Effects Of Preservation On Wet Weight Dry-Weight Nitrogen And Carbon Contents Of Calanus-Helgolandicus (Crustacea Copepoda)

The lengths, wet and dry weights, nitrogen and carbon contents of fresh, frozen and formaldehyde-fixed specimens of Calanus helgolandicus (Claus) were determined. Samples were collected during May 1980 in the Celtic Sea. Individual Copepodite Stages 3, 4, 5, and Adult Male and Female Stage 6 were measured and analysed, and 36 linear regression equations derived for these variables together with mean values, standard deviations and 95% confidence limits. The range of nitrogen values in the fresh material, expressed as a percentage of dry weight, ranged from 8.08%±0.80 (Copepodite Stage 3) to 10.89%±0.27 (adult female); carbon values changed from 41.6%±3.05 (mean ±95% confidence limits) for Copepodite Stage 3 to 50.97%±2.63 in Copepodite Stage 5. The adult females had a high nitrogen and relatively low carbon content, while the converse was true for Stage 5 copepodites. There was a loss of dry weight from the frozen samples (57%) and the fixed samples (38%) compared with the mean of the fresh dry weight of all stages. The material lost from the copepods was rich in nitrogen, thus, artificially high percentage carbon values were determined from the frozen and fixed samples (52.0 to 60.3% and 44.7 to 58.5%, respectively).

Enhanced toxicity of ‘bulk' titanium dioxide compared to ‘fresh' and ‘aged' nano-TiO2in marine mussels (Mytilus galloprovincialis)

Marine bivalves (Mytilus galloprovincialis) were exposed to titanium dioxide (10 mg L-1) either as engineered nanoparticles (nTiO(2); fresh, or aged under simulated sunlight for 7 days) or the bulk equivalent. Inductively coupled plasma-optical emission spectrometry analyses of mussel tissues showed higher Ti accumulation (>10-fold) in the digestive gland compared to gills. Nano-sized TiO2 showed greater accumulation than bulk, irrespective of ageing, particularly in digestive gland (>sixfold higher). Despite this, transcriptional expression of metallothionein genes, histology and histochemical analysis suggested that the bulk material was more toxic. Haemocytes showed significantly enhanced DNA damage, determined by the modified comet assay, for all treatments compared to the control, but no significant differences between the treatments. Our integrated study suggests that for this ecologically relevant organism photocatalytic ageing of nTiO(2) does not significantly alter toxicity, and that bulk TiO2 may be less ecotoxicologically inert than previously assumed.

Dynamic responses of the benthic bacterial community at the Western English Channel observatory site L4 are driven by deposition of fresh phytodetritus

The impact of the seasonal deposition of phytoplankton and phytodetritus on surface sediment bacterial abundance and community composition was investigated at the Western English Channel site L4. Sediment and water samples were collected from January to September in 2012, increasing in frequency during periods of high water column phytoplankton abundance. Compared to the past two decades, the spring bloom in 2012 was both unusually long in duration and contained higher than average biomass. Within spring months, the phytoplankton bloom was well mixed through the water column and showed accumulations near the sea bed, as evidenced by flow cytometry measurements of nanoeukaryotes, water column chlorophyll a and the appearance of pelagic phytoplankton at the sediment. Measurements of chlorophyll and chlorophyll degradation products indicated phytoplankton material was heavily degraded after it reached the sediment surface: the nature of the chlorophyll degradation products (predominantly pheophorbide, pyropheophorbide and hydroxychlorophyllone) was indicative of grazing activity. The abundance of bacterial 16S rRNA genes g−1 sediment (used as a proxy for bacterial biomass) increased markedly with the onset of the phytoplankton bloom, and correlated with measurements of chlorophyll at the surface sediment. Together, this suggests that bacteria may have responded to nutrients released via grazing activity. In depth sequencing of the 16S rRNA genes indicated that the composition of the bacterial community shifted rapidly through-out the prolonged spring bloom period. This was primarily due to an increase in the relative sequence abundance of Flavobacteria.