Pan-tropical distribution of the Jurassic ostreid bivalves

Globally, the Jurassic cemented ostreid bivalves from northern Tibet, SW China, have a pan-tropical distribution pattern between palaeolatitudes of 60° South and North. Ostreid bivalves have tiny to large larvae, and nearly all of them have a cemented mode of life during their adult stage. The distribution pattern and the habits of the Jurassic ostreid bivalves revealed that, in the Jurassic time interval, all seas and oceans were interconnected, and ostreid bivalves were very capable of dispersion through their planktonic larval stage or as pseudoplankton during the post-larval stage, and even were able to cross the palaeo-Pacific Ocean from east to west. However, latitudinal temperature variation limited the distribution of these thermophilous bivalves to the lower and middle latitudes.     

New bivalves from the Jurassic of Iran

Three new subgenera, Gervillaria (Platygervillaria), Isognomon (Iranognomon), and Mytilaster (Persiaster), and seven new species, Gervillaria (Platygervillaria) alifera, Isognomon (Iranognomon) arkelli, Inoperna (Inoperna) striata, Mytilaster (Persiaster) ancestralis, Astarte persipulla, Orthotrigonia fazli, and Gissaromya abramovi, from the Jurassic of Iran are described.     

Preserved life positions of some Jurassic bivalves

The observed life positions of 23 species of Jurassic bivalves are recorded and compared to reconstructions derived from functional interpretations of their morphology and comparisons with Recent relatives. In the majority of cases, these inferences correspond with field observations. There are, however, cases such ashognomon where likely reconstructions differ. These could easily lead to an erroneous interpretation of the autecology of some species.     

Ecology and evolution of Jurassic trigoniid bivalves in Europe

 A modern palaeobiological approach to the taxonomy, making full allowance for a wide range of variation, has allowed the distinction of 22 Jurassic trigoniid species in Europe, grouped into 7 genera. Most species were confined to shallow marine habitats ranging up to a few tens of metres in depth but were adapted to low energy environments as well as environments of moderate to high energy. The presence of external ornament on the shell flanks was probably an adaptation to facilitate burrowing, but in the absence of useful external ornament other adaptations to increase burrowing efficiency may have been realized by the development of an elongate shape. Because their occurrence in Jurassic strata is only intermittent, confident inferences on evolutionary patterns are limited to the two commonest genera, Trigonia and Myophorella. Phyletic size increase has been recognized in the latter but not the former genus. The calculated species longevities correspond fairly closely with those established for Jurassic bivalve species in general. The mode of speciation is dominantly punctuational, but only one likely example of species splitting is recognized.     

Biostratinomy of bivalves from Jurassic and Early Cretaceous lakes of NE China

Bivalves are comparatively rare elements of the benthic faunas of Jurassic and Early Cretaceous lakes of northeastern China. In the past, Arguniella and Sphaerium have been regarded as belonging to the communities that populated the offshore areas of lake Sihetun, represented by the Lower Cretaceous Yixian Formation of western Liaoning. A detailed biostratinomic analysis of these bivalves suggests, however, that they were introduced from marginal lake habitats where they were reworked by storms and occasionally were transported in suspension offshore. Some of these bivalves were dead and settled on the lake floor as single valves or articulated but opened valves (butterfly position). Others were transported alive but died on their arrival at the bottom due to inimical conditions caused by reduced oxygen levels. A similar interpretation is given for articulated valves of Ferganoconcha in thinly bedded siltstones of the Jurassic Daohugou Fossil Beds of Inner Mongolia, which were also carried alive by hyperpycnal flows to their burial site where they died due to lack of oxygen.     

On the evolutionary ecology of symbioses between chemosynthetic bacteria and bivalves

Mutualistic associations between bacteria and eukaryotes occur ubiquitously in nature, forming the basis for key ecological and evolutionary innovations. Some of the most prominent examples of these symbioses are chemosynthetic bacteria and marine invertebrates living in the absence of sunlight at deep-sea hydrothermal vents and in sediments rich in reduced sulfur compounds. Here, chemosynthetic bacteria living in close association with their hosts convert CO₂ or CH₄ into organic compounds and provide the host with necessary nutrients. The dominant macrofauna of hydrothermal vent and cold seep ecosystems all depend on the metabolic activity of chemosynthetic bacteria, which accounts for almost all primary production in these complex ecosystems. Many of these enigmatic mutualistic associations are found within the molluscan class Bivalvia. Currently, chemosynthetic symbioses have been reported from five distinct bivalve families (Lucinidae, Mytilidae, Solemyidae, Thyasiridae, and Vesicomyidae). This brief review aims to provide an overview of the diverse physiological and genetic adaptations of symbiotic chemosynthetic bacteria and their bivalve hosts.     

Jurassic evolution of Southern Hemisphere marine palaeobiogeographic units based on benthonic bivalves

The distribution of benthonic Jurassic bivalve genera in the Southern Hemisphere is analysed here. For this region, palaeobiogeographic units (biochoremas) are quantitatively characterized according to their biologic contents (mainly levels of endemism). Their evolution through time is followed from the latest Triassic to the earliest Cretaceous. The Tethyan Realm is undoubtedly the most mature and persistent through time, with three subordinate units: an Australian unit restricted to the Late Triassic, a North Andean unit, which appears sporadically as an endemic centre, and an East African unit which is recognisable from Bajocian times onwards. From Late Triassic times, a South Pacific Realm has been recognised, with a Maorian Province mostly based on the distribution of monotoid genera. A South Andean unit is also recognisable through most of the Jurassic, and its reference either to the South Pacific unit or to the Tethyan Realm is a matter of debate. Being a transitional biogeographic setting between Tethyan and South Pacific first-order units, it is included in the South Pacific unit due to the common presence of antitropical (didemic) genera. The East African unit is included within the Tethyan Realm during the Jurassic, but during Early Cretaceous times, it splits into two units, one of which was regarded as part of the “South Temperate Realm” by Kauffman. The rank of all these units changed with time. Throughout the Jurassic, the ecotone between South Pacific and Tethyan palaeobiogeographic units fluctuated in position with time. The approximate latitudinal location of the ecotonal boundary area and its shift through time are recognised on the basis of faunal composition along the Andean region.     

Toarcian (Lower Jurassic) brachiopods in Asturias (Northern Spain): Stratigraphic distribution, critical events and palaeobiogeography

Brachiopod assemblages recorded in the Toarcian outcropping of the Asturian coast, between Gijón and Ribadesella, are described. In the Tenuicostatum Zone of the Early Toarcian, an assemblage dominated by Gibbirhynchia cantabrica nov. sp., which also includes some other species of North European affinities, has been recorded. Brachiopods disappear in the region at the end of this Zone, coinciding with a sedimentary episode of black shales, and they are not recorded again until the Variabilis Zone of the Middle Toarcian. Between this zone and the Aalensis Zone, several species appear with wide stratigraphic distribution but scarce representation, except for Soaresirhynchia renzi, which is very abundant, particularly in the Insigne Subzone. This assemblage differs from the ones recorded in other nearby Spanish basins and can be related to the ones described in part of the Lusitanian Basin (Portugal), Western Pyrenees and South-Western France. This similarity can be related to environmental characteristics, such as the existence in these cases of an external, relatively deep platform environment.     

Filtration rate capacities in 6 species of European freshwater bivalves

Summary Filtration rate capacities in undisturbed freshwater bivalves were determined by means of two different methods (indirect clearance and suction methods) in Anodonta anatina (L.), Unio tumidus Philipsson, Unio pictorum (L.), Unio crassus Philipsson, Dreissena polymorpha (Pallas) and Sphaerium corneum (L.). In A. anatina, D. polymorpha, and S. corneum the filtration rate (FR, 1 h^-1) at 19–20°C as a function of dry tissue weight (DW, g) or ash-free dry weight (AFDW, g) could be expressed by the equations: 1.10 DW^0.78, 6.82 DW^0.88, and 2.14 AFDW^0.92, respectively. In U. tumidus, U. pictorum, and U. crassus filtration rates were comparable with those of A. anatina. In D. polymorpha the b value of the corresponding regression of gill area on dry weight was 0.87. The rates of water transport in freshwater bivalves are 2–8 times lower than in marine bivalves of comparable size. A corresponding difference in the filtration rate per gill area unit is found. The measured filtration rates in undisturbed bivalves are substantially higher (at least 4 times) than previously reported. This indicates that the impact of bivalve water processing on freshwater ecosystems is greater than hitherto suggested.     

Evidence and cause of small size in Bathonian (Middle Jurassic) marine bivalves of north-western Europe

Data from the monographic literature indicate a general size reduction amongst Bathonian marine bivalves in southern England: mean size is reduced in all subclasses and major mode-of-life categories relative to the immediately preceding Bajocian stage (27 per cent. reduction) and the later Oxfordian stage (41 per cent. reduction). Smaller size cannot be explained in terms of sedimentary facies, nor as a 'pure' evolutionary phenomenon (involving no environmental change); it therefore probably reflects some quality of the ambient water. A comparable reduction in average size (19 per cent. relative to Bajocian, 46 per cent. relative to Oxfordian) is evident amongst oyster and scallop lineages studied throughout Europe and a sedimentary-facies (and pure evolutionary) control can be ruled out at least for an area extending from southern England to the east side of the Paris Basin. A lowering of salinity to the mid-twenties per mil is the likeliest cause of size reduction in this area. Isolation of the region from the oceans, combined with high fresh water runoff, was probably the determining factor in such widespread lowering of salinity. High runoff may have been caused by increased rainfall. Tests are proposed for the ubiquity of the pattern identified, and the suggested proximate and ultimate causes. It is noted that recognition of widespread reduced salinity has implications for the salinity tolerances of certain 'stenohaline-marine' taxa and the salinity ranges ascribed to certain nearshore faunal associations. In addition, recognition that environmentally determined size reduction may occur over a broad area has implications for the general issue of interpreting phyletic size change.     

Temperature tolerance of circatidal bivalves in relations to their distribution

The temperature tolerances of six species of bivalve from Dublin Bay were calculated from the respiration rates of winter condition and summer condition animals measured at 50°C intervals. The results showed, that, in general, the tolerance of the species was inversely proportional to its distribution with respect to tidal height. However, considerable variation occurs between species taken from the same location and this difference may be linked to their life style and vertical distribution within the sediment.     

Slope breccias colonized by bivalves and serpulids during the Middle Jurassic (Subbetic,SE Spain)

The Middle Jurassic of the Intermediate Domain, in the northern Subbetic (External zones of the Betic Cordillera, SE, Spain), reveals the transition from hemipelagic limestones (Baños Formation) to overlying shallow-water oolitic limestones (Jabalcuz Formation). Near La Guardia (Jaén), the basal part of the succession that records this transition comprises clast-supported calcareous breccias 24 m thick. Transverse sections reveal a fan shape close to a normal fault. The upper parts of some breccia beds were colonized by bivalve patches that locally evolve to bivalve-serpulid bioherms. The bioherms are massive, with low relief and a metre-scale lenticular shape. Two main parts have been differentiated: a bivalve bioherm and a serpulid bioherm. The bivalve bioherm consists of densely packed mytiloids in life position with secondary serpulids, where the matrix is a grainstone of bioclasts, peloids, and ooids. Laterally, there are accumulations of reworked bivalves. The serpulid bioherm is made up of serpulid aggregates in a bioclast wackestone. On an unstable slope with abundant breccias, bioherm development took place in favourable periods of low sedimentation rate. The pioneer colonisers of the sea-bottom were mytiloid bivalves in relatively high-energy waters. Shell comissures were aligned parallel to the dip of the slope as an adaptation to feeding from the plankton and seston inputs associated with palaeocurrents. The intercalation of reworked bivalve beds likely indicates brief periods of higher-energy storm events. The serpulid bloom in the upper part of the buildups was probably related to a stage of low-energy conditions (as evidenced by the delicacy of these structures), which is congruent with the wackestone texture. The relief provided by the bivalves favoured the development of the serpulid bioherm phase in an elevated and advantageous position for suspension-feeding. The dense packing in these bioherms offered clear advantages in this unstable palaeoenvironment: (1) dense populations are less susceptible than isolated individuals to overgrowth by other sessile organisms or predator attacks; and (2) the interconnection among individuals enhances stability and resistance against high-energy events, and increases the growth potential of future generations. The interruption of bioherm growth was probably related to the deposition of new breccia beds and reworked oolitic limestones.     

Stratigraphic and paleogeographic distribution of the Upper Ordovician bryozoans of Mongolia

The taxonomic diversity and distribution of the Upper Ordovician bryozoans of Mongolia are analyzed. Five heterochronous assemblages of bryozoans are established: Chigertei and Tsagaan del in the Sandbian Stage and Bairim Ovoo, Uuregnur, and Sairin in the Katian Stage. The bryozoans are shown to be important for solving complex problems of stratigraphy of the Ordovician of Mongolia and for paleogeographic reconstructions.     

Estuarine benthic ecology: A European perspective

The study of benthic ecology within European estuaries is discussed. The history of estuarine science, and the definition of an estuary is briefly reviewed. Estuarine benthic ecology is considered with regard to its geographical, economic and political context. It is shown that much recent study has been motivated by attempts to clean up estuaries, which were polluted after decades, or even centuries of pollution. Much has been achieved in the control of pollution, and many estuaries show clear signs of recovery. Particular focus has been on the estuaries entering the North Sea, with the realization that it is not the North Sea that is polluted, but its estuaries. The scientific appraisal of the benthos of estuaries has been particularly assisted by the ecosystem approach, which has both aided our understanding of their function as well as answering some of the questions posed by the impact of mankind. The European Union is identified as a powerful factor in benthic ecology, either through legislation or through the encouragement of collaborative programs, some of which have been particularly important in identifying common factors across a wide geographical spread of estuaries. It is concluded that in general estuaries have got cleaner, but that many problems remain, ranging from eutrophication through to sea-level change. The future of estuarine benthic ecology lies in meeting the new challenges.     

The feeding ecology of the European Water shrew

This review examines our knowledge of the feeding ecology of the European Water shrew, Neomys fodiens. It describes and discusses the different methods which have been used to study the diets of Water shrews, from the first casual observations to the discovery of food caches and food remains in the wild, and the analysis of stomach contents and faecal pellets of trapped animals. These studies have revealed that Water shrews feed on a variety of invertebrate and vertebrate prey from tiny freshwater dip-teran larvae to sizable fish and frogs. Although aquatic prey are seen to be the major dietary component in most studies, terrestrial prey are also important and may be eaten in an equal proportion. Laboratory studies have increased our knowledge of the foraging behaviour of Water shrews but there is still much to be learnt, especially about underwater prey location.     

黏菌分布格局与生态学研究进展

黏菌是一类广泛分布于全球各种陆地生态系统的菌物,生态功能独特。随着物种资源调查的极大拓展以及分子标记和高通量测序技术等的成熟应用,黏菌的生态学研究在近年来取得了长足的发展。本文综述了国内外黏菌物种分布与群落生态学的研究进展,旨在为基于经典分类和分子标记研究黏菌的物种演替、群落结构和生态作用等提供重要参考和有益借鉴。