Abstract. Nutrient enrichment affects bacteria and fungi associated with detritus, but little is known about how biota associated with different size fractions of organic matter respond to nutrients. Bacteria dominate on fine (,1 mm) and fungi dominate on coarse (.1 mm) fractions, which are used by different groups of detritivores. We measured the effect of experimental nutrient enrichment on fungal and bacterial biomass, microbial respiration, and detrital nutrient content on benthic fine particulate organic matter (FPOM) and coarse particulate organic matter (CPOM). We collected FPOM and CPOM from 1 reference and 1 enriched stream. CPOM substrates consisted of 2 litter types with differing initial C:nutrient ratios (Acer rubrum L. and Rhododendron maximum L.). Fungal and bacterial biomass, respiration, and detrital nutrient content changed with nutrient enrichment, and effects were greater on CPOM than on FPOM. Fungal biomass dominated on CPOM (,99% total microbial biomass), whereas bacterial biomass dominated on FPOM (,95% total microbial biomass). These contributions were unchanged by nutrient enrichment. Bacterial and fungal biomass increased more on CPOM than FPOM. Respiration increased more on CPOM (up to 300% increase) than FPOM (,50% increase), indicating important C-loss pathways from these resources. Microbial biomass and detrital nutrient content were positively related. Greater changes in nutrient content were observed on CPOM than on FPOM, and changes in detrital C:P were greater than changes in detrital C:N. Threshold elemental ratios analyses indicated that enrichment may reduce P limitation for shredders and exacerbate C limitation for collector-gatherers. Changes in CPOMdominated pathways are critical in predicting shifts in detrital resource quality and C flow that may result from nutrient enrichment of detritus-based systems.
Rapid analytical methods are needed to quantify living microorganisms to determine if ships' discharged ballast water is in compliance with national and international standards. Traditionally, regrowth assays and microscope counts of stained organisms-which are time-consuming, require expensive equipment, and require extensive staff training-are used to assess microorganisms. The goal of this study was to evaluate other approaches. Both ambient microorganisms from an oligotrophic marine environment and laboratory cultures of marine algae were evaluated following exposure to two types of ballast water treatment: ultraviolet (UV) light and chlorine dioxide (ClO 2 ). Microorganisms in two size classes (<10 and ≥10 to <50 μm) were quantified using regrowth assays and vital staining, and samples were evaluated using two rapid approaches: (1) chlorophyll a fluorescence and photochemical yield were measured using a pulse amplitude modulated fluorometer and (2) the concentration of adenosine triphosphate (ATP) was measured with a handheld luminometer. The response of microorganisms to UV and ClO 2 was evident in measurements of photochemical yield, as photochemical yield decreased at high doses. However, initial values of photochemical yield were variable and species-specific. Oddly, in some trials, initial fluorescence increased at intermediate UV doses; this phenomenon could lead to overestimation of total biomass. In samples treated with UV light, ATP was not significantly different among any of the doses used; however, concentrations of ATP were significantly lower at the highest dose of ClO 2 than control samples. These results demonstrate that approaches used for ballast water testing can be treatment-specific, and compliance approaches should be validated to determine their utility with the appropriate treatments.
Vessel biofouling is a major pathway for the introduction, establishment, and subsequent spread of marine non-indigenous macro-organisms. As a result, national and international regulations and guidelines have been implemented to manage the risks associated with this pathway, yet widespread enforcement and uptake are still in their infancy. By comparison, translocation of marine pathogens by vessel biofouling has received little attention despite a mounting body of evidence highlighting the potential importance of this pathway. Using molluscan pathogens as a model, this paper examines the potential for translocation of marine pathogens via the vessel biofouling pathway by reviewing: (1) examples where vessel biofouling is suspected to be the source pathway of non-indigenous pathogen introduction to new areas, and (2) the association between pathogens known to have detrimental effects on wild and farmed mollusk populations with species known to foul vessels and anthropogenic structures. The available evidence indicates that vessel biofouling is a viable and important pathway for translocating marine pathogens, presenting a risk to marine values (i.e., environmental, economic, social, and cultural). While preventive measures to minimize the translocation of macro-organisms are the most efficient way to minimize the likelihood of associated pathogen translocation, the application of reactive management measures to biofouled vessels, including post-filtration treatment, requires further and explicit consideration.
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