SEASONAL AND SPATIAL VARIATIONS OF CAULERPA SERTULARIOIDES FROM NATURAL POPULATIONS AND UNDER CULTURE CONDITIONS IN SHRIMP PONDS IN TUMACO BAY, COLOMBIAN PACIFIC

Abstract

The biomass of natural populations and biomass under cultured conditions in shrimp ponds of the green alga Caulerpa sertularioides (Chlorophyta, Bryopsidales) was evaluated during March-December 2010 and January- June 2011. The algal biomass in the estuary was collected monthly at low tide using 625 cm2 quadrants. Water quality variables, such as dissolved oxygen, salinity, temperature, Secchi disk, NO3 -, NH3 and PO4 3-, were taken simultaneously with algal samples. Algal biomass was taken to the lab to remove debris. Afterward, wet and dry weights were obtained to get final biomass. Relative growth rate (RGR% d-1) in ponds as well as physicochemical variables was evaluated weekly. Growth rates of plants registered a mean of 1.69 % day-1 (± 0.97). There were no significant differences (p = 0.315) in terms of biomass of C. sertularioides between Natal and Pajal creeks, showing averages between 4.09 and 4.67 g cm-2. Algal biomass showed significant differences between seasons (p = 0.000039), with highest values recorded between July and September. Salinity in Natal creek showed a direct relationship with seasonal variation of algal biomass (p = 0.019), with highest values of biomass in July-September related to higher levels of salinity in the study area. In contrast, salinity values and algal biomass in Pajal creek did not show significant relationship (p = 0.97). Nitrates, ammonia nitrogen, and orthophosphate were not significant with respect to changes in algal biomass (p = 0.93; p = 0.33; p = 0.55, respectively). Significant differences (p = 0.0021) between biomass of natural populations and algal biomass in shrimp ponds were reported, with higher values in cultured conditions, being those three times the biomass of natural creeks. Values of algal biomass from natural creeks suggested the importance of perform culture techniques, since natural populations would not sustain a commercial exploitation of this species. This study reports the first data of growth of a potential algal species and it is necessary to develop additional experiments to assess the impact of additional environmental factors on the relative growth rate.