Spotlight on sea lettuce
Monday, 14 December 2015 10:00 a.m.
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 is 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 is just one component of Regional Council’s three pronged approach to sea lettuce management.
“In partnership with Tauranga City Council and Western Bay of Plenty District Council, 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
Video interviews of Chris Battershill and Bruce Gardner are available for media use:
- Raw video file (.mov, 1.4GB) 13 min https://filetransfer.boprc.govt.nz/message/ZgQY9fLipl7ca8l6KyktD4
- Edited, compiled video (.mov, 797MB) 5 min 23 sec https://filetransfer.boprc.govt.nz/message/ymz67sr8f3MS3eL4gKCXd3 or view on YouTube at https://youtu.be/EhAD57cAucw
Sea lettuce PhD project summaries:
- Julien Huteau researched nutrient uptake by sea lettuce and found that it can uptake nutrients and some pollutants from the harbour and release them again when the plant decomposes. The uptake patterns are different from those of sea grass and that there can be an antagonistic exchange between the two. He also found that sea lettuce transports nutrients and some metal pollutants throughout the harbour, making this available to organisms that eat the plant.
- Alex Port looked into drivers of sea lettuce in the southern Tauranga Harbour and found that nitrogen rather than phosphorus was the prime agent that triggered sea lettuce blooms and determined the extent of them. The nitrogen was sourced both from land runoff and ocean upwelling events. Mr Port also created a model that can be used to predict how much sea lettuce will turn up, and when based on measured nutrient loading. His model will be available next year as new information on nutrient sources is uploaded.
- Clarrise Nieman has been examining how sea lettuce interacts with or impacts on other marine life. She’s found that sea lettuce can impact mud flat communities by smothering them.
- Ben Stewart has just started research on nutrient sources and re-cycling in the harbour. This work is expected to quantify what’s in the sediments and what enters the harbour from land run-off and groundwater aquifers, as compared to ocean derived nutrient sources. Mr Stewart’s work will feed into the use of the model that Alex Port has developed. He’ll be estimating the age of groundwater that enters the harbour to help identify any legacy issues that might be contributing to sea lettuce growth. That work will be ongoing next year, initial results are expected to be available in early 2016.
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