Links between viral and prokaryotic communities throughout the water column in the (sub)tropical Atlantic Ocean

Viral and prokaryotic abundance, production and diversity were determined throughout the water column of the subtropical Atlantic Ocean to assess potential variations in the relation between viruses and prokaryotes. Prokaryotic abundance and heterotrophic activity decreased by one and three orders of magnitude, respectively, from the epi- to the abyssopelagic layer. Although the lytic viral production (VP) decreased with depth, lysogenic VP was variable throughout the water column and did not show any trend with depth. The bacterial, archaeal and viral community composition were depth-stratified as determined by the automated ribosomal intergenic spacer analysis, terminalrestriction fragment length polymorphism and randomly amplified polymorphic DNA-PCR, respectively. Generally, the number of operational taxonomic units (OTUs) did not reveal consistent trends throughout the water column. Viral and prokaryotic abundance were strongly related to heterotrophic prokaryotic production, suggesting similar linkage strength between the viral and prokaryotic communities from the lower epi- to the abyssopelagic layer in the Atlantic Ocean. Strikingly, the prokaryotic and viral parameters exhibited a similar variability throughout the water column down to the abyssopelagic layers, suggesting that the dark ocean is as dynamic a system as is the lower epipelagic layer. It also indicates that viruses are apparently having a similar role for prokaryotic mortality in the dark oceanic realm as in surface waters. The more than twofold increase in bacterial OTUs from 2750m depth to 45000m depth and the concurrent decrease in viral OTUs, however, suggests that viruses might exhibit a wider host range in deep waters than in surface waters

A long-term view on recent changes in abundance of common skate complex in the North Sea

Following decades of declines, populations of large fish recently started to increase in the North Sea, presumably due to reduced fishing pressure. However, population recovery may be too readily claimed, since standardised sampling of fish stocks commenced only in the 1970s, well after many species had already collapsed. A true recovery must be seen from a long-term perspective. The critically endangered common skate (Dipturus batis, Rajidae) species-complex is an example of a large-bodied fish that mostly disappeared before standardised monitoring took place. Here we put the recent increase in population size into a 120-year perspective, throughout three geographical divisions in the North Sea. We analysed a large range of mostly undisclosed historical data and contemporary sources. A reconstruction of Dutch commercial landings data confirms that the species used to be very abundant between 1902 ? 1920, and shows how it steadily declined from 1920 onwards until it got extirpated around 1970. Based on a quantitative analysis of standardized catch numbers from fishery-independent surveys time we conclude that the current abundance of the species is still below historical baselines and represents a local recovery at most. We further demonstrate a prominent and consistent pattern in size-distribution, with larger (mature) individuals only occurring in the northern North Sea. A large dataset on historical stomach contents from the central North Sea confirmed the diet of young common skate, which consisted predominantly of shrimps. Our review exemplifies the importance of marine historical ecology to deduce the natural richness of the North Sea

Supplementary data

For nanoSIMS measurements of R. mucilaginosa cells, we analyzed three sample sets: (i) the original inoculum (Control), (ii) after incubation with 13C-labelled polyethylene without and (iii) with UV-treatment. We measured a total of 1144 regions of interest (ROIs, i.e., corresponding to 1144 individual cells). For IRMS and GCMS measurements we measured 3 replicates for the development of ?13C-CO2 values and CO2 concentration in incubations with R. mucilaginosa (RM) and with 13C-polyethylene (PE), with prior UV-treatment (+UV) and without (-UV) as the sole carbon source as well as in incubations with UV-treated 13C-polyethylene (PE) without R. mucilaginosa