Infaunal Suspension-feeding Bivalves Research Articles

Untold muddy tales: Paleoenvironmental dynamics of a “barren” mudrock succession from a shallow Permian epeiric sea

During the late Paleozoic, the intracratonic Paraná Basin, Brazil, in central Gondwanaland, was covered by a huge (>1.600.000 km2), shallow and isolated epeiric sea. Within the Permian succession, oxygen-deficient facies are commonly recorded in the Mesosaurus-bearing Irati Formation (Cisuralian, Artinskian/Kungurian) and the overlaying Serra Alta Formation (Guadalupian, Wordian/Capitanian). Barren, dark-grey mudstones are the main facies preserved in this last unit, which has usually discouraged extensive and detailed stratigraphical and paleontological investigations. However, exhaustive sedimentological, taphonomic and paleontological surveys in those deposits reveal a dynamic and complex depositonal history. Based on sedimentary fabric, autochthonous to parautochthonous occurrences of shelly benthic invertebrates (bivalves) and the presence/absence of concretion-bearing and phosphate-rich layers, we report variations in the oxygen levels of bottom and pore waters, in bathymetry, sedimentation rates, and changes in benthic colonization. Our data indicate that the deposition of this “apparently barren” mudstone-dominated succession was driven by a complex interplay of variations in sedimentation rate and oxygen pulses tied to tectonic and climate changes. Three distinct populations or invertebrate paleocommunities were recorded, which were adapted to (a) normal background low-oxygen (dysoxic) conditions (i.e., minute infaunal suspension-feeding bivalves associated with the trace fossil Planolites), (b) chemically toxic (anoxic/extreme dysoxic) substrates, including gigantic burrowing bivalves (probable chemosymbiotic taxa), and (c) oxic/dysoxic substrates following short-term bottom disruptions.

A new Permian bivalve-dominated assemblage in the Rio do Rasto Formation, Paraná Basin, Brazil: Faunal turnover driven by regional-scale environmental changes in a vast epeiric sea

The basal portion of the Permian Rio do Rasto Formation (Serrinha Member), Passa Dois Group, Paraná Basin, Brazil, records an entirely new bivalve fauna intercalated between the underlying Pinzonella neotropica assemblage (uppermost portion of the Teresina Formation) and the overlying Leinzia similis assemblage (Rio do Rasto Formation). Mollusks of these assemblages lived in marginal shallow-water habitats of an immense epeiric sea and were dominated by endemic bivalve species. Taxonomic analysis revealed the presence of Terraia curvata (60.61%), Astartellopsis prosoclina (19.70%), Cowperesia emerita (10.61%), Leinzia curta (4.55%), Terraia bipleura (3.03%) and Beurlenella elongatella (1.52%), which are associated with conchostracans and plant remains. Species composition, abundance, and dominance in this novel assemblage differ notably from the preceding ones, suggesting a substantial evolutionary turnover. Regional-scale environmental changes recognized based on taphonomy, facies analysis, and geochemical data consist of progressive freshening of the marginal habitats of the Paraná Basin and taxic changes that include the following: (a) loss of genera, (b) decrease in bivalve abundance and ecological guilds, (c) disappearance of the dominant bivalve group (Pinzonellinae) and (d) diversification of Terrainae bivalves. The ecological signature also changed notably because only infaunal suspension-feeding bivalves are present, indicating a significant loss of functional diversity at the regional scale. Likely stressor factors (among others) are tied to freshening events, suggesting profound changes in (a) salinity, (b) primary productivity and (c) a lack of coarse, stable substrates coupled with high bioturbation rates. Hence, our regional example could offer valuable clues to benthic (bivalve) community responses in a habitat subjected to (a) rapid climate changes and (b) freshening events in shallow-water settings. Finally, the stratigraphic range of the dominant species (T. curvata) appears to be restricted to the basal portion of the Rio do Rasto Formation. Based on the presence of this species and of C. emerita, the novel assemblage is tentatively correlated with that of the Permian Gai-As Formation in the Huab region of Namibia, thus supporting previous assumptions of a seaway connecting both basins during the Guadalupian Epoch.

Molluscan subfossil assemblages reveal the long-term deterioration of coral reef environments in Caribbean Panama

Caribbean reef corals have declined sharply since the 1980s, but the lack of prior baseline data has hindered identification of drivers of change. To assess anthropogenic change in reef environments over the past century, we tracked the composition of subfossil assemblages of bivalve and gastropod mollusks excavated from pits below lagoonal and offshore reefs in Bocas del Toro, Panama. The higher prevalence of (a) infaunal suspension-feeding bivalves and herbivorous and omnivorous gastropods in lagoons and (b) epifaunal and suspension-feeding bivalves and carnivorous and suspension-feeding gastropods offshore reflected the greater influence of land-based nutrients/sediments within lagoons. Temporal changes indicated deteriorating environmental conditions pre-1960 in lagoons and post-1960 offshore, with offshore communities becoming more similar to lagoonal ones since 1960. Relative abundances of dominant bivalve species tracked those of their coral hosts, revealing broader ecosystem effects of coral community change. The nature and timing of changes implicate land-based runoff in reef deterioration.

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...

DEPENDENCE OF THE SURF CLAM PSEUDOCARDIUM SACHALINENSE (BIVALVIA: MACTRIDAE) ON THE NEAR-BOTTOM LAYER FOR FOOD SUPPLY

We investigated the food sources of the surf clam Pseudocardium sachalinense by comparing the microalgal composition in the stomach with that of the overlying water and in the bottom sediment. The microalgal composition in the stomach contents resembled that of the sediment, in which four microalgal species groups: Melosira, Coscinodiscus, solitary species of Nitzschiaceae and Naviculaceae constituted a large proportion of the total throughout the study. By contrast, the dominant microalgae in the water column changed through the year and was different from those in the stomach contents and the sediment. Since the surf clam is an obligate suspension feeder, these results indicate that it relies on the overlying water close to the bottom surface as a food source layer. Since there is little vertical transport of pelagic microalgae near the bottom, microalgae dominant even 1 m above the bottom rarely enter the food source layer. Consequently, the surf clam may rarely ingest pelagic microalgae that are produced in the upper layers of the water column. Unlike bivalves on tidal flats or mussels in intertidal rocky areas, few pelagic microalgae produced in the upper layers are supplied to infaunal suspension-feeding bivalves on open shallow sandy bottoms. So measurements of chrorophyll a in the water column do not indicate the food supply for such bivalves.

中新統竜串層に産する定向配列した生痕化石Ｌｏｃｋｅｉａ ｓｉｌｉｑｕａｒｉａ：埋在性ろ過食二枚貝の古生態とその堆積学的意義

中新統竜串層に産する定向配列した生痕化石Ｌｏｃｋｅｉａ ｓｉｌｉｑｕａｒｉａ：埋在性ろ過食二枚貝の古生態とその堆積学的意義

Shell concentrations as tools in characterizing sedimentary dynamics at sequence-bounding unconformities: examples from the lower unit of the Canoa Formation (Late Pliocene, Ecuador)

The Canoa Basin in Manabì, Ecuador, contains a mainly marine, clastic sedimentary succession of Late Pliocene and Pleistocene Age (Canoa Formation and Tablazo Formation). A stratigraphic and sedimentologic study of the entire sedimentary succession indicated that sedimentary facies recur in consistent deepening–shallowing transgressive–regressive patterns and that on this basis it can be divided into three different informal units ( C low, C upp, Tb). The lowest of these units ( C low) is composed of at least four depositional sequences, each bounded by a ravinement surface and containing a basal environmentally time-averaged shell bed accumulated during rapid sea-level rise under conditions of reduced terrigenous sediment supply (transgressive systems tract). Owing to intense heavy bioturbation, the internal architecture of these shell beds is not recognizable. Each of these shell beds is mantled by poorly fossiliferous sandy and silty shales accumulated during subsequent progradation (highstand and regressive systems tract). Fossil assemblages, accounting for inner/middle shelf settings, are dominated by infaunal suspension-feeding bivalves ( Linga cancellaris, Chione mariae, etc.), most of which require sandy substrate or are ubiquitous. In terms of trophic/life-habit groups, the total succession shows an increase of infaunal suspension-feeder species’ richness from the lowest (C1) to the upper (C4) shell bed, whereas epifaunal taxa decrease in richness. Shell packing density also decreases from C1 to C4. The reconstruction of the short-term sedimentary dynamics based on taphonomic and paleoecologic observations indicates a slightly progradational staking pattern of depositional sequences, representing high-frequency sixth-order eustatic sea-level fluctuations within a third-order tectonically induced cycle.

Nitrogen Budget of the Bivalve Mactra veneriformis, and its Significance in Benthic—pelagic Systems in the Sanbanse Area of Tokyo Bay

To examine the nitrogen budget of the suspension feeding bivalve Mactra veneriformis in the Sanbanse, a shallow (<5 m) part of Tokyo Bay, Japan, field surveys and laboratory experiments were conducted in early summer, 1998. The Sanbanse area is one of the few remaining areas of intertidal wetland in Tokyo Bay and is an area of significant importance for migrating waders and as a clam fishery and for laver culture. Three infaunal suspension-feeding bivalves, Mactra veneriformis, M. chinensis and Ruditapes philippinarum, were found as the dominant species in terms of biomass. Of these three species, Mactra veneriformis was dominant in the Funabashi area of the Sanbanse. In laboratory experiments, the filtration rate of M. veneriformis (525–918 mg of flesh dry weight), a representative size of the bivalve in the Funabashi area, was 0·95 l g −1 flesh dry weight h −1 corresponding to 408 μg N g −1 flesh dry weight h −1. The excretion rates of ammonia and faeces were 35·0 μg N g −1 flesh dry weight h −1 and 45·4 μg N g −1 flesh dry weight h −1, respectively, at 20 °C. Based on the nitrogen budget of M. veneriformis in the Funabashi area in early summer, the population excreted 8·6% of the filtered nitrogen as ammonia and egested 22·2% of the filtered nitrogen as faeces and pseudofaeces, and converted 69·2% as growth. The high growth ratio indicates that the M. veneriformis population efficiently transfers the pelagic primary production to higher trophic levels in the early summer.

Late Cretaceous Mollusca from the Chatham Islands, New Zealand

The Cretaceous Mollusca (Bivalvia, Gastropoda, Scaphopoda) from the Chatham Islands, New Zealand consists of a moderately diverse faunule of 37 species in the Kahuitara Tuff of Pitt Island. At least 16 (c.43%) of the taxa are conspecific with mainland New Zealand species and at least 15 (c.41%) taxa are endemic to Chatham Islands. New species proposed are Crenella n. sp., Chlamys (Lyriochlamys) n. sp., Chlamys s. l. n. sp., Camptonectes n. sp., Eburneopecten freneixae n. sp., Dimyodon n. sp., Purpurocardia n. sp., Lahillia n. sp., Solyma flemingae n. sp., Brookula s. l. n. sp., Calliomphalus s. l. n. sp., Pyrgulifera kahuitara n. sp., and Ageria? n. sp. Most taxa (c.41%) are epifaunal suspension feeding bivalves and dominate the Cretaceous macrofauna. Less dominant are infaunal suspension feeding bivalves (30%). Epifaunal browsers (c.14%), deposit feeders (8%) and carnivores (5%) are minor components. An open marine, shallow shelf environment is advocated. A latest Cretaceous (Campanian?-Maastrichtian) age is supported for the Kahuitara Tuff macrofossils.

The Role of Fire in Maintaining a Small-Scale Vegetation Gradient: A Test of Mutch's Hypothesis

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Bivalve Associations of Cannonball Formation (Paleocene, Danian) of North Dakota: ABSTRACT

The Paleocene Cannonball Formation, cropping out primarily in southwest-central North Dakota, is a marine deposit with variable lithologic characteristics ranging from medium to dark-gray-weathering mudstone to fine-grained, well-sorted, brownish-yellow-weathering sandstone. Also, two distinct tongues of the formation, exposed in southwestern North Dakota, are comprised of organic-rich siltstones and claystones. There are 30 known species of bivalves in the Cannonball. Because bivalves are abundant and well known, and because their morphology and life habits are highly reflective of environmental demands, they are used to more accurately define depositional environments of the Cannonball sea. Based on Q-mode and R-mode cluster analysis, five bivalve associations are defined: Ostrea-Corbicula, Crassostrea-Corbula, Isognomon, Crassatella-Nucula, and Glycymeris-Arctica associations. The Ostrea-Corbicula association, in the lower Cannonball tongue, and the Crassostrea-Corbula association, in the upper tongue, suggest that the Cannonball sediments in southwestern North Dakota were deposited in lagoonal or estuarine environments. Where present, Isognomon occurs in abundance. However, it is found at only a few known localities in southwest-central North Dakota, and it has not been found in association with any other macrofossils. Isognomon, found in organic-rich sands, appears to have lived attached to vegetation in shallow-water environments. The Crassatella-Nucula and Glycymeris-Arctica associations, common throughout southwest-central North Dakota, are most characteristic of the Cannonball. The Crassatella-Nucula association occurs in silty, clayey sand with moderately high organic content. It is dominated by both deposit and suspension-feeding bivalves, and has a high species diversity. It appears to have been deposited in a low energy environment with moderately high turbidity. In contrast, the Glycymeris-Arctica association is found in fine-grained, well-sorted sandstone with low organic content. It is dominated by infaunal suspension-feeding bivalves that indicate both a higher energy environment and low turbidity. Crabs and Ophiomorpha commonly occur stratigraphically above this association. These two associations m st likely represent foreshore, shoreface, and/or shelflike environments. The distribution of these bivalve associations, along with lithologic characteristics, suggest that the Cannonball Formation was primarily deposited in a barrier island complex and included lagoonal, beach, and offshore environments. End_of_Article - Last_Page 1347------------

Structure of Upper Cretaceous chalk benthic communities, southwestern Arkansas

Paleoecological investigation of chalk facies in the Saratoga and Annona Formations includes paleoenvironmental analysis as well as examination of benthic macro-invertebrate faunas. The Saratoga sandy chalk facies was deposited in a middle shelf environment (25–50 m depth), while the Annona chalk-marly chalk facies was deposited in a outer shelf environment (75–125 m depth). Each facies is characterized by a distinct community of benthic macro-invertebrate fossils dominated in occurence by epifaunal suspension-feeding bivalves and deposit-feeding echinoids. However, sandy chalk also contains moderately common infaunal suspension-feeding bivalves and gastropods, and rare infaunal deposit-feeding bivalves, while chalk-markly contains only rare infaunal bivalves and no reported gastropods. Differences in composition within and between the two communities apparently reflect original distribution of shelled taxa. Trace fossil preservation indicates that substrates in both facies were thixotropic. Functional analysis demonstrates that many taxa show adaptations for living on soft substrates. Differences in diversity within each facies may be owing to non-uniformity of substrate softness, because many suspension-feeders were unable to cope with the softest substrates and are therefore sparse in rocks apparently representing these substrates. Variations in substrate softness may have been caused by differing rates of bioturbation. Presence of infaunal suspension-feeding bivalves in the Saratoga, but relative lack in the Annona, may be primarily a manifestation of softer Annona substrates caused by generally finer grain size of Annona sediments. Several studies of chalk faunas have concluded that sparseness of originally aragonitic fossils was caused by secondary sea-floor dissolution or diagenetic processes. Results of this study demonstrate that primary organism-sediment interactions could have also played a significant role in causing the general lack of originally aragonitic fossils in Upper Cretaceous chalks.