Ecological Organization and Succession during Natural Recolonization of a Tropical Pond

Abstract

"The structure of a planktonic community was studied in April 1990 for 24 days (D1 to D24) during the natural recolonization of a tropical pond (Côte d’Ivoire) made azoic by emptying and liming (DO). Abundances of bacterioplankton, phytoplankton, protozoans and zooplankton were studied twice daily, whereas hydrological descriptors(temperature, conductivity, oxygen, pH, dissolved nutrients, sestonic weights) were recorded several times daily. After the pond treatment, the natural refilling from groundwater began immediately. The microheterotrophic (bacteria, flagellates, ciliates), phytoplanktonic (Coelastrum microsporum) and zooplanktonic (the rotifers Brachionus plicatilis and Hexarthra intermedia) communities were first based on opportunist species favored by the initially large nutritive availability. This close link with the trophic resources induced their rapid elimination, as soon as the food source was depleted by overconsumption. Due to liming effects, great amounts of degradable organic compounds allowed bacterial communities to develop before phytoplankton. This biological succession was first based on a catastrophic-type system, successively controlled by bottom-up factors (proliferation) and top-down factors(species collapse). Then, the colonization was completed with the development of secondary consumers (last stages of Apocyclops panamensis and chironomids). The progressive complexity of the system ensured the attenuation of the disturbing events. Finally, due to volume variations of the pond along the recolonization steps, the effects of the dilution process on bacteria and chlorophyll biomass were studied. In a context of non-limiting nutrient substrata, the microbial community was able to colonize the new volume within a few hours. Phytoplankton showed a more complex adaptation to the volume increase, with mixed effects of grazing, sedimentation and diurnal productions."