The use of Pseudokirchneriella subcapitata as a test organism for the ecotoxicological evaluation of Irish freshwater aquaculture effluent and as a potential early indicator of climate change.

Abstract

Aquaculture is one of the fastest growing food producing industries in the world. The dramatic increase in the growth of global aquaculture production has many environmental concerns. The evaluation of aquaculture effluent is frequently assessed by the measurement of physicochemical parameters but this only indicates a potential degradation caused by the effluent, not the effects on aquatic ecosystems and organisms. Thirteen physicochemical parameters were used to assess the water quality of a freshwater finfish aquaculture effluent in Ireland, including; temperature, pH, nitrogen, phosphorus, oxygen, hardness, alkalinity and conductivity. The Pseudokirchneriella subcapitata algal bioassay ISO (8692:2012), was used to evaluate the potential ecotoxicological effects the freshwater aquaculture effluent on its receiving aquatic ecosystems and organisms. Influent and effluent samples were collected from a freshwater aquaculture facility every two weeks from April 2018 to October 2018. Physicochemical analysis found that concentrations of ammonium, nitrite, orthophosphate, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand and suspended solids determined in the effluent may be cause for concern. After exposure of algae to the aquaculture effluent, stimulation of algal growth rates increased by up to >50% during the sampling period. This stimulation was observed during periods of increased temperatures which were as a result of heat wave and drought conditions experienced during the summer of 2018. Correlation studies identified a strong relationship between algal stimulation and temperature increases (-0.619), suggesting that Pseudokirchneriella subcapitata should be included in the assessment of aquaculture effluent. Comparison of these findings to revised studies have also indicated that standard water quality parameters may not be applicable to aquaculture effluent. The results determined in this study indicate that changes in weather patterns, as a result of issues such as climate change, may have a direct impact on aquaculture effluent and its receiving aquatic ecosystem. Therefore Pseudokirchneriella subcapitata may have use as a potential early indicator of climate change and its effects.