THE EFFECT OF NUTRIENT LIMITATION AND METAL TOXICITY FOR THE GROWTH OF MARINE DIATOM PHAEODACTYLUM TRICORNUTUM BOHLIN: MICROPLATE BIOASSAY
Authors: Vesna Peršić, Darija Vukić Lušić and Janja Horvatić
Abstract: In this chapter we consider the trophic state and ambient nutrient limitation by the trophic index (TRIX) calculation and nutrient enrichment bioassay using the unicellular marine diatom Phaeodactylum tricornutum at two differently eutrophicated NE coastal Adriatic locations (in the Rijeka Bay area). The first location in Rijeka Port had significantly higher concentrations of dissolved inorganic nutrients and TRIX indices (up to 7.53) than the location near the Shipbuilding Industry “3 Maj”. The DIN/TP ratios in the seawater at Rijeka Port were lower (11.03 to 44.47) than those at the Shipbuilding Industry “3 Maj” (11.65-73.91), indicating P limitation in Shipbuilding Industry waters. The nutrient enrichment bioassays revealed P as the key limiting nutrient for the diatom growth at both sites. In addition, silica and nitrogen limitation was found in all water samples with the exception of the surface water samples in Rijeka Port. To determine the toxicity of metals (Ni2+, Co2+, Zn2+, Cd2+ and Hg2+), algal growth inhibition test was carried out with the unicellular marine diatom Phaeodactylum tricornutum. The basic design of toxicity test followed the International Standard ISO 10253 marine algal growth inhibition test and was modified for microplates. The following order of toxicity was achieved: Hg>Cd>Ni>Co>Zn in the exponential phase of growth, and Hg>Ni>Co>Zn>Cd in the stationary phase of growth, with mercury as the most toxic metal.