Tesis (Doctor en Medicina de la Conservación)Fish farming in floating cages, like salmon farming in fjords, contribute to the ammonium
(NH4+) enrichment due to salmon excretion, feces and non-eaten food. This "extra"
NH4+ can be assimilated by phytoplankton and microorganisms, and be aerobically
oxidized through nitrification to nitrate (N03-) by bacteria and archaea.
The response of ammonia-oxidizers (archaea and bacteria, AOA and AOB), nitriteoxidizers
(Nitrospina sp) and bacterial community structure to NH4+ enrichment were
studied in situ and experimentally using molecular (cloning, qPCR, T-RFLP and 454
pyrosequencing) and chemical approaches.
In situ: Brackish and marine water were collected from a salmon farming transect at
Comau fjord during contrasting salmon production periods: rest (winter 2012), growth
and harvest (summer and winter 2013). Nitrifier community was characterized by C.
Nitrosopumilus maritimus (AOA) and Nitrosomonas sp. (AOB), where maximum
abundances of C. Nitrosopumilus maritimus (AOA), Nitrospina sp. and Nitrospina sp.
transcripts occurred in the brackish layer, while during productive periods C.
Nitrosopumilus maritimus abundances were co-varied with NH4+ concentrations inside
salmon cages (summer) and adjacent areas (winter). cDNA:DNA ratios indicated higher
growth during winter 2013 associated with NH4+ enrichment derived from salmon
production accumulated in the brackish layer inside salmon cages and in the vicinity
(up to 700 m from the cages at summer and >1 000 winter, whereas during rest period
the highest NH4+ concentration was at Vodudahue river.
Experiments: Mesocosms simulating different salmon farming NH4+ enrichment
contributions (from 0.3 to 4.7 umol NH4+ L-1 o-1) were carried out at contrasting fjords
ecosystems, Comau Fjord (Chile) and Hopavagen (Norway), at summer and late
summer 2011, respectively.
Large variations were found in Chilean richness (60±28 genus) and diversity (7.93±0.47
H, 'Shannon) between treatments and incubation days, while Norwegian experiments
only showed small variations between them (54.2±8.0 and 2.2±0.2, Richness and H,
'Shannon, respectively).
Our results suggest that in Camau Fjord, NH4+ enrichment events occur from salmon
production and also naturally fram river inputs, supporting an abundant and active
nitrifying community potentially processing only part of the extra NH4+ that occurs,
predominantly outside the salmon cages. On the other hand, mesocosms results
indicate that Chilean bacterial community structure are sensitive ta NH4+ enrichment
and incubation days, causing a decrease in richness, diversity and community
composition dominating Alphaprateabacteria over Cyanabacteria and Flavabacteria.
Alphaprateabacteria species change drastically, from Rhadabacteraceae and
Rhadabacter to sulfite oxidation bacteria, while Norwegian mesocosms were
dominated by the same Alphaprateabacteria species without changing species
abundance and composition even at high addition treatments and maximum incubation
days.
These results highlight Chileans microbial community as sensitive ta NH4+ enrichment
which represent an environmental concern, which could be related with production
problems, leading ta economic and indirectly public health issues
