June 2011

Andrea Frommel reports about her miniproposal.


Gene Expression in Cod Larvae under Ocean Acidification  

Andrea Frommel, ISOS PhD, GEOMAR

Differential gene expression patterns in response to ocean acidification in larvae of a commercially important fish species, Gadus morhua

In a large, land-based mesocosm experiment from June to August 2011 at the marine facilities of the University of Bergen in Espegrend, Norway, Andrea Frommel tested the impact of CO2  on the development of cod (Gadus morhua), a commercially important fish species of the North Sea.

Newly fertilized eggs were reared for two months in twelve 2500 l tanks in a flow-through system with natural seawater taken directly from the Bergen Fjord. Natural conditions such as light, temperature and salinity were maintained while the larvae were fed with natural zooplankton filtered from the fjord. Using a pH-controlled computer system, CO2 was bubbled into the tanks at three different treatment levels: control = 380 ppm, medium = 1800 ppm and control = 4000 ppm. Larvae were sampled 18, 32 and 46 days post hatch (dph) for relative gene expression analysis looking at 19 different genes related to growth, metabolic activity and functioning.

What Andrea found out was that young larvae (at 18 dph) invested most of their energy in growth under increased CO2 conditions. Later (at 32 dph), the growth pattern switched from protein-based growth to lipid-based growth. The response range at these two developmental stages was very diverse. Some of the larvae showed a strong up or down regulation of genes while others behaved closer to the control group.

The larvae stage is a critical phase in development, where energetically costly re-organization of organs and processes take place – such as the final switch from cutaneous to branchial respiration and acid-base regulation, coiling of the gut that enhances digestion and filling of the swim bladder that aides locomotion and buoyancy. Therefore this stage acts as a bottleneck allowing only a selected cohort of larvae to survive to the next stage at which they are able to better cope with the CO2 stress and recover from possible damage.