Communities Of Benthic Organisms Research Articles

Relative species abundance and population densities of the past: developing multispecies occupancy models for fossil data

AbstractThe number of individuals of species varies, but estimating abundance, given incomplete and biased sampling in both contemporary and fossilized communities, is challenging. Here, we describe a new occupancy model in a hierarchical Bayesian framework with random effects, in which multispecies occupancy and detection are modeled as a means to estimate relative species abundance and relative population densities. The modeling framework is suited for temporal samples of fossil communities with repeated sampling including multiple species with similar preservation potential. We demonstrate our modeling framework using a fossil community of benthic organisms to estimate relative species abundance dynamics and changing relative population densities of focal species in nine (geological) time intervals over 2.3 Myr. We also explore potential explanatory factors (paleoenvironmental proxies) and temporal autocorrelation that could provide extra information on unsampled time intervals. The modeling framework is applicable across a wide range of questions on species-level dynamics in paleoecological community settings.

МЕЛКОМАСШТАБНАЯ ПЯТНИСТОСТЬ В ПРОСТРАНСТВЕННОЙ МОДЕЛИ ТРОФИЧЕСКОЙ СИСТЕМЫ ДИАТОМОВЫЕ МИКРОВОДОРОСЛИ – ГАРПАКТИКОИДЫ

A predator–prey model that describes littoral trophic communities consisting of diatom microalgae and benthic copepod crustaceans (order Harpacticoida) was built and investigated. The model is a system of three partial differential equations of the taxis–diffusion–reaction type. The Neumann boundary condition specifies zero-flux through the borders of a rectangular habitat. The movements of copepods is described by the classical Patlak – Keller – Segel flux expression, which includes both taxis and diffusion. The feeding migrations of consumers are modelled as indirect prey–taxis stimulated by harpacticoid satiety, i.e. with the diffusion coefficient being a decreasing function of individual satiety. Inasmuch as demographic processes in the predator population occur at slow time scale, the model includes no birth/death terms for predator. Hence, taking into account the boundary condition, the average density of predators remains constant. The analytical condition for the oscillatory instability of the homogeneous stationary state of species coexistence reveals the crucial role of the indirect prey–taxis for emergence of spatiotemporal patterns in the system. The proposed model can be viewed as the minimal model capable of explaining heterogeneity of the harpacticoid density. With parameters identified on the basis of field observation data, the model simulates small-scale spatial patterns with characteristic size and the expected lifetime of density patches typical for the considered community of benthic organisms. In spatially-heterogeneous dynamics both density of microalgae and individual consumption of harpacticoid copepods exceed equilibrium values observed without feeding migrations. This suggests that prey–taxis behavior is an evolutionary advantageous strategy

Carbonate Platform Development in an Intraoceanic Arc Setting: Costa Rica’s Largest Limestone Sequence - The Fila de Cal Formation (Middle Eocene to Lower Oligocene)

The limestones of the Fila de Cal Formation build the largest carbonate platform sequence of Costa Rica extending over 180 km from southern Costa Rica into the Panamanian boarder area of David. The detailed limestone microfacies analysis and micropaleontologic dating based on the contained larger foraminiferal assemblages of 22 samples selected from the most representative exposures reveal three main carbonate facies: (1) Eoannularia eocenica-bearing spiculite facies from the Middle Eocene, (2) large lepidocyclinid-nummilitid facies from the Upper Eocene lead by the Lepidocyclina chaperi-Lepidocyclina tobleri panamensis assemblage and (3) dominant Lower Oligocene Lepidocyclina yurnagunensis-Lepidocyclina undosa assemblage. These three biostratigraphically successive facies record circa 14 to 19 m.y. of continuous shallow-marine carbonate sedimentation in the Pacific frontal arc region of southern Costa Rica. During this time large communities of benthic organisms: larger foraminifera, calcareous algae, corals, bryozoans, mollusks and equinoderms rapidly grew in warm tropical waters to build the largest and long-lasting carbonate platform on the Costa Rican arc. The carbonate sedimentation ended abruptly with accumulation of thick volcaniclastic marine platform-to-slope deposits of the Térraba Formation. Tectonically, the Fila de Cal carbonate platform development coincides with rapid convergence rates of the Farallón plate beneath southern Central America leading to strong arc uplift and new widespread neritic environments. The correlation with contemporaneous carbonate arc sequences clearly indicates that primarily their proximity to the inner volcanic arc areas and strong subsidence in response to emerging volcanic edifices are probably the main factors that controlled growing and persistence of carbonate environments within the arc setting.

Lithofacies of the Devonian Marcellus Shale In the Eastern Appalachian Basin, U.S.A.

The Marcellus Shale is an important hydrocarbon source rock and an unconventional reservoir whose origin has engendered much recent debate among geologists. Our analysis of the formation in West Virginia and adjacent States aims to identify and describe the several lithofacies in the eastern Appalachian basin and to interpret their depositional setting. The study is based on field, hand-sample, and microscopic observations, supplemented by X-ray diffraction, thermogravimetric, and gamma-ray-scintillometer data. We identify five major lithofacies: (1) calcitic coarse mudsto ne, quartz-silty and sparsely fossiliferous; (2) skeletal wackestone–packstone limestone , exhibiting a low to moderate faunal diversity; (3) calcitic carbonaceous medium mudstone , containing a high organic-carbon content and low-density, low-diversity fossil community; (4) siliceous carbonaceous fine mudstone , exceedingly radioactive with a high organic-carbon content and usually barren of benthic fossils; and (5) argillaceous coarse mudstone , quartz-silty, micaceous, and kaolinitic. Most layers of Facies 4 mudstone—the quintessential black shale of the Marcellus—formed in a stagnant, anoxic environment beneath a stratified water column and starved of terrigenous sediment. Yet, some layers of this same facies plus the other closely associated mudstones and limestone record markedly different conditions. Rhythmic organic-rich and -poor laminae indicate periods of a stratified water column followed by mixing of the water body. Rip-up clasts, graded bedding, and small-scale cross-bedding resulted from moderate storm action down to the sea floor. Alternating styliolinid-rich and -poor laminae point to a repeated disruption of the thermocline and the recycling of bottom nutrients up to the surface water. The communities of benthic organisms and reduced organic-carbon contents reflect times of oxic–dysoxic bottom water. Widely varying thorium/uranium geochemical ratios suggest that the redox potential in the depositional environment shifted frequently between anoxic (Th/U 4.0). Finally quartz-silty, micaceous, and kaolinitic mudstones demonstrate a considerable influx of terrigenous coarse mud. Our research argues for a relatively shallow marine setting in which the sea floor everywhere in the study area remained above storm-wave base, the thermocline was intermittent being tied to a seasonal stratification–mixing cycle, the redox state of the benthic zone varied considerably, and the supply of detrital silt was at times quite high.

Studies on the Mangrove Macro Faunal Diversity and Assessment among Different Sites in Port Blair Bay, South Andaman Islands

The mangrove intertidal zone is characterised by plenty floral and faunal diversity. The mangroves provide important habitat for a wide range of species like diverse communities of benthic organisms and function as nursery habitats for different types of crab, prawn and fish species and support offshore fish populations and fisheries. To assess the occurrence, spatial distribution and species composition of macro fauna in a mangrove area, core samples were taken along with transect in Portblair bay, South Andaman Islands. Three sites were taken; each study area was divided into three zones viz. Proximal, middle and distal zones, which were analyzed according to the floral composition. The highest value was observed at Barmanallah (2061 no.m-2), followed by Carbyn’s Cove (1710 no.m-2) and the lowest value was noticed at Manjery (882 no.m-2). Terebralia palustris, Cerithidea sp., Periopthalmus sp., Uca sp., Balanus sp. and Polychaetes were dominated in order. Some locations were found to support a high diversity of organisms across habitats, while other locations had high densities of a few species only.

Heavy metal distribution and enrichment in sediments of Mejillones Bay (23° S), Chile: a spatial and temporal approach

Concentrations of Ni, Cd, Pb, Cu, and Zn were measured in the surface sediments of Mejillones Bay at 32 sites ranging in depth from 10 to 95 m. A similarity dendrogram analysis separated the study area into two large sedimentary facies: a coastal zone with low metal concentrations and a deep zone with high metal concentrations. The abundances of Zn, Ni, and Pb increased between two sampling periods (5 years apart) in association with greater anthropogenic activity along the coastline of the bay at the present. The results were analyzed with the index of geoaccumulation and by applying the sediment quality guideline. Although similar to preindustrial levels, current Cu and Ni concentrations pose a likely threat to communities of benthic organisms. Concentrations of Zn and Pb are enriched, probably in connection with the industrial development of the zone, but do not reach dangerous levels for the benthic communities. Cd concentrations are toxic to benthic life, even though those measured herein are similar to preindustrial levels. Thus, these Cd levels are a result of the bay's natural characteristics (e.g., high biological productivity, the microxic water-sediment interface). The results of the Chilean aquatic sediment quality standards and the international standard (sediment quality guideline) were similar but differed from those found using the index of geoaccumulation, which suggests that the proposed reference values for Chilean aquatic sediment should be reviewed.

Spectral wave flow attenuation within submerged canopies: Implications for wave energy dissipation

Communities of benthic organisms can form very rough surfaces (canopies) on the seafloor. Previous studies have shown that an oscillatory flow induced by monochromatic surface waves will drive more flow inside a canopy than a comparable unidirectional current. This paper builds on these previous studies by investigating how wave energy is attenuated within canopies under spectral wave conditions, or random wave fields defined by many frequencies. A theoretical model is first developed to predict how flow attenuation within a canopy varies among the different wave components and predicts that shorter‐period components will generally be more effective at driving flow within a canopy than longer‐period components. To investigate the model performance, a field experiment was conducted on a shallow reef flat in which flow was measured both inside and above a model canopy array. Results confirm that longer‐period components in the spectrum are significantly more attenuated than shorter‐period components, in good agreement with the model prediction. This paper concludes by showing that the rate at which wave energy is dissipated by a canopy is closely linked to the flow structure within the canopy. Under spectral wave conditions, wave energy within a model canopy array is dissipated at a greater rate among the shorter‐period wave components. These observations are consistent with previous observations of how wave energy is dissipated by the bottom roughness of a coral reef.

Benthic macro-invertebrate community composition within a mangrove/seagrass estuary in northern New Zealand

In the tropics and sub-tropics, estuarine environments with mangrove and seagrass habitats provide important structures and resources for diverse communities of benthic organisms. However, temperate estuarine habitats, especially in mangrove areas, may differ significantly in their community associations and interactions. The community composition of benthic macro-fauna was investigated within temperate Matapouri Estuary, northern New Zealand. The density and distribution of fauna were sampled within six distinctive habitats (mangrove stands, pneumatophore zones, Zostera beds, channels, banks, and sand flats), within four sampling events between December 2002 and September 2003. Each type of habitat was replicated seven times within different locations in the estuary. Counts of all infauna and epifauna within four replicate cores were recorded from each habitat and location. Multidimensional scaling plots were used to identify differences in structure and composition of assemblages among habitats and locations within each sampling event. Results from these benthic samples indicate that Matapouri Estuary has a high overall biodiversity, with distinctive faunal assemblages found within different habitats, and some seasonal variations also apparent. In terms of both number of individuals and taxa per unit area, seagrass beds had the highest numbers and mangrove areas had the lowest numbers, with all other habitats in between. Some locations were found to support a high diversity of organisms across habitats, while other locations had high densities of a few species only. Several physical and biological differences between tropical/sub-tropical and New Zealand's temperate mangrove habitats are put forth as potential reasons for the lower density and diversity of the benthic component observed herein. Further ongoing studies aim to elucidate the structure and interactions within food webs in this estuarine ecosystem.

State of Communities of Benthic Organisms in the Upper Volga

State of Communities of Benthic Organisms in the Upper Volga

Oceanographic processes and the preservation of sedimentary structure in Eckernförde Bay, Baltic Sea

The sedimentary structure preserved within the seabed of Eckernförde Bay was investigated together with the oceanographic processes influencing that structure. A series of four cruises were undertaken during winter to summer conditions. An instrumented tetrapod was deployed to monitor boundary-layer processes controlling sediment transport. Coring devices recovered sediment to examine the benthic biological community, to measure rates of sedimentological processes, and to document sedimentary structure. During fair-weather conditions, the dominant mechanism for supplying sediment to Eckern-förde Bay is import from the Baltic Sea associated with internal waves. Earlier work has documented the erosion of shallow deposits during storms and the transport of this material to deeper sites in the Bay. Bottom shear stresses exerted in the Central Basin during all conditions are below critical stresses, which makes the Bay an excellent sediment trap. Sediment from both distant and local origins is reworked in the Central Basin of Eckernförde Bay by a pioneering community of benthic organisms, which is maintained by seasonal hypoxia/anoxia. The population is characterized by few species, small body sizes, young ages, and limited depth of mixing (∼1 cm). However, the community effectively pelletizes most of the sediment reaching the seabed. The very restricted thickness for the surface mixed layer (∼1 cm) and the substantial sediment accumulation rates (mean of 0.39 cm yr -1 for the Central Basin) give sediment a short exposure to modern oceanographic processes before being buried. These conditions allow for partial preservation of sediment deposited as storm layers, thus forming laminations of unpelletized sediment. These laminations separate thick beds of pelletized sediment deposited during fair weather or as thin storm layers (i.e., <1 cm thick). In general, the oceanographic processes in Eckernförde Bay allow for preservation of a high-resolution record of environmental processes. For example, changes recorded for the past half century indicate that slower sediment accumulation rates previously characterized some portions of the study area.

Patch Structure in a Tropical Rocky Shore Community in Brazil: A Mosaic of Successional States?

Abstract The community of benthic organisms in the lower zone of a rocky shore at Praia Rasa, Brazil is distinctly patchy in structure. We examined the hypothesis that two types of patch (a. red algal turf and b. colonial coelenterate) represent different temporal stages in the same successional trajectory. We made observations on a) the stability of patch boundaries, b) successional sequence in experimental clearings within both patch types and c) species composition through time in undisturbed patches. In most cases, the coelenterate overgrew the algae at the patch boundaries, thus showing a competitive asymmetry. In the successional sequence, diatoms were followed by ulvoid species. Thereafter, within clearings in the algal patches, a red algal turf was once more established over one year. In contrast, the mid successional period in clearings within the coelenterate patch was characterized by very low cover of sessile organisms. Colonization by red algal turfs and by the coelenterate colony is largely ...