Program
 
General Session 3: Biological oceanography & global change
 

 
 
1135
Co-limitation of coastal phytoplankton growth by inorganic nutrients and vitamins B1 or B12 varies seasonally off NW Spain
Monday 9th @ 1135-1155
Multi-function Hall
Emilio Fern¨¢ndez* , Biological Oceanography Group. Faculty of Marine Sciences. University of Vigo. Spain.
Esther Barber, Biological Oceanography Group. Faculty of Marine Sciences. University of Vigo. Spain.
Antonio Fuentes, Biological Oceanography Group. Faculty of Marine Sciences. University of Vigo. Spain.
Marta Hern¨¢ndez, Biological Oceanography Group. Faculty of Marine Sciences. University of Vigo. Spain.
Vanessa Joglar, Biological Oceanography Group. Faculty of Marine Sciences. University of Vigo. Spain.
Clara P¨¦rez, Biological Oceanography Group. Faculty of Marine Sciences. University of Vigo. Spain.
Mar¨ªa P¨¦rez, Biological Oceanography Group. Faculty of Marine Sciences. University of Vigo. Spain.
Antero Prieto, Biological Oceanography Group. Faculty of Marine Sciences. University of Vigo. Spain.
Eva Teira, Biological Oceanography Group. Faculty of Marine Sciences. University of Vigo. Spain.
Presenter Email: esuarez@uvigo.es
Previous investigations carried out by our research group suggest that the response of planktonic primary producers to inputs of inorganic nutrients is frequently controlled by bacterial-mediated supply of organic compounds needed for phytoplankton growth. Among the potential candidates to play a significant role in this process, relatively scarce attention has been historically devoted to vitamins. Only recently, some emergent studies pointed out that bacteria may provide B-vitamins to microalgae and also compete with them for these molecules. Our objective was to assess whether B-vitamins may act as a limiting factor of planktonic primary production. To this aim, we conducted three oceanographic cruises in coastal waters off the NW Spain in winter, spring and summer. Triplicate surface sea water samples were collected at the beginning of the cruise and enclosed in 180 L mesocosms on deck for 8 days. In the case of the summer cruise, nutrient-rich subsurface water was mixed with surface water simulating the summer upwelling process characteristic of this area. Mesocosms were sampled daily and size-fractionated chlorophyll a, primary production and bacterial abundance and production, were determined. At days 0 and 5, twenty-four, two litre seawater samples were drawn from the mesocosms and poured into plastic bags for nutrient addition experiments. Inorganic nutrients, B1 and B12 vitamins were added alone and in combination to triplicate bags and incubated on deck for 96 h. Chlorophyll a concentration and bacterial abundance was daily monitored in the experimental bags. In the mesocosms, chlorophyll-a increased in the three seasons. Phytoplankton growth was limited by inorganic nutrients in 5 out of the 6 experiments. In winter and early spring, co-limitation by B1 and B12 vitamins was observed. In February, the stimulation of phytoplankton growth by inorganic nutrients was reinforced by the joint addition of B1 or B12 vitamins (up to 50% increase in 24 h). A similar response pattern was found in early spring, with chlorophyll-a concentrations in the I+B1 and I+B12 treatments exceeding by 17% the values measured in the inorganic treatment. In summer, by contrast, enhanced chlorophyll a levels were measured in response to inorganic nutrient addition, but neither B1 nor B12 vitamins limited or co-limited phytoplankton growth. Our results indicate that B-vitamins may play an important role in regulating the dynamics of coastal phytoplankton and in modulating species succession during the spring-summer transition.