Dominant phytoplankton morphotypes in relation to light conditions in a south American wetland.

INÉS O'FARRELL; IRINA IZAGUIRRE; PAULA DE TEZANOS PINTO

Sapanca, Turquía

Workshop; 14th Workshop of the International Association of Phytoplankton Taxonomy and Ecology; 2005

International Association of Phytoplankton

Light influence on phytoplankton cell and individual morphological characteristics was analyzed for the assemblages from a river floodplain wetland during two different periods. From 1998 to 2000 a dense macrophyte cover determined a poor underwater climate in three profusely vegetated relictual oxbow lakes (ROLs). In these environments the bulk of individuals were not flagellated, mostly unicellular, and filamentous in a minor percentage. On the contrary, up to near 30% of flagellated forms were encountered in the lake that was characterized by better light conditions, and even though unicellular individuals also predominated, filamentous forms were rare and coenobial specimens were frequent. Regarding size, more than 80% of the individuals at ROL1 were shorter than 10 µm, whereas at the lake this proportion was achieved with a MLD of less than 30 µm. A similar pattern was registered for volume, as individuals of less than 1000 µm3 represented almost the entire assemblage at ROL1, whereas at the lake the mean percentage dropped to less than 80%. The most relevant parameter is perhaps the surface/volume ratio that remains higher in the ROLs, particularly at ROL1, as compared to the lake. More recently during spring 2004 and summer 2005 a more extensive sampling was performed that comprised the previously sampled sites together with other environments. The floating macrophyte cover was considerably lower establishing minor light limitations, mostly occasioned by humic acids content. A higher surface/volume ratio also seems to characterize the phytoplankton of environments with a poor light quality. In this occasion the occurrence of the smallest fraction (picoplancton) was also analyzed.