Spatial and temporal variations in the copper and zinc concentrations of two green seaweeds from Otago Harbour, New Zealand

Copper and zinc concentrations of the cosmopolitan green seaweeds Enteromorpha intestinalis and Ulva lactuca were obtained for the first time from various sites within Otago Harbour, southern New Zealand. Spatial variation in the concentrations of both metals was found, with increasing levels at stations in the upper harbour basin. While temporal fluctuations were apparent, a significant seasonal trend was evident only for zinc in U. lactuca; concentrations varied from approximately 10 μg g⁻¹ dry weight in winter to 2 μg g⁻¹ in summer. Over four consecutive years of sampling there was little change in metal concentrations of either species. Concentrations of both metals were invariably higher in E. intestinalis than U. lactuca, at all sampling stations and at all sampling times. These results are compared with those from other studies employing the same two green seaweed genera and are discussed in the context of the value of seaweeds as biomonitors of trace metal pollution. The levels of copper and zinc recorded in both species indicate that Otago Harbour is relatively free of trace metal contamination. This conclusion concurs with that reached in previous studies of dissolved copper and zinc concentrations in the surface waters of the harbour.