Primary productivity in the water column of Estero Morales, a mangrove system in the Gulf of Nicoya, Costa Rica

Abstract

Primary productivity was measured in the estuary Estero Morales during 15 months (1990-199 I). Water column primary productivity was determined using the dissolved oxygen method 31 two different depths (1=50% and 1=10%) at each 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 productivity was also measured with lower sampling frequency at the Cortezas Islands to obtain a point of comparison. These sites are all located in the Gulf of Nicoya, Costa Rica (10°N, 85°W). Water column net primary productivity in Estero Morales presented average values from 1.20 ± 0.70 g C/m² d (around 450g C/m² year). Values obtained from Islas Cortezas were around 1.69 gC I m² 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=50% and 1=10% in terms of net primary productivity (z=2,51, p<0.006). The values obtained for primary productivity establish Nicoya Gulf as one of the most productive estuarics in the world. A follow-up study is recommended for this area, consisting of simultaneous sampling at different points of the Gulf of Nicoya. These samples should be taken at a minimum of five different incubation depths for each sample in order to obtain more detailed information in calculating productivity by layers in water column. It is also recommended that frequency of sampling be increased for greater assurance that results are not produced by the distribution of patches of phytoplankton.