Is there competition among ciliates and nematodes?

1. Biotic interaction between the ciliate Cyclidium glaucoma and the nematode Caenorhabditis elegans was investigated by manipulating the densities of the organisms in microcosms with and without sediment. 2. After 11 days the abundance of ciliates, nematodes and bacteria as well as extracellular enzyme activity were determined. Ciliates had a negative effect on nematode abundance in microcosms without sediment and in microcosms with sandy sediment, whereas in muddy sediment the effect was less distinctive. An effect of nematodes on ciliates was not observed. 3. The common resource bacteria were not affected negatively by the activity of the grazers. Overall grazer biomass increased with the addition of sediment to the microcosms, suggesting a rise of the carrying capacity in the experimental system. Especially in muddy sediment the abundance of bacteria and extracellular enzyme activity was higher compared to the microcosms without sediment. 4. The results of the experiment suggest a strong interspecific competition between nematodes and ciliates, where nematodes are, at least temporary, strongly affected.     

Variability in intertidal communities along a latitudinal gradient in the Southern Ocean

Despite being one of the most intensely studied habitat types worldwide, the intertidal region around Antarctica has received little more than superficial study. Despite this, the first detailed study of a single locality on the Antarctic Peninsula reported previously unanticipated levels of species richness, biomass and diversity in cryptic intertidal habitats. The current study extends the coverage achieved from this single locality. The intertidal zone at sites in the Scotia Arc, the Falkland Islands and the Antarctic Peninsula was investigated. At all the study sites selected, a wide range of macrofauna was found inhabiting the littoral fringe. These communities, although generally cryptic and occupying predominantly the undersides of boulders and protected interstices, at some locations and sites were rich at multiple taxonomic levels. Across the study locations species richness in the intertidal zone ranged from 7 to 30 species. The highest species richness and diversity were found at high latitude localities, which experienced the highest physical disturbance due to ice scour, and appeared superficially to be denuded of life. Species assemblages varied with latitude with Adelaide Island having a high proportion of bryozoans relative to all other localities.     

Poor design of behavioural experiments gets poor results: examples from intertidal habitats

Many patterns of distribution and abundance of intertidal animals are explained by processes of movements of animals, selecting particular habitats or levels on the shore, or interacting with other species. Movements of intertidal animals have therefore been studied over many years. During this long history, much intertidal ecology has changed in focus from broad-scale to small-scale patterns and processes, although there has been recent refocus on a combination of many scales. Simultaneously, there has been an increase in the incidence of field experiments and growing recognition that behaviour is more flexible than originally thought. This review examines changes in the ways that experiments on movements on intertidal animals have been and are being done, taking into account these changes in emphasis. Although some progress has been made, there is still a long way to go. The idea is still prevalent that behaviour is simple, rather invariant and that the animals respond to broad-scale cues that have traditionally been of interest to many investigators. This means that many experiments are still designed to minimise (or ignore) natural variation in behaviour rather than to measure it and that any associated disturbances are considered irrelevant and therefore not evaluated. Understanding the role that behaviour has in establishing and maintaining many of the patterns observed on intertidal shores is crucial to our understanding of the ecology of these habitats. Better experiments, designed logically with appropriate controls to evaluate realistic processes and to measure how behaviour varies among places and from time to time can only improve this understanding.     

In depth review of the ecology of arenicolous marine fungi

As an ecotone, sandy beaches exist within a multi-dimensional mesh of environmental gradients, shaped by numerous parameters (e.g. temperature, humidity, wave action, sand particle size and salinity). These limit the proliferation of a narrow group of fungal species. Obligate arenicolous marine fungi are an ecological assemblage of sand-associated heterotrophs that inhabit sandy beaches. These organisms have evolved to cope with dynamic beach conditions, having a cosmopolitan distribution across tropical, subtropical and temperate regions. Herein we provide an overview of published works relating to the fungi of sandy beaches, focusing on the past half-century. We outline a broad range of topics in ecology including fungal adaptive traits to intertidal conditions at the morphological and genetic levels, temporal and spatial patterns in community structure, and species variations in substrate preference. Collectively, these concepts should encourage marine mycologists to embrace a holistic set of perspectives to shape the outlook for beach ecology.     

Distributional Characteristics of Nano-and Microalgae in the Intertidal Zones of the Zhongshan Station,Antarctica

This paper first reports the composition, distribution and similarities among various flats of nano-and microalgae in sand and gravel covered by ice and snow in the intertidal zones of the Zhongshan Station in Larsemann Hills (69°21′—69°25′S, 76°00′—76°25′E), East Antarctica. The samples were collected from six gravel-sand flats during January 1989 to February 1990. The following distributional characteristics of nano-and microalgae in the intertidal zones were revealed: small cell size, high cell abundance and up to 80% of cells less than 30 μm. The average cell abundance was 1011.2× 103 and 661.82 × 103 cells per gram of gravell-sand in January and February respectively. The maximum cell abundance of nano-and microalgae occurred at station B. One hundred and sixty taxa of nano-and microalgae were observed, of which, 45 species occurred at all substations, and Navicula glaciei was the dominant species.     

Small‐Sized Benthic Organisms of the Alpha Ridge,Central Arctic Ocean

Abundance, biomass and activity of the small‐sized benthic organisms (bacteria to meiofauna, including foraminifera) was studied in summer 1998 during the expedition ARK XIV/1a to the Amerasian area of the perennially ice covered central Arctic Ocean. With the help of two icebreakers, the German research vessel POLARSTERN and the Russian nuclear‐powered ARCTICA, it was possible to reach this remote, heavily ice‐covered region in order to carry out the first benthic investigations. These focus on effects on the benthic community of the expected low food availability under perennial ice coverage. Bacterial and meiofaunal abundances were determined by direct counting. Biomass determinations on bacteria and nematodes were undertaken by size‐imaging techniques. In addition biochemical analyses were carried out to estimate food availability (as sediment‐bound chloroplastic pigments indicating phytodetritus) at the sea floor, the total microbial biomass (TMB; i.e. the total amount of sediment inhabiting bacteria, flagellata, protozoa and small metazoa, estimated by phospholipid quantification) and the potential bacterial activity (turnover rates of ester‐cleaving exoenzymes). Concentrations of chloroplastic pigment equivalents (CPE) in the main target area (Alpa‐Ridge) ranged between 0.10 ± 0.02 and 0.17 ± 0.04 μg/ml. A 2–3 times higher concentration was determined at a station on the Lomonosov Ridge crest (0.40 ± 0.15 μg/ml). The standing stock of meiobenthic organisms (including foraminiferans) was extremely low and varied between 72 ± 17 individuals 10 cm^–2 in the deep Makarov Basin (3,170 m) and 190 ± 56 individuals 10 cm^–2 on the Alpha Ridge (1,470 m). Significantly higher numbers (U‐test, p = 0.049) were found on the Lomonosov Ridge (297 ± 82 individuals 10 cm^–2). Meiobenthic abundances from the area of investigations, were up to ten times lower than those reported from non‐ice covered deep‐sea regions. However a significant water depth depending decrease of meiobenthic abundances was still detectable. A comparison of biomass data determined by volumetric measurements and biochemical methods showed that about 67% of the TMB are held by organisms of nanofauna size (2–32 μm), approx. 32% belongs to bacteria. Only 0.5–1.5% of the TMB were held by metazoan meiofauna.     

Comparison of the Benthic Size Structure Between Sublittoral,Upper-slope and Deep-Sea Areas of the Western Pacific

Benthic size structures were compared between sublittoral, upper-slope and deep-sea areas of the Western Pacific using the mesh-size fractionated distribution of organisms. The average size of the individuals became smaller with increasing water depth, suggesting that the dwarfism is a more common phenomenon than the gigantism in the deep sea. Nonetheless, the mesh size of 0.037 mm was fine enough to retain meiobenthic specimens quantitatively. When the whole benthos was divided into macro- and meiofauna, the size distributions overlapped considerably in a mesh-size fraction between 1.0 and 0.5 mm. In this fraction, the meiofauna predominated over macrofauna in the deep sea, while the opposite applied to the shallower depths. From these results, recommended mesh sizes of the sieves for the studies of macro- and meiobenthos were proposed.     

Problems in meiofauna energy-flow studies

The direct estimation of energy flow through marine meiobenthic populations poses several difficulties, mainly relating to sampling problems. The usefulness of some indirect estimation methods is discussed.Direct production estimates and respiration measurements for three brackish water crustacean populations are given, indicating a relative constant proportion between population production and respiration. The production: assimilation ratio for these populations fluctuates between 0.3 and 0.4. This is contrasted to literature data revealing much higher production: assimilation ratios as determined in the laboratory for nematode populations. Using data on laboratory cultures of the nematode Monhystera disjuncta some factors that can possibly generate this discrepancy are discussed. An analysis of P:B in different life stages of this population justifies the use of a life-cycle turnover of about 3 for meiobenthic populations, provided some conditions are met. Among these is that no drastic change in productivity occurs between juveniles and adults, and that the biomass of hatchlings, not of freshly laid eggs, is considered as generative production.     

The effect of benthic sediments on dissolved nutrient concentrations and fluxes

The Ria Formosa is a meso-tidal coastal lagoon experiencing enhanced nutrient concentrations. Assessment of sediment–seawater interaction is essential if nutrient dynamics and the risk of eutrophication are to be fully understood. Pore water concentrations of dissolved inorganic and organic phosphorus, ammonium, nitrate and nitrite were determined in cores from six sites. Changes in nutrients concentrations were measured in intertidal pools on sand and mud between tides. Dissolved inorganic phosphorus (DIP) concentrations (~200 μmol l⁻¹) and effluxes (123 ± 14 μmol m⁻² h⁻¹) were greater from sand than mud (37 ± 10 μmol m⁻² h⁻¹), possibly due to the binding of P with the <63 μm fraction. NH₄⁺ effluxes were high outside the Anc?o Basin (821 ± 106 μmol m⁻² h⁻¹) and were associated with Enteromorpha sp. mats. The greatest NO₃⁻ efflux was from sediments near a salt marsh (170 ± 67 μmol m⁻² h⁻¹). These sediment fluxes of P were not sufficient to account for elevated P concentrations seen by other workers on the ebb tide from the Anc?o Basin. Intertidal pools were sinks for Dissolved Inorganic Nitrogen (DIN) and DIP over the 6 h exposure period. Thus, tidepools may be an important route of nutrients into sediments that enhances the effects of sediments on seawater nutrient concentrations.     

Patterns and controlling factors of species diversity in the Arctic Ocean

Aim The Arctic Ocean is one of the last near‐pristine regions on Earth, and, although human activities are expected to impact on Arctic ecosystems, we know very little about baseline patterns of Arctic Ocean biodiversity. This paper aims to describe Arctic Ocean‐wide patterns of benthic biodiversity and to explore factors related to the large‐scale species diversity patterns. Location Arctic Ocean. Methods We used large ostracode and foraminiferal datasets to describe the biodiversity patterns and applied comprehensive ecological modelling to test the degree to which these patterns are potentially governed by environmental factors, such as temperature, productivity, seasonality, ice cover and others. To test environmental control of the observed diversity patterns, subsets of samples for which all environmental parameters were available were analysed with multiple regression and model averaging. Results Well‐known negative latitudinal species diversity gradients (LSDGs) were found in metazoan Ostracoda, but the LSDGs were unimodal with an intermediate maximum with respect to latitude in protozoan foraminifera. Depth species diversity gradients were unimodal, with peaks in diversity shallower than those in other oceans. Our modelling results showed that several factors are significant predictors of diversity, but the significant predictors were different among shallow marine ostracodes, deep‐sea ostracodes and deep‐sea foraminifera. Main conclusions On the basis of these Arctic Ocean‐wide comprehensive datasets, we document large‐scale diversity patterns with respect to latitude and depth. Our modelling results suggest that the underlying mechanisms causing these species diversity patterns are unexpectedly complex. The environmental parameters of temperature, surface productivity, seasonality of productivity, salinity and ice cover can all play a role in shaping large‐scale diversity patterns, but their relative importance may depend on the ecological preferences of taxa and the oceanographic context of regions. These results suggest that a multiplicity of variables appear to be related to community structure in this system.