How do harpacticoid grazing rates differ over a tidal cycle? Field verification using chlorophyll-pigment analyses

Four species of meiobenthic copepods were examined for diatom feeding. Microscopic analysis of gut-pellet contents from field-collected individuals indicated frequent ingestion of diatoms by 3 harpacticoids (Scottolana canadensis, Microarthridion littorale, Cletocamptus deitersi) while occasional diatom ingestion occurred Paronychocamptus huntsmani. Frustules were usually empty and broken, indicating that contents were digested. Laboratory experiments using 14C-labeling showed assimilation of diatoms by the 3 species examined. Field grazing rate studies were conducted over different portions of a tidal cycle using fluorescent chlorophyll-pigment analysis of gut-contents. Highest diatom consumption (p\u3c0.05) occurred just after the mudflat became exposed (i.e. Early Low Water level, ELW) for S. canadensis, while consumption at Late Low Water (LLW, i.e. after mudflat is exposed for several hours) was reduced. M. littorale showed a somewhat similar pattern in that highest consumption rates (p\u3c0.05) also occurred during ELW. However, during High Water (HW) and LLW a similar (but reduced) feeding rate was measured. P. hunstmani appeared to only ingest diatoms (i.e. chl-pigments) during HW. Relationships of feeding processes over a tidal cycle are discussed with regard to distributional patterns in intertidal and subtidal habitats

Water-cover influences on diatom ingestion rates by meiobenthic copepods

Laboratory experiments on meiobenthic copepods using 14C-diatoms were conducted to investigate whether: (1) feeding rates or (2) food sources (planktonically-suspended foods or benthic sediment-associated foods) vary in response to the presence or absence of water-cover (i.e. simulated Higher-water vs Low-water conditions). Three diatom-feeding harpacticoids were examined. Scottolana canadensis feeds at significantly higher rates (2x) during Higher-water (HW) conditions (P\u3c0.001), at which time it consumes planktonic foods; during Low-water (LW), feeding is greatly reduced. These feeding patterns are related to its burrow-dwelling and to its subtidal habitat. Cletocamptus deitersi remains virtually unaffected by changes in ambient water-cover, feeding at nearly equal rates during HW and LW conditions but always tending to consume more benthic diatoms. Microarthridion littorale consumes food at nearly equal rates during HW and LW conditions, but does so by shifting its feeding mode. During HW-times it makes excursions into the water column, feeding on planktonically-suspended foods. During LW-times it feeds benthically, moving over the sediment surface. Such feeding differences must affect meso-scale distributions of meiobenthos in the field, total benthic consumption and energy-flow estimates over a tidal-cycle, and the coupling of benthic and pelagic systems

Microbial Extracellular Polymeric Substances (EPSs) in Ocean Systems

Microbial cells (i.e., bacteria, archaea, microeukaryotes) in oceans secrete a diverse array of large molecules, collectively called extracellular polymeric substances (EPSs) or simply exopolymers. These secretions facilitate attachment to surfaces that lead to the formation of structured ‘biofilm’ communities. In open-water environments, they also lead to formation of organic colloids, and larger aggregations of cells, called ‘marine snow.’ Secretion of EPS is now recognized as a fundamental microbial adaptation, occurring under many environmental conditions, and one that influences many ocean processes. This relatively recent realization has revolutionized our understanding of microbial impacts on ocean systems. EPS occur in a range of molecular sizes, conformations and physical/chemical properties, and polysaccharides, proteins, lipids, and even nucleic acids are actively secreted components. Interestingly, however, the physical ultrastructure of how individual EPS interact with each other is poorly understood. Together, the EPS matrix molecules form a three-dimensional architecture from which cells may localize extracellular activities and conduct cooperative/antagonistic interactions that cannot be accomplished efficiently by free-living cells. EPS alter optical signatures of sediments and seawater, and are involved in biogeomineral precipitation and the construction of microbial macrostructures, and horizontal-transfers of genetic information. In the water-column, they contribute to the formation of marine snow, transparent exopolymer particles (TEPs), sea-surface microlayer biofilm, and marine oil snow. Excessive production of EPS occurs during later-stages of phytoplankton blooms as an excess metabolic by product and releases a carbon pool that transitions among dissolved-, colloidal-, and gel-states. Some EPS are highly labile carbon forms, while other forms appear quite refractory to degradation. Emerging studies suggest that EPS contribute to efficient trophic-transfer of environmental contaminants, and may provide a protective refugia for pathogenic cells within marine systems; one that enhances their survival/persistence. Finally, these secretions are prominent in ‘extreme’ environments ranging from sea-ice communities to hypersaline systems to the high-temperatures/pressures of hydrothermal-vent systems

The EPS Matrix as an Adaptive Bastion for Biofilms: Introduction to Special Issue

The process of biofilm formation has knowingly, and even unsuspectingly, baffled scientists for almost as long as the field of microbiology itself has existed. This Special Issue of the International Journal of Molecular Sciences (IJMS) specifically addresses an important component of the biofilm, the extracellular matrix. This matrix forms the protective secretions that surround biofilm cells and afford a “built environment” to contain biofilm processes. During the earlier days of microbiology, it was intriguing to Claude ZoBell that attached bacteria sometimes were able to proliferate when their planktonic counterparts were unable to grow [1]. During the 1970s, this attached state was beginning to be explored [2], and it was realized to be anchored in a matrix of slime-like molecules. The slime-like matrix together with cells was to be called the “biofilm”, a term developed by the late Bill Costerton, Bill Characklis and colleagues. The scientific revelation that attached bacteria were different from free (i.e., planktonic) cells in their physiological behavior and adaptability, launched an era of focused exploration in this area of microbiology. It was initially surprising, though not unexpected in retrospect, that interest in biofilms has grown and now infiltrates virtually all aspects of our scientific study. Since that time there has been a near-exponential growth in the numbers of scientific publications addressing biofilms owing to their immediate relevance to ecology, biotechnology, health and industry

Time-courses in the retention of food material in the bivalves \u3cem\u3ePotamocorbula amurensis\u3c/em\u3e and \u3cem\u3eMacoma balthica\u3c/em\u3e: significance to the absorption of carbon and chromium

Time courses for ingestion, retention and release via feces of microbial food was investigated using 2 bivalves with different feeding strategies, Potamocorbula amurensis, and Macoma balthica. The results showed 2 pathways for the uptake of food material in these clams. The first is represented by an initial label pulse in the feces. The second pathway operates over longer time periods. Inert 51Cr-labeled beads were used to determine time frames for these pathways. The first pathway, involving extracellular digestion and intestinal uptake, is relatively inefficient in the digestion of bacterial cells by P. amurensis but more efficient in M. balthica. The second pathway involving intracellular digestion within the digestive gland of both clams, was highly efficient in absorbing bacterial carbon, and was responsible for most chromium uptake. Differences in the overall retention of microbial 51Cr and 14C relate not to gut passage times but to the processing and release strategies of the food material by these 2 clams

Humic and fulvic acids: sink or source in the availability of metals to the marine bivalves \u3cem\u3eMacoma balthica\u3c/em\u3e and \u3cem\u3ePotamocorbula amurensis\u3c/em\u3e?

Humic acids (HA) and fulvic acids (FA) are common forms of organic matter in marine sediments, and are routinely ingested by deposit- and suspension-feeding animals. These compounds may be a sink for metals, implying that once metals are bound to humic substances they are no longer available to food webs. A series of experiments was conducted to quantitatively examine this premise using 2 estuarine bivalves from San Francisco Bay, USA: the suspension feeder Potarnocorbula arnurensis and the facultative deposit feeder Macoma balthica. HA and FA, isolated from marine sediments, were bound as organic coatings to either hydrous ferric oxides (HFO) or silica particles. Cd and Cr(III) were adsorbed to the organic coatings or directly to uncoated HFO and silica particles. Pulse-chase laboratory feeding experiments using 109Cd and 51Cr(III) were then conducted to determine absorption efficiencies of Cd and Cr for individual specimens using each of the particle types. The results demonstrated that: (1) absorption of Cr(III) from all types of non-living particles was consistently low (\u3c 11%). Ingested Cd showed greater bioavailability than Cr(III), perhaps due to differences in metal chemistry. (2) Bivalves absorbed Cd bound to uncoated HFO or silica particles (i.e. with no HA or FA present). (3) The presence of organic coatings on particles reduced Cd bioavailability compared with uncoated particles. (4) Both geochemical and biological conditions affected the food chain transfer of Cd. The data suggest that in marine systems inorganic and organic-coated particles are predominantly a sink for Cr in sediments. In the transfer of Cd to consumer animals, inorganic particles and humic substances can act as a link (although not a highly efficient one) under oxidized conditions

Feeding and Microspatial Relationships of Meiobenthic Harpacticoid Copepods With Microbial Flora.

Feeding processes and their relationship to microspatial patterns were examined for several harpacticoid species. Field evidences and laboratory radiolabel experiments suggest that diatoms comprise a major portion of the food resources ingested by harpacticoids. Bacteria and mucus-exopolymer secretions (associated with the bacteria and diatoms) are also ingested, coincidently while ingesting diatoms. Also, significant ontogenetic shifts in food resource utilization occur from naupliar to adult stages. Field grazing rate studies were conducted on an intertidal mudflat over different portions of a tidal cycle using several harpacticoid species (Scottolana canadensis, Microarthridion littorale, Paronychocamptus huntsmani). Highest grazing rates for S. canadensis occurred just after the mudflat becomes exposed (i.e. early low-water ELW) with very low grazing rates during late low-water (i.e. after mudflat is exposed for several hours LLW). M. littorale also showed highest grazing rates during ELW. Similar grazing rates occurred during high-water (HW) and LLW. Laboratory experiments indicated that M. littorale maintained similar grazing rates at HW and LLW by changing its food resource utilization. During HW, M. littorale feeds planktonically while swimming in the water column. During LLW it feeds benthically while actively crawling over the sediment surface. S. canadensis feeds during HW by drawing suspended plankton into its burrow. During LLW feeding is greatly reduced by the absence of water cover. Microspatial (mm) patterns of harpacticoids in the field as determined by spatial autocorrelation indicate that at low-water high density patches of the harpacticoid M. littorale were positively correlated with microbial food resource patchiness (as measured by chlorophyll-a concentrations). Laboratory experiments show that this harpacticoid actively seeks out sediment patches containing high concentrations of diatom food resources and their exudates. Microspatial patchiness of M. littorale may be regulated by patchiness of its microbial food resources. During HW patchiness patterns disappear as individuals leave the sediment to feed in the water column. The patchiness of S. canadensis is not correlated with benthic food abundances and this harpacticoid does not actively migrate to food patches in the laboratory. Its microspatial patchiness is probably regulated by other factors. Mechanisms of microspatial patchiness for intertidal mudflat harpacticoids vary depending on the species and portion of the tidal cycle examined

When Nanoparticles Meet Biofilms — Interactions Guiding the Environmental Fate and Accumulation of Nanoparticles

Bacteria are essential components of all natural and many engineered systems. The most active fractions of bacteria are now recognized to occur as biofilms, where cells are attached and surrounded by a secreted matrix of “sticky” extracellular polymeric substances. Recent investigations have established that significant accumulation of nanoparticles (NPs) occurs in aquatic biofilms. These studies point to the emerging roles of biofilms for influencing partitioning and possibly transformations of NPs in both natural and engineered systems. While attached biofilms are efficient “sponges” for NPs, efforts to elucidate the fundamental mechanisms guiding interactions between NPs and biofilms have just begun. In this mini review, special attention is focused on NP–biofilm interactions within the aquatic environment. We highlight key physical, chemical, and biological processes that affect interactions and accumulation of NPs by bacterial biofilms. We posit that these biofilm processes present the likely possibility for unique biological and chemical transformations of NPs. Ultimately, the environmental fate of NPs is influenced by biofilms, and therefore requires a more in-depth understanding of their fundamental properties