Iron and zinc content of <i>Hormosira banksii</i> in New Zealand

In the Northern Hemisphere, brown seaweeds in the Order Fucales have been used extensively as bio‐monitors of heavy metal contamination in sea water, but in New Zealand there has been no assessment of the suitability of the Fucales in this role. We measured iron (Fe) and zinc (Zn) concentrations in the intertidal fucalean seaweed <i>Hormosira banksii</i> at three sites in Otago, southeastern New Zealand and two sites at Leigh, northeastern New Zealand. There was no evidence of Zn or Fe contamination at any site studied. Zn levels for <i>H. banksii</i> from Otago Harbour followed a trend similar to an earlier study of <i>Ulva</i> sp. and the Fe content reflected patterns previously observed in sea water. Thus, as for Northern Hemisphere fucalean seaweeds, <i>H. banksii</i> is potentially useful as a bio‐monitor for heavy metals in sea water. Levels of Fe and Zn were among the lowest of any brown seaweed worldwide, and the Fe content of <i>H. banksii</i> from Waterfall Reef, Goat Island Marine Reserve, Leigh, was 50% lower than samples from Otago. These low trace metal levels led us to examine if the growth of H. banksii in New Zealand is limited by Fe or Zn. The physiological requirements of Fe and Zn for growth were calculated and compared with measured values and we suggest that despite low Zn and Fe levels, these trace elements do not limit the growth of <i>H. banksii</i>.