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Most studies on sediment-inhabiting microphytobenthos are based on the biomass present on the surface layers of intertidal flats. However, large amounts of microalgal biomass are known to exist below the surface. This study tested the role of subsurface microalgal biomass as a potential source of photosynthetically active cells for the biofilm on the surface. The resilience of buried cells was evaluated by exposing samples from various depths to surface conditions and investigating the recovery of photosynthetic activity. Additionally, vertical migration by subsurface epipelic diatoms was followed at sub-millimeter scales to evaluate its role for transporting cells to the vicinity of the sediment surface. Finally the relative importance of subsurface microalgal biomass was assessed by estimating the proportion of subsurface:surface biomass for different types of sediments from the Ria de Aveiro. Vertical profiles of chlorophyll a , 10 cm-deep, were measured on samples from three intertidal sites, representative of the range of sediment characteristics found in this estuary. The ratio of total biomass to surface biomass ('subsurface biomass fraction') based on total biomass (0–10 cm depth interval; C sub, total) and on viable biomass (between the surface and the maximum depth with significant photosynthetic recovery; C sub, viable). The experiments showed that buried cells were able to recover photosynthetic activity within 1.5–3 h of light exposure, with the rate of recovery being dependent on depth and type of sediment. Furthermore, subsurface vertical migration was found to enable motile cells to reach the surface from layers deeper than 1 mm within a low tide period. Overall, the results showed that surface biomass (0–0.5 cm) only accounted for one fifth to one third of the total biomass present between the surface and 10 cm, and that the amount of subsurface viable biomass reached 2–3 times the biomass present at the surface. Applying the estimates of C sub, total and C sub, viable to the whole intertidal area of the Ria de Aveiro, spatially-weighted averages for subsurface biomass fractions were found to reach 3.8 and 2.1 respectively. • Buried microphytobenthos cells can recover photosynthetic activity within 3 h. • Rates of recovery of photosynthetic activity vary with depth and sediment type. • Subsurface vertical migration allows cells buried 1 mm deep to reach the surface. • Subsurface biomass (0–10 cm) represents 3–5 times the amount at the surface (0–0.5 cm). [ABSTRACT FROM AUTHOR]

Eunotogramma litorale sp. nov. is described from marine littoral epipsammic assemblages collected from San Diego County, Southern California, USA. The valves of this common species are semi-elliptical in outline with a curved dorsal margin and a more or less straight ventral margin. Each valve has 1–6 transapical costae. Areolae are absent on the valve face; a small rimoportula is usually present on the valve face or uppermost mantle near each pole. One or more rimoportulae are usually found in a row along the dorsal mantle between the costae. Small areolae, visible only with SEM, are typically found between costae on the ventral mantle and along the ventral portion of the pars exterior of the valvocopulae. E. litorale can be distinguished from three other Eunotogramma species with hyaline valve faces by the semi-elliptical shape of its valve outline. The similarity of the internal openings of the rimoportuale of E. litorale and some Aulacodiscus species suggests that E. litorale may be allied with Aulacodiscus, a marine genus associated with inshore beaches. [ABSTRACT FROM AUTHOR]

Penicillin, a β-lactam antibiotic, cannot affect diatoms directly but does so through bacteria. Its effects on viable benthic diatom assemblages in a tropical environment were evaluated across spatial (intertidal sandflat, mangrove site, port environment) and seasonal (post-monsoon, pre-monsoon, monsoon) scales. Penicillin treatment resulted in bacterial suppression and a reduction in diatoms at the intertidal and mangrove sites having stable pennate-dominated assemblages. Diatom response at the port site, dominated by transient centric diatoms, ranged from total inhibition to enhancement. The monsoon diatom assemblages, which differed in composition from those in other seasons, showed reduced susceptibility to penicillin. These observations highlight the bacterial influence on diatom assemblages and the significance of species composition of diatom assemblages in these interactions. Epipsammic diatoms (Cocconeis, Grammatophora and Thalassionema) were more sensitive to penicillin than epipelic forms, probably due to: (1) their inability to escape unfavourable bacterial metabolites because of limited diffusion in benthic environments; and (2) the interference of penicillin with the bacterial 'conditioning' film required for their attachment. Overall, the observations from the present, preliminary, ecological study provide insights into the relevance of bacteria in influencing viable benthic diatom assemblages across spatial and seasonal scales and emphasise the need for future mesocosm experiments on these aspects. Bacterial influence on viable, benthic diatom assemblages was investigated using a novel approach involving the application of penicillin (antibiotic affecting diatoms only through bacteria). The results highlighted the spatial and seasonal variations in bacterial influence on diatom assemblages, and the crucial role of diatom assemblage composition in these interactions. This investigation provides a basis for future studies on the mechanisms underlying diatom-bacterial interactions in benthic environments. [ABSTRACT FROM AUTHOR]

Abstract: The objective of the current study was to assess the applicability of the Pampean Diatom Index (the PDI) to natural communities other than epipelic diatom communities as well as those growing on artificial substrates in Monjolinho River and its tributaries, São Carlos-SP, Brazil. Benthic diatoms and water quality sampling was done at 10 sites during summer base flow period (2008 and 2009). The PDI scores were calculated based on epilithic, epiphytic, epipsammic and epipelic diatom communities as well as those growing on bricks and glass substrates. Pearson correlation was used to determine the relationship between the PDI scores from different substrates sampled and measured physical and chemical water quality data. Two-way ANOVA was used to compare these correlation values among substrates. The PDI scores based on all the substrates showed significant correlations with physical and chemical variables. Insignificant differences in the PDI scores based on different natural substrates were recorded, with all substrates classifying the sites into to roughly the same categories. In the light of these results, the PDI can be applied to communities other than epipelic, and is applicable to the study area. The choice of substrate sampled may not affect accuracy of the PDI-based water quality assessment. [Copyright &y& Elsevier]

The Rio Grande silvery minnow ( Hybognathus amarus ) was historically an abundant and widespread species in the Rio Grande Basin. Its decline to endangered status had many probable causes and has spanned more than a century. Specimens of H. amarus collected in July 1874 at San Ildefonso, near Santa Fe, New Mexico, allowed a retrospective assessment of the ecology and morphology of the species and the environmental conditions of the Rio Grande in areas foraged by these minnows. Analysis of diatoms from the gut showed that H. amarus foraged mainly in nutrient-enriched areas on mud substrates in 1874 and to lesser extents on periphyton associated with plant, sand, and rock substrates. Gut contents included a considerable amount of fine-grained sediment and a wide variety of organic materials including detritus, pine pollen, cyanobacteria, algae, and diatoms. Scale annuli showed that H. amarus was once a relatively long-lived minnow; all age classes from 1 to 5 were present in 1874. The presence of multiple individuals of several ages suggested that annual survival rates were high historically and that the species may be iteroparous, rather than short-lived and semelparous as widely held. The morphology of H. amarus from a captive stock in 2003 was consistent with the morphology of the 1874 specimens. [ABSTRACT FROM AUTHOR]

The distribution of epipsammic phytoplankton in the coastal shore (Ibeno beach) of Qua Iboe River estuary was studied in the early summer (between October and December) of 1998. The results revealed the presence of Actinoptychus undulatus, Aphanizomenon flos-aquae, Astasia fustis, Chromulina globosa, Cocconeis pediculus, Cymatopleura solea, Cymbella lanceolata, Euglena intermedia, Lyngbya majusculata, Microcystis sp., Nodularia spumigena, Navicular rhynocephala, Oscillatoria nigroviridis, Pinnularia viridis, Rhoicosphenia curvata, Trachelomonas volvocina and Urceolus cyclostomus in the sandy beach. The mean species density of the epipsammic algae encountered in the beach ranged from 16 to 7600 organisms per hectare. The density, however, decreased with increase in sampling distance from the low tide level. Actinoptychus undulatus was the most abundant and widely distributed phytoplankton while Aphanizomenon flos-aquae was the least encountered species. The occurrence of A. flos-aquae and other toxin producing cyanobacterial species of Lyngbya majusculata, Microcystis sp., N. spumigena and O. nigroviridis in the sandy beach are of serious health significance. [ABSTRACT FROM AUTHOR]