Ecological Monitoring of Marine Fish Farming Activities by Enteromorpha Intestinalis (Chlorophyta)

Abstract

The biomass production of algae was markedly enhanced near a large fish farming establishment in the northern Baltic Sea, SW coast of Finland. The mean biomass values of the dominant filamentous green alga Enteromorpha intestinalis at sites near the fish farming establishment were 3-fold the values at the control site (160–190 g/ m2 vs. 64 g/m2). The nutrient discharges from the fish farms were reflected in the elemental contents of the algal tissues. The contents of phosphorus (mean values in the farming area vs. at the control site) were 0.30–0.33% (dry weight) vs. 0.25%,and the levels of N were 1.8–2.1 % vs. 1.6%. On the basis of the nutrient contents, nitrogen is the growth-limiting nutrient in these coastal waters. The results are thus in contrast with the commonly accepted view that the reduction of phosphorus discharges is the main objective in water management. In addition, the accumulation of zinc in the tissues of Enteromorpha appeared to be a useful indicator of fish farming activities