New research into Bay's sea lettuce problem

Sea lettuce on Mount Maunganui beach last month. Photo/George Novak

Bay of Plenty Regional Council is hoping that new research will assist ongoing work to reduce sea lettuce nuisance for Tauranga visitors and residents.

Tauranga Harbour projects manager Bruce Gardner said that Regional Council was investing $210,000 a year to support research led by the University of Waikato Coastal Chair of Science and local PhD students.

Sea lettuce is a naturally occurring algae that's native to New Zealand. Its growth is mainly influenced by coastal currents, nutrient levels, water temperature and water clarity. Regional Council has warned western Bay of Plenty residents to expect increased levels of sea lettuce this summer due to long term trends which show that the largest blooms coincide with the El Nino weather patterns which are forecast this year.

Mr Gardner said the research was just one component of Regional Council's three pronged approach to sea lettuce management.

"... We regularly monitor busy beaches and arrange sea lettuce clean ups as practical and necessary. So far this season we've removed about 430 tonnes of sea lettuce from Tauranga City beaches, Ongare Point, Kauri Point and Pahoia.

''We're also reducing all the land-derived nutrient inputs to the harbour that we can, through our work with land and business owners to improve run-off and storm water management," Mr Gardner said.

Bay of Plenty Regional Coastal Science chair, Chris Battershill said his Waikato University research team are building on a solid platform of Regional Council monitoring data to better understand of sea lettuce dynamics and management options.

"We're also collaborating with other New Zealand and international researchers including a group from Tauranga's sister city Yantai, who happen to be experts in marine nuisance algae. The Yantai group was directed by the Chinese government to work on the sea lettuce problem that caused issues in the 2008 Olympic Games sailing event in Qingdao.

''They've found uses for sea lettuce so that they're now harvesting it. A key use in addition to biofuel is fertilizer. They'll be helping us with research starting next year to see what else can be done with Tauranga Harbour sea lettuce," Mr Battershill said.

Professor Battershill said that three major PhD projects examining aspects of local sea lettuce ecology have been completed this year and are currently being reviewed. Another further PhD project has just been started.

Mr Battershill said that the PhD findings are complemented by other coastal research work. Manaaki Taha Moana has previously completed an assessment of nutrient and species interactions in the intertidal zone throughout the harbour and has now started exploring the subtidal channel areas.

"Following the MV Rena grounding, near shore coastal habitats were also mapped, showing shallow emergent reefs with sea lettuce on them. The near shore reefs are a very likely additional source of sea lettuce. We'll be looking further at the ecology of those systems next year.

''We're also starting new work to map sea grass health using drones. That will confirm the nutrient sources and sinks in the harbour as well as exploring the interactions between sea grass health and sea lettuce abundance," Professor Battershill said.

"In combining all of these new projects we'll be in a position to better understand how we can manage sea lettuce blooms or make better use of the blooms when they occur," he said.

Sea lettuce concerns should be reported to Bay of Plenty Regional Council's Pollution Hotline on 0800 884 883 or Tauranga City Council on 07 577 7000. Further information about sea lettuce in Tauranga Harbour is available at www.boprc.govt.nz/sealettuce