Validity of an Ecotoxicological Test System: Short-Term and Long-Term Effects of Arsenate on Marine Periphyton Communities in Laboratory Systems

Abstract

Periphyton communities were established on glass substratum in the Gullmar Fjord (Sweden) and their sensitivity to arsenate was determined with short-term photosynthesis experiments. The study was done in May 1984 when phosphate levels were low. A 1-h exposure to arsenate gave IC20 (concentration required to inhibit photosynthesis by 20%) values of 0.4 .mu.M. Communities established indoors in a flow-through aquaria system were substantially different from the fjord communities in terms of structure and biomass, although photosynthesis, showed a similar sensitivity (IC2-0 = 0.6 .mu.M). To explore the validity of this short-term ecotoxicological test system, we used a set of indoor, flow-through aquaria to study long-term effects (3 wk) on communities established under arsenate stress. Arsenate was added continuously at 0.1-10 .mu.M above background levels (7 nM). Species composition as well as carbon, nitrogen, and chlorophyll a content of the communities were affected at 0.2-0.8 .mu.M (IC20). This is in good agreement with the sensitivity of the short-time test. We conclude that inhibition of the physiological parameter photosynthesis is relevant information for the understanding of ecological events caused by arsenate stress in the periphyton communities. At least for effects of arsenate, the short-term metabolic test system can be used for valid predictions of gross changes in periphyton community structure and production. Comparison with arsenic levels in polluted coastal areas of Sweden lead to the conclusion that periphyton commumities may be affected, particularly when phosphorus levels are low.