Marlborough Express - Weekend Express
Cook Strait heatwaves increase water temperature in Sounds
The influence of the Cook Strait on water temperatures in Te Hoiere/Pelorus and Tōtaranui/Queen Charlotte Sound was explained at a recent Environment and Planning Committee meeting.
Principal Coastal Scientist Katie Littlewood delivered the results of the annual Coastal Water Quality
Report Card 2015-2023, which was analysed and produced by Dr Pauline Mitterwallner. Water quality is Council’s longest running coastal science programme and analyses data from 22 sites across both Sounds.
“The programme is important for measuring changes over time. Several water parameters are measured using a Sonde, a measuring instrument consisting of a set of sensors that you lower into the water to measure temperature throughout the water column,” Katie told the committee.
The latest results show that on average, water temperatures in the Sounds have increased by 0.7C degrees in the past eight years, with a marked upturn since late 2020.
“The Sounds are strongly influenced by oceanic currents such as the Pacific and Tasman and by tidal currents in Cook Strait which has some of the strongest tidal currents in the world. The proximity and exposure of the Sounds to this influences sea temperatures,” Katie said.
In the past few years, Cook Strait has had several marine heatwaves, with the longest lasting 114 days.
A marine heatwave is categorised as Sea Surface Temperatures (SSTs) remaining warmer than the 90th percentile of the local 25-year average for at least five consecutive days.
“As a result of these remarkably intense heatwaves, the Sounds experienced unusually warm ocean temperatures in recent years. Our monitoring data shows that both Sounds have had record-breaking high temperatures in
2022 and 2023,” Katie said. “What we are seeing here is constant with other regions around the country.”
Warming water temperatures can, and have had, devastating effects on marine species and habitats. A well-documented example of this is the substantial range retractions of Macrocystis in Tōtaranui/ Queen Charlotte Sound over the past decade and the loss of algae beds (Adamsiella) across Puriri Bay and
Hou Hou Point.
“We’re doing what we can, with the resources that we have, and this includes continued monitoring of coastal water quality to assess further changes, establishing baseline data and identifying areas most at risk through the Ecologically Significant Marine Sites (ESMS) programme.”
Council also supports marine restoration projects involving kelp, shellfish and green-lipped mussels, and catchment care projects such as Te Hoiere Restoration project. “Research has shown that the mitigation of additional stressors like sedimentation can help strengthen the resilience of highly vulnerable marine ecosystems to escalating ocean temperatures,” Katie said.
“It’s hoped there is a change coming and that cooler waters are heading our way as we transition from El Niño weather patterns to La Niña.”