Gh. Tilstone et al., Significance of nanophytoplankton photosynthesis and primary production ina coastal upwelling system (Ria de Vigo, NW Spain), MAR ECOL-PR, 183, 1999, pp. 13-27
The Rias Baixas are reported to have the highest primary production along t
he NW coast of Spain due to the influence of upwelling, which occurs from A
pril to October. Samples were taken over 2 wk periods at a single station i
n the Ria de Vigo during spring, summer and autumn 1993 to study the variat
ion in the phytoplankton photosynthetic parameters (light limited slope, al
pha(B) and light saturated chlorophyll specific rate, P-m(B)) and daily pri
mary production in relation to phytoplankton size class, species and hydrog
raphic parameters. The range in primary production for the Ria was 65 to 36
89 mg C m(-2) d(-1) for total phytoplankton, 65 to 2533 mg C m(-2) d(-1) fo
r net phytoplankton and 0 to 1650 mg C m(-2) d(-1) for nanophytoplankton. T
he data suggest that most of the variation in primary production in the Ria
during the upwelling season was due to nanophytoplankton. Upwelling/downwe
lling cycles in the Ria therefore give rise to a larger variation in energy
transfer through the microbial loop than through the classic, short, food
chain. This is caused mainly by increases in nanophytoplankton aB coupled w
ith high NO3 due to upwelling events. The data also suggest that there are
3 principal factors that give high primary production in the Ria. Periodic
relaxation and stratification events linked to water column heating during
upwelling/downwelling cycles coincided with periods of high productivity. S
ize class also influences the primary production; net phytoplankton had sig
nificantly higher primary production during the upwelling season than the n
anophytoplankton and was responsible for 66% of the mean primary production
. Species differences affected the primary production in the Ria; highest v
alues coincided with blooms of Chaetoceros spp, and the lowest with dinofla
gellate blooms of Gymnodinium catenatum.