Physiological responses and productivity of the seaweed Ulva ohnoi (Chlorophyta) under changing cultivation conditions in pilot large land-based ponds

Abstract

Land based intensive cultivation systems have been proposed as an ideal option for the commercial production of high value products from seaweeds. However, many cultures on Ulva and other seaweeds are based on relatively small-scale facilities. The high variability of culture conditions can strongly affect the physiological performance of seaweeds, but few studies examine their phenotypic plasticity by integrating critical biological descriptors, e.g. photobiology, oxidative stress, nutrient acquisition. The purpose of this study was to determine the physiological plasticity and growth of Ulva ohnoi during its cultivation in land-based 40 m3 ponds. Through an entire culti-vation cycle (four-weeks), photosynthesis, respiration, pigments, antioxidant capacity and nutrient content were measured. Light, temperature, pH, and dissolved inorganic nitrogen (DIN) were simultaneously monitored in seawater. Additionally, the N-uptake kinetics of U. ohnoi were examined in the laboratory in order to explain the efficiency of the seaweed biomass for DIN-incorporation in the ponds after fertilization. Generally, the gradual increase in seaweed density throughout the cultivation period was directly associated to a drop in light avail-ability and dissolved inorganic carbon (i.e. higher pH) within the ponds. These changes in cultivation conditions were related to a reduction of photosynthetic capacities, nutrient content and growth of U. ohnoi. N-uptake kinetics of U. ohnoi and the behavior of DIN within the ponds after fertilization, indicated that U. ohnoi was able to incorporate ammonium more efficiently than nitrate, and the presence of the former likely inhibits nitrate acquisition. The understanding of the capacity of U. ohnoi to acclimate to the extreme changing culture condi-tions, could be applied to improve its productivity and chemical composition.