The surveying vessel Kaharoa was part of Niwa's efforts to map the seabed off the coast of Hawke's Bay and Tairāwhiti after Cyclone Gabrielle, along with research vessel Ikatere. Photo / Niwa
The surveying vessel Kaharoa was part of Niwa's efforts to map the seabed off the coast of Hawke's Bay and Tairāwhiti after Cyclone Gabrielle, along with research vessel Ikatere. Photo / Niwa
Efforts to track how sediment is affecting the ecosystem off the coast of Hawke’s Bay and Tairāwhiti after Cyclone Gabrielle show encouraging signs of life but more investigation is needed.
The National Institute of Water and Atmospheric Research (Niwa) is working to develop models to work out where all the sediment washed into the ocean by the cyclone has ended up.
It has involved analysis of sediment using tools like satellite imagery and several sea voyages throughout the year to collect samples of the sediment, get video footage of the seafloor, and map it using sound waves.
This was followed by a 19-day voyage in June where they captured additional video footage and took samples through sediment coring which tests through layers.
Project leader Dr Daniel Leduc said the cyclone caused considerable damage to land and property, but effects on the ocean were harder to gauge.
“Our job is to assess where the impacts have been felt and to what extent, particularly in vulnerable habitats and places where species like flounder and gurnard live close to the seafloor,” Leduc said.
Dr Joshu Mountjoy said the Wairoa Hard, which hosts an important nursery for juvenile fish, showed no large-scale sediment build-up in April but research trawls in June turned up large amounts of wood debris. Photo / Niwa
Leduc said the crew observed encouraging signs of life in the seafloor sediment cores, such as sand dollars, hermit crabs, juvenile shellfish, and sea cucumbers.
“These are important parts of the food web, and their presence could either mean that they were able to survive the increased sediment or that the sediment did not collect in these areas,” he said.
“The water has been too murky to get any good images of the seafloor, but this area will be followed up again this year to gain more insights,” Leduc said.
Dr Joshu Mountjoy, a Niwa marine geologist who specialises in seafloor mapping, says areas of the seafloor have been affected differently with many areas needing further investigation.
“The Wairoa Hard, which hosts an important nursery for juvenile fish, showed no large-scale sediment build-up when we mapped the area in April. However, sediment cores taken in June had high mud contents that could be cyclone-related,” Mountjoy said.
“In addition, when the team conducted research trawls in June, they returned little biology, but lots of wood debris,” Mountjoy said.
Fisheries New Zealand commissioned Niwa to do the research.
Simon Lawrence, Ministry for Primary Industries director of science and information, said a third voyage is planned in October.
