Rc. Munoz, Primary productivity in the water column of Estero Morales, a mangrove system in the Gulf of Nicoya, Costa Rica, REV BIOL TR, 46, 1998, pp. 257-262
Primary productivity was measured in the estuary Estero Morales during 15 m
onths (1990-1991). Water column primary productivity was determined using t
he dissolved oxygen method at two different depths (1=50% and 1=10%) at eac
h research site and during two consecutive days of sampling. Rosettes were
incubated for five hours with three clear bottles and two dark bottles. The
Winkler method was used to determine dissolved oxygen. Primary productivit
y was also measured with lower sampling frequency at the Cortezas Islands t
o obtain a point of comparison. These sites are all located in the Gulf of
Nicoya, Costa Rica (10 degrees N, 85 degrees W). Water column net primary p
roductivity in Estero Morales presented average values from 1.20 +/- 0.70 g
C/m(2) d (around 450g C/m(2) year). Values obtained from Islas Cortezas we
re around 1.69 gC / m(2) d. There was a significant difference between the
dry and rainy seasons with respect to net primary productivity (z=2.196, p<
0.03). Another significant difference was determined between the depths 1=5
0% and 1=10% in terms of net primary productivity (z=2.51, p<0.006). The va
lues obtained for primary productivity establish Nicoya Gulf as one of the
most productive estuaries in the world. A follow-up study is recommended fo
r this area, consisting of simultaneous sampling at different points of the
Gulf of Nicoya. These samples should be taken at a minimum of five differe
nt incubation depths for each sample in order to obtain more detailed infor
mation in calculating productivity by layers in water column. It is also re
commended that frequency of sampling be increased for greater assurance tha
t results are not produced by the distribution of patches of phytoplankton.