Epifaunal Bivalves Research Articles

Finding of the pea crab Pinnaxodes mutuensis Sakai, 1939 (Crustacea: Decapoda: Pinnotheridae) in an unusual host in Busse Lagoon, southern Sakhalin

The symbiotic crab Pinnaxodes mutuensis Sakai, 1939 was found in the mantle cavity of the mud-burrowing bivalve Mya arenaria Linnaeus, 1758 (the family Myidae) in Busse Lagoon at southern Sakhalin Island. Along the Russian coasts, this species has been previously found in the mantle cavity of epifaunal bivalves of the family Mytilidae [Modiolus difficilis (Deshayes in Maillard, 1863), Modiolus modiolus (Linnaeus, 1758), Mytilus edulis Linnaeus, 1758, Crenomytilus grayanus (Dunker, 1853)] and the family Ostreidae [Crassostrea gigas (Thunberg, 1793)]. New data on the morphology and ecology of this crab are presented.

Macroinvertebrate palaeo-communities from the Jurassic succession of Gebel Maghara (Sinai, Egypt)

Macrobenthic palaeo-communities of the Middle and Upper Jurassic strata of G. Maghara, Egypt, were investigated to identify relationships with environmental parameters and to trace the temporal changes of the ecosystem associated with sea-level fluctuations. The quantitative analysis of a data matrix comprising 198 macrobenthic taxa in 138 samples collected from four sections identified nine associations and three assemblages, interpreted to be representative of their original environment. Non-Metric Multidimensional Scaling (NMDS) delineated the same degree of habitat partitioning as hierarchical clusters with very little overlap. Detrended Correspondence Analysis (DCA) identified water depth as the primary environmental gradient controlling the distribution of the fauna, while Axis 2 reflects substrate consistency. Community structure is related to the various ramp environments. Based on diversities, the associations and assemblages have been divided into two major groups, low-stress polyspecific associations and high-stress paucispecific associations. The low-stress polyspecific associations were interpreted to represent two different habitats, a high-energy, firm substrate habitat, in which epifaunal bivalves and brachiopods in addition to solitary corals dominated during advanced stages of transgression, and a low-energy, soft substrate habitat dominated by infaunal bivalves during the maximum flooding. The high-stress paucispecific associations are dominated by one or few taxa and occurred (1) in an oligotrophic setting that developed during episodes of sediment starvation in restricted inner ramp environments or during early transgression, (2) in a setting characterized by high sedimentation rates which developed during advanced regression, (3) in a distal prodelta setting with soft substrate and dysoxia during sea-level lowstand, and (4) in a high-energy shoal environment during peak regression. A combined stress involving a shortage in food supply, episodic dysoxia, in addition to a soupy substrate may have developed during maximum flooding episodes. Hydrodynamic conditions were most likely the main factor controlling the benthic communities. Hydrodynamic conditions influenced the substrate type, redistributed nutrients and were responsible for stratified water masses and hypoxia. Animal-sediment relationships in addition to replacement between bivalves and brachiopods are also discussed. Middle ramp settings were found to provide the best conditions for macrobenthos.

Recognizing cryptic environmental changes by using paleoecology and taphonomy of Pleistocene bivalve assemblages in the Oga Peninsula, northern Japan

Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies.

Drilling Intensity Varies Among Neogene Tropical American Bivalvia in Relation to Shell Form and Life Habit

We calculated the incidence of drilling on bivalve genera from the Neogene fossil record of Panama and Costa Rica to determine differences in predation intensity among groups based on shell architecture, life habit, mobility, and taxonomic affinity. Bulk samples from 28 localities yielded >106,000 bivalve specimens, which were examined for characteristic drilling traces of muricid and naticid gastropods. We calculated the drilling intensity for the 90 most common genera, and characterized the size, ornament, life habit, and mobility for each genus. Large size confers considerable protection from drilling, but shell ornamentation does not. Life habit is strongly linked with drilling intensity. Epifaunal bivalves experience higher predation than infaunal bivalves and shallow burrowers experience higher drilling than deep burrowers. Mobility is also important for epifaunal bivalves; cemented taxa are twice as likely to be drilled as their uncemented counterparts. Our results suggest that bivalve behavior and life habits are more important than shell architecture for defense against drilling predators.

The significance of mudstone fabric combined with palaeoecological evidence in determining sedimentary processes – an example from the Middle Jurassic of southern Poland

Mudstones were deposited below the storm wave base in the shallow epicontinental sea, however, structures reflecting quiet settling from the suspension are not common. Most of recognized lamina types resulted from activity of bottom suspension currents generated by storms, suggesting that accumulation of mudstones proceeded under prevailing energetic conditions. Composition of benthic association indicates that bottom environment was depleted in oxygen but reoxygenetion events, linked with storms, were frequent. Short oxygenetion episodes resulted in development of microbioturbation, which was the most effective in destruction of subtle lamination. L onger lasting oxygenation led to development of more diversified association, consisting of ichnofossils Chondrites , Trichichnus , pyritized burrows, Palaeophycus and Protovirgularia and bivalves Bositra , nuculids and nuculanids. Analysis of fabric of laminated black mudstones of the Ore-Bearing Częstochowa Clay Formation (Bathonian, southern Poland) was used for reconstruction of sedimentary processes and environmental energy. Small-scale sedimentary features indicate that ore-bearing clays were deposited below the storm-wave base in the shallow epicontinental sea but structures reflecting quiet settling from the suspension are not common. Most of recognized lamina types record activity of bottom suspension currents generated by storms, suggesting that mudstones accumulated under prevailing energetic conditions. Composition of benthic faunal association indicates that on the seafloor suboxic conditions prevailed, restricting infaunal activity to cryptobioturbation. Recurrent short-lived reoxygenetion events, linked probably with storms, resulted in development of dysoxic conditions, recorded by more diversified trace fossil association (consisting of Chondrites , Trichichnus , pyritized burrows, Palaeophycus and Protovirgularia ) and colonization of the seafloor by epifaunal bivalves Bositra . Truly anoxic conditions might establish only for a short time, leading to mass mortality of Bositra . Analysis of the fabric of laminated black mudstones of the Ore-Bearing Częstochowa Clay Formation (Bathonian, southern Poland) is used for reconstruction of sedimentary processes and conditions. Small-scale sedimentary features indicate that ore-bearing clays were deposited below storm-wave base in a shallow epicontinental sea, but structures reflecting quiet settling from suspension are not common. Most of recognized lamina types record the activity of bottom currents generated by storms. The benthic faunal association indicates that suboxic conditions prevailed on the seafloor, restricting infaunal activity to cryptobioturbation. Recurrent short-lived reoxygenetion events, linked probably to storms, resulted in the development of dysoxic conditions, recorded by a more diverse trace fossil association (consisting of Chondrites , Trichichnus , pyritized burrows, Palaeophycus and Protovirgularia ) and colonization of the seafloor by epifaunal bivalves ( Bositra ). Truly anoxic conditions might have been briefly established, leading to mass mortality of Bositra .

Thick brachiopod shell concentrations from prodelta and siliciclastic ramp in a Tortonian Atlantic–Mediterranean strait (Miocene, Guadix Basin, southern Spain)

Carbonate production by brachiopods in shallow-water habitats is generally expected to be not sufficiently high and temporally persistent to allow them to form very thick and densely packed shell concentrations. The formation of thick brachiopod concentrations requires long-term persistence of populations with high density of individuals, and such circumstances are assumed to be rare especially during the Cenozoic. However, here we show that the large-sized brachiopod Terebratula terebratula, the most common species in benthic assemblages with epifaunal bivalves and irregular echinoids, formed several decameter- to meter-thick, densely packed concentrations in shallow siliciclastic, high-energy environments, in a seaway connecting the Atlantic Ocean with the Mediterranean Sea during the Latest Tortonian (Late Miocene, Guadix Basin, southern Spain). This brachiopod formed (1) meter-scale, thick, parautochthonous concentrations in a prodelta setting and (2) thin, mainly allochthonous, tide- and storm-reworked concentrations in megaripples and dunes. The abundance of brachiopods at the spatial scale of the Guadix Basin seems to be mainly related to intermediate levels of sedimentation rate and current velocity because abundance and thickness of shell concentrations decline both (1) in onshore direction towards delta foresets with high sedimentation rate generated by debris flows and (2) in offshore direction with increasing levels of tide- and storm-induced substrate instability. Although brachiopods in dune and megaripple deposits are more fragmented, disarticulated, and sorted, and have a higher pedicle/brachial valve ratio than in prodelta deposits, taphonomic damage is still relatively high in prodelta deposits. Terebratula terebratula thus formed thick concentrations in spite of that disintegration processes were relatively intense along the whole depositional gradient. Therefore, population dynamic of this species was probably characterized by production maxima that were comparable to some Cenozoic molluscs in terms of their productivity potential to form thick shell concentrations in shallow subtidal environments. We suggest that temporal changes in brachiopod carbonate production have a significant spatial and phylogenetic component because multiple large-sized species of the family Terebratulidae, which underwent radiation during the Cenozoic, attained high abundances and formed shell concentrations in temperate regions.

Vision and the diversification of Phanerozoic marine invertebrates

Identifying biological traits that promote evolutionary success is fundamental for understanding biodiversity dynamics and for assessing the evolutionary response of organisms to global change. We tested the hypothesis that image-forming eyes have contributed to the diversification of taxa in the geological past. Using fossil occurrences in the Paleobiology Database, we analyzed the diversity and evolutionary rates of more than 17,000 Phanerozoic genera of marine invertebrates living on or above the shallow-water seafloor according to their visual capabilities. Analysis of the complete data set shows a peak in the proportional diversity of sighted genera early in the Phanerozoic, and their continuance at a relatively low and stable level after the Ordovician. As an explanation of this pattern we suggest that selection pressure to develop eyes rose in the Cambrian, and that behavioral constraints had a balancing effect thereafter. In contrast to the pooled data, a clade-level study of those subgroups that contain both sighted and blind genera revealed that—in trilobites, all epifaunal bivalves, pectinoid bivalves, gastropods, and echinoderms—sighted genera diversified more strongly than blind genera. This difference is controlled by significantly raised extinction rates of blind genera. These more finely resolved patterns support the hypothesis that good vision is a key trait that promoted preferential diversification.

Changes in bivalve functional and assemblage ecology in response to environmental change in the Caribbean Neogene

We documented changes in the relative abundance of bivalve genera and functional groups in the southwest Caribbean over the past 11 Myr to determine their response to oceanographic changes associated with the closure of the Central American Seaway ca. 3.5 Ma. Quantitative bulk samples from 29 localities yielded 106,000 specimens in 145 genera. All genera were assigned to functional groups based on diet, relationship to the substrate, and mobility. Ordinations of assemblages based on quantitative data for functional groups demonstrated strong shifts in community structure, with a stark contrast between assemblages older than 5 Ma and those younger than 3.5 Ma. These changes are primarily due to an increase in the abundance of attached epifaunal bivalves (e.g.,Chama,Arcopsis, andBarbatia) and a decrease in infaunal bivalves (e.g.,VaricorbulaandCaryocorbula). Taxa associated with seagrasses, including deposit-feeding and chemosymbiotic bivalves (e.g.,Lucina), also increased in relative abundance compared to suspension feeders. The composition of bivalve assemblages is correlated with the carbonate content of sediments and the percentage of skeletal biomass that is coral. Our results strongly support the hypothesis that increases in the extent of coral reefs andThalassiacommunities were important drivers of biologic turnover in Neogene Caribbean benthic communities.

Epifauna on ammonites from the Lower Jurassic of the Severn Basin, southern England, and their palaeoenvironmental and taphonomic significance

Ammonites with bivalves or worm tubes attached are relatively rare among the abundant specimens in the Lower Jurassic (Sinemurian) mudstones at Bishop's Cleeve, Gloucestershire, UK, but provide evidence for ammonite taphonomy, environmental conditions and biological interactions between ammonites and epifauna. Epifauna attached only to one side or within the body chambers of ammonites usually indicate post-mortem attachment. Epifauna on both sides of, or overgrown by, ammonites attached in vivo. One large example of Oxynoticeras has at least 51 encrusting bivalves attached exclusively to one side indicating it formed a ‘benthic island’. Four, presumably annual, bivalve cohorts are recognized, with variation in preferred orientation in each cohort suggesting that current direction varied. Both the ammonite and its epifauna were buried by a single sedimentation event. Other informative examples include a Cheltonia that overgrew an epifaunal bivalve, and an example of Bifericeras which bears two clusters of four worm tubes, one of which apparently attached in vivo, the other post-mortem. Other examples bear too few specimens to be certain of the timing of attachment, but most probably attached post-mortem.

Carbonate sediments in a cool-water macroalgal environment, Kaikoura, New Zealand

Brown and red, and to a lesser extent green, macroalgae are a hallmark of intertidal rocky coasts and adjacent shallow marine environments swept by stormy seas in middle and high latitudes. Such environments produce carbonate sediment but the sediment factory is neither well-documented nor well-understood. This study documents the general marine biology and sedimentology of rocky coastal substrates around Kaikoura Peninsula, a setting that typifies many similar cold-temperate environments with turbid waters and somewhat elevated trophic resources along the eastern coast of South Island, New Zealand. The macroalgal community extends down to 20 m and generally comprises a phaeophyte canopy beneath which is a prolific rhodophyte community and numerous sessile calcareous invertebrates on rocky substrates. The modern biota is strongly depth zoned and controlled by bottom morphology, variable light penetration, hydrodynamic energy and substrate. Most calcareous organisms live on the lithic substrates beneath macroalgae or on algal holdfasts with only a few growing on macroalgal fronds. A live biota of coralline red algae [geniculate, encrusting and nodular (rhodoliths)], bryozoans, barnacles and molluscs (gastropods and epifaunal bivalves), together with spirorbid and serpulid worms, small benthonic foraminifera and echinoids produce sediments that are mixed with terrigenous clastic particles in this overall siliciclastic depositional system. The resultant sediments within macroalgal rocky substrates at Kaikoura contain bioclasts typified by molluscs, corallines and rhodoliths, barnacles and other calcareous invertebrates. In the geological record, however, the occurrence of macroalgal produced sediments is restricted to unconformity-related early transgressive systems tract stratigraphic intervals and temporally constrained to a Cenozoic age owing to the timing of the evolution of large brown macroalgae.

Filtering capacity and endoscopic analysis of sympatric infaunal and epifaunal bivalves of southern Chile

The bivalves Mytilus chilensis, Venus antiqua, Mulinia edulis and Tagelus dombeii inhabit different levels of the tidal flats in Yaldad Bay, southern Chile. Mytilus chilensis is an epifaunal bivalve, which, at this location, is also farmed in culture rafts; whereas the other species belong to the infauna. The objective of this study was to compare filtering capacity of these species; in order to do this, measurements of food consumption were taken by quantifying clearance rates, as well as taking morphological measurements of their feeding systems (gills and labial palps), and endoscopic observations to determine the velocity of particle transport within the gills. All of these parameters were related to the sediments present in environments occupied by these species. In Mytilus chilensis, both wild and farmed, gill area was significantly higher than in the three infaunal species. Mulinia edulis and Venus antiqua did not show any significant differences in gill area. As far as Tagelus dombeii is concerned, the species presented the lowest values among all species studied. Weight of labial palps was significantly higher in Mulinia edulis compared to the other species. There were no significant differences between labial palps of either wild or farmed Mytilus chilensis or in those of Venus antiqua and Tagelus dombeii. A positive, significant relationship was identified between labial palps size and mud sediment content. Both culture-rafts and intertidal Mytilus chilensis displayed a clearance rate that was significantly higher than the infaunal species, concurring with a significant relationship between clearance rate and gill area in the different species studied. Clearance rates displayed by Venus antiqua, Mulinia edulis and Tagelus dombeii did not show significantly different results among them. Mytilus chilensis from both culture-rafts and intertidal zone displayed higher values of particle transport velocity than the infaunal species. Particle transport was not observed in the dorsal canal of any of the species studied. The conclusion is that in these species filtering capacity is determined mostly by gill size and that labial palp size displays a strong relationship with sediment content in the mud of Yaldad tidal flats.

Miocene intertidal zonation on a volcanically active shoreline: Porto Santo in the Madeira Archipelago, Portugal

Santos, A., Mayoral, E.J., da Silva, C.M., Cachao, M., Johnson, M.E. & Baarli, B.G. Miocene intertidal zonation on a volcanically active shoreline: Porto Santo in the Madeira Archipelago, Portugal. Lethaia, Vol. 44, pp. 26–32. Short-term biological colonization of rockgrounds on the basaltic shorelines of oceanic islands has, as yet, been poorly explored. A Miocene sea cliff on Ilheu de Cima off Porto Santo in the Madeira Archipelago of Portugal provides a case study showing intertidal zonation with two types of barnacles, serpulid worm tubes, two coral species, epifaunal bivalves and the trace fossils of endolithic bivalves. Large barnacles (Balanus sp.) and serpulids are limited to the upper 400 mm of a basalt cliff of 1.6 m in height. Small barnacles, possibly of the same species, extend to the base. The upper half includes the corals Isophyllastrea orbignyana and Tarbellastraea reussiana, to which many small, coral-inhabiting, barnacles (Ceratoconcha costata) are fixed. Borings identified as Gastrochaenolites torpedo appear through the bottom two-thirds of the cliff face. Rarely, Gastrochaenolites lapidicus is exposed in longitudinal section with borings up to 45 mm deep in solid basalt. Epifaunal bivalves, such as Spondylus sp., are limited to a middle zone. Associated with the sea cliff is an outer platform on which a multitude of T. reussiana colonies occur in growth position. The corals exhibit planar erosion over180 m2. The shelf was faulted and cut by a basalt dike prior to the brief recolonization of I. orbignyana, found attached to low fault scarps. Habitation of the sea cliff was facilitated by rising sea level, but abruptly terminated by burial under volcanoclastic ejecta. □Basalt bioerosion, coastal dynamics, Ilheu de Cima (Porto Santo), Miocene intertidal zonation, volcanogenic perturbations.

Radiation of Middle Triassic bivalve: Bivalve assemblages characterized by infaunal and semi-infaunal burrowers in a storm- and wave-dominated shelf, An Chau Basin, North Vietnam

In North Vietnam, Lower to Middle Triassic storm- and wave-dominated shelf deposits are widely exposed and yield abundant Tethyan bivalves indicating recovery and diversification following the end-Permian mass extinction. We reconstructed the habitats of characteristic bivalve species on the basis of shell preservation and mode of occurrence. Bivalves that diversified in the Middle Triassic Anisian to Ladinian Stages in the Na Khuat Formation, An Chau Basin, can be divided into four fossil assemblages: (1) an autochthonous to parautochthonous Costatoria goldfussi mansuyi and Trigonodus tonkinensis assemblage (sandy bottom of inner shelf facies); (2 and 3) a parautochthonous to allochthonous Costatoria goldfussi mansuyi and Pteria sturi assemblage, and a Costatoria paucicostata and Hoernesia angusta assemblage (muddy bottom of inner to outer shelf facies); and (4) a typical allochthonous Costatoria ngeanensis and Leptochondria albertii assemblage. These assemblages are characterized by a diversity of species of Costatoria and Trigonodus, and by several genera of twisted Bakevellidae, such as Hoernesia, Langsonella, and Lilangina. These bivalve assemblages are composed of shallow-infaunal and semi-infaunal burrowers and epifaunal species, though in Vietnam the Lower Triassic Induan to early Olenekian bivalves are dominated by epifauna. In the eastern part of the Tethys, infaunal bivalves show a remarkable delay in recovering from the end-Permian mass extinction compared to epifaunal bivalves.

Intensities of drilling predation of molluscan assemblages along a transect through the northern Gulf of Trieste (Adriatic Sea)

Drilling predation is one of the most studied biotic interactions in the fossil record and potentially controls biodiversity, but its history may be confounded by natural patchiness across environments. This aspect has been inconsistently evaluated. The current study contributes to our understanding of drilling predation in the Northern Adriatic, which has been previously classified as a low-predation setting, and examines the roles of environment, patchiness, and ecology of prey organisms in modern seas. Nearly 49,000 molluscs from two intertidal and six sublittoral bulk samples along a transect in the Gulf of Trieste were analysed for drill frequency (DF) and prey effectiveness (PE), a measure of prey's ability to resist predatory attacks. DF across all samples was 20.6%, but varied between the intertidal (1.4%) and sublittoral (27.4%). Among the latter, DF differed between the delta foreset beds (18.1%) and level bottom muds and sands (∼ 28% each). PE was low in the intertidal (1.1%) and sublittoral (4.5%). Overall DF and PE among the three mud samples varied by nearly 10%, while that within the two sand samples varied little; however, significantly different DFs were observed only among the families Nuculidae, Galeommatidae and Corbulidae in level bottom mud and Cerithiidae in level bottom sand samples. Only Corbulidae displayed significant variation in PE among level bottom mud samples (16.5–43.7%). PE varied significantly between level bottom sand samples only within the families Cerithiidae and Trochidae. Suspension-feeding bivalves and gastropods had the highest DFs (24.3% and 39.1%, respectively), and the value of epifaunal bivalves (32.0%) was nearly twice as high as that of infaunal bivalves (17.9%). DFs of cementing (43.0%) and byssate (27.0%) bivalves were higher than that of recliners (9.9%). Considering their cryptic life habits, parasitic gastropods (20.3%) and commensal bivalves (40.6%) had exceptionally high DF. For each ecological category, PE was highest on suspension-feeding (11.1%), infaunal (15.8%) and cementing (10.5%) bivalves, and on parasitic gastropods (11.9%). DF did not correlate with diversity indices or predator abundance in the sublittoral; therefore, drilling predation probably does not control diversity on the local scale here. DFs support paleoecological theory relating predation to changes in ecological guilds through the Phanerozoic. DFs were highest on suspension feeders, parasites and sessile prey, and were lowest on predators, recliners, and endobenthic molluscs. While cementation likely reduces bivalve susceptibility to durophages, it apparently does not to impede drilling predators. Finally, DF did not vary across size classes in any species examined except Venerupis rhomboides, where the smallest fraction was drilled more often. Additionally, as the proportion of large individuals in our samples was small, disparities in DF across size classes probably did not influence our results. With respect to predation intensity the relatively high DF in the sublittoral, as well as high DF and PE for various taxa and guilds, places the Northern Adriatic Sea among typical Cenozoic shelf environments.

QUALITY OF THE TRIASSIC–JURASSIC BIVALVE FOSSIL RECORD IN NORTHWEST EUROPE

Abstract: The quality of the Triassic–Jurassic bivalve fossil record in northwest Europe has been measured using the Simple Completeness Metric (SCM). The SCM has been applied to the fossil record of total bivalve diversity and to the records of different ecological guilds. The Westbury and Lilstock Formations record high SCM values for most ecological groups. The ‘Pre‐Planorbis Beds’ of the lower Lias Group, however, witness a precipitous decline in the completeness of most guilds and emigration of taxa due to localized marine anoxia is a likely cause. Neither variation in lithofacies, shell mineralogy, sedimentary rock outcrop area, nor sequence architecture can convincingly explain the observed patterns of completeness. Our SCM data reveal that the Early Jurassic fossil record of infaunal suspension‐feeding bivalves is significantly poorer than that of epifaunal bivalves. Any differences in the apparent Rhaetian extinction rates between these two guilds should therefore be viewed with caution. Analyses of selectivity during the Late Triassic mass extinction based on studies of global databases appear robust in light of our SCM data. Nevertheless, future investigations of the Triassic–Jurassic benthic marine ecosystem undertaken at a finer‐resolution, may need to account for the poor quality of the Early Jurassic fossil records of certain ecological guilds, such as the infaunal suspension‐feeding taxa.

Substrate exploitation and resistance to biotic disturbance in the brachiopod Terebratalia transversa and the bivalve Pododesmus macrochisma

To test the hypothesis that epifaunal bivalves are more resistant to biotic disturbance than brachiopods, I evaluated abundances and body size of the brachiopod Terebratalia transversa and the anomiid bivalve Pododesmus macrochisma, which co-occur in the San Juan Islands (Washington State, USA, eastern Pacific). The proportion of bare space correlated with intensity of biotic disturbance had negative effects and surface rugosity had positive effects on abundance of T. transversa. Both rugophilic settlement and post-settlement mortality of juveniles due to biotic disturbance restrict T. transversa to crevices and complex substrates formed by solitary ascidians and giant barnacles. Its juveniles are under-represented on flat substrates, implying lower survivorship than in crevices, where juveniles are common. Abundance of the byssally-cemented bivalve P. macrochisma is negatively affected by rugosity and does not decrease with increasing bare space. P. macrochisma size patterns do not differ between crevices and flat substrates. Flat valves and high post-settlement mobility probably increase its juvenile survivorship under grazing pressure. T. transversa is not able to re-attach after settlement and is thus less resistant to grazing effects than P. macrochisma. This study supports the hypothesis that brachiopods are more negatively affected by biotic disturbance than epibyssate bivalves. Although brachiopods can be less preyed upon by carnivorous predators than epibyssate bivalves, T. transversa is affected more negatively by grazing than P. macrochisma. The evolutionary decline of brachiopod abundance in shallow habitats may represent responses to a heavy pressure on juveniles by grazers that evolved during the Mesozoic.

Shell‐bearing Mollusca (Bivalvia and Gastropoda) from submarine caves in Hong Kong

In October 2002, the Hong Kong Marine Caves Expedition was convened jointly by the Swire Institute of Marine Science, The University of Hong Kong and the Natural History Museum, London. The expedition explored the marine cave habitats of Hong Kong and their fauna. This paper describes the diversity of marine cave molluscs collected using SCUBA from two marine caves at Conic Island and Steep Island in the eastern waters of Hong Kong. Twenty, and eight species of shell‐bearing epifaunal bivalves and gastropods, respectively, were collected from the ceilings and walls of the two caves. Another 11 infaunal bivalve species were collected from the sediment‐filled floors of the caves. Of the species identified, eight are new records for Hong Kong. These are the bivalves Spondylus anacanthus, Hiatella cf. orientalis, Panomya turgida, Nuculana sp., Abra cf. fujitai, Pinguitellina cf. nux, and Lyonsiella cf. parva, and the epitonid gastropod Epitonium bullatum. The epibenthic molluscs recorded during this survey were mostly adults whereas the endobenthic bivalves were all juveniles. Although the above species are recorded from Hong Kong for the first time, they have been identified from non‐cave habitats elsewhere. In particular, the often singular presence of juvenile infaunal bivalves in the cave sediments suggests their opportunistic colonization by such species and thus further evidence for a lack of endemicity. That the epibenthic molluscs are non‐endemic is probably also because Hong Kong's submarine caves are very modern, that is, Middle Holocene.

Palaeoecology of solitary corals in soft-substrate habitats: the example of Cunnolites (upper Santonian, Eastern Alps)

The upper Santonian Hofergraben Member (Eastern Alps) provides an example of a soft-substrate habitat suited mainly for solitary corals (Cunnolites), for colonial forms of solitary coral-like shape (Placosmilia, Diploctenium), and for colonial corals of high sediment resistance (e.g. Actinacis, Pachygyra). The Hofergraben Member consists mainly of silty-sandy marls of wave-dominated, low-energy shore zone to shallow neritic environments. Substrates of soft to firm mud supported level-bottoms of non-rudist bivalves, gastropods, solitary corals, colonial corals, rudists, echinoids, and benthic foraminifera. Boring and/or encrustation of fossils overall are scarce. In the marls, Cunnolites is common to abundant. Both a cupolate shape and a lightweight construction of the skeleton aided the coral to keep afloat soft substrata. Cunnolites taphocoenoses are strongly dominated by small specimens (about 1–3 cm in diameter). Cunnolites was immobile and mostly died early in life upon, either, smothering during high-energy events, rapid sedimentation associated with river plumes, or by toppling and burial induced by burrowing. Comparatively few large survivor specimens may show overgrowth margins interpreted as records of partial mortality from episodic sedimentation or tilting on unstable substrate. Scattered pits and scalloped surfaces on large Cunnolites may have been produced, in some cases at least, by predators (durophagous fish?). Post-mortem, large Cunnolites provided benthic islands to corals, epifaunal bivalves and bryozoans. In a single documented case of probable in vivo contact of Cunnolites with the colonial coral Actinastraea, the latter prevailed.

BRACHIOPOD AND BIVALVE ECOLOGY IN THE LATE TRIASSIC (ALPS, AUSTRIA): ONSHORE-OFFSHORE REPLACEMENTS CAUSED BY VARIATIONS IN SEDIMENT AND NUTRIENT SUPPLY

Abstract Although onshore to offshore retreat of brachiopods, in terms of their community-level abundance, took place through the Mesozoic and Cenozoic, this study shows that comparable trends also occurred repeatedly on a short time scale and mainly were driven by variations in sediment and nutrient supply. In the Kossen Formation (Upper Triassic), brachiopods retreated to offshore habitats during nutrient-rich, siliciclastic regimes and expand to onshore habitats during nutrient-poor, carbonate regimes. Epifaunal bivalves occupied onshore and offshore habitats during both siliciclastic and carbonate regimes. Infaunal suspension-feeding bivalves expanded to offshore habitats during nutrient-rich, siliciclastic regimes and retreated from offshore habitats during nutrient-poor, carbonate regimes. Thus, the onshore to offshore retreat of brachiopods and the offshore expansion of infaunal bivalves repeatedly coincided with the switch from a nutrient-poor, carbonate regime to a nutrient-rich, siliciclastic re...

Bioerosive Structures of sclerozoan foraminifera from the Lower Pliocene of Southern Spain: a contribution to the palaeoecology of marine hard substrate communities

Abstract: A palaeoecological study of sclerozoan foraminifera of the families Saccamminidae (aff. Sagenina), Lituolidae (Placopsilina), Cibicididae (Cibicides, Dyocibicides, Cibicidella) and Planorbulinidae (Planorbulina and Planorbulinella) that colonized epifaunal bivalves (ostreids and pectinids) during the early Pliocene in southern Spain has led to the recognition of two new boring ichnogenera: Camarichnus ichnogen. nov., with two ichnospecies, C. subrectangularis ichnosp. nov. and C. arcuatus ichnosp. nov., and Canalichnus ichnogen. nov., with one ichnospecies, C. tenuis ichnosp. nov. The first two ichnospecies were produced by adnate lituolids and cibicidids, the last by saccamminids. Their recognition is very important when quantifying populations of these organisms. Colonisation took place after death of the host bivalves, when they acted as very stable substrates whose topography probably controlled the initial settlement pattern of the foraminifera. The colonisation sequence started with the foraminifera (lituolids‐saccamminids‐cibicidids‐planorbulinids) and was followed by vermetid gastropods, serpulids, spirorbids, cheilostome bryozoans and/or ostreids. Preferred orientations and overgrowth relationships between cheilostome bryozoans and serpulids have been detected in this material.