49,171 research outputs found

    Fish and bivalves at Bolsa Chica Marsh re-establishment project; Progress report III

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    The objectives of our fish and bivalve study are: 1. Determine changes in the number of species of fish and bivalves before Phase I and during Phase 1 at Bolsa Chica Marsh. 2. Determine if California Department of Fish and Game's predicted benefits in Phase I were achieved by increases in fish species. 3. Determine influences of water management practices upon fish and bivalve composition. Thirteen species of fish and five species of bivalves were collected from Inner Bolsa Bay and South Bolsa Slough. Deepbody anchovy, Anchoa compressa; jacksmelt, Atherinopsis californiensis; longjaw mudsucker, Gillichthys mirabilis; specklefin midshipman, Porichthys myriaster; round stingray, Urolophus halleri; banded chione, Chione californiensis; bentnose clam, Macoma nasuta; and common littleneck clam, Protothaca staminea have not been reported previously from Inner Bolsa Bay. Nine species of fish and four species of bivalves were collected from outer Bolsa Bay. Yellowfin goby, Acanthogobius flavimanus; longjaw mudsucker; tilapia, Tilapia mossambica; and bay pipefish, Syngnathus leptorhynchus have not been reported previously from Outer Bolsa Bay. (11pp.

    Cosmology, Oscillating Physics and Oscilllating Biology

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    According to recent reports there is an excess correlation and an apparent regularity in the galaxy one-dimensional polar distribution with a characteristic scale of 128 h1h^{-1} Mpc. This aparent spatial periodicity can be naturally explained by a time oscillation of the gravitational constant GG. On the other hand, periodic growth features of bivalve and coral fossiles appear to show a periodic component in the time dependence of the number of days per year. In this letter we show that a time oscillating gravitational constant with similar period and amplitude can explain such a feature.Comment: 9 pages. latex using revtex. This revised version is supposed to be free of e-mail nois

    Linking eye design with host symbiont relationships in pontoniine shrimps (crustacea, decapoda, palaemonidae)

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    Symbiosis is prevalent in the marine environment with many studies examining the effects of such interactions between host and symbiont. Pontoniine shrimps are a group whose ecology is characterised by symbiotic interactions. This investigation examines the gross morphology of Pontoniinae compound eyes and superficial optical parameters with reference to their symbiotic relationship or lifestyle category; free-living, ectosymbiont, endosymbiont (bivalves) or endosymbiont (non-bivalves). The eye morphologies of free-living and ectosymbiotic species are very similar, yet differ from both forms of endosymbiotic species. Endosymbionts have significantly smaller and simpler eyes with larger facets and bigger interommatidial angles and eye parameters for increased sensitivity levels. However bivalve endosymbionts form an intermediary group between non-bivalve endosymbionts and ectosymbionts as a result of their more active lifestyle. The accessory eye or "nebenauge", although of uncertain function, commonly occurs in free-living Pontoniinae species but rarely in endosymbionts apart from in more primitive species. The variation in morphology reflects tensions between functional requirements and ecological pressures that have strongly influenced eye design in Pontoniinae. © 2014 Dobson et al

    Faunal change in Cretaceous endemic shallow-marine bivalve genera/subgenera of the northeast Pacific

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    Endemic shallow-marine Cretaceous bivalves in the northeast Pacific region (NEP), extending from southwestern Alaska to the northern part of Baja California Sur, Mexico, are tabulated and discussed in detail for the first time. Twenty-three genera/subgenera are recognized. Their first appearance was in the Valanginian, and their biodiversity continued to be very low during the rest of the Early Cretaceous. The bivalves of the middle Albian Alisitos Formation in northern Baja California are excluded because they did not live in the NEP. The highest number (13) of NEP endemic bivalve genera/subgenera occurred during the Turonian, which was the warmest time of the Cretaceous. At the Turonian/Coniacian boundary, when cooler waters migrated southward, there was a moderate dropoff in endemics that persisted until an origination event near the beginning of the early Maastrichtian, when 11 were present. Five of the 11 were present also during the Turonian, but the others were newcomers. Only three survived the turnover associated with the “Middle Maastrichtian Event” (MME), and none survived the K/Pg boundary mass-extinction event

    Will improving wastewater treatment impact shorebirds? Effects of sewage discharges on estuarine invertebrates and birds

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    Human communities often discharge wastewaters into estuaries, influencing their organic and pollutant loading, benthic community and trophic structure. The implementation of the Water Framework Directive has encouraged the treatment of wastewater discharges across European estuaries, but the implications for invertebrate and waterbird communities are poorly understood. We explore the effects of untreated sewage discharges on the distribution and abundance of foraging black-tailed godwits Limosa limosa and their main benthic prey (bivalves and polychaetes) on the Tejo estuary in Portugal, a major European Special Protection Area with ongoing wastewater improvements. Patches of mudflat in close proximity to sewage streams (70 m), and godwits foraging in these areas can attain the highest intake rates recorded for the estuary. However, high intake rates can also be attained on bivalve prey, and bivalve biomass and density increase slightly with distance from sewage streams. As the organic input from sewage outfalls influences invertebrate abundance and godwit foraging rates over relatively small areas, the ongoing implementation of a sewage treatment network on the Tejo estuary seems likely to have only a limited impact on the wintering godwit population. The localized effect of untreated sewage discharges on benthic communities suggests that the implications for predatory birds are relatively minor where alternative prey are available, but may be more severe in locations with more depauperate, polychaete-dominated invertebrate communities

    Physico-chemical variables determining the invasion risk of freshwater habitats by alien mollusks and crustaceans

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    The aim of this study was to assess the invasion risk of freshwater habitats and determine the environmental variables that are most favorable for the establishment of alien amphipods, isopods, gastropods, and bivalves. A total of 981 sites located in streams and rivers in Germany. Therefore we analyzed presence-absence data of alien and indigenous amphipods, isopods, gastropods, and bivalves from 981 sites located in small to large rivers in Germany with regard to eight environmental variables: chloride, ammonium, nitrate, oxygen, orthophosphate, distance to the next navigable waterway, and maximum and minimum temperature. Degraded sites close to navigable waters were exposed to an increased invasion risk by all major groups of alien species. Moreover, invaded sites by all four groups of alien species were similar, whereas the sites where indigenous members of the four groups occurred were more variable. Increased temperature and chloride concentration as well as decreased oxygen concentration were identified as major factors for the invasibility of a site. Species-specific analyses showed that chloride was among the three most predictive environmental variables determining species assemblage in all four taxonomic groups. Also distance to the next navigable waterways was similarly important. Additionally, the minimum temperature was among the most important variables for amphipods, isopods, and bivalves. The bias in the occurrence patterns of alien species toward similarly degraded habitats suggests that the members of all four major groups of freshwater alien species are a non-random, more tolerant set of species. Their common tolerance to salinity, high temperature, and oxygen depletion may reflect that most alien species were spread in ballast water tanks, where strong selective pressures, particularly temperature fluctuations, oxygen depletion, and increased salinity may create a bottleneck for successful invasion. Knowledge on the major factors that influence the invasion risk of a habitat is needed to develop strategies to limit the spread of invasive species

    Polinices Predation Patterns and Mercenaria Morphology Models

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    DeAngelis et al. (1985) have described a model of the evolutionary response of bivalve prey to size-selective naticid snail predation. The model analyzed the allocation of bivalve energy among reproduction, overall growth in size, and supplementary growth in shell thickness (p. 818). Using parameter values for Polinices duplicatus as the predator and Mercenaria mercenaria as the prey, the model predicted three optimal strategies for bivalves faced with naticid predation: (1) delayed reproduction with energy diverted into rapid growth in order to reach a size refuge; (2) early reproduction, possibly with some extra shell thickness; and (3) greatly increased shell thickness for deterring predator attacks. This model and an earlier one (DeAngelis et al. 1984) are elaborations on a general qualitative model for bivalve prey (Seed and Brown 1978). [excerpt

    Taxonomy of some Galeommatoidea (Mollusca, Bivalvia) associated with deep-sea echinoids: A reassessment of the bivalve genera Axinodon Verrill & Bush, 1898 and Kelliola Dall, 1899 with descriptions of new genera Syssitomya gen. nov. and Ptilomyax gen. nov.

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    The type species of Axinodon ellipticus Verrill & Bush, 1898 and Kellia symmetros Jeffreys, 1876 are re-described. It is concluded that the two species are not conspecific and that K. symmetros cannot be placed in the genus Axinodon. The family affinity of Axinodon is not resolved, although it is probable that this genus belongs to the Thyasiridae. Kellia symmetros is the type species of Kelliola and is placed in the Montacutidae. Kelliola symmetros is most probably associated with the echinoid Aeropsis rostrata and is not the species previously recorded from North Atlantic Pourtalesia echinoids under the name of Axinodon symmetros. This commensal associated with the North Atlantic Pourtalesia is here described as new and placed in the new genus as Syssitomya pourtalesiana gen. nov. sp. nov., Syssitomya gen. nov. differs from all other genera in the Montacutidae by having laminar gill filaments modified for harbouring symbiotic bacteria and it is thus assumed to be chemosymbiotic. A montacutid associated with the hadal Pourtalesia heptneri is described as Ptilomyax hadalis gen. nov. sp. nov

    Ecological studies of the aquatic soil invertebrates in three inundation forests of Central Amazonia

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    From January 1971 till August 1972 ecological studies were carried out on the aquatic macroinvertebrates of the benthos community of three Central-Amazonian inundation forests. The three investigated forests were chosen according to the influence of different water types. These forests were: 1. a site with an inflow of whitewater on Ilha de Curarí, 2. a site in a mixed water area at Lago Janauarí, and 3. a site in a black water area at Rio Tarumã Mirím. The annual water level fluctuations caused similar ecological conditions concerning seasonal changes, whereas the differences between the forests depended on the inflow of the different water types. The benthos composition differs according to the inundation forest type. Stenecious species, occurring only in one of the three forests, as well as euryecious species, inhabiting the three forests, were found. In addition many species were obtained which live either in white and mixed water or in mixed and black water. The soil invertebrates adapted to the annual water level fluctuations. The most common adaptation may be seasonal dispersal, being developed as a migration or a translocation. Migrations could be detected for Campsurus notatus and Eupera simoni in white respectively mixed water. In black waters numerous species show a translocation, caused by the oxygen deficit of the deep water. A diapause stage can be assumed for Eupera simoni. This dormant stage enables the bivalve to persist in the forest during the dry period. Brasilocaenís irmleri assumingly transports its eggs by the current in optimal habitats, where it develops rapidly in 14-21 days. A dependence on the forest habitat was detected for some species of the mixed and black water. Other species of the inundation area, particularly of the white water area, are not dependent on the forest habitat. In addition to seasonal changes in the benthos composition, a vertical stratification was found. The inundation forest can be subdivided in a river or lake near part, a central part, and a terra firme near part. The intestinal content studies on the soil invertebrates and the oxygen conditions in the three inundation forests indicate the probable different breakdown of the litter in the forest of the várzea on the one hand and the igapó on the other hand. Secondary productions could be estimated for the white water area with 10-15 g/m2 and year and for the mixed water area with 90-110 g/m2 and year. In the inundation forest of the mixed water, having the highest production of the three forests, environmental factors like oxygen concentration, sedimentation etc. and trophic factors offer favourable conditions for the inhabitation of the benthos