reefs.

The composition of strand-line dead-shell accumulations on the Isle of Cumbrae, Scotland

Data are presented on the composition of identifiable molluscan shell debris from the surface of supralittoral strand-line accumulations from three topographically distinct coastal sites and aspects on the Isle of Cumbrae, Scotland sampled in summer and winter. Interpretation of these death assemblages, termed taphocoenoses, is given with reference to the biology and distribution of the same species living on- and off-shore and prevailing physical conditions at each site. Understanding such relationships allows the reconstruction of fossil deposits of dead shells, termed thanatocoenoses. The significance of dead-shell accumulations as carbon sinks has relevance to current modelling of climate change.

EVIDENCE OF MASS MORTALITY OF THE LONG-LIVED BIVALVE MERCENARIA STIMPSONI CAUSED BY A CATASTROPHIC TSUNAMI

ABSTRACTTsunamis are huge disasters that can significantly damage benthic organisms and the sea-bottom environment in coastal areas. It is of great ecological importance to understand how benthic ecosystems respond to such destructive forces and how individual species are affected. Investigating the effect of such disasters on animals that are seldom caught alive is particularly difficult. Bivalve mollusks are especially suitable for investigating how a tsunami affects coastal benthic species because they preserve an environmental record in their shells that can be extended back in time by crossdating the records of multiple individuals. Here we studied dead shells of Mercenaria stimpsoni, a long-lived clam, and precisely determined the time of death by using nuclear bomb–induced radiocarbon (bomb-14C) and by counting annual growth increments. First, a quasi-continuous, regional bomb-14C record was created by analyzing the shells of 6 live-caught M. stimpsoni individuals. Then 27 dead shells collected from the seafloor of Funakoshi Bay were 14C-dated and analyzed. The results showed that the huge tsunami that struck northeastern Japan on 11 March 2011 caused mass mortality of this bivalve in Funakoshi Bay. Nine of the 27 clams died during the March 2011 tsunami, probably by starvation after burial by tsunami deposits or exposure above the seafloor as a result of sediment liquefaction during the earthquake. The dating method used in this study can help us understand how long-lived marine organisms with low population density are affected by huge natural disasters such as a tsunami.

Missing seashells: a subtle detail of an inadequate policy

In Santos Beach, southwest coast of Brazil, cleaning operations are intensified during the summer using manual and mechanical techniques, driven mainly by sanitary and aesthetic aspects that neglect basic ecological standards. This study evaluated the abundance, richness, and diversity of dead shells, after spring and neap tides, found in two strips of sandy beaches: the "damp" and the "wet "sectors, where only the former undergoes mechanical cleaning. We collected and counted all fragmented and whole shells, identified each down to the species levels, and measured their weight. We used mixed statistical modeling to evaluate the effect of the sector over the abundance (in weight and number), richness, and Shannon-Wiener diversity (). We found a significantly greater abundance of fragmented shells in the damp sector. Since this is the sector where mechanical cleaning is applied, we understand such a strategy promotes potential harmful impacts over the conchological structure in Santos Beach, requiring mitigatory measures to protect empty shells. Finally, we fathom incorrectly discarded litter is brought from the surrounding mangrove to the beach after the spring tides; thus, integrated cleaning management with the participation of the local population, are also required to reduce the mechanical cleaning and its impacts.

The last fortress fell: mass mortality of Pinna nobilis in the Sea of Marmara

A spring 2021 cruise to the south Marmara Islands revealed a mass mortality event of Pinna nobilis, which were reported to be healthy just seven months ago. The cause of death might be associated with the epidemic infection or a catastrophic mucilage event seen after November 2020 in the Sea of Marmara. A total of 191 Pinna nobilis individuals were found at seven stations out of 10, of which 88% were dead. In the present study, the population density (dead and alive individuals) of P. nobilis was found to be between 0.3 ind.100 m-2 and 12 ind.100 m-2 in the area. A total of three live and four dead juvenile individuals were observed in the area, indicating low recent recruitment. The highest number of dead Pinna nobilis individuals (92 specimens) was encountered in shallow-waters (0-4 m depth). A total of 34 species belonging to six taxonomic groups (Sipuncula, Oligochaeta, Polychaeta, Crustacea, Mollusca, and Pisces) were found within the dead shells of four P. nobilis individuals. The mass mortality of Pinna nobilis in the Sea of Marmara, the last remaining disease-free sea, indicates the necessity of establishing and implementing emergency action plans for this species, including ex-situ conservation.

Diversity and abundance of terrestrial Gastropods on the slopes of Mount Arjuna-Welirang, East Java, Indonesia

Abstract. Nurhayati PA, Affandi M, Nurinsiyah AS. 2021. Diversity and abundance of terrestrial Gastropods on the slopes of Mount Arjuna-Welirang, East Java, Indonesia. Biodiversitas 22: 4193-4202. Before this study, the latest list of land snail species from Mt. Arjuna-Welirang was published in 1952. The current study aims to update the list of terrestrial Gastropods in the area, focusing on Sumber Brantas Arboretum and Raden Soerjo Forest Park Conservation Area (Tahura), East Java, Indonesia. Live snails and dead shells were collected from 24 10 × 10 m2 sampling plots to determine species richness, composition, and abundance. Sampling was carried out by combining visual observation (direct collection) and sorting-sieving soil-leaf litter samples. Total 646 specimens belonging to eight families and 13 species were collected, all new records to the area. Thus, the number of species known from Mt. Arjuna-Welirang was increased to 16 species from nine families. The diversity index of the Mt. Arjuna-Welirang slope was 1.1, and the dominance index was 0.54. The Tahura had a higher diversity index than the Arboretum, at 2.0 and 0.38, respectively, but the dominance index for Tahura was lower (0.18 and 0.85, respectively). This was due to the dominance of Bradybaena similaris, an invasive species in the latter area. Less canopy cover and more human activity in the Arboretum are factors that might cause this discrepancy. Many land snail species are sensitive to desiccation and habitat disturbance. Therefore, minimizing habitat changes and human activities is necessary to maintain or increase native land snail species diversity.

Fossils explained 81

Dead shells are common allochthonous clasts on British beaches. How much information of relevance to palaeontology can be gleaned from such bioclasts? One exceptional shell, a common Buccinum, is described, which preserves an array of borings and other ichnological evidence. It provides confirmation that we need to look harder at fossil gastropods, too.

Taphonomy of a limpet

Limpets are a group of gastropods that generate distinctive traces – their homing scars – and whose shells are bored both by predators and invertebrates forming domiciles. A Recent shell of Patella vulgata Linnaeus shows a distinctive and unusual preservation. It was collected from the north (Solent) coast of the Isle of Wight, southern England, from Queen Victoria’s private bathing beach, Osborne House. The specimen preserves only the lower third of the shell, adjacent to the aperture. The surface of breakage is densely infested by the U-shaped boring Caulostrepsis taeniola Clarke, commonly the spoor of spionid polychaetes such as Polydora spp. The inferred taphonomic history is that the lower third of the dead shell was protected by burial in sediment while the apex was destroyed by a dense infestation of boring spionids. Such preservation is highly distinctive and might not be recognized in the fossil record when shells are only seen in two dimensions in a lithified rock surface.

Photosynthetic response of a cultivated red alga, Neopyropia yezoensis f. narawaensis (=Pyropia yezoensis f. narawaensis; Bangiales, Rhodophyta) to dehydration stress differs with between two heteromorphic life-history stages

The chronic effect of dehydration on photochemical efficiency was determined in two heteromorphic life-history stages of a cultivated red alga, Neopyropia yezoensis f. narawaensis (=Pyropia yezoensis f. narawaensis; Bangiaceae, Bangiales) from Saga, Kyushu Island, Japan. The response to acute emersion (~1440-min) under 50% humidity was dissimilar between the two life-history stages, and the effective quantum yields of photosystem II of the microscopic sporophyte dropped to zero after a 5-min of emersion. The effective quantum yields did not recover to initial values, regardless of a subsequent 24h immersion in seawater. In contrast, those of the macroscopic gametophyte almost returned to initial values after the subsequent 24h immersion in seawater. However, when the two life-history stages were under 99% humidity, effective quantum yields did not drop after 504-h (21days) of emersion, suggesting that the thallus was never truly dehydrated due to 99% humidity. Furthermore, effective quantum yields fell when the absolute water content of the sporophyte in the dead oyster shells dropped below the absolute water content of 90% under the 50% humidity condition, and it did not recover to initial values even after a subsequent 24-h immersion in seawater. In contrast, effective quantum yields of the gametophyte decreased when the absolute water content was less than 60%; however, effective quantum yields quickly recovered after a subsequent 30-min immersion in seawater for individuals with the absolute water content over 10%. All absolute water content treatments, including 1%, of gametophytes eventually returned to initial values after 24-h immersion in seawater. Consequently, unlike the macroscopic gametophyte, photochemical efficiency in microscopic sporophyte appears to be sensitive to dehydration stress, suggesting that farming protocols for the conchospore seeding in Nori-net cultivation need to pay careful attention to dehydration to ensure a successful production.

Hyriid mussels (Unionoida) enhance benthic organic matter and meiofauna densities in a temperate Australian river

Abstract Studies in the Northern Hemisphere have shown that mussels play important roles as benthic‐pelagic couplers in freshwater systems, transferring filtered material, nutrients, and energy from the water column to sediments, through biodeposition and excretion. However, we know little of the functional roles of species of the Southern Hemisphere Hyriidae, the second most diverse family of the Unionoida. The aims of this study were to determine the biodeposition and excretion rates of nutrients and organic matter of the hyriid Alathyria jacksoni in an unregulated Australian river and test experimentally if the physical structure and biodeposition of A. jacksoni influenced sediment nutrients, organic matter, periphyton concentrations and meiofauna densities. In a lowland Australian river in late summer over 4 weeks, we measured biodeposition and excretion rates of A. jacksoni, and conducted a mesocosm experiment, during which we compared the effects of live mussels, dead mussel shells (shams), and controls without mussels on nutrients, organic matter, and meiofauna invertebrate densities in the sediment. Mean (± SE) mass of biodeposition was 70.85 ± 3.20 mg mussel−1 hr−1 and the relative rates of inorganic and organic biodeposition were 60.9 ± 3.1 and 9.9 ± 0.8 mg mussel−1 hr−1, respectively. Organic matter was significantly greater in the sediment of the mesocosms with live mussels than in that of the control mesocosms. There was also a trend of greater mean sediment chlorophyll‐a and total nitrogen concentrations in mussel treatments than in the controls. No significant difference was detected in sediment total phosphorous between mussel and control enclosures. The valves of live mussels had significantly higher amounts of organic material and chlorophyll‐a concentrations than the valves of sham mussels. There was a consistent trend of higher meiofauna densities collected in the benthos of the mussel enclosures than the control enclosures for total density and densities of Rotifera, Copepoda, Cladocera, Diptera, Oligocheata, Nematoda, and Ostracoda; this trend was near significant for total density; and significant for densities of Ostracoda, Rotifera, Cladocera, and Nematoda. Using our biodeposition and excretion rate estimates, and estimates of population size of A. jacksoni in the Lower Ovens River, we estimated that in a typical 1‐km reach in a month over summer, A. jacksoni would be biodepositing approximately 4.8 kg/day of organic matter (dry mass), 137 g N/day and 19 g P/day, and excreting 21 g N/day and 3.7 g P/day. Our findings are similar to those for Northern Hemisphere families of the Unionoida and serve to highlight the roles mussels play in processing of organic matter and cycling of nutrients in freshwater ecosystems.

Crab Diets Differ Between Adjacent Estuaries and Habitats Within a Sheltered Marine Embayment

Portunid crabs contribute to significant commercial and recreational fisheries globally and are commonly fished in estuaries and/or marine embayments, which are amongst the most degraded of all aquatic ecosystems. Portunus armatus were collected seasonally between April and February from five locations across three systems in temperate south-western Australia. The dietary composition of crabs was quantified and compared between two estuaries (Peel-Harvey and Swan-Canning) and a sheltered marine embayment (Cockburn Sound) containing three distinct habitats: shallow seagrass, shallow sand and deep sand. Overall, crabs ingested large volumes of bivalves (both live organisms and dead shell), polychaetes, crustaceans (e.g., amphipods, small decapods), and smaller volumes of teleosts, echinoderms and plant material (seagrass, algae). Analysis of Similarities showed that dietary composition varied significantly among the five locations (two estuaries and three habitats within Cockburn Sound) and seasons, with greater location than seasonal differences in the two estuaries. Diets were most distinct in the Cockburn Sound seagrass due to greater volumes of decapods and teleosts and smaller volumes of bivalve shell consumed in this habitat. Crabs from both estuaries consumed greater quantities of bivalves than those from Cockburn Sound. Seasonal differences in both estuaries were greatest between summer and winter, with a more diverse range of prey and large quantities of bivalves ingested in summer, whereas small bivalves and bivalve shell in the Peel-Harvey and polychaetes and other crustaceans in the Swan-Canning, were consumed in greater quantities in winter. The summer diet in the Peel-Harvey Estuary in the current study was compared to that 20 years previous and with documented change in the benthic macroinvertebrate fauna. Currently, crabs consume smaller volumes of high-calorie prey, i.e., polychaetes, small bivalves and teleosts, and instead ingest greater proportions of calcareous material than previously. This marked shift in dietary composition parallels changes in benthic macroinvertebrates in the Peel-Harvey Estuary. Overall, prey availability appears to be the major factor influencing the spatial and temporal differences in P. armatus diets in these three coastal systems.

European native oysters and associated species richness in the presence of non‐native species in a southern North Sea estuary complex

AbstractThere are growing calls to restore populations of European native oysters (Ostrea edulis), on the premise that restored populations will support a range of ecosystem services with an emphasis placed on restored oyster habitats promoting biological diversity, however benefits associated with naturally occurring O. edulis remain unclear. We undertook biannual surveys in the Blackwater, Crouch, Roach and Colne Estuaries Marine Conservation Zone (BCRC.MCZ), a highly sedimented estuary complex in the southern North Sea, to investigate links between natural densities of O. edulis (0–4.2 m−2), the prevalence of other dominant habitat features such as non‐native slipper limpet (Crepidula fornicata), dead shell abundance and epibenthic macroinvertebrate species richness. Increased epibenthic species richness was associated with O. edulis, even at densities below the OSPAR Commission recognized definition of an oyster bed (5 oysters m−2). Our analysis predicts increased associated species richness with density of native oysters (e.g., +1.6 additional species at 1 oyster m−2 or + 2.8 species at 5 oysters m−2), but only in areas with lower density of C. fornicata. Where C. fornicata are at higher density, the potential benefits of oyster restoration for associated species were curtailed. This may explain the observed asymptotic relationship between oyster density and diversity at 1 oyster m−2. In these and other high Crepidula density areas we recommend extending native oyster habitat even at low density. This may be of particular interest to areas with the protozoan oyster parasite Bonamia ostreae, which spreads more easily in high‐density areas. These lower density thresholds should also be considered for future management decisions—closing harvests so they do not reduce density further and impair biodiversity services of the habitats. In conclusion, while C. fornicata may be a useful oyster settlement substrate, we find that it limits the potential increases in associated species gains of oyster restoration.

Modeling structural mechanics of oyster reef self-organization including environmental constraints and community interactions

Self-organization is a process of establishing and reinforcing local structures through feedbacks between internal population dynamics and external factors. In reef-building systems, substrate is collectively engineered by individuals that also occupy it and compete for space. Reefs are constrained spatially by the physical environment, and by mortality, which reduces production but exposes substrate for recruits. Reef self-organization therefore depends on efficient balancing of production and occupancy of substrate. To examine this, we develop a three-dimensional individual-based model (IBM) of oyster reef mechanics. Shell substrate is grown by individuals as valves, accumulates at the reef level, and degrades following mortality. Single restoration events and subsequent dynamics are simulated for a case study in South Carolina (USA). Variability in model processes is included on recruitment, spatial environmental constraints, and predation, over multiple independent runs and five predator community scenarios. The main goal for this study is to summarize trends in dynamics that are robust across this uncertainty, and from these generate new hypotheses and predictions for future studies. Simulation results demonstrate three phases following restoration: initial transient dynamics with considerable shell loss, followed by growth and saturation of the live population, and then saturation of settlement habitat several years later. Over half of simulations recoup initial shell losses as populations grow, while others continue in decline. The balance between population density, substrate supporting the reef, and exposed surfaces for settlement is mediated by overall population size and size structure, presence of predators, and relative amounts of live individuals and intact dead shells. The efficiency of settlement substrate production improves through time as population size structure becomes more complex, and the population of dead valves accumulates.

Superior adsorption removal of dye and high catalytic activity for transesterification reaction displayed by crystalline CaO nanocubes extracted from mollusc shells

Nano structuring and surface functionalization of industrially important Calcium Oxide (CaO) material has broad spectrum applications in daily civic life. In this context, cubical shape CaO nanoparticles are extracted via an eco-friendly green approach from dead mollusc shells collected from sea beaches. The surface structural morphology of as-prepared catalyst is thoroughly characterized by XRD, DLS particle size, SEM, TEM-EDS, TGA, TPD, BET surface area (80 m2g−1) analysis, adsorption and electro-kinetic (zeta potential/point of zero charge) properties etc. measurement. Practical applications of this cubic nano crystal (lattice constant 12.51 Å and size 60–80 nm) for adsorption removal of toxic neutral red dye and catalytic activity for transesterification are systematically studied relative to commercial CaO particles under similar experimental conditions. Influential factors responsible for optimum dye adsorption isotherms, kinetics/thermodynamics of catalytic activity, stability and reusability/leaching are properly investigated in correlation with its observed crystal structural and physicochemical properties.

Dying, Decaying, and Dissolving into Irrelevance: First Direct in-the-Field Estimate of Crassostrea virginica Shell Loss—a Case History from Mississippi Sound

A mass mortality event that occurred in the Mississippi Sound in September 2016 provided an opportunity for the first natural field study of the rate of taphonomic loss of oyster shell. At the Pass Christian Reef, limited recruitment in the years following the mortality event resulted in little shell addition over a 2.67-y period, thereby permitting a direct comparison between shell present as living oysters in August 2016 and dead shell collected in April/May 2019. By April 2019, most oyster shell valves were riddled with holes, some of which perforated the valves. Deterioration of the shell surface was ubiquitous, and edge erosion was commonplace. Left valves were preferentially preserved: the left valves comprised 67% of the intact valves and 85% of the minor fragments after 2.67 y. Thus, at the time of collection, minimally 50% of the right valves originally present on the reef had disappeared. The increased differential between left and right valves of the minor fragments suggests a continuing differential in preservation, leading to cultch being overwhelmingly represented by left valves. Based on estimates derived from changes in shell weight at length and estimates of right-valve loss, by April 2019, between 30% and 51% of the carbonate originally added to the reef in 2016 was lost, yielding an estimated oyster shell half-life of between 2.6 and 5.1 y in the Mississippi Sound. The half-lives estimated from this first infield experiment fall precisely within the range of previous less direct estimates from laboratory experiments or survey time series. Oyster shell degrades rapidly: case histories now include a wide latitudinal range and a wide temperature range, which suggests that these rapid shell degradation rates are the norm over most of the range of the eastern oyster. Understanding the impermanence of oyster shell is crucial to the sustainable management of oyster reefs, as the addition of shell to the reef framework must balance rapid shell degradation rates to prevent stock collapse and ultimately the loss of reef structure.

Dendritic microborings in brachiopod shells from the Silurian of the Barrandian area, Czech Republic

Four types of dendritic microborings preserved as natural casts were observed on the surfaces of brachiopod shells from the Silurian in Central Bohemia: Rhopalondendrina jakubinka isp. nov., ? Clionolithes isp., and an indeterminate dendrinid are of Llandovery (Aeronian) age, Clionolithes amoebae isp. nov. is of Ludlow (Gorstian) age. Rhopalondendrina jakubinka forms a dense plexus of thin rhizoidal tunnels extending from a broad and curved entrance tunnel. ? Clionolithes isp. forms characteristically rarely branching thin meandering tunnels with a globular central node, while C. amoebae forms rosette-like microborings with sinuously curved primary branches and scarce lateral branches of smaller size. Microborings are present both on outer and inner surfaces of shells; their location and number confirm massive infestation of dead shells which were exposed on the sea floor for long time intervals and which were not affected by mechanical abrasion of the shells. This indicates narrow ecological limits for these endobionts, most likely within the deeper euphotic zone.

Anatomy and ontogenetic changes of the facial and gular musculature of the tetra Astyanax brucutu: A remarkable case of adaptation to durophagy.

Astyanax brucutu is a peculiar species of Neotropical tetra endemic from the Chapada Diamantina, a large plateau in northeastern Brazil. Individuals of this species undergo a dramatic ontogenetic shift in their diet that is accompanied by equally remarkable changes in their feeding apparatus. Whereas juveniles of A.brucutu feed mostly on algae, adults feed almost exclusively on an endemic species of hydrobiid snail and other associated living organisms that inhabit their dead shells (including infaunal invertebrates and algae). Skeletal adaptations associated with this change in diet were previously reported, but until now, the changes in the musculature remained mostly unknown. The present paper describes the facial and gular muscles, as well as the buccal ligaments of A.brucutu in different life stages, and identifies the major ontogenetic changes in these systems associated with the diet shift in the species. Such changes primarily involve expansions of specific portions of the adductor mandibulae and associated tendons and ligaments that likely represent adaptations to increase the biting power necessary to crush copious amounts of shells ingested by larger individuals of A.brucutu. Those adaptations are absent in specimens of any size of Astyanax cf. fasciatus, a sympatric congener lacking durophagous feeding habits. Anatomical comparisons and landmark-based principal components analysis (PCA) suggest that most specializations to durophagy in A.brucutu arose by peramorphosis. We also found that several of the muscular specializations of adults of A.brucutu are paralleled in species of Creagrutus and Piabina, two other characid genera distantly related to Astyanax, but that also feed on hard food items.