Report States Concerns For Tauranga Harbour’s Health
Friday, December 2, 2011
Fears about the ecological impact the grounding of the container ship Rena will have on surrounding wildlife may have grabbed all the headlines, but researchers are expressing concern about the ecological state of Tauranga Harbour, too.
A report prepared by researchers from several agencies, including Massey University, has identified concerning changes in the harbour’s delicate ecosystem.
The report found some good news – overall, stable nutrient levels in the harbour and water quality suitable for recreation – but also concerns with other trends. Sea grass area has declined 34 per cent since the middle of last century while mangroves have expanded; some species of fish and shellfish have declined; and nutrient levels in some rivers entering the harbour are elevated.
Professor Murray Patterson, from the School of People and Environment and Planning leads the research consortium called Manaaki Taha Moana, which contributed to the report as part of a harbour research project along with the Cawthron Institute, Manaaki Awanui Trust and a Tauranga based IT company Waka Digital.
He says the reasons for the harbour’s unhealthy state were unclear. “Although there has been a justified concern over the grounding of the Rena and its associated ecological impact on the coast, the longer term decline of coastal systems in Tauranga Harbour is just as concerning – happening more insidiously and under the radar.”
A key recommendation of the report Health of Te Awanui Tauranga Harbour is to undertake an ecological study of the harbour that will provide comprehensive data on the coastal ecosystem health and biodiversity.
Lead author Jim Sinner from the Cawthron Institute says the survey, which starts next week, is necessary to address the shortfall in knowledge about the ecology of the harbour environment.
“More research is required to determine the cause of the problems before we can begin to restore the health of the harbour.”
His colleague, marine ecologist Dr Joanne Ellis, will lead the survey with support from iwi and hapu, the Bay of Plenty Regional Council and Professor Chris Battershill of the University of Waikato.
The survey is the latest stage of the six-year-long harbour research project that has received funding from the Ministry of Science and Innovation till 2015.
A copy of the report
can be downloaded from the Manaaki Taha Moana website http://www.mtm.ac.nz
For
media enquiries about the report, contact senior scientist
Jim Sinner from the Cawthron Institute, Nelson +
64-3-539-3208 or 021-548-011
For media
enquiries about the Manaaki Taha Mona research programme,
contact Professor Murray Patterson, School of People,
Environment and Planning, +64-6-356-9099 x
7235
For media enquiries from a Maori
perspective, contact Caine Taiapa, MTM research leader
Tauranga case study, +64-7-578-4054 or 027-578-4054; or
Kevin Haua, Chairperson Te Manaaki Awanui Trust,
027-270-7247.
Further details of the report’s
main findings:
The Health of Te Awanui Tauranga
Harbour report, which chronicles the current ecological
health of the harbour based on the scientific information
already available, found some good news and some cause for
concern – particularly:
• Nutrients: Reported
levels of nitrogen and phosphorus showed little change
within Tauranga Harbour between the early 1990s and 2005.
Most major point source discharges of nitrogen and
phosphorous were removed from the harbour in the early to
mid 1990s. In many rivers and streams entering the harbour,
nutrient levels have declined due to improved rural
practices. However, many of these rivers still have elevated
nutrient levels, and some show increasing trends associated
with agriculture and runoff from recently harvested
forest.
• Water quality for recreation: Despite
frequent bacterial contamination in rivers and streams
within the catchment, according to BOPRC monitoring reports
the microbiological water quality standards for recreation
are rarely exceeded in Tauranga Harbour, although shellfish
contamination can occur, which is of concern to iwi and
hapu.
• Shellfish: Macroinvertebrate species
richness, an indicator of ecosystem health, remained stable
during 1990-2000. Information on shellfish abundance is
limited and mixed; pipi from Otumoetai declined between 2001
and 2010 whereas numbers of cockles are reported to have
risen.
• Seagrass Decline: 34% sea grass decline
over 40 years, with losses of up to 90% in subtidal areas
(areas not exposed by the tide). Seagrass
communities contain so much biodiversity that they have
been called the ‘tropical rainforests of marine
environments’. They provide animals with food and shelter,
offer a safe home for juvenile fish, stabilise the sediment
with their roots and remove nutrients from the water.
• Mangrove Expansion: Mangroves have
increased by 160% over the last 60 years. Ongoing
sedimentation from land has been identified as the primary
cause of mangrove spread. Sediment inputs raise the level of
the seabed, allowing mangroves to colonise areas that were
once frequently inundated by the tide. The Bay of Plenty
Regional Council is, however, targeting the source of the
problem by working with land holders in local catchments to
reduce sediment runoff.
• Sea lettuce blooms: In
recent years the harbour has been plagued with well
documented sea lettuce blooms. These blooms are caused by
high levels of nutrients in the harbour but it is unclear,
based on the scientific evidence, where these nutrients are
coming from – possibly from land use activities, although
there is some evidence to suggest a link with El Nino
weather patterns pushing deep nutrient-rich water to the
surface.
• Biodiversity. The report assesses the
biodiversity of the harbour, noting the decline of some fish
and shellfish species, effects of toxic phytoplankton, and
the ongoing risk of invasive species from Port activities.
It was concluded, however, that it is very difficult to
assess the overall state of biodiversity in the harbour due
to the lack of data and ongoing
monitoring.
ENDS